The Pyrazolone Scaffold: A Privileged Motif for Molecular Hybridization in Drug Discovery

Abstract

Pyrazolone and its keto‐enol tautomers constitute a privileged class of scaffolds in contemporary medicinal chemistry, characterized by remarkable structural plasticity. This review comprehensively summarizes recent advancements in the structural optimization of pyrazolone‐based compounds, highlighting how molecular hybridization drives polypharmacology against complex conditions, including neurodegenerative disorders, inflammation, metabolic syndromes, cancer, and infectious diseases. By detailing structure–activity relationships, the review elucidates how the strategic pharmacophore merging at the N‐1, C‐3, and C‐4 positions transforms the pyrazolone core into highly potent therapeutics. Mechanistically, these hybrid molecules exhibit diverse capabilities, such as inhibiting key survival kinases, blocking pathogenic protein aggregation, antagonizing immune checkpoints, and restoring cellular redox homeostasis via robust reactive oxygen species scavenging. Ultimately, this review underscores the critical role of molecular hybridization in overcoming drug resistance, minimizing systemic toxicity, and driving the future discovery of pyrazolone‐based precision therapeutics.

This review highlights the structural plasticity and keto‐enol tautomerism of the pyrazolone scaffold, a privileged motif in modern drug discovery. By emphasizing strategic molecular hybridization, it elucidates how pyrazolone‐derived multitarget agents combat complex neurodegenerative, oncological, inflammatory, infectious, and metabolic diseases. This versatile framework overcomes clinical resistance and toxicity, driving the future design of highly potent precision therapeutics.

1. Introduction

Pyrazolone and its derivatives represent one of the most significant “privileged scaffolds” in medicinal chemistry, with a research history dating back to the late 19th century. In 1883, the German chemist Ludwig Knorr synthesized antipyrine, which not only marked the beginning of the synthetic pharmaceutical industry but also initiated over a century of clinical applications for the pyrazolone framework [1]. The pyrazolone scaffold consists of a five‐membered heterocycle containing two adjacent nitrogen atoms and a carbonyl group; this unique electronic structure confers high chemical stability, structural plasticity, and diverse pharmacological activities. By introducing various functional groups (such as aryl, heterocyclic, Schiff base, or metal complexes) at the N‐1, C‐3, and C‐4 positions, the lipophilicity, hydrogen‐bonding capacity, and metabolic stability of pyrazolone derivatives can be precisely tuned to interact specifically with multiple biological targets [2, 3]. Furthermore, extensive literature reports that pyrazolone compounds (with the nucleus of 1H‐pyrazol‐3‐ol and pyrazolin‐5‐one) exhibit a broad spectrum of pharmacological activities, such as antibacterial, antitumor, antitubercular, antiviral, hypoglycemic, and hypolipidemic effects [1, 4]. They also demonstrate activities against central nervous system (CNS) diseases, including anti‐Alzheimer's disease (AD), anti‐Parkinson's disease (PD), antiamyotrophic lateral sclerosis (ALS), antiepileptic, antistroke, antidepressant, anxiolytic, and antimanic properties [5, 6, 7] (Figure 1).

FIGURE 1.

The two skeleton structures of pyrazolones and their therapeutic potential.

Currently, several pyrazolone compounds have been marketed and applied in clinical practice, including nonsteroidal anti‐inflammatory drugs (NSAIDs) for the treatment of musculoskeletal and joint diseases, and the free radical scavenger edaravone (EDA) for ALS [8, 9]. Typical marketed drugs based on the pyrazolone skeleton are presented in Table 1. In modern drug discovery, the status of the pyrazolone scaffold has become increasingly prominent [10]. Their unique tautomeric properties—specifically the keto‐enol tautomerism between the carbonyl group and the adjacent double bond—provide the structural basis for their potent antioxidant and radical scavenging activities [11]. As medicinal chemistry shifts toward multitarget‐directed ligands (MTDLs), the pyrazolone scaffold has become an ideal core for constructing hybrid molecules designed to simultaneously intervene in complex pathological processes, such as oxidative stress and neuroinflammation in neurodegenerative diseases, or immune escape and kinase dysregulation in the tumor microenvironment [12, 13].

TABLE 1.

The drugs that have been marketed with pyrazolone as the skeleton.

Drug name	Structure	Treatment	Approved
Antipyrine		Anti‐inflammatory and antirheumatic	1884
Aminophenazone		Antipyretic and anti‐inflammatory	1897
Propylantipyrine		Treat fever, headache, neuralgia, etc.	1931
Edaravone		Free radical scavenger, for the treatment of CIS	2001
Metamizole sodium		Treat pain, acute injuries, etc.	2008
Eltrombopag		Treat immune thrombocytopenia	2008

This review aims to integrate recent research to comprehensively explore the therapeutic potential of pyrazolone derivatives in neurodegenerative diseases, other CNS disorders, anti‐inflammatory and analgesic treatments, metabolic diseases, oncology, and infectious diseases. By analyzing structure–activity relationship (SAR), design concept, in vitro and in vivo biological evaluations, this review highlights the unique advantages of the pyrazolone core as a privileged scaffold for molecular hybridization. In addition, this review outlines innovative directions for leveraging this versatile motif in the future discovery of precision therapeutics. Of note, in line with common medicinal chemistry literature practices, the hybrid compounds in this review are primarily designated systematically by their constituent pharmacophores (e.g., “pyrazolone‐Schiff base hybrids” or “NBP‐Edaravone hybrids.”

2. Biological Activities of Pyrazolone

2.1. Antineurodegenerative Diseases

Neurodegenerative diseases are characterized by progressive neuronal degeneration and apoptosis, clinically manifesting as cognitive decline, memory impairment, and motor dysfunction [14, 15]. Their complex pathogenesis is closely linked to mitochondrial dysfunction, reactive oxygen species (ROS) dysregulation, excessive oxidative stress, chronic neuroinflammation, and protein misfolding [16]. Because current clinical drugs provide only symptomatic relief and often carry significant side effects without halting disease progression, the discovery and development of novel, safe, and highly efficient molecular scaffolds remain a critical priority for therapeutic intervention [17].

2.1.1. Anti‐AD

AD, the most prevalent progressive neurodegenerative disorder, is clinically characterized by severe cognitive dysfunction, memory loss, and personality changes that ultimately rob patients of their independence [18, 19, 20]. Pathologically, AD manifests as extensive neuronal and synaptic loss, delineated by two core hallmarks: extracellular amyloid‐beta (Aβ) plaques and intracellular neurofibrillary tangles composed of hyperphosphorylated Tau protein [21]. While the exact etiology remains elusive, prevailing mechanistic hypotheses implicate cholinergic deficits, Aβ deposition, Tau hyperphosphorylation, neuroinflammation, and oxidative stress [22]. Consequently, contemporary drug discovery relies heavily on structure‐based design and screening against these specific targets [23]. However, current therapeutics—such as acetylcholinesterase (AChE) inhibitors—provide only temporary symptomatic relief without halting or reversing disease progression [24, 25].

Restoring the levels of cholinergic neurotransmitters and regulating monoaminergic systems remain primary clinical pathways. Considering the intrinsic high affinity of the pyrazolone scaffold for various enzymes, Tok et al. [7] employed a precise molecular hybridization strategy to incorporate a Schiff base pharmacophore into this framework, successfully designing and synthesizing a novel series of pyrazolone‐Schiff base hybrids. In this design, the rigid pyrazolone core acts as an ideal spacer, properly orienting its substituents to simultaneously occupy both the catalytic active site (CAS) and peripheral anionic site (PAS) of AChE, effectively mirroring the binding mode of donepezil. Further SAR analysis revealed that the introduction of a polar, basic nitrogen atom into the side chain significantly enhances AChE inhibitory activity. Specifically, compound 1g (Figure 2), which features a dimethylaminopropoxy side chain, exhibited excellent AChE inhibitory efficacy (IC₅₀ = 0.057 μM). In contrast, the incorporation of a strong electron‐withdrawing group (such as a nitro group) onto the phenyl ring substantially potentiates the binding affinity toward monoamine oxidase‐B (MAO‐B); for instance, the para‐nitro substituted compound 1h demonstrated exceptional MAO‐B inhibitory activity (IC₅₀ = 0.049 μM). Molecular docking studies confirmed that the nitrogen atom and carbonyl group of the pyrazolone core act synergistically with the electron‐withdrawing nitro group on the phenyl ring to facilitate key hydrogen bonding and π–π stacking interactions with MAO‐B residues.

FIGURE 2.

Structures of compounds 1 a – p.

As AD progresses, butyrylcholinesterase (BuChE) assumes the primary catalytic role for acetylcholine hydrolysis [12, 26]. Guided by the MTDLs, Zhang [12] et al. designed and synthesized a novel series of dual‐binding‐site piperidine‐pyrazolone hybrids. This was achieved by coupling a pyrazolone scaffold—which possesses inherent antioxidant potential and affinity for the enzyme's PAS—to amine pharmacophores targeting CAS via aliphatic chains of varying lengths (Figure 3). SAR analysis reveals that aliphatic chain length and terminal amine type are critical for targeted inhibition. Accommodating the broad BuChE catalytic gorge, extending the carbon chain to 14 atoms maximizes inhibitory activity, selectivity, and blood–brain barrier (BBB) permeability; however, further extension to 16 carbons decreases efficacy due to excessive steric bulk. For the terminal amine, compact unsubstituted piperidine or pyrrolidine moieties yield optimal activity, whereas increasing steric hindrance or hydrophilicity compromises inhibition. Conversely, shorter carbon chains are more favorable for preserving antioxidant capacity. After undergoing activity screening (including ChE inhibition, antioxidant activity, BBB permeability, and cytotoxicity), the optimal compound 2i exhibits an excellent multitarget profile: featuring potent and highly selective BuChE inhibition (IC₅₀ = 0.42 μM, SI > 200), favorable free radical scavenging capacity (equivalent to 1.04 of trolox), and ideal BBB permeability.

FIGURE 3.

Structures and hybridization strategy of compounds 2a–p.

Similarly, Xu et al. [26] utilized SuFEx click chemistry to design and synthesize a novel series of δ‐sultone‐pyrazoles hybrids (Figure 4). SAR studies revealed that the substituents at the C4, C5, and N7 positions of this scaffold profoundly influence BuChE inhibitory activity. Specifically, the presence of a hydrogen atom at the C4 position substantially enhances the inhibitory efficacy. Furthermore, the introduction of a substituent with moderate steric bulk (such as a cyclopropyl or p‐methoxyphenyl group) at the C5 position, combined with halogenation (fluorine or chlorine) at the ortho‐position of the N7‐phenyl ring, synergistically endows these molecules with exceptional inhibitory potency and excellent selectivity toward BuChE. The lead compound 3d demonstrated reversible, mixed‐type noncompetitive BuChE inhibition (IC₅₀ = 0.42 μM), establishing stable binding via a π−S interaction with Trp82 and extensive hydrophobic interactions facilitated by the heterocyclic core.

FIGURE 4.

Structures and SARs of the BuChE inhibitor based on compound 3.

The dual inhibition of AChE and BuChE in the brain is considered an effective approach to improving cognitive and memory functions in patients. Against this background, utilizing a pharmacophore hybridization strategy, Khan et al. [27] integrated the highly bioactive pyrazolone, thiazolidinone, and chalcone scaffolds to successfully design and synthesize a novel series of thiazolidinone‐chalcone‐pyrazolone hybrids, with dual ChE inhibitory activity (Figure 5). SAR analysis reveals that the electronic effects and steric properties of the phenyl substituents critically determine enzyme inhibitory activity. Introducing highly electronegative moieties significantly strengthens hydrogen‐bonding interactions with the target enzymes. Notably, a para‐trifluoromethyl substitution increases lipophilicity and imparts a cationic character to the phenyl ring, firmly anchoring it to the electron‐rich regions of the enzyme. Furthermore, strong electron‐donating groups enhance binding affinity by functioning as dual hydrogen bond donors and acceptors. Conversely, bulky substituents impede the molecule's optimal fit within the CAS due to steric hindrance, resulting in a marked decline in inhibitory efficacy. In vitro data indicated that the IC₅₀ values of this series of compounds against AChE ranged from 3.20 to 20.10 μM, while those against BuChE ranged from 3.70 to 21.10 μM. Among them, compound 4h exhibited the strongest cholinesterase activity, with an IC₅₀ of 3.2 μM for AChE and 3.7 μM for BuChE, demonstrating an inhibitory efficacy comparable to the clinical standard drug Donepezil. Molecular docking studies indicated that this compound could bind accurately and stably within the catalytic active pockets of the AChE and BuChE enzymes, confirming its powerful ability to block the abnormal degradation of neurotransmitters at the molecular mechanism level.

FIGURE 5.

Structures and hybridization strategy of compounds 4a – n.

