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. 2025 Dec 29;11(1):2142–2151. doi: 10.1021/acsomega.5c10907

Design, Synthesis, and Antibacterial Evaluation of Pyrido[2,3‑d]Pyrimidine and Pyrido[3,2‑e]Pyrimido[1,2‑c]Pyrimidine Derivatives

Farag A El-Essawy †,*, Mohammad Ahmad Ahmad Odah ‡
PMCID: PMC12809839  PMID: 41552441

Abstract

A new series of N-substituted pyrido2,3-dpyrimidines and pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidine derivatives were synthesized. The synthesis was initiated from pyridopyrimidin-4­(3H)-one derivatives which were prepared via a tandem Pinner/Dimroth rearrangement in the presence of phosphoryl chloride. Its N-substituted derivatives were prepared after treatment of chloro-derivative with a series of amines, and then some of these derivatives underwent cyclization to give the tricyclic derivatives. The fused pyridopyrimidopyrimidines were obtained via the reaction of amino compound with malonates derivatives. Most of these compounds were evaluated for their antibacterial activity. The structures of the synthesized compounds were confirmed by elemental analysis and spectroscopic techniques (IR, NMR, and EI-MS). Several derivatives, particularly compounds 5b, 5c, 5f, 6, 7, and 14a, exhibited potent antibacterial activity against both Gram-positive and Gram-negative bacteria, with minimum inhibitory concentration (MIC) values ranging from 0.48 to 3.91 μg/mL. Notably, tricyclic derivatives demonstrated enhanced efficacy, suggesting a promising scaffold for the development of new antibacterial agents.

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1. Introduction

The pyridopyrimidine scaffold acts as a cornerstone in modern drug discovery, evidenced by the extensive volume of clinical trials and literature dedicated to its therapeutic applications. − This structural moiety is central to several approved medications; prominent examples include Palbociclib, a breast cancer treatment developed by Pfizer, and Dilmapimod, which shows potential in treating rheumatoid arthritis (Figure ).

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Examples of interesting molecules. Palbociclib: breast cancer drug developed by Pfizer and Dilmapimod: potential activity against rheumatoid arthritis.

These derivatives typically function by interacting with specific biological targets, including dihydrofolate reductase (DHFR), biotin carboxylase, and various kinases such as the Abl tyrosine-protein kinase or MAP kinases. In medicinal chemistry, heterocycles containing multiple noncarbon atoms are fundamental building blocks. , The literature suggests that combining distinct bioactive heterocyclic pharmacophores into a single molecular entity is a highly effective strategy for designing new drugs with enhanced potency. Consequently, pyridopyrimidines have long captivated the attention of synthetic and biological researchers, yielding compounds with diverse properties ranging from anticonvulsant, antitumor, and antiproliferative effects to antifungal, adenosine kinase inhibition, and general cytotoxicity. ,

Nitrogen-based heterocycles are of particular interest because they mimic structures naturally abundant in nucleic acids, vitamins, antibiotics, and hormones. Within this broad class, imidazopyrimidine and imidazopyridine derivatives stand out as valuable pharmaceutical targets, illustrated by clinical agents such as fasiplon and divaplon. , Given their pharmacological significance, researchers have developed numerous synthetic protocols over the years to access these scaffolds.

The fusion of pyrimidine and pyridine rings can result in four distinct isomeric skeletons, depending on the nitrogen placement. Synthetic strategies typically involve ring fusion or the use of cyclic intermediates. , While traditional methods exist, modern approaches favor multicomponent reactions (MCRs) and one-pot procedures using specific catalysts. These modern methods are generally preferred over older techniques that rely on expensive or toxic organic solvents. , For example, Rangel et al. (2017) successfully demonstrated the efficiency of one-pot cyclocondensation to create pyrido­[2,3-d]­pyrimidine indole derivatives.

Building upon these precedents and our prior research into novel fused-pyrimidine scaffolds, − this study aims to design and synthesize a new series of pyrido­[2,3-d]­pyrimidine, pyrido­[2,3-e]­pyrimido­[1,2-c]­pyrimidine, and imidazo­[1,2-c]­pyrido­[3,2-e]­pyrimidine derivatives. , Herein, we describe an efficient synthetic pathway for these novel compounds and evaluate their structure-activity relationships (SAR), specifically focusing on their antibacterial potential.