Similarly, Çakmak et al. [28] using the pyrazolone ring as the core pharmacophore, designed and successfully synthesized a series of novel Schiff base‐pyrazolone hybrids (compounds 5a–e, Figure 6) for the first time. Enzymatic evaluation results showed that this series of hybrid molecules exhibited outstanding multitarget inhibitory activity against various enzyme networks related to AD and metabolism. All synthesized compounds exhibited exceptional nanomolar multitarget inhibition against AChE (15.07–77.10 nM) and BuChE (14.15–107.62 nM). Additionally, these compounds also showed highly efficient inhibitory effects against human carbonic anhydrase isozymes (hCA I and II) associated with the pathological microenvironment of neurodegenerative diseases, further reflecting the unique advantages of this skeleton in regulating multiple metabolic enzyme networks.

FIGURE 6.

Structures of compounds 5a – e, 6, and 7e.

Transitioning to disease‐modifying strategies, targeting Aβ aggregation and restoring intracellular protein homeostasis have become critical frontiers. Santoro et al. [29] discovered that the specific spatial geometry of the pyrazolone scaffold allows molecules like compound 6 (Figure 6) to selectively bind to the outer surface of the 20S proteasome's α‐ring. By acting as a noncompetitive allosteric activator, the pyrazolone derivative stabilizes the substrate‐entry channel in an open conformation, accelerating the degradation of misfolded proteins and antagonizing Aβ‐induced neuronal apoptosis.

Furthermore, Soares et al. [30] recently reported a series of arylpyrazolone compounds designed to simultaneously combat Aβ toxic assembly and the neuronal ferroptosis pathway (Figure 6). In‐depth in vitro pharmacological evaluations showed that the preferred lead compound of this series (compound 7e) exhibited outstanding neuroprotective efficacy, effectively antagonizing apoptosis induced by oxidative stress and ferroptosis (EC₅₀ = 270 nM). Moreover, in vivo pharmacokinetic experiments further confirmed that this compound not only possesses excellent BBB penetration capabilities but also exhibits good in vivo metabolic stability and pharmacokinetic characteristics. Arylpyrazolone compounds have demonstrated their potential in the development of novel and potentially more effective therapeutic drugs for AD.

Given that high concentrations of transition metals (Cu²⁺/Zn²⁺) in the AD brain significantly exacerbate the toxic assembly of Aβ, the development of multitarget chemical modulators capable of simultaneously regulating both pathogenic pathways is of significant importance. To overcome the inherent limitations of classic 1,4‐benzoquinone (BQ)—namely, its inability to chelate metal ions and its high cytotoxicity, Yi et al. [31] designed and synthesized a novel series of benzoquinone‐pyrazolone hybrids (Figure 7). The core of this design strategy lies in fusing 3‐pyrazolone, which possesses metal‐chelating properties, with the BQ scaffold. Concurrently, by modifying the substituents on the 3‐pyrazolone moiety and annulating a benzene ring at the 5‐ and 6‐positions of BQ to form naphthoquinone (NQ), the polarity, steric hindrance, and chemical reactivity of the molecules can be precisely tuned. SAR and mechanistic studies reveal that the optimized compound 8a, featuring a benzyl substituent at the N1 position, exhibits the most potent activity. This benzyl moiety facilitates effective contact between the molecule and Aβ via a network of noncovalent interactions, including hydrophobic and cation‐π interactions, thereby directing the BQ functionality to undergo stable covalent cross‐linking with the lysine residues (Lys16 and Lys28) of Aβ. Furthermore, compound 8a is prone to o‐hydroxylation in aqueous solutions; the resulting bidentate metal chelation site endows it with the ability to competitively bind metal ions against Aβ. In the presence of Cu(II) and oxygen, this molecule can also promote the oxidative modification of histidine (His) and methionine (Met) residues within the Aβ sequence, synergistically redirecting the assembly of Aβ into less toxic amorphous aggregates. In contrast, NQ derivatives exhibit relatively weaker modulatory effects due to the absence of reactive sites required for Michael addition or o‐hydroxylation. Cell‐based assays further confirm that these novel heterocycle‐fused derivatives not only significantly mitigate the inherent cytotoxicity of the classical BQ scaffold but also profoundly alleviate the neurotoxicity induced by both metal‐free and metal‐associated Aβ.

FIGURE 7.

Structures and hybridization strategy of compounds 8a – e.

In pursuit of multitarget‐directed therapeutic strategies for AD, Qiang et al. [32] employed a molecular hybridization approach to integrate the core scaffolds of DL‐3‐n‐butylphthalide (DL‐NBP) and EDA, successfully designing and synthesizing a series of DL‐NBP‐EDA hybrids (Figure 8). However, subsequent pharmacological evaluations revealed critical limitations in their comprehensive profiles. Primarily, the absence of metal‐chelating sites, coupled with mediocre antioxidant efficacy, rendered these hybrids incapable of fully abrogating the cascading oxidative stress damage triggered by metal dyshomeostasis in the AD brain. More crucially, their nonselective inhibition of MAOs presents a significant risk of adverse effects, emerging as a fatal bottleneck that restricts their further development as viable anti‐AD agents.

FIGURE 8.

Design and SAR of compound 9.

To overcome the inherent defects of early DL‐NBP‐EDA hybrids, Cong et al. [3] ingeniously integrated the core pharmacophore of the classic metal chelator clioquinol to successfully design and synthesize a novel series of 5‐(2‐hydroxyphenyl)‐2‐phthalide‐3(3H)‐pyrazolone derivatives (Figure 8). SAR analysis reveals that the introduction of the 2‐hydroxyphenyl moiety plays a decisive role in enhancing the overall molecular activity. This group not only imparts a high degree of planar rigidity to the molecule—allowing it to fit perfectly into the MAO‐B binding pocket to drastically improve inhibitory potency and target selectivity, but its phenolic hydroxyl group also functions as a bidentate ligand, significantly boosting the molecule's metal‐chelating capability (especially for Cu²⁺) and antioxidant efficacy. In the optimal candidate 9x, the precise spatial arrangement between the pyrazolone carbonyl/nitrogen and the adjacent hydroxyl group forms a perfect bidentate chelation center. This structural feature endows 9x with potent metal‐chelating capabilities and significant MAO‐B inhibition (IC₅₀ = 0.41 μM, SI > 24.4). Notably, 9x demonstrated remarkable bidirectional regulatory capabilities on Aβ kinetics: it inhibited spontaneous and Cu²⁺‐mediated aggregation and exhibited potent “active disaggregation” efficacy, disrupting preformed dense Aβ fibrils with disaggregation rates exceeding 81%. Supported by the inherent radical‐scavenging nature of the pyrazolone backbone, 9x substantially downregulated pro‐inflammatory factors (NO and TNF‐α) and reversed oxidative stress‐induced neuronal death, leading to significant amelioration of spatial memory deficits in AD mouse models.

Finally, Kanwal et al. [33] structurally hybridized the rigid, electron‐rich pyrazolone core with nicotinic acid to yield the nicotinic acid‐pyrazolone hybrid 10, which successfully reversed scopolamine‐induced spatial learning and memory dysfunction in rats (Figure 9). At the molecular level, 10 comprehensively regulated the ROS/NF‐κB/COX‐2 signaling axis, rebuilding the antioxidant defense system and providing robust antiapoptotic protection to neurons by upregulating Bcl‐2 and suppressing Bax and Caspase‐3, thereby establishing the pyrazolone scaffold as a highly promising foundation for comprehensive AD therapy. Of note, Table 2 comprehensively summarizes the specific hybridization strategies, targets, and biological activities of pyrazolone derivatives against AD.

FIGURE 9.

Structures and hybridization strategy of compound 10.

TABLE 2.

Summary of the anti‐AD activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity	Cell or in vivo assay
Tok et al.	1g, 1h	Pyrazolone + Schiff base	AChE, MAO‐B	AChE (1g) IC50: 0.057 μM; MAO‐B (1h) IC50: 0.049 μM	In silico molecular docking analysis
Zhang et al.	2i	Antipyrine + piperidine	BuChE, ROS	BuChE (2i) IC50: 0.42 μM, (SI > 200); ORAC = 1.04)	Cytotoxicity assays
Xu et al.	3d	Pyrazolone + δ‐sultone	BuChE	BuChE (3d) IC50: 0.42 μM	Neuroprotective effects assays
Khan et al.	4h	Pyrazolone + thiazolidinone +  chalcone	AChE, BuChE	AChE (4h) IC50: 3.20 μM; BuChE (4h) IC50: 3.70 μM	In silico ADMET and docking profiling
Çakmak et al.	5a–e	4‐aminoantipyrine + schiff base	AChE, BuChE; hCA I, hCA II	Potent AChE and BuChE inhibition	In silico docking analysis
Santoro et al.	6	Pyrazolone core (Known drugs)	20S proteasome	Activates 20S proteasome via “open gate” mechanism	Protected SH‐SY5Y from Aβ 42 toxicity
Yi et al.	7e	3‐pyrazolone + 1,4‐benzoquinone (BQ)	Metal‐free and metal‐bound Aβ aggregation	Covalent cross‐linking with Aβ	Alleviated Aβ‐induced cytotoxicity in SH‐SY5Y
Soares et al.	8	BQ + 3‐pyrazolone	Aβ, ferroptosis, ROS	Reversed Aβ toxicity (8) EC50: 270 nM; ORAC = 4.15	Protected MC65 cells; in vivo pharmacokinetics
Cong et al.	9x	DL‐NBP + edaravone + clioquinol features	MAO‐B, Aβ, ROS, Cu2+ chelation	MAO‐B (9x) IC50: 0.41 μM (SI > 24.4)	Aβ‐induced AD mice model
Kanwal et al.	10	Pyrazolone + nicotinic acid	AChE, p‐NF‐κB, TNF‐α, COX‐2, p‐JNK	Potent AChE inhibition	Scopolamine‐induced model

2.1.2. Anti‐PD

As the second most prevalent neurodegenerative disorder, PD is clinically characterized by motor deficits such as bradykinesia, tremors, and postural instability, with incidence rates rising sharply due to global aging [34, 35]. Pathologically, PD is defined by the abnormal aggregation of α‐synuclein into Lewy bodies and the progressive degeneration of dopaminergic neurons in the substantia nigra [36, 37]. A primary catalyst for this neuronal death is oxidative stress, driven by an imbalance between ROS and the body's antioxidant defenses, which are regulated by the Nrf2‐Keap1 signaling pathway [38]. Because progressive, population‐specific neuronal loss is a hallmark of these disorders—such as dopaminergic neurons in PD—developing therapies that target the Nrf2‐Keap1 pathway to mitigate oxidative stress [39], alongside broad neuroprotective agents to halt neuronal degeneration, represents a critical direction for novel drug discovery [40, 41].

The toxic aggregation of α‐SN is a primary driver of dopaminergic neuronal death. Kurnik et al. [42] utilized time‐resolved fluorescence resonance energy transfer technology to screen a massive library of 746,000 compounds, identifying pyrazolone derivative 11 (Figure 10) as a uniquely potent inhibitor of early α‐SN oligomerization. Leveraging the specific spatial geometry and hydrogen‐bond donor/acceptor sites of the pyrazolone core, compound 11 precisely anchors to the monomeric state and N‐terminal region of α‐SN (IC₅₀ = 10.4 μM). This targeted spatial occupancy effectively blocks early pathogenic oligomers from binding to cell membranes. In Thioflavin T (ThT) kinetic assays, 11 dramatically suppressed fibril growth, reducing terminal fluorescence from ~40,000 a.u. down to 15,518 a.u.—matching the efficacy of the preclinical standard Baicalein. Mechanistically, the pyrazolone skeleton successfully “redirects” the assembly of dense, highly toxic fibril networks into short, low‐toxicity fragments, halting PD protein aggregation at its structural source.

FIGURE 10.

Structures of compounds 11 – 13.

Addressing the oxidative stress and apoptosis triggered by mitochondrial dysfunction, Zaiter et al. [6] designed a novel class of spiropyrazolone derivatives. The spiro‐fusion at the pyrazolone core significantly enhances the structural rigidity and lipophilicity of the molecule, optimizing its cellular penetrance to exert targeted intracellular neuroprotection. In SH‐SY5Y cellular assays, this class of compounds exhibited negligible cytotoxicity (84.92% viability at 50 μM). Against MPP⁺‐induced neurotoxicity (a classic dopaminergic PD model), the optimal candidate, compound 12, demonstrated extraordinary neuroprotective efficacy. Pretreatment with just 10 μM of 12 remarkably restored cell viability to 95% (compared to 54% in the unmedicated model group), outperforming the positive control curcumin. Further cellular evaluations confirmed that the spiropyrazolone core effectively stabilizes intracellular homeostasis by significantly elevating the mitochondrial membrane potential, thereby reversing the fatal mitochondrial collapse induced by MPP⁺.

Furthermore, activating the Keap1‐Nrf2 signaling pathway is a critical endogenous defense strategy to combat oxidative dopaminergic neuronal loss. Kim et al. [43] identified compound 13 through virtual screening as a highly active pyrazolone‐based Nrf2 activator. The electron‐rich nature and versatile heteroatomic backbone of the pyrazolone ring allow it to act as a potent protein–protein interaction (PPI) disruptor, selectively competing at the Keap1 binding interface to release and activate Nrf2. Compound 13 demonstrated excellent drug‐like pharmacokinetic properties, including high BBB permeability (Pe = 2.5 × 10⁻⁶ cm/s), low cytotoxicity in BV‐2 microglia (96% viability at 30 μM), and an outstanding oral bioavailability of 90.7% with a Tmax of 2 h. In cellular models of neuroinflammation, 13 markedly suppressed LPS‐induced microglial activation by downregulating the release of pro‐inflammatory cytokines NO, TNF‐α, and IL‐1β. Crucially, in an MPTP‐induced PD mouse model, oral administration of 13 (30 mg/kg/day, p.o.) successfully induced the expression of Nrf2‐dependent antioxidant genes and significantly reversed motor deficits (behavioral score: 3.86 ± 0.26, compared to 2.44 ± 0.35 in the model group). These findings underscore the versatility of the pyrazolone framework in coordinating both anti‐inflammatory and antioxidant defenses to prevent motor deterioration in vivo. Of note, the detailed hybridization strategies, therapeutic targets, and neuroprotective profiles of pyrazolone compounds against PD are summarized in Table 3.

TABLE 3.

Summary of the anti‐PD activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity	Cell or in vivo models
Kurnik et al.	11	Pyrazole/pyrazolone core + polar groups	α‐synuclein aggregation	α‐SN aggregation inhibition (11) IC50: 10.4 μM	Reduced lewy body‐like inclusions in neuronal cells
Zaiter et al.	12	pyrazolone + aldehydes (spiropyrazoles)	Neuroprotective effect	extraordinary neuroprotective efficacy	MPP+‐induced neuron damage model of PD
Kim et al.	13	Pyrazolone + benzenesulfonyl chloride derivatives	Keap1‐Nrf2 PPI, neuroinflammation	Nrf2 activation (13) EC50: 1.46 μM	MPTP‐induced PD mice model

2.1.3. Anti‐ALS

ALS, also known as Lou Gehrig's disease, is an irreversible and fatal neurodegenerative disorder defined by the progressive degeneration of upper and lower motor neurons, culminating in severe muscle atrophy and loss of motor function [44, 45]. Despite a low global incidence (~5 per 10,000), ALS progresses rapidly, typically resulting in death within 3–5 years and yielding the highest mortality rate among CNS diseases [8, 46]. While the exact pathogenesis remains elusive, progressive motor neuron death is driven by a complex interplay of oxidative stress, neurofilament damage, protein misfolding, mitochondrial dysfunction, glutamate excitotoxicity, and altered hypoxia responses [47]. Currently, the FDA has approved only two treatments: Riluzole (a glutamate receptor antagonist) and EDA [8]. Because these agents only delay disease progression without offering a cure, the discovery and development of novel, highly efficient therapeutics for ALS remain a formidable challenge.

The misfolding and aggregation of superoxide dismutase 1 (SOD1) are primary biomarker for ALS, making it a highly attractive target for contemporary drug design and screening [48]. Through cell‐based high‐throughput screening, Radhia et al. [49] identified the pyrazolone skeleton as a potent inhibitor of mutant SOD1‐induced cytotoxicity. SAR studies showed that the activity of the 1H‐pyrazol‐3(2H)‐one core (Type II) was generally superior to that of the 4‐ethylidene‐substituted derivatives (Type I). Systematic optimizations of the 1H‐pyrazol‐3(2H)‐one core yielded the arylsulfanyl pyrazolone derivative 14 (Figure 11), featuring a dichloro‐substituted aryl ring. This compound demonstrated remarkable anticytotoxic effects induced by SOD1 (EC₅₀ = 170 nM) and afforded complete (100%) survival protection in mutant SOD1‐challenged PC12 cells, vastly outperforming the positive control Radicanin. However, the in vivo viability of this thioether linkage was fundamentally bottlenecked by high hepatic microsome clearance and a deficient biological half‐life. To overcome this metabolic vulnerability, Chen et al. [50] executed a bioisosteric replacement strategy, exchanging the sulfur atom bridging the pyrazolone and aryl rings for an oxygen atom. The resulting aryloxy pyrazolone (AOP) derivative, compound 7e, completely reversed the metabolic instability while concurrently enhancing neuroprotective potency (ED₅₀ = 67 nM). Supported by a favorable pharmacokinetic profile and robust BBB permeability, chronic oral administration of compound 7e (20 mg/kg) in the G93A ALS transgenic mouse model dose‐dependently prolonged survival time by 13.3%, surpassing the in vivo efficacy of the clinical standard, riluzole.

FIGURE 11.

Structures and hybridization strategy of compounds I‐II and 14–17.

Despite the marked success of AOPs, their susceptibility to high first‐pass elimination prompted Zhang et al. [51] to further structurally evolve the scaffold by substituting the ether oxygen with amine linkers, thereby generating secondary and tertiary arylamino pyrazolone (AAP) derivatives. Crucially, in‐depth SAR investigations elucidated that the inherent keto‐enol tautomerism of the pyrazolone ring is indispensable for its biological activity: the free N2‐H structure and its corresponding tautomeric phenolic hydroxyl form serve as the essential pharmacophoric centers mediating neuroprotection. Among this optimized library, compounds 15 and 16 (Figure 11) effectively rescued cortical neurons from SOD1‐G93A‐induced toxicity, with ED₅₀ values of 0.78 and 0.57 μM, respectively. Notably, the tertiary amine 16 exhibited substantially superior metabolic stability in human liver microsomes compared to its oxygen‐linked predecessors. To further overcome the inherent polarity and BBB penetration limitations associated with heterocyclic CNS drugs, Zhang et al. [52] converted the tertiary amine pyrazolone into various salts. The optimal formulation, phosphate salt 17, successfully balanced aqueous solubility and lipophilicity, achieving a highly favorable brain‐to‐plasma (B/P) ratio of 0.6. Coupled with an exceptionally high in vivo safety margin (maximum tolerated dose of 640–1280 mg/kg), this targeted molecular evolution from thioether to phosphate salt firmly establishes the pyrazolone nucleus as a highly translatable foundation for novel ALS therapeutics. Table 4 provides a comprehensive summary of the hybridization strategies, targets, and in vivo/in vitro efficacies of pyrazolone derivatives against ALS.

TABLE 4.

Summary of the anti‐ALS activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity	In vivo models or efficacy
Radhia et al.	14	Arylsulfanyl pyrazolone	Mutant SOD1‐G93A aggregation and toxicity	Cytotoxicity protection (14) EC50: 0.17 μM	Permeated the BBB
Chen et al.	7e	Aryloxanyl pyrazolone	Mutant SOD1 aggregation and toxicity	Cytotoxicity protection (7e) EC50: 0.067 μM	Extended survival of G93A ALS mice; favorable PK
Zhang et al.	15, 16	Arylazanylpyrazolone (AAP)	Mutant SOD1‐ protein aggregation	Cytotoxicity protection (15, 16) EC50: 0.78, 0.57 μM	Enhanced microsome stability
Zhang et al.	17	Tertiary amine pyrazolone (Phosphate salt)	Mutant SOD1‐ protein aggregation	Cytotoxicity protection (17) EC50: 0.45 μM	High dose (640–1280 mg/kg) and BBB permeation (B/P = 0.6)

2.2. Other CNS Diseases

2.2.1. Antiepileptic and Anticonvulsant Activity

Epilepsy is a chronic neurological disorder characterized by recurrent unprovoked seizures associated with a functional imbalance between excitatory and inhibitory neurotransmission within the CNS [53], which affects more than 70 million people worldwide [54]. Clinical manifestations include loss of consciousness and involuntary movements, which frequently precipitate secondary cognitive impairments and complex psychiatric comorbidities [55, 56]. Current antiepileptic drugs (AEDs), primarily benzodiazepines (BZs) and γ‐aminobutyric acid (GABA) analogs, are frequently limited by adverse effects such as ataxia and anemia [57, 58]. Consequently, there is an urgent demand for the development of novel AEDs that combine enhanced efficacy with a superior safety profile.

Recent investigations have highlighted the versatile pharmacological profile of pyrazole and pyrazolone derivatives, particularly their potent anticonvulsant, anti‐inflammatory, antidepressant, and analgesic activities [59]. Building on this scaffold, Yousef Al‐ebini et al. [60] designed and synthesized a series of novel pyrazolinone derivatives. Molecular docking simulations indicated that these compounds interact with key protein targets involved in seizure modulation and microbial pathogenesis, specifically the GABA receptor (β‐3 subunit, PDB: 4COF), the NMDA receptor (NR1/NR2A subunits, PDB: 5TP9), and the AMPA receptor (Glutamate receptor 2, PDB: 5L1F). Among the synthesized library, compound 18a (Figure 12) demonstrated the highest binding affinity and significant antibacterial activity. Its stable binding is primarily driven by hydrogen bonding and π–π interactions between the pyrazolone core (including its substituents) and key amino acid residues such as Leu, Asp, and Ile. Furthermore, in vivo evaluation using a pentylenetetrazole (PTZ)‐induced seizure model demonstrated that compound 18a exhibited dose‐dependent anticonvulsant effects at 25, 37.5, and 50 mg/kg. At the 50 mg/kg dose, it significantly delayed seizure onset, reduced seizure duration, and achieved a 100% survival rate. The data indicate that compound 18a modulates the seizure threshold via GABAergic and glutamatergic pathways, thereby altering neuronal excitability.

FIGURE 12.

Structures of compounds 18a–c and 19a–b.

Viveka et al. [61] reported the structural modification of 1,3‐diarylpyrazole derivatives to yield diaryl‐pyrazolone hybrids 19a and 19b with promising anticonvulsant properties (Figure 12). The in vivo anticonvulsant profile, neurotoxicity, and analgesic activity were systematically evaluated using the maximal electroshock seizure (MES) test, the rotarod test, and the tail‐flick method, respectively. In the MES assay, anticonvulsant potency was quantified by comparing the duration of tonic hindlimb extension (THE) in mice against the reference drug phenytoin (25 mg/kg). SAR analysis revealed that the pyrazolone scaffold significantly enhanced anticonvulsant efficacy. Furthermore, the introduction of chlorine substituents at the R₁ and R₂ positions of the phenyl ring conferred superior anticonvulsant and analgesic activities compared to fluorine‐substituted analogs. These results suggest that compounds 19a and 19b are highly effective, low‐toxicity leads for the development of novel antiepileptic agents.

2.2.2. Antidepressant Activity

Depression remains one of the most prevalent psychiatric challenges globally, affecting ≈300 million people [62]. As a chronic and recurrent neurological syndrome, depression manifests across all demographics—with a notably higher incidence in females—and is characterized by persistent sadness, cognitive deficits, and neuroanatomical alterations such as hippocampal atrophy [63]. Projections by the World Health Organization (WHO) suggest that depression will become a leading cause of global mortality by 2030 [64]. Despite its prevalence, the exact pathogenesis of depression, involving complex neurochemical and neuroinflammatory pathways, is not yet fully elucidated [65]. Current clinical pharmacotherapy primarily utilizes selective serotonin reuptake inhibitors (SSRIs), monoamine oxidase inhibitors, and tricyclic antidepressants [66]. Additionally, certain anesthetic agents such as ketamine, isoflurane, and tramadol have also been reported to exert rapid antidepressant effects through multiple targets [67]. However, many existing treatments are hindered by limited efficacy and significant adverse effects, including cognitive impairment and sleep disturbances [68]. Consequently, identifying novel chemical scaffolds with improved therapeutic windows and fewer side effects remains a high priority in medicinal chemistry.

Merugumolu et al. [69] synthesized a series of pyrazolone‐based hybrids and evaluated their antidepressant potential (Figure 13). Antidepressant efficacy was evaluated by measuring the duration of immobility (DI) in behavioral models. In the forced swimming test (FST), compound 20e exhibited the highest potency (DI = 97.7 s at 100 mg/kg), which was comparable to the reference drug imipramine (DI = 94.0 s at 10 mg/kg) (Table 5). Similarly, in the tail suspension test (TST), compounds 20e and 20f demonstrated significant activity with DI values of 114.3 and 111.0 s, respectively, rivaling the imipramine control (109.0 s). Because reduced immobility in the FST and TST typically reflects enhanced central serotonergic (5‐HT) and catecholaminergic neurotransmission, the pyrazolone core likely mediates these antidepressant effects by blocking monoamine reuptake. SAR analysis indicated that disubstitution on the phenyl ring is critical for optimal activity. Specifically, derivatives with 3,4‐disubstitution—whether featuring strongly electron‐donating methyl groups (20e) or electron‐withdrawing chlorine atoms (20f)—displayed profoundly enhanced efficacy compared to their monosubstituted counterparts. Monosubstituted analogs, such as those bearing a single nitro (20b), fluoro, or bromo group, generally exhibited only weak to moderate activity. While these pyrazolone derivatives represent promising lead compounds, further investigation into their precise molecular targets and mechanisms of action is essential to guide future structural optimization.