2. Results and Discussion

Building of pyrimidine ring on a starting material containing ortho-amino-cyano is synthesized in previous methods according to, for instance, the reaction of 5-amino-pyrazole-4-carbonitile with various hydrazides in ethanolic sodium ethoxide medium affording 4-imino-fh-pyrazolo­[3,4-d]­pyrimidine-5-amines. In this study, a starting material of 2-amino-4,6-dimethylnicotinonitrile 1 , was allowed to react with excess carboxylic acids 2a,b in the presence of POCl3, as the chlorinating agent, according to the reported procedure. , The formation of 5,7-dimethylpyrido­[2,3-d]­pyrimidin-4­(3H)-one derivatives 3a,b via the intramolecular Pinner/Dimroth rearrangement, as shown in Scheme .

1. Synthesis of Pyrido­[2,3-d]­Pyrimidenes Derivatives.

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The acids 2a, b were chlorinating by POCl3 to give the acid chloride I which readily reacted with compound 1 affording the intermediate II. The latter intermediate II undergoes an intramolecular Pinner reaction followed by the Dimroth reaction to afford the derivatives 3a, b, from intermediate III as shown in Scheme . The products 3a, b were confirmed by the spectral data and elemental analysis. Where, the IR spectra showed the disappearance of the characteristics peaks corresponding to nitrile and amino groups and the new peaks belong to the carbonyl and imino groups at ν 3429, 3431 (NH), 1670, 1673 (CO) cm–1 respectively. 1H NMR spectra showed a new signal at the aliphatic area corresponding to the methyl and ethyl groups attributed to the derivative 3a, b, respectively. The Pyridopyrimidine derivatives 3a, b were chlorinated, by POCl3/pyridine, to afford the corresponding chloropyridopyrimidine derivatives 4a, b which contained an active chlorine atom that could be easily subjected to nucleophilic reactions with various amines. The reaction of the selected derivative 4a with secondary amines derivatives, in absolute ethanol, afforded the formation of corresponding pyrido­[2,3-d]­pyrimidine derivatives 5a–f in reasonable yield. All the derivatives 5a–f were confirmed by IR, MS, 13C, and 1H NMR spectra which showed a new signal corresponding to aliphatic, aromatic, hydroxyl group, and imino protons, in addition the appearance of new signals in aliphatic area corresponding to the aliphatic carbons in 13C NMR. Besides, the MS spectra for all the derivatives gave the expected molecular ion peak under the EI condition, as illustrated in Scheme .

2. Intramolecular Pinner/Dimroth Rearrangement for the Formation of Pyridopyrimidene.

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In order to prove the structure of derivatives 5a–f chemically, it was found that derivatives 5d and 5e were converted to the tricyclic fused derivatives 6, 7, after treatment with excess POCl3 and then treated with basic medium (KOH). The structure of the products were confirmed based on spectra and analytical data. In 1H NMR, the signals corresponding to the NH and OH disappeared, which indicated the cyclization reaction performed afforded the derivatives 6 and 7 in good yield, as shown in Scheme .

3. Cyclization Reaction of Pyrido2,3-Dpyrimidenes Derivatives.

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Chloropyridopyrimidine 4a could provide the opportunity for another new cyclization method, after its converted into the target 2,5,7-trimethylpyrido­[2,3-d]­pyrimidin-4-amine (10), as illustrated in Scheme .

4. Synthesis of the Pyrido­[2,3-e]­Pyrimido­[1,2-c]­Pyrimidine Derivatives.

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First, treatment of compound 4a with NaN3/DMF to give 4-azido-2,5,7-trimethylpyrido­[2,3-d]­pyrimidine (8). Which readily converted into 1,1,1-triphenyl-N-(2,5,7-trimethylpyrido­[2,3-d]­pyrimidin-4-yl)-l5-phosphanimine (9), in good yield (85%), after its treatment with triphenyl phosphine (Ph3P). Then, on the hydrolysis of the phosphonamine 9 with ACOH (80%), under reflux condition, affording the corresponding amino derivative 10. The structures of these compounds 8–10 was elucidated besides 1H NMR also by, the simple technique such as IR spectra which showed characteristics peaks belongs to azido group (-N3) for compound 8, at ν 2152 cm–1 which disappeared in the IR spectrum of product 9, but the IR spectrum of compound 10 showed peaks at ν 3444, 3319 corresponding to the NH2 group. On the reaction of malonates derivatives with amino compound 10 via the nucleophilic cycloaddition reactions affording the pyrido­[3,2-e]­pyrimido­[1,2-e]­pyrimidin-2-one, and/or 4-one derivatives 13a–c and 14a, b, respectively, were obtained under reflux conditions. The structures of these derivatives 13 and 14 were clearly confirmed besides elemental analysis by spectral data, where the 1H NMR spectra, showed appearance of new signals in aliphatic region, corresponding to Me (δ 2.50 ppm), Et groups (δ 1.13, 3.22 ppm) for derivative 13a, b but signals in aromatic region corresponding to phenyl group (7.10–7.76) for derivative 13c, respectively. Also, 1H NMR of derivatives 14a, b showed new peaks corresponding to the ester group triplet (δ 1.29), quartet (δ 4.32), with a new peak for aromatic proton at δ 8.53 ppm in derivative 14a but at δ 8.47 ppm corresponding to the aromatic proton in derivative 14b. Besides, IR spectra showed a strong peak for the carbonyl group at 1705 cm–1 for the ester group of derivative 14a and a characteristic peak at 2225 cm–1 for the nitrile group of derivative 14b. MS spectra of all these compounds gave the expected molecular ion peak which corresponds to the molecular weight.