FIGURE 13.

Structures of compounds 20a–g.

TABLE 5.

Antidepressant activity of the compounds by FST method.

Compounds	DI, s	% Change in immobility
20b	141.5 ± 3.6	−30.3
20e	97.7 ± 7.7	−51.9
20f	129.5 ± 12.7	−36.3
20g	171.0 ± 14.0	−15.8
Control	203.3 ± 6.2	—
Imipramine	94.0 ± 9.2	−53.8

Monoamine oxidases are flavin adenine dinucleotide‐dependent enzymes existing as two distinct isoforms, MAO‐A and MAO‐B. MAO‐A primarily regulates the catabolism of monoamine neurotransmitters (e.g., serotonin and norepinephrine) associated with mood regulation; its inhibition is a validated strategy for alleviating depressive symptoms. Conversely, MAO‐B targets dopamine and phenethylamine, and its inhibitors are typically explored for neuroprotective and mood‐stabilizing effects [70]. In this context, Eldebss et al. [71] synthesized a series of pyrazolone derivatives to evaluate their in vitro MAO inhibitory profiles and in vivo antidepressant efficacy (Figure 14). Using a sensitive fluorometric assay on bovine brain mitochondria, screening revealed that these novel compounds exhibited exceptionally potent and highly selective MAO‐A inhibition. Compounds 21a (Ki = 0.014 nM), 21b (Ki = 0.023 nM), and 21c (Ki = 0.034 nM) emerged as the most prominent inhibitors. Their selectivity indices (e.g., an SI of 10,159.71 for 21c) far surpassed those of the clinical standards clorgyline, moclobemide, and selegiline. This potent MAO‐A inhibition was further corroborated by radioligand binding assays in rat brain synaptosomes (e.g., IC₅₀ = 2.34 × 10⁻⁶ nM for 21a). In vivo, tryptamine‐induced seizure potentiation assays in rats demonstrated that compounds 21a and 21b possessed ED₅₀ values of 19.23 19.23 and 20.39 μM, respectively. Although their potency was lower than that of the standard drug deprenyl (ED₅₀ = 0.30 μM), these findings clearly confirmed their in vivo biological efficacy. Finally, molecular docking studies elucidated their binding modes within the MAO‐A active site, highlighting robust hydrogen bonding and π–π stacking interactions between the pyrazolone core and key residues such as Arg42, Tyr435, and Tyr398.

FIGURE 14.

Structures of compounds 21a–k.

2.2.3. Antianxiety Activity

Anxiety disorder, commonly referred to as anxiety neurosis, is a neurological disorder characterized by generalized and persistent anxiety or recurrent panic attacks [72]. The pathogenesis of anxiety involves a sophisticated network; notably, neurons in the central amygdala modulate anxiety‐related behaviors by regulating corticotropin‐releasing factor, GABA, and various neuropeptides [73]. While SSRIs and norepinephrine reuptake inhibitors (SNRIs) are the current clinical mainstays, they are frequently limited by a therapeutic lag and low response rates. BZs offer a more rapid onset of action but are associated with significant adverse effects, including cognitive impairment, sedation, ataxia, and the risk of tolerance and withdrawal [74]. Consequently, there is a substantial impetus to develop novel anxiolytics with high efficacy and improved safety profiles. GABA, the primary inhibitory neurotransmitter, exerts its physiological effects via the GABA_A receptor [75]. This receptor's α1, α2, α3, and α5 subunits contain binding sites for small‐molecule ligands like BZs. Specifically, the α1 subunit is primarily associated with sedative effects, whereas the α2 and α3 subunits are linked to anxiolytic activity [76]. Agonists that bind to the GABA_A receptor enhance GABAergic inhibitory neurotransmission, providing therapeutic benefits for CNS disorders [77].

López Rivilli et al. [78] designed and synthesized a series of quinoline‐pyrazolone hybrids (Figure 15). The ability of the compounds to displace specifically bound [³H]‐flunitrazepam ([³H] FNZ) was evaluated via a radioligand competition binding assay. SAR analyses revealed that introducing an 8‐methyl or 8‐bromo group, alongside an N‐1 p‐methoxyphenyl moiety, is highly beneficial for binding affinity. Notably, compounds 22f (IC₅₀ = 0.326 nM) and 22l (IC₅₀ = 0.370 nM) exhibited the highest affinities. Conversely, an 8‐methoxy substitution (22m, 22n) reduced affinity due to negative steric hindrance stemming from an increased van der Waals volume. In vivo behavioral evaluations using the classic elevated plus‐maze model in adult male Wistar rats revealed divergent pharmacological profiles. Importantly, these compounds did not inhibit spontaneous locomotor activity, suggesting they act as efficacious BZD_BS agonists devoid of the sedative side effects typical of classical BZs. In contrast, derivatives featuring an N‐1 unsubstituted phenyl (22e) or p‐fluorophenyl group (22g) significantly reduced open‐arm time at 0.25–0.5 mg/kg, displaying marked anxiogenic effects that the authors attributed to potential sedative or toxic actions. Furthermore, minor substituent modifications can cause a fundamental shift in pharmacological activity from an anxiolytic to an anxiogenic profile, providing crucial SAR data to support the design of allosteric modulators in this field.

FIGURE 15.

Structures of compounds 22a–n.

2.2.4. Antiacute Ischemic Stroke

Acute ischemic stroke (AIS) is a debilitating cerebrovascular disorder initiated by vascular occlusion, which triggers a catastrophic ischemic cascade characterized by focal neuronal dysfunction, severe neuroinflammation, compromised BBB integrity, and massive oxidative stress [79, 80]. While current therapeutic strategies aim to restore cerebral perfusion and minimize ischemia‐reperfusion (I/R) injury [81], their clinical utility is severely hampered by narrow therapeutic windows, significant reperfusion toxicity, and high attrition rates in clinical trials [82, 83]. Given that oxidative stress is a pivotal driver of the AIS pathogenic cascade, its inhibition remains a primary and highly validated therapeutic strategy [84]. In this domain, the pyrazolone scaffold—exemplified by the clinically approved agent EDA—serves as a prototypic antioxidant, utilizing its electron‐rich heterocyclic core to act as a potent electron donor that captures ROS and nitrogen species (RNS) [85]. However, the clinical efficacy of EDA is significantly constrained by its weak superoxide anion scavenging capability, fleeting biological half‐life, and suboptimal BBB permeability.

To address these pharmacokinetic limitations while amplifying the scaffold's inherent antioxidant potency, Li et al. [86] proposed a “dual‐antioxidant” strategy: combining a pyrazolone core—an EDA analogue with radical scavenging capacity to directly eliminate ROS, with a Danshensu (DSS) moiety derived from traditional Chinese medicine to indirectly exert long‐term neuroprotection via activation of the endogenous Keap1‐Nrf2 defense pathway (Figure 16). Based on this rationale, a library of 24 novel DSS–pyrazolone hybrids was designed and synthesized. DPPH assays revealed that most derivatives exhibited excellent in vitro direct radical scavenging capabilities (EC₅₀ = 27.78–63.63 μM). SAR analysis demonstrated that the length of the aliphatic linker connecting the two pharmacophores is critical for activity, with an n‐propyl chain exhibiting markedly superior potency over other lengths. Furthermore, ester‐linked conjugates afforded enhanced neuroprotective efficacy compared to their amide‐linked counterparts. Substituent modifications on the pyrazolone ring indicated that introducing an electron‐donating methyl group at the 3’‐position significantly outperformed electron‐withdrawing trifluoromethyl substitution. Finally, methylation of the phenolic hydroxyl groups on the DSS moiety resulted in a dramatic loss of cytoprotective activity, underscoring their indispensable role.

FIGURE 16.

Design concept and structure of Danshensu‐pyrazole derivative.

In an H₂O₂‐induced oxidative injury model using PC12 neural cells, compound 23c demonstrated the most potent, dose‐dependent neuroprotective activity (viability > 94% at 50 μM) without exhibiting prominent intrinsic cytotoxicity. At the molecular level, compound 23c effectively halted oxidative damage by downregulating lipid peroxidation markers (MDA and LDH) and restoring endogenous SOD activity. Crucially, Western blot analysis confirmed that this DSS‐pyrazolone hybrid actively stimulated the translocation of Nrf2 from the cytoplasm to the nucleus, subsequently upregulating the expression of the downstream antioxidant enzyme HO‐1, thereby fortifying the intrinsic cellular defense network. The translational potential of this design was validated in a permanent middle cerebral artery occlusion (pMCAO) mouse model, where oral administration of compound 23c (20 mg/kg) significantly ameliorated neurological deficits and reduced cerebral infarct volume, demonstrating profound in vivo superiority over both EDA monotherapy and an unlinked EDA/DSS coadministration.

Given that thrombosis induced by platelet aggregation is a primary etiological driver of AIS, and neuronal damage remains a hallmark pathological feature [83], Ting Cai et al. [87] designed and synthesized a series of 20 EDA–pyridazinone hybrids by merging the pyridazinone moiety of amipizone with the EDA core (Figure 17). Initial in vitro functional screening across 3D identified compound 24p as the most potent derivative, prompting its selection as the lead candidate for subsequent in vivo efficacy and safety evaluations. In vivo pharmacodynamic evaluation in a FeCl₃‐induced rat carotid artery thrombosis model showed that high‐dose compound 24p (10 mg/kg) outperformed the clinical benchmarks aspirin and clopidogrel in both delaying blood flow reduction and minimizing thrombus weight. In the MCAO ischemic stroke model, three consecutive days of treatment with compound 24p significantly attenuated neurological deficits (score: 1.17 ± 0.4 vs. 2.67 ± 0.52 in the model group). 2,3,5‐triphenyltetrazolium chloride staining results showed that compared with the model group (infarct volume: 23.97% ± 0.49%), compound 24p effectively reduced cerebral infarct volume (infarct rate: ≈10.88%), an effect superior to EDA and butylphthalide. The structural hybridization strategies, target pathways, and anti‐AIS activities of these pyrazolone derivatives are summarized in Table 6.

FIGURE 17.

Structures and hybridization strategy of compounds 24a–t.

TABLE 6.

Summary of the anti‐AIS activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity	In vivo models or efficacy
Li et al.	23c	Prazolone + danshensu	ROS, Keap1‐Nrf2/HO‐1, SOD	DPPH scavenging; cytoprotection in H2O2‐injured PC12 cells (viability > 94% at 50 μM)	pMCAO mouse model; reduced cerebral infarct volume and neurological deficits
Cai et al.	24p	EDA + amipizone	PDE3A, ROS	Inhibited ADP‐induced platelet aggregation (IC50 = 6.72 μM); DPPH scavenging (EC50 = 30.80 μM); cytoprotection in H2O2‐injured PC12 cells (viability 83.62% at 50 μM)	FeCl3‐induced rat thrombosis model; rat MCAO model; exhibited low bleeding risk

2.3. Anti‐Inflammatory Activity

The pyrazolone scaffold holds a crucial position in the development of anti‐inflammatory drugs due to its high structural similarity to the core pharmacophores of NSAIDs. In recent years, driven by precise molecular hybridization strategies, novel pyrazolone derivatives have not only made significant breakthroughs in inhibiting traditional cyclooxygenase (COX) and lipoxygenase (5‐LOX) pathways, but have also demonstrated outstanding potential and safety in regulating pro‐inflammatory cytokine storms and complex inflammatory networks (such as neuroinflammation) [88].

Because inhibiting solely the COX‐2 enzyme often leads to cardiovascular side effects, the dual inhibition of COX‐2 and 5‐LOX is considered a rational approach for developing safe and effective anti‐inflammatory agents. Based on this rationale, Shabaan et al. [89] designed a series of novel celecoxib‐pyrazolone hybrids structurally related to celecoxib and FPL 62064. The design strategy specifically incorporated a sulfonamide or carboxylic acid moiety linked to a dihydropyrazolone nucleus, while substituting position 4 with various chalcone derivatives to potentiate activity (Figure 18). SAR analysis revealed that the presence of the grafting phenyl group at position 1 and the sulfonamide (SO₂NH₂) moiety significantly enhanced COX‐2 affinity by fitting into its larger secondary pocket. Concurrently, substitution at the C‐4 position with a bulkier trimethoxybenzylidene group greatly optimized COX‐2 selectivity. In vitro assays demonstrated that compound 26h exhibited extremely high COX‐2 selectivity (IC₅₀ = 99.19 nM; S.I. = 121.79). Meanwhile, compounds 25g and 26b displayed excellent 5‐LOX inhibitory activity (IC₅₀ values of 0.67 and 0.46 μM, respectively). In vivo evaluation using the carrageenan‐induced rat paw edema model confirmed that these optimized compounds (25f, 25h, 26d, 26h) reduced edema volume by 34%–46%, with compound 26d robustly inhibiting serum PGE2 production by 69%. Macroanatomical observations verified that these selective leads were completely devoid of ulcerogenic effects.

FIGURE 18.

Structures and hybridization strategy of compounds 25a–h and 26a–h.

Similarly, aiming to combat the COVID‐19‐related hyper‐inflammatory syndrome alongside typical replication, Abdelall et al. [90] developed a series of novel dual‐acting agents by hybridizing the antipyrine core with celecoxib and various bioactive heterocycles (such as thiazole, pyrazole, and pyridine) (Figure 19). SAR refinement indicated that 1,3,5‐triaryl pyrazole derivatives (27) possess significantly higher COX‐2 selectivity than 1,5‐diaryl analogs (28). Furthermore, maintaining a p‐chlorophenyl group generally yielded superior selectivity compared to p‐methoxyphenyl substitutions. Within this library, compound 27d achieved superior selective COX‐2 inhibition (IC₅₀ = 1.36 μM, S.I. = 6.94). The multitarget compounds 27e and 28f exhibited potent anti‐inflammatory efficacy in vivo, achieving a maximal edema inhibition rate of 54.31% and markedly downregulating core pro‐inflammatory cytokines (TNF‐α, IL‐6, and IL‐1β). Crucially, compound 27e demonstrated exceptional gastric tolerability with an ulcer index (U.I.) as low as 1.3, while significantly downregulating myocardial injury biomarkers (CK‐MB, AST, LDH) to overcome typical coxib‐related risks. Additionally, 27e effectively targeted viral replication by noncovalently inhibiting the SARS‐CoV‐2M^pro enzyme (IC₅₀ = 13.2 μM) [91].

FIGURE 19.

Structures and hybridization strategy of compounds 27a–f and 28a–f.

Furthermore, to simultaneously disrupt interconnected inflammatory and oncogenic cascades, Biltekin Kaleli et al. [92] synthesized a novel series of thiazole‐pyrazolone hybrids by derivatizing the nonsubstituted position of the pyrazolone ring to shift metabolic pathways and enhance CNS penetration (Figure 20). SAR principles highlighted that introducing specific aromatic or heterocyclic groups on the thiazole ring allowed the molecules to mimic nonselective, classical frameworks while leaning toward safe configurations. Strikingly, the lead compounds 29g and 29h showed absolutely no inhibitory activity against COX‐1, while maintaining high selectivity toward COX‐2. Compound 29g emerged as a highly versatile multitarget agent, demonstrating potent simultaneous inhibition against signaling kinases including p38 MAPK and EGFR [93]. This dual‐binding characteristic targeting both COXs and inflammatory‐oncogenic kinase networks serves as a key mechanism for drugs to exert deep, synergistic anti‐inflammatory effects. To further enhance the local therapeutic effects of such multipathway scaffolds in peripheral conditions (e.g., osteoarthritis), current efforts are dedicated to discovering emerging targets such as renin‐angiotensin system inhibition [94], and combining them with targeted delivery systems (such as neutrophil‐manipulating nanosystems or polymeric nanocapsules that enhance cartilage penetration) to precisely release drugs, which has become a frontier consensus to amplify efficacy and circumvent systemic side effects [95, 96].

FIGURE 20.

Structures and hybridization strategy of compounds 29a–h.

Beyond downstream prostaglandin (PG) blockade, directly intercepting upstream core transcription factors presents a frontier in recent pyrazolone research. Rizk et al. [97] reported the design and synthesis of novel pyranopyrazole‐nicotinamide hybrids as safe NSAID candidates with lower side effects (Figure 21). SAR data demonstrated that the inclusion of an electron‐donating substituent (such as a methoxy group) on the phenyl ring of the pyranopyrazole core substantially enhanced the anti‐inflammatory profile. Driven by computational screening, compound 30d exhibited the supreme docking binding energy of −9.4578 kcal/mol against the target NF‐κB protein. In vivo evaluation using the carrageenan‐induced rat paw edema model corroborated these findings, where 30d led to an excellent regression of all inflammatory biomarkers (TNF‐α, IL‐6, INF‐γ, and NF‐κB) back to nearly normal ranges. Furthermore, acute toxicity profiling revealed an LD₅₀ > 5000 mg/kg with complete absence of hepatorenal toxicity, highlighting the safe therapeutic window of this hybrid framework. Indeed, the targeted modulation of core inflammatory pathways including TNF, alongside interventions in specific cellular states like microglial ferroptosis, is increasingly recognized as a universal strategy to alleviate severe inflammatory pathologies [98]. Moreover, whether intercepting the systemic cascade via pyroptosis inhibition [99], or restoring immune homeostasis by regulating macrophage glycolysis [100], these advanced mechanisms provide entirely new perspectives for the future mechanistic design of multitarget pyrazolone drugs.

FIGURE 21.

Structure and hybridization strategy of compound 30.

Chronic neuroinflammation in the brain is a core pathological factor leading to cognitive impairment and neurodegenerative diseases. Targeting this pathology, Kanwal et al. [101] developed a series of central neuroprotective agents by hybridizing the pyrazolone core with picolinic and nicotinic acid pharmacophores (Figure 22). SAR analysis clearly showed that coupling the pyrazolone ring with an ortho‐hydroxyl group (‐OH) on the benzylidene moiety dramatically augmented the hydrogen‐bonding capacity and free radical scavenging potential. In a PTZ‐induced neurodegeneration model, the lead compound 31a significantly reversed brain oxidative stress (elevating GSH and CAT levels) and potently suppressed the phosphorylated NF‐κB/TNF‐α inflammatory cascade, exhibiting excellent anticonvulsant and neuroprotective activities. In a subsequent study targeting dementia, their optimized pyrazolone‐nicotinic acid derivative 31b (at doses of 10–30 mg/kg) was validated. Compound 31b not only significantly ameliorated short‐term memory and spatial learning deficits in mice but also drastically downregulated the aberrant expression of p‐NF‐κB, TNF‐α, and COX‐2 in brain tissues. Concurrently, 31b effectively prevented neuronal apoptosis and promoted cellular recovery by modulating downstream p‐JNK pathways and maintaining neuronal viability [33]. These sequential studies systematically demonstrate that such pyrazolone hybrids possess exceptional multitarget potential to combat neuroinflammation by precisely targeting the ROS/NF‐κB/COX‐2 signaling axis, aligning perfectly with broader neuroprotective paradigms: specifically, activating the Nrf2 pathway, exerting antiexcitotoxicity, or suppressing abnormal glial activation to combat secondary brain injury [38, 98, 102]. Of note, Table 7 summarizes the specific hybridization strategies, biological targets, and anti‐inflammatory efficacies of these pyrazolone hybrids.

FIGURE 22.

Structures and hybridization strategy of compounds 31a–b.

TABLE 7.

Summary of the anti‐inflammatory activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity (IC 50 /binding)	In vivo models or efficacy
Shabaan et al.	25f, 26b, 26d, 26h	Pyrazolone + celecoxib	COX‐2, 5‐LOX	COX‐2 (26h): 99.19 nM (S.I. = 121.79); 5‐LOX (25f, 26b): 0.67 μM, 0.46 μM	Carrageenan rat paw edema
Abdelall et al.	27d, 27e, 28f	Antipyrine + celecoxib + thiazole /pyrazole/pyridine	COX‐2, SARS‐CoV‐2 Mpro	COX‐2 (27d): 1.36 μM (S.I. = 6.94); Mpro (7e): 13.24 μM	Carrageenan rat paw edema
Biltekin Kaleli et al.	29g, 29h	Pyrazolone + thiazole + aromatic groups	COX‐2, p38 MAPK, EGFR	Selective COX‐2; p38 MAPK and EGFR (29g)	In silico glioblastoma/cancer models
Rizk et al.	30d	Dihydropyrano[2,3‐c]pyrazole + nicotinamide	NF‐κB; Pro‐inflammatory cytokines	Docking binding energy to NF‐κB (−9.4578 kcal/mol)	Carrageenan rat paw edema
Kanwal et al.	31a	Pyrazolone + picolinic acid + benzaldehyde derivatives	ROS, p‐NF‐κB, TNF‐α	Free radical scavenging and antioxidant enzyme preservation	PTZ‐induced mouse
Kanwal et al.	31b	Pyrazolone + nicotinic acid + hydroxybenzylidene moiety	AChE, p‐NF‐kB, TNF‐a, COX‐2, p‐JNK	Potent AChE inhibition	Scopolamine‐induced mouse

2.4. Analgesic Activity

Pyrazolone derivatives (including classical drugs like dipyrone and antipyrine) have long been recognized as a pivotal scaffold for pain management. Considering that traditional nonsteroidal analgesics (such as acetaminophen and ibuprofen) frequently face safety challenges, including potential hepatorenal toxicity in specific populations like minors, recent structural modifications and molecular hybridization strategies have aimed to enhance the potent analgesic efficacy of pyrazolone drugs across different pain modalities—ranging from peripheral nociception to central and neuropathic pain—while maximally mitigating systemic side effects [103].

At the peripheral level, pyrazolone drugs primarily exert their analgesic effects by inhibiting COX, thereby preventing the synthesis of PGs (such as PGE2) that sensitize peripheral nociceptors to pain stimuli. Sahin et al. [104] evaluated novel benzofuran‐pyrazolone hybrids, designed to merge two distinct anti‐inflammatory pharmacophores into a single entity. SAR revealed that specific α‐hydroxy substitutions optimized enzymatic binding, with compound 32b (Figure 23) identified as a potent inhibitor of both COX‐1 (IC₅₀ = 12.0 μM) and COX‐2 (IC₅₀ = 8.0 μM). In addition, the COX‐2 inhibitory activities of compounds 32a and 32b were comparable to that of the reference analgesic indomethacin (7.44 μM). All compounds (with the exception of compound 32e) displayed a certain, albeit nonsignificant, degree of selectivity toward COX‐2. Further cellular assays demonstrated that these compounds possessed low cytotoxicity and exerted inhibitory effects on nitric oxide (NO) production, among which compounds 32d, 32f, and 32h also displayed weak inhibitory activity against IL‐6.

FIGURE 23.

Structures and hybridization strategy of compounds 32a–i.

Similarly, Al‐Sanea et al. [105] utilized a molecular hybridization strategy to incorporate oxadiazole, thiadiazole, and pyrimidine pharmacophores into an antipyrine scaffold, aiming to synthesize oxadiazole/thiadiazole‐antipyrine hybrids to circumvent ulcerogenic gastric side effects (33–35, Figure 24). In vitro enzymatic assays demonstrated that compounds 33b–d and 35d exhibited potent COX‐2 inhibitory activity, with IC₅₀ ranging from 53 to 69 nM. Notably, SAR analysis indicated that introducing halogen substituents (chlorine or bromine) at the para‐position of the oxadiazole‐linked phenyl ring significantly enhanced binding within the COX‐2 secondary pocket. Consequently, compounds 33b (Cl‐substituted) and 33c (Br‐substituted) demonstrated optimal COX‐2 selectivity, with selectivity indices of 4.44 and 1.86, respectively. In carrageenan‐induced in vivo animal models, compounds 33b and 33c not only significantly reduced tissue swelling but also substantially downregulated the tissue levels of prostaglandin PGE2, while significantly inhibiting the release of pro‐inflammatory cytokines such as TNF‐α. Mechanistic investigations demonstrated that these compounds drive their analgesic and anti‐inflammatory efficacy via a multitarget mechanism. This encompasses the direct structural inhibition of COX enzymes, blockade of the NF‐κB signaling cascade, downregulation of COX‐2 overexpression, and robust amelioration of oxidative and nitrosative stress markers (e.g., MDA and NO) in target tissues. Overall, this research demonstrates that these novel nonacidic antipyrine hybrids effectively disrupt the signaling networks of inflammatory pain, providing highly promising lead scaffolds for the development of safe analgesics.

FIGURE 24.

Structures and hybridization strategy of compounds 33–35.