3. Experimental Section

Commercially available reagents 11 and 12 were used as received, while starting material 1 was synthesized following previously described protocols. Melting points were recorded using a Kofler block apparatus and are uncorrected. Infrared (IR) spectra were obtained using KBr pellets on a PerkinElmer 1720 FT-IR spectrometer. Reaction progress and product purity were monitored via thin-layer chromatography (TLC) on silica gel-coated plates. Proton (1H) and carbon (13C) NMR spectra were acquired on a Bruker WH-300 spectrometer operating at 300 and 75.5 MHz, respectively, using DMSO-d 6 or CDCl3 as solvents and TMS as the internal reference. Mass spectra were recorded on a Finnigan MAT SSQ 7000 spectrometer (70 eV, EI mode). Elemental analyses (C, H, N) were conducted using a PerkinElmer CHN 2400 analyzer at the Microanalysis Laboratory, Cairo University. Biological evaluations were performed at the Pharmaceutics Department, Prince Sattam Bin Abdulaziz University.

3.1. General Procedure for the Preparation of Pyrido­[2,3-d]­pyrimidin-4­(3H)-One Derivatives (3a,b)

Phosphoryl chloride (POCl3, 10 mL) was added dropwise to a mixture containing 2-amino-4,6-dimethylnicotinonitrile 1 (1.47 g, 10 mmol) and an excess of either acetic acid 2a (20 mL) or propionic acid 2b (20 mL). The reaction mixture was refluxed for 5–6 h until TLC indicated completion. The mixture was subsequently poured into cold water (400 mL) to precipitate the crude product. The solid 3a,b was collected by filtration, washed thoroughly with water, and purified via recrystallization from methanol.

3.1.1. 2,5,7-Trimethylpyrido­[2,3-d]­pyrimidin-4­(3H)-one 3a

Yield 1.89g, 70%; mp 149–152 οC. IR (KBr), ν; cm1: 3020 (NH), 1612 (CO). 1H NMR (DMSO-d 6): δ: 2.23, 2.33, 2.47 (3s, 9H, 3CH3), 7.53 (s, 1H, H ArH), 9.36 (s, 1H, NH). 13C NMR (DMSO-d 6): δc: 14.42, 16.22, 18.73 (3Me), 115.11, 123.95, 129.39, 149.91, 150.60, 164.83, 165.71 (C Ar). MS (EI) m/z (%) 189­(2, M+), 187 (100, M+ – 2H), 159 (60, M+ – CH5), 129 (30, M – C3H11). Anal. Calcd for C10H11N3O (189.23): C, 63.48; H, 5.86; N, 22.21. Found: C, 63.42; H, 5.73; N, 20.16%.

3.1.2. 2-Ethyl-5,7-dimethylpyrido­[2,3-d]­pyrimidin-4­(3H)-one 3b

Yield 1.82g, 89%; mp 133–136 οC. IR (KBr), ν, cm1: 3022 (NH), 3100, 2989 (CH aliph), 1610 (CO). 1H NMR (DMSO-d 6): δ 1.23 (t, J = 5.6 Hz, 3H, CH 3CH2), 1.48 (s, 3H, CH3), 2.31 (q, J = 5.6 Hz, 2H, CH3CH 2) 2.64 (s, 3H, CH3), 7.31 (s, 1H, H ArH), 9.72 (s, 1H, NH). 13C NMR (DMSO-d 6): δc 10.15, 16.13, 19.45 (3Me), 23.83 (CH2), 93.81, 113.35, 116.13, 118.40, 155.50, 162.50, 160.62 (C Ar). MS (EI) m/z (%) 189­(2, M+), 187 (100, M+–2H), 159 (60, M+–CH5), 129 (30, M–C3H11). Anal. Calcd for C11H13N3O (203.25): C, 65.01; H, 6.45; N, 20.68. Found: C, 64.98; H, 6.41; N, 20.56%.