Furthermore, through structure‐based virtual screening, da Silveira et al. [106] rationally designed and identified four dioxobutenyl‐antipyrine hybrids combining the active dipyrone metabolite 4‐aminoantipyrine with a 1,4‐dioxo‐2‐butenyl moiety. Analgesic activity evaluations demonstrated that all four compounds (compounds 36–39, Figure 25) inhibited the involvement of biogenic amines in the formation of paw edema and attenuated pain responses during the inflammatory phase. Among them, compound 39 likely exerts its effects by specifically blocking the production of PGs, whereas compound 37 acts by reducing the actions of reactive oxygen/nitrogen species and/or cytokines. Furthermore, compounds 37 and 39 successfully mitigated leukocyte recruitment induced by intraperitoneal injection of carrageenan in animal models, decreasing the response intensity by 77.8% and 35.6%, respectively. Molecular docking SAR indicated that these compounds structurally block arachidonic acid from entering the COX‐2 hydrophobic channel, specifically preventing access to the essential Tyr385 residue. These studies confirm that the targeted blockade of peripheral inflammatory mediator networks is the foundation for achieving safe and long‐lasting analgesia.

FIGURE 25.

Structures of compounds 36–39, 40a–d.

Beyond peripheral targets, recent investigations have deeply explored the nonopioid central analgesic pathways of pyrazolones. Anwar et al. [107] synthesized novel pyrazolone derivatives to explore their dual antioxidant and antinociceptive potential. SAR observations revealed that the introduction of a strong electron‐withdrawing nitro group profoundly enhanced both radical scavenging capability and central analgesic efficacy. Consequently, the synthesized pyrazolone derivatives (40a–d, Figure 25) all exhibited significant central analgesic activity in the hot‐plate test at a remarkably low dose of 6 mg/kg. Among them, compound 40b, featuring a nitro substituent, demonstrated the most potent efficacy, with a reaction latency exceeding that of the standard centrally acting analgesic tramadol. Crucially, pretreatment with naloxone (0.5 mg/kg) failed to reverse these analgesic effects, confirming that these molecules operate via a nonopioid central mechanism, and this efficacy correlated strongly with their potent radical scavenging properties.

Mohammad et al. [108] also evaluated isoniazid‐antipyrine hybrids combining a 4‐aminoantipyrine core with isoniazid‐derived heterocycles (41– 43, Figure 26). SAR indicated that incorporating oxadiazole or tetrazole rings into the pyrazolone backbone optimized the physicochemical profile for comprehensive pain relief. Analgesic activity evaluations revealed that compounds 41b, 42b, and 43a exhibited optimal activity in the hot‐plate test, while compounds 41a, 42b, and 43b demonstrated significant efficacy in the writhing test. Notably, compound 42b emerged as a versatile lead candidate, displaying favorable effects in both pain models (with an inhibition rate of 45% in the hot‐plate test and 52% in the writhing test), demonstrating dual efficacy against both central and peripheral pain modalities. To fully unlock the clinical potential of such multitarget, nonopioid scaffolds, future research must bridge their broad analgesic effects with emerging mechanisms of refractory chronic pain. For instance, investigating how pyrazolone derivatives might modulate specific ion channels involved in painful diabetic neuropathy, or exploring their potential synergy with novel neuroimmune targets like the P2Y14 receptor in the trigeminal ganglion, represents a critical next step [109, 110]. Of note, a summary of the hybridization strategies, relevant targets, and analgesic profiles of pyrazolone derivatives is presented in Table 8.

FIGURE 26.

Structures and hybridization strategy of compounds 41–43.

TABLE 8.

Summary of the analgesic activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity (IC 50 /binding)	In vivo models or efficacy
Sahin et al.	32a–b	Benzofuran + pyrazolone	COX‐1, COX‐2, IL‐6, NO	COX‐2 (2): 8.0 μM	Cellular assays: reduced NO and IL‐6
Al‐Sanea et al.	33b–c	Antipyrine + oxadiazole (nonacidic)	COX‐2, NF‐κB, PGE2, ROS/NO	COX‐2 (4b): 53 nM (S.I. = 4.44)	Carrageenan paw edema
da Silveira et al.	37, 39	4‐aminoantipyrine + 1,4‐dioxo‐2‐butenyl	COX‐2 (Hydrophobic channel blockade)	Potent Tyr385 shielding	Reduced leukocyte recruitment
Anwar et al.	40b	Pyrazolone + nitro substitution	Central nonopioid pathway, ROS	Prominent free radical scavenging	Hot‐plate
Mohammad et al.	41a–b, 42b, 43a–b	4‐aminoantipyrine + isoniazid (oxadiazole/tetrazole)	Central and peripheral pain modalities	Favorable docking scores (−8.7 to −9.2 kcal/mol)	Hot‐plate and writhing

2.5. Anticancer Activity

In recent years, with the deepening of molecular hybridization strategies and precision targeted drug design, the pharmacological potential of pyrazolone derivatives in the antitumor field has been greatly explored and yielded significant breakthroughs. By introducing diverse pharmacophores (such as aryl groups, heteroaryl rings, Schiff bases, metal complexes, etc.) at the C‐3, C‐4, or N‐1 positions of the pyrazolone scaffold, these compounds can be endowed with multitargeted anticancer activities. Through mechanisms including the inhibition of specific protein kinases, interference with tubulin polymerization, induction of apoptosis, blockade of immune checkpoints (e.g., PD‐1/PD‐L1), and modulation of tumor metabolic networks, these novel pyrazolone‐based anticancer agents have demonstrated excellent inhibitory efficacy across various malignant tumor models, including nonsmall cell lung cancer, colorectal cancer (CRC), breast cancer, and cervical cancer.

The aberrant expression and constitutive activation of protein kinases, particularly receptor tyrosine kinases (RTKs), play pivotal roles in tumor proliferation, invasion, and chemoresistance [111, 112]. The pyrazolone structure can specifically block signal transduction pathways crucial for tumor survival by mimicking kinase substrates or occupying the ATP‐binding pocket. The treatment of CRC is frequently challenged by drug resistance resulting from mutations (e.g., TRAIL) [113]. The FLT3 gene encodes an RTK that is overexpressed in colon cancer patients. Moghaddam et al. [114] designed a series of novel FLT3‐targeted inhibitors based on a 1,3‐diarylpyrazolone scaffold by introducing various heterocycles via Suzuki cross‐coupling reactions (Figure 27). SAR analysis revealed that compounds 44b, 44e, 44i, and 44j exhibited strong cytotoxicity against tumor cells. However, compounds 44b and 44e, which contain large fused aromatic systems, showed limited selectivity between malignant and nonmalignant cells. Among them, compound 44j, which contains a pyrimidine ring linked to a piperidine moiety, exhibited potent and selective binding affinity for FLT3 (IC₅₀ = 8.2 μM). Pharmacological evaluations indicated that compound 44j exerted a robust antiproliferative effect on WiDr CRC cells harboring multiple mutations (IC₅₀ = 0.47 μM), while displaying minimal toxicity toward noncancerous colon fibroblasts (CRL‐1459). Kinase profiling and molecular docking confirmed that the compact bicyclic structure is critical for conferring its high activity and selectivity. Mechanistically, compound 44j not only suppressed tumor cell colony formation and blocked cell migration in a time‐dependent manner, but also induced autophagy by upregulating LC3A/B and triggered the intrinsic mitochondrial apoptotic pathway through the activation of caspase‐9 and PARP cleavage.

FIGURE 27.

Structures of compounds 44a–l.

Furthermore, hyperactivation of the PI3K/Akt signaling pathway leads to the alternative activation of macrophages [115], directly promoting cancer cell proliferation, angiogenesis, and survival. Meanwhile, it exhibits cross‐talk with the Raf‐1/ERK1/2 cascade [116]. Noser et al. [13] designed and synthesized a novel series of chalcone‐pyrazolone hybrids. Among these derivatives, compound 45 demonstrated exceptionally high binding energy to PI3K and Akt in molecular docking studies (Figure 28). In vitro cellular assays confirmed that compound 45 effectively inhibited the Caco cancer cell line (IC₅₀ = 23.34 μM). Its underlying pharmacological mechanism lies in its ability to significantly inhibit PI3K/Akt protein activity and increase ROS production by inducing oxidative stress. The accumulation of ROS leads to mitochondrial dysfunction, which in turn upregulates the expression of the pro‐apoptotic protein Bax and the tumor suppressor gene p53, while downregulating the antiapoptotic protein Bcl‐2, ultimately arresting the cancer cell cycle at the sub‐G0/G1 phase. In addition, this compound can significantly downregulate Raf‐1 gene expression, thereby inhibiting downstream ERK1/2 proteins to achieve the dual efficacy of suppressing tumor proliferation and metastasis.

FIGURE 28.

Structures of compound 45.

In a parallel approach, AboulWafa et al. [117] utilized the anticancer‐active “2‐anilino‐pyrimidine” scaffold as the core framework, introducing various flexible chains or rigid ring systems (such as hydrazone moieties, esters, fused triazole rings, and a cyano‐bearing pyrazolone core) at the C4 position of the pyrimidine ring. This structural modification aimed to identify novel small molecules capable of forming optimized conformations alongside enhanced hydrogen‐bonding and hydrophobic interactions with the target protein. Among the synthesized library, four pyrimidine‐pyrazolone hybrids were identified (Figure 29). In vitro antiproliferative assays revealed that compounds 46a and 46c exhibited outstanding antiproliferative profiles, which were significantly superior to those of the classic chemotherapeutic agent 5‐fluorouracil (5‐FU). SAR analysis demonstrated that the tolerance of substituents on the pyrazolone ring followed the order of phenyl > H > sulfur. This trend suggests that the bulky, hydrophobic phenyl group likely participates in favorable hydrophobic labeling and aromatic π–π stacking interactions within the binding pocket. Further enzymatic assays elucidated that compound 46a is a potent EGFR inhibitor (IC₅₀ = 139.59 ng/mL), exhibiting activity comparable to erlotinib (IC₅₀ = 138.53 ng/mL). Apoptosis is one of the most common pathways through which anticancer drugs induce cell death. Caspase‐9, as an indicator of apoptosis induction, activates intracellular endonucleases and proteases, leading to chromosomal DNA degradation and the breakdown of nuclear and cytoskeletal proteins, ultimately resulting in the formation of apoptotic bodies. Mechanistically, compound 46a was found to trigger apoptosis in MCF‐7 cells through the activation of the caspase‐9 signaling pathway.

FIGURE 29.

Structures of compounds 46a–d.

Microtubules are essential components of the cytoskeleton and play a central role in mitosis [118]. Small‐molecule compounds that bind to the colchicine‐binding site of tubulin can induce microtubule depolymerization, thereby disrupting the tumor blood supply and inducing apoptosis [118, 119]. To overcome the drawback of activity loss in Combretastatin A‐4 (CA‐4) due to the cis‐trans isomerization of its double bond, Burja et al. [120] innovatively utilized a pyrazolone ring to “lock” the two aryl groups of CA‐4 at the C‐4 and C‐5 positions, synthesizing CA‐4‐pyrazolone hybrids (Figure 30). Biological evaluations demonstrated that the free hydrazine precursors (such as compound 47) and the deprotected pyrazolone analogs (compounds 48a–c) exhibited excellent antitubulin and broad‐spectrum anticancer activities. Notably, compound 47 showed potent cytotoxicity against human cervical cancer HeLa cells (IC₅₀ = 0.048 μM) and highly effectively inhibited tubulin polymerization (achieving a 97% inhibition rate at 20 μM). N‐1 deprotected pyrazolone compounds 48a and 48b were more cytotoxic to cisplatin resistant human laryngeal carcinoma CK2 cells compared to the parental HEp‐2 cells. In addition, compounds 48a–c were more cytotoxic to invasive urinary bladder carcinoma T‐24 cells than to noninvasive urinary bladder carcinoma RT‐112 cells.

FIGURE 30.

Structures and design concept of compounds CA‐4, 47, and 48a–c.

The blockade of the PD‐1/PD‐L1 immune checkpoint pathway is a core strategy in modern tumor immunotherapy; however, current clinical practices predominantly rely on monoclonal antibodies [121, 122]. The development of orally bioavailable small‐molecule inhibitors is critical to overcoming the limitations of antibody‐based drugs. EDA, an approved free radical scavenger possessing a phenylpyrazolone scaffold, does not possess anti‐PD‐L1 activity. Nevertheless, Regnault et al. [123] designed a class of high‐affinity small‐molecule PD‐L1 antagonists (PyrDLones) utilizing a dichlorophenylpyrazolone core. Microscale thermophoresis experiments confirmed that a fluorophenylpyrazolone derivative (compound 49, Figure 31) exhibited nanomolar binding affinity (Kd = 27 nM) with the recombinant human PD‐L1 protein. More importantly, compound 49 displayed a unique mechanism of action—it could directly induce PD‐L1 protein dimerization (Kd = 1.2 nM) in a dose‐dependent manner, thereby generating a “gene silencing” effect that prevented its binding to the PD‐1 receptor. At the cellular level, the compound blocked the activation of the tyrosine phosphatase SHP‐2 mediated by the PD‐L1/PD‐1 interaction and successfully restored the proliferative capacity of cytotoxic T cells (CTLL‐2) that had been suppressed by PD‐L1, achieving reactivation of the immune system. Concurrently, it retained the antioxidant and aldehyde‐reactive properties (scavenging DPPH and DMPO radicals) derived from the pyrazolone core, which aids in ameliorating the oxidative stress state within the tumor microenvironment.

FIGURE 31.

Structures of compound 49.

Zinc(II) ions are indispensable for maintaining the proper spatial conformation and transcriptional activity of the tumor suppressor protein p53. Over 50% of cancers harbor p53 mutations, many of which (such as R175H and R273H) tend to cause the loss of Zn²⁺ bound to the DNA‐binding domain, triggering protein unfolding and aggregation [2]. This results not only in the loss of tumor‐suppressive function but also in the acquisition of oncogenic activities. Xhafa et al. [2] synthesized a series of Schiff base ligands derived from 4‐aminoalkylidene‐5‐pyrazolones and their homoleptic Zn(II) complexes [Zn(Ln)₂] (Figure 32). Research demonstrated that these pyrazolone‐containing Zn(II) complexes could undergo hydrolysis in solution to release zinc ions. In vitro 3D tumor spheroid proliferation models and scratch‐wound healing assays evidenced that complexes capable of efficient dissociation and zinc ion release (such as compounds 50a–e) exhibited potent antiproliferative and anti‐invasive capabilities in breast cancer (SKBR3) and glioblastoma (U373 MG) cells carrying mutp53. Their pharmacological mechanism involves acting as zinc donors to exogenously replenish the chelated or lost Zn²⁺, significantly downregulating mutp53 protein expression levels, thereby inducing tumor regression and restoring cellular sensitivity to chemotherapy.

FIGURE 32.

Structures and design concept of compound 50.

Thymidine phosphorylase (TP) is an angiogenic enzyme highly expressed in solid tumors such as breast and lung cancers, directly promoting tumor invasion and metastasis [124]. Bensaber et al. [125] designed and synthesized Schiff base‐antipyrine hybrids (Figure 33). Spectroscopic studies confirmed that compound 51 could engage in tight intercalation with calf thymus DNA, directly interfering with DNA replication and transcription, thereby generating robust cytotoxicity in the human breast cancer (MCF‐7) cell model, and demonstrating a dual potential to inhibit tumor angiogenesis and induce apoptosis.

FIGURE 33.

Structures and design concept of compound 51.

Aljohani et al. [126] developed a series of pyrazolone derivatives (compounds 52, 53, Figure 34) integrated into a chitosan/polyvinyl alcohol (Cs/PVA) nanogel delivery system. The in vitro cytotoxicity of these compounds and their nanoformulations was evaluated against HepG2, A549, MCF‐7, and HCT‐116 cell lines. The pyrazolone derivatives exhibited robust antiproliferative effects; for instance, compound 52 yielded 6.30, 10.60, 8.80, and 8.30 μM, respectively. Notably, the nanogel encapsulation significantly augmented cytotoxicity, achieving a 50.0% increase in potency against MCF‐7 cells. Mechanistic investigations revealed that these derivatives act as dual‐action agents, demonstrating both DNA intercalating ability (IC₅₀: 30.78–38.65 μM) and Topoisomerase II inhibitory activity (IC₅₀: 0.900–1.485 μM), positioning them as promising leads in DNA‐targeted therapy.

FIGURE 34.

Structures of compounds 52–53.

The structural modification of compounds can lead to highly efficient inhibition of specific cancer cell lines. The acquired resistance of lung cancer to traditional TKI inhibitors and their toxic side effects have created an urgent need for the development of non‐TKI drugs [127]. Dahal et al. [128] synthesized a series of 1,3‐diarylpyrazolone derivatives using a microwave‐assisted approach. Biological evaluations showed that this class of compounds exhibited strong antiproliferative activity in A549 and NCI‐H522 lung adenocarcinoma cells. In particular, compound 54a (containing a p‐bromophenyl group) and 54b (containing a p‐trifluoromethylphenyl group) demonstrated activity and selectivity against cancer cells that were even superior to those of the clinical first‐line drugs Afatinib and Gefitinib (Figure 35). Cell cycle analysis indicated that 54a and 54b arrested NSCLC cells at the G0/G1 phase, whereas 54c and 54d, which contain ortho‐halogen substitutions, induced G2/M phase arrest. This SAR suggests that the aryl substitution at the C‐3 position of the pyrazolone ring and the presence of halogens/strong electron‐withdrawing groups on the ring are crucial determinants for enhancing antinonsmall cell lung cancer activity. Additionally, Saidachary et al. [129] hybridized benzoxepine with the pyrazolone scaffold; the resulting benzoxepinoisoxazolone and pyrazolone compounds (such as compound 54e) not only possessed antimycobacterial activity but also exhibited favorable cytotoxicity in cancer cell lines like HeLa.

FIGURE 35.

Structures of compounds 54a–e.

Due to its high structural plasticity, the pyrazolone has evolved from a traditional NSAID drug scaffold into a broad‐spectrum anticancer pharmacophore with immense potential. By introducing targeting ligands, forming bicyclic/polycyclic systems, or complexing with metals, pyrazolone derivatives have exhibited diverse anticancer pharmacological mechanisms. They can selectively inhibit key survival kinases such as FLT3 and PI3K/Akt, directly interfere with tubulin polymerization, antagonize PD‐1/PD‐L1 immune checkpoints, inhibit tumor angiogenic enzymes (TP), and act as zinc donors to correct p53 mutations. These findings suggest that molecular hybridization strategies based on the pyrazolone backbone represent an excellent pathway for the future development of novel small‐molecule targeted antitumor drugs characterized by low toxicity, multitargeting capabilities, and the ability to overcome resistance. Future research should further focus on optimizing their in vivo pharmacokinetic properties and conducting more in vivo pharmacodynamic studies and early‐stage clinical trials to accelerate the translation of these highly promising hit compounds into clinical applications. Of note, Table 9 summarizes the structural hybridization strategies, diverse targets, and broad‐spectrum anticancer activities of these pyrazolone‐based hybrids.

TABLE 9.

Summary of the anticancer activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity (IC 50 /binding)
Moghaddam et al.	44j	1,3‐diarylpyrazolone + pyrimidine + piperidine	FLT3, LC3A/B, caspase‐9, PARP	FLT3: 8.2 μM; WiDr cells: 0.47 μM
Noser et al.	45	Pyrazolinone + chalcone	PI3K/Akt, ROS, Bax, p53, Bcl‐2, Raf‐1/ERK1/2	Caco cells: 23.34 μM
AboulWafa et al.	46a, 46c	Pyrazolone + 2‐anilino‐pyrimidine	EGFR, Caspase‐9	EGFR inhibition (46a): 139.59 ng/mL; superior to 5‐FU in MCF‐7 cells
Burja et al.	47, 48a–c	Pyrazolone + combretastatin A‐4 (CA‐4)	Tubulin	HeLa cells (47): 0.048 μM; tubulin inhibition (47); cytotoxicity in CK2/T‐24 (48a–c)
Regnault et al.	49	Dichlorophenylpyrazolone + fluorophenyl	PD‐L1 dimerization, SHP‐2, ROS scavenging	PD‐L1 binding: Kd = 27 nM; PD‐L1 dimerization: Kd = 1.2 nM
Xhafa et al.	50a–e	4‐aminoalkylidene‐5‐pyrazolone Schiff base + Zn(II)	mutp53, Zn2+ donor	Anti‐proliferative/anti‐invasive in mutp53 SKBR3 and U373MG
Bensaber et al.	51	4‐aminoantipyrine + schiff base	DNA intercalation	Cytotoxicity in MCF‐7 cells
Aljohani et al.	52, 53	Pyrazolone + Cs/PVA nanogel delivery	DNA intercalation, topoisomerase II	Topo‐II (IC50: 0.900–1.485 μM); HepG2 (6.30 μM), A549 (10.60 μM), MCF‐7 (8.80 μM), HCT‐116 (8.30 μM)
Dahal et al.	54a–d	1,3‐diarylpyrazolone	Cell cycle (G0/G1 or G2/M arrest)	Antiproliferative in A549 and NCI‐H522
Saidachary et al.	54e	Benzoxepinoisoxazolone + pyrazolone	—	Cytotoxicity in HeLa cells

2.6. Antibacterial and Antifungal Effects

Pyrazolones have demonstrated remarkable pharmacological potential not only in the antitumor and anti‐inflammatory fields but also in the anti‐infective domain, where their applications are attracting increasing attention. Currently, the development of anti‐infective drugs with novel structural scaffolds has become an urgent requirement for global public health, particularly in the face of increasingly complex pathogenic environments; research into new strategies, such as nonantibiotic‐dependent antibacterial agents like graphene‐based nanomaterials, has also provided important references for this field [130].

Invasive fungal infections pose a severe threat to immunocompromised patients; in particular, the emergence of drug‐resistant Candida and Cryptococcus neoformans has greatly diminished the clinical efficacy of existing antifungal drugs (such as fluconazole) [131, 132]. To overcome the resistance of traditional drugs, the development of new strategies, such as green drugs utilizing phytochemicals and their secondary metabolites, as well as nanomedicines, has been proven effective [133, 134].

However, structurally modified compounds remain the primary focus of antifungal drug research and development. Structurally modified pyrazolone compounds have shown remarkable potential in the antifungal field, especially in reversing drug resistance and exploring novel target mechanisms. By introducing distinct pharmacophores at specific positions of the pyrazolone scaffold, researchers have synthesized a series of novel pyrazolone derivatives possessing dual or even multiple pharmacological activities, which have demonstrated profound research value and clinical application potential in combating drug‐resistant pathogens (such as ESKAPE pathogens and azole‐resistant fungi).

A critical mechanism of fungal drug resistance is the overexpression of drug efflux pump genes (e.g., CDR1). In Candida glabrata, this overexpression is mediated by the interaction between the pleiotropic drug resistance transcription factor Pdr1 and its activation target, the KIX domain (Pdr1‐KIX). Wang et al. [135] based on previously discovered pyrazolone‐carbothioamide Pdr1‐KIX inhibitors, designed and synthesized a series of novel derivatives. Among them, compound 55 (Figure 36), which features a hydrindene pharmacophore, exhibited a stronger KIX binding affinity (Ki = 11.7 μM). Pharmacological evaluations indicated that compound 55 not only possessed direct antifungal activity but could also significantly downregulate the expression of resistance‐related genes by blocking the Pdr1‐KIX interaction and inhibiting drug efflux pumps, thereby exerting an exceptionally potent synergistic antiresistant C. glabrata effect when combined with fluconazole (FICI = 0.28) and reducing the minimum inhibitory concentration (MIC) by 32‐fold. To further enhance activity, researchers conducted in‐depth structural optimization of the pyrazolone‐carbothioamide scaffold and discovered that some compounds exhibited entirely new antifungal mechanisms independent of KIX target binding. Compound 56, synthesized by Liang et al. [136], displayed remarkable picomolar in vitro antifungal activity (with an MIC of only 0.00012 μg/mL against C. glabrata and C. neoformans), and its mechanism of action did not involve targeting the KIX domain (Ki > 100 μM). In‐depth mechanistic studies revealed that 56 disrupts iron homeostasis within fungal cells, inducing a massive accumulation of intracellular ROS and lipid peroxides, which ultimately results in severe oxidative stress damage, destroying organelles and cell membrane structures. This novel mechanism allowed the compound to demonstrate excellent antivirulence effects in vitro (such as inhibiting biofilm formation and cryptococcal polysaccharide capsule growth) and potent in vivo therapeutic potential in murine models of candidiasis and cryptococcosis.

FIGURE 36.

Structures and optimization process of compounds 55 and 56.

Beyond targeting clinical deep fungal infections, 4‐substituted‐4‐nitropyrazolin‐5‐ones (nitropyrazolones) have been confirmed as a class of structurally novel and highly efficient fungicides (Figure 37). Budnikov et al. [137] developed an atom‐economical synthetic methodology, demonstrating that nitropyrazolones bearing the rare tert‐C(sp³)‐NO₂ fragment (compound 57a–b) could strongly inhibit the mycelial growth of various phytopathogenic fungi (e.g., Venturia inaequalis, Fusarium oxysporum), with activities comparable to or even better than kresoxim‐methyl. They also possessed potential inhibitory capabilities against human pathogens such as Candida albicans and Aspergillus niger in vitro. SAR indicated that the aromatic substituent on the N1 atom of the pyrazolone ring, along with small‐volume substituents (such as methyl groups) at the C3 and C4 positions, are the key structural features responsible for its high fungicidal activity.

FIGURE 37.

Structures of compounds 57–59.

In recent years, the clinical treatment of drug‐resistant bacteria has faced tremendous challenges [138, 139]. Owing to their aza‐heterocyclic properties, pyrazolone derivatives can strongly bind to bacterial targets through hydrogen bonding and hydrophobic interactions, displaying excellent broad‐spectrum antibacterial activity and targeting precision.