3.2. Chlorination of pyrido­[2,3-d]­pyrimidin-4­(3H)-one Derivatives 3a,b

Dissolve the pyridopyrmidine 3a,b (15 mmol) in dry pyridine 10 mL and POCl3 (2.3 g, 15 mmol) was added in dropwise. The mixture was boiled under reflux for 6 h until the reaction was complete (tlc). Then the reaction was cooled to room temperature and added by portions to an ice bath with smooth shaking until a colorless precipitate appeared which was collected by filtration. Washed with distilled water and recrystallized with ethanol to afford the pure chloro derivatives 4a,b.

3.2.1. 4-Chloro-2,5,7-trimethylpyrido­[2,3-d]­pyrimidine 4a

Yield 2.3 g, 94%; mp 105–107 οC. IR (KBr), ν, cm1: 3150, 2990 (CH aliph), 1H NMR (DMSO-d 6): δ 2.22, 2.25, 2.50 (3s, 9H, 3CH3), 7.43 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 17.41, 19.12, 26.34 (3Me), 110.5, 119.7, 120.9, 138.1, 141.3, 144.6, 148.6 (C Ar). MS (EI) m/z (%) 207 (5, M+), 192 (30, M+–Me), 162 (100, M+–3Me). Anal. Calcd for C10H10ClN3 (207.66): C, 57.84; H, 4.35; N, 20.24. Found: C, 57.66; H, 4.24; N, 20.19%.

3.2.2. 4-Chloro-2-ethyl-5,7-dimethylpyrido­[2,3-d]­pyrimidine 4b

Yield 1.9 g, 57%; mp 94–96 οC. IR (KBr), ν; cm1: 3140, 2996 (CH aliph). 1H NMR (DMSO-d 6): δ 2.27, 2.48 (2s, 6H, 2CH3),2.87 (t, J = 7.2 Hz, 3H, CH 3CH2), 4.22 (q, J = 7.0 Hz, 2H, CH3CH 2), 6.37 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 18.62, 21.64 (2Me), 24.83 (CH3CH2), 25.34 (CH3 CH2), 102.6, 107.9, 115.8, 146.1, 149.0, 151.9, 160.8 (C Ar). MS (EI) m/z (%) 207 (5, M+), 192 (30, M+–Me), 162 (100, M+–3Me). Anal. Calcd for C11H12ClN3 (221.68): C, 59.60; H, 5.46; N, 18.96. Found: C, 59.56; H, 5.54; N, 18.89%.

3.2.3. General Procedure for the Synthesis of N-Substituted Pyrido­[2,3-d]­pyrimidines (5a–f)

A solution containing the chloro-derivative 4a (1.1 g, 5 mmol) and the appropriate amine (10 mmol) in absolute ethanol (50 mL) was refluxed for a period of 8–10 h. Following the reaction, the mixture was allowed to cool to room temperature, and water (150 mL) was added while being stirred to induce precipitation. The resulting solid crystals were collected via filtration, washed thoroughly with water, dried, and subsequently purified by recrystallization from an appropriate solvent.

3.2.4. 2,5,7-Trimethyl-4-(piperidin-1-yl)­pyrido­[2,3-d]­pyrimidine 5a

Yield 1.1 g, 79% (ethanol); mp 112–115 οC. IR (KBr), ν; cm1: 3210–2989 (CH aliph). 1H NMR (DMSO-d 6): δ 2.01–2.06 (m, 4H, 2CH2), 2.32, 2.44, 2.49 (3s, 9H, 3CH3), 2.93–3.29 (m, 6H, 3CH2), 6.35 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 13.15, 14.10, 17.15, 20.72 56.10 (3CH3, 5CH2), 103.19, 118.82, 124.56, 133.87, 136.87, 141.18, 159.15 (C Ar). MS (EI) m/z (%) 256 (60, M+), 245 (100, M+–C), 239 (50), 124 (70) Anal. Calcd for C15H20N4 (256.35): C, 70.28; H, 7.86; N, 21.86. Found: C, 70.19; H, 7.73; N, 21.79%.