To combat multidrug‐resistant bacteria and mitigate the oxidative stress damages to host cells triggered by antibiotic bactericidal processes, developing drug molecules with dual antibacterial and antioxidant functions has emerged as a new strategy. Othman et al. [140] designed and synthesized novel benzenesulfonamide‐pyrazolone hybrids (Figure 37). Among them, pyrazolone derivatives 58 and 59 containing a benzenesulfonamide fragment exhibited outstanding inhibitory activity against Staphylococcus aureus (MICs of 8.98 and 7.61 μM, respectively), which was not only superior to the standard drug tetracycline (MIC = 11.77 μM) but also demonstrated excellent ABTS radical scavenging capabilities (antioxidant activity). Molecular docking studies revealed their underlying mechanism: these pyrazolone molecules can robustly and precisely bind into the active pocket of S. aureus tyrosyl‐tRNA synthetase, achieving antibacterial effects by blocking bacterial protein synthesis; simultaneously, the molecules can target and bind to human peroxiredoxin‐5 (PRDX5), thereby exerting an antioxidant protective effect.

Fusing and hybridizing the pyrazolone with other heterocycles known to possess antibacterial activity (such as indole and 1,2,3‐triazole) can produce synergistic antibacterial effects. Upadhyay et al. [141] utilized click chemistry to synthesize a series of triazole‐indole‐pyrazolone hybrids. These hybrid molecules demonstrated broad activity against both Gram‐positive and Gram‐negative bacteria, particularly against highly drug‐resistant Acinetobacter baumannii (A. baumannii), where compounds 60a–c (Figure 38) showed potent inhibitory effects (MIC = 10 μg/mL), outperforming chloramphenicol and ampicillin. Moreover, triazole‐pyrazolone derivatives containing o‐chloro or o‐nitrophenyl substituents displayed significant bactericidal activity against methicillin‐resistant S. aureus and vancomycin‐resistant Enterococcus, while showing no significant cytotoxicity against the human neuroblastoma cell line (SH‐SY5Y) at concentrations up to 100 μg/mL, demonstrating an excellent safety window.

FIGURE 38.

Structures of compounds 60a–c and 61.

Based on green chemistry principles, synthesizing highly functionalized pyrazolones via multicomponent reactions and expanding their dual pharmacological activities is also a research hotspot. Ali et al. [4] utilized an aqueous catalytic system to synthesize multicyanomethylene‐substituted pyrazolinone derivatives and spiro‐pyrazole‐epoxy derivatives, some of which exhibited significant antibacterial activity when screened against multiple pathogenic bacteria. Taking it a step further, considering that epilepsy patients are often more susceptible to infections, Al‐ebini et al. [60] innovatively designed pyrazolone derivatives with dual antibacterial and antiepileptic effects (Figure 38). The synthesized compound 61 displayed good zones of inhibition against Escherichia coli and S. aureus, and molecular docking results indicated that this class of pyrazolones achieves synchronized regulation of antibacterial activity and CNS protection through multiple hydrogen bonds (e.g., with Ser residues) and hydrophobic interactions with bacterial and neuronal targets, demonstrating the immensely high druggability potential of this scaffold in polypharmacology.

Due to their structural modifiability and high affinity, pyrazolone compounds have demonstrated inestimable value in the field of anti‐infective medicinal chemistry. Through rational molecular design, introducing different pharmacophores (such as carbothioamide, triazole heterocycles, and sulfonamides) onto the pyrazolone scaffold can endow them with novel antifungal mechanisms, such as blocking fungal resistance targets (Pdr1‐KIX), disrupting fungal iron homeostasis, and inducing oxidative stress; concurrently, in combating bacterial infections, pyrazolone derivatives can accurately target bacterial enzyme systems (like tyrosyl‐tRNA synthetase) and display potent bactericidal capabilities against MDR and ESKAPE pathogens. Of note, the detailed hybridization strategies, molecular targets, and antimicrobial/antifungal efficacies of pyrazolone derivatives are summarized in Table 10.

TABLE 10.

Summary of the antibacterial and antifungal activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity (IC50/binding)	In vivo models or efficacy
Wang et al.	55	Pyrazolone‐carbothioamide + hydrindene	Pdr1‐KIX, drug efflux pumps	KIX binding: Ki = 11.7 μM; synergistic with fluconazole (FICI = 0.28)	—
Liang et al.	56	Pyrazolone‐carbothioamide	Iron homeostasis, ROS, lipid peroxides	C. glabrata and C. neoformans MIC: 0.00012 μg/mL	Murine models of candidiasis and cryptococcosis
Budnikov et al.	57a–b	Nitropyrazolone + tert‐C(sp3)‐NO2	—	Inhibit mycelial growth in phytopathogenic and human fungi	—
Othman et al.	58, 59	Pyrazolone + benzenesulfonamide	Tyrosyl‐tRNA synthetase, PRDX5	S. aureus MIC: 8.98 μM (58), 7.61 μM (59); ABTS radical scavenging	—
Upadhyay et al.	60a–c	1,2,3‐triazole + indole + pyrazolone	—	A. baumannii MIC = 10 μg/mL	—
Al‐ebini et al.	61	Pyrazolone	Bacterial and neuronal targets (SER residues)	Zones of inhibition against E. coli and S. aureus	—

2.7. Antidiabetes Mellitus

Diabetes mellitus (DM) is a chronic metabolic disorder characterized by persistent hyperglycemia resulting from impaired insulin secretion, defective insulin action, or both. The global burden of DM continues to escalate, with clinical statistics reporting ≈589 million affected adults in 2024—projected to reach 853 million by 2050, primarily driven by the prevalence of type 2 diabetes mellitus (T2 DM) [142, 143]. T2 DM is defined by insulin resistance and β‐cell dysfunction, leading to systemic complications including cardiovascular disease, nephropathy, retinopathy, and an increased risk of malignancy, making it the ninth leading cause of death worldwide [144, 145]. Although various therapeutic classes exist—including metformin, sulfonylureas, thiazolidinediones, incretin‐based therapies (DPP‐4 inhibitors, GLP‐1 RAs, and dual GLP‐1/GIP RAs), and SGLT2 inhibitors—their clinical utility is often constrained by adverse effects, secondary complications, and administration limitations [142].

To address these challenges, Khowdiary et al. [146] designed a series of oxadiazole‐pyrazolone hybrids as dual inhibitors of α‐amylase and α‐glucosidase (Figure 39). In in vitro assays, compound 62c (3.20 ± 0.20 µM for α‐amylase; 3.60 ± 0.10 µM for α‐glucosidase) exhibited exceptionally potent inhibitory activities, which were significantly superior to those of the positive control acarbose. The suboptimal molecule, compound 62i, likewise displayed outstanding potency: 3.90 ± 0.20 µM; 4.10 ± 0.10 µM, respectively. SAR analysis revealed that the electronic properties and positions of the substituents on the phenyl ring exert a profound impact on the overall activity. Specifically, the presence of electron‐donating hydroxyl groups (‐OH) at the ortho‐ and para‐positions of the phenyl ring (62c, 62i) enabled the formation of a robust hydrogen‐bonding network within the enzyme active site, thereby conferring high inhibitory potency. Additionally, introducing small halogens with high electronegativity (62a, 62d) also enhanced the binding affinity. Conversely, bulkier substituents such as a bromo group or a cyano moiety (62f, 62h) hindered target engagement, resulting in diminished activity. Enzyme kinetic studies successfully identified a competitive inhibition mechanism. Furthermore, molecular docking simulations indicated that the carbonyl group on the pyrazolone core forms key hydrogen bonds with essential amino acid residues, including Ile287 and Trp565.

FIGURE 39.

Structures of compounds 62a–i.

Furthermore, human carboxylesterase 1 (CES1), a key member of the serine hydrolase superfamily, has emerged as a promising metabolic target. CES1 is integral to the biotransformation of endogenous lipids, and its expression is significantly upregulated in the adipose tissue of patients with obesity and T2 DM. Recent evidence suggests that CES1 inhibition can improve metabolic homeostasis and glucose regulation [147, 148]. Wang et al. [149] synthesized a series of pyrazolinone derivatives, identifying compounds 63 (IC₅₀ = 0.056 μM), 64 (IC₅₀ = 0.049 μM), and 65 (IC₅₀ = 0.053 μM) as potent CES1 inhibitors (Figure 40). Cellular assays using HepG2 cells confirmed that these compounds dose‐dependently inhibited intracellular CES1 activity with low cytotoxicity (viability > 90% up to 100 μM). Notably, in 3T3‐L1 adipocytes, these inhibitors significantly reduced intracellular lipid droplet accumulation, as visualized by Oil Red O staining. These findings highlight pyrazolinone‐based CES1 inhibitors as potential therapeutic candidates for managing T2 DM and associated metabolic syndromes. Table 11 summarizes the specific hybridization strategies, targets, and antidiabetic activities of pyrazolone compounds.

FIGURE 40.

Structures of compounds 63–65.

TABLE 11.

Summary of the antidiabetes mellitus activity of pyrazolone compounds.

Authors	Compd.	Hybridization strategy	Targets/signaling pathway	In vitro activity	In vivo models or efficacy
Khowdiary et al.	62c	Pyrazolone + oxadiazole + benzamide	α‐amylase, α‐glucosidase	α‐amylase (62c): 3.20 μM; α‐glucosidase (62c): 3.60 μM	—
Wang et al.	63–65	N1, C3, and C4‐substituted pyrazolones	CES1, intracellular lipid droplet accumulation	CES1 inhibition in HepG2 cells; inhibited lipid droplet accumulation in 3T3‐L1 adipocytes	—

3. Conclusion

In conclusion, the pyrazolone heterocycle has firmly established itself as a highly versatile and privileged scaffold in modern drug discovery. The inherent chemical stability and multiple derivatization sites (N‐1, C‐3, and C‐4) of pyrazolones enable the precise tuning of their lipophilicity, hydrogen‐bonding capacity, and target affinities. This structural plasticity has catalyzed the development of numerous MTDLs designed to simultaneously intervene in complex pathological networks.

In the realm of CNS and neurodegenerative disorders, pyrazolone derivatives have exhibited exceptional neuroprotective properties. Through targeted structural modifications, these compounds can simultaneously inhibit key metabolic enzymes (such as AChE, BuChE, and MAO), antagonize the toxic aggregation of hallmark proteins (including Aβ, α‐synuclein, and mutant SOD1), and deeply mitigate oxidative stress via the activation of the Keap1‐Nrf2 signaling pathway. Furthermore, iterative molecular evolution—such as the transition from thioether‐linked pyrazolones to stable aryloxy and phosphate salt derivatives—has successfully addressed pharmacokinetic bottlenecks, yielding highly potent anxiolytic, antidepressant, and neuroprotective agents with superior BBB permeability and clinical safety profiles.

Beyond neurological applications, pyrazolone hybrids have revolutionized anti‐inflammatory and analgesic treatments. They achieve profound efficacy by selectively acting as COX‐2/5‐LOX dual inhibitors, directly modulating the NF‐κB inflammatory cascade, and providing robust nonopioid central analgesia without the severe gastrointestinal or cardiovascular liabilities associated with traditional NSAIDs. In the field of oncology, pyrazolone derivatives have demonstrated potent broad‐spectrum antiproliferative activity by selectively blocking critical survival kinases (e.g., FLT3, PI3K/Akt, and EGFR), inducing microtubule depolymerization, facilitating novel PD‐L1 protein dimerization, and acting as specific zinc donors to correct p53 mutations. Additionally, their application in infectious and metabolic diseases highlights their unique potential to disrupt multidrug resistance in ESKAPE pathogens and azole‐resistant fungi, as well as to regulate metabolic homeostasis through the targeted inhibition of CES1, α‐amylase, and α‐glucosidase.

Despite these remarkable in vitro and in vivo achievements, future research must continue to prioritize the optimization of pharmacokinetic parameters, particularly concerning metabolic stability and high first‐pass elimination. The continued integration of rational target‐based design, advanced targeted delivery systems (such as nanogels), and comprehensive early‐stage clinical evaluations will be imperative to successfully translate these highly promising pyrazolone‐based hits into safe, multitargeted, and efficacious clinical therapeutics.

Author Contributions

Ke Tang: writing – original draft, review & editing. You Liu: writing – original draft, review & editing. Jingning Luo: writing – original draft, review & editing. Shiqin Cong: writing – original draft, review & editing, investigation, formal analysis.

Conflicts of Interest

The authors declare no conflicts of interest.

Tang Ke, Liu Yao, Luo Jingning, Cong Shiqin, The Pyrazolone Scaffold: A Privileged Motif for Molecular Hybridization in Drug Discovery, ChemMedChem 2026, 21, e70466. 10.1002/cmdc.70466

Data Availability Statement

No new data was used for the research described in the article.