3.2.5. 2,5,7-Trimethyl-4-(4-methylpiperidin-1-yl)­pyrido­[2,3-d]­pyrimidine 5b

Yield 1.3 g, 90% (ethanol); mp 119–121 οC. IR (KBr), ν; cm1: 3209–2996 (CH aliph). 1H NMR (DMSO-d 6): δ 1.43- 161 (m, 8H, CH3, 2CH2, CH), 2.45, 2.50, 2.54 (3s, 9H, 3CH3), 0.40–3.50 (m, 4H, 2CH2), 7.54 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 25.78, 28.92 (2CH3), 31.48 (2CH3), 31.65 (2CH2), 38.49 (2CH2, CH), 123.29, 127.86, 128.91, 149.92, 150.54, 161.66, 162.12. MS (EI) m/z (%) 270 (15, M+), 226 (40, M+–C3H8), 196 (20, M+–C4H11) 77 (100) Anal. Calcd for C16H22N4 (270.38): C, 71.08; H, 8.20; N, 20.72. Found: C, 71.03; H, 8.13; N, 22.69%.

3.2.6. 4-(2,5,7-Trimethylpyrido­[2,3-d]­pyrimidin-4-yl)­morpholine 5c

Yield 0.9 g, 64% (methanol); mp 132–136 οC. IR (KBr), ν; cm1: 3230–2994 (CH aliph), 1150 (C–O). 1H NMR (DMSO-d 6): δ 2.32, 2.50, 2.54 (3s, 9H, 3CH3), 2.94- 2.97 (m, 4H, 2CH2), 4.19–4.24 (m, 4H, 2CH2), 6.36 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 18.94, 20.68, 23.01 (3Me), 32.16, 33.45 (4CH2), 105.15, 109.52, 116.74, 127.11, 143.35, 152.21, 155.25 (C Ar). MS (EI) m/z (%) 259 (40, M+ + 1), 258 (5, M+), 227 (85, M+–C2H7) 159 (100, M+–C7H15)) Anal. Calcd for C14H18N4O (258.33): C, 65.09; H, 7.02; N, 21.69. Found: C, 65.03; H, 6.98; N, 21.63%.

3.2.7. 2-((2,5,7-Trimethylpyrido­[2,3-d]­pyrimidin-4-yl)­amino)­ethan-1-ol 5d

Yield 0.8 g, 66% (ethyl acetate); mp 143–145 οC. IR (KBr), ν; cm1: 3340–3298 (NH, OH), 3230–2994 (CH aliph). 1H NMR (DMSO-d 6): δ 2.43, 2.64, 2.84 (3s, 9H, 3CH3), 3.16- 3.21 (m, 2H, CH2), 3.93–4.01 (m, 2H, CH2), 4.40–4.44 (m, 1H, OH), 6.67 (s, 1H, H ArH), 7.28 (s, 1H, NH). 13C NMR (DMSO-d 6): δc 24.66, 20.00, 22.00 (3CH3), 42.54 (N–CH2), 60.00 (O–CH2), 121.39, 127.06, 134.38, 147.93, 160.28, 161.55, 177.76 (C Ar). MS (EI) m/z (%) 232 (2, M+), 217 (3, M+–CH3) 202 (2, M+–C2H6), 43 (100) Anal. Calcd for C12H16N4O (232.29): C, 62.05; H, 6.94; N, 24.12. Found: C, 62.01; H, 6.91; N, 24.08%.

3.2.8. 3-((2,5,7-Trimethylpyrido­[2,3-d]­pyrimidin-4-yl)­amino)­propan-1-ol 5e

Yield 1.1 g, 84% (ethyl acetate); mp 159–162 οC. IR (KBr), ν; cm1: 3400–3390 (NH, OH), 3230–2994 (CH aliph). 1H NMR (DMSO-d 6): δ 2.43, 2.64, 2.84 (3s, 9H, 3CH3), 3.16- 3.21 (m, 2H, CH2), 3.93–4.01 (m, 2H, CH2), 4.40–4.43 (m, 3H, OH, CH2), 6.67 (s, 1H, H ArH), 7.28 (s, 1H, NH). 13C NMR (DMSO-d 6): δc 18.03, 20.03, 24.32 (3CH3), 35.75 (CH2), 42.93 (N–CH2), 63.04 (O–CH2), 121.38, 125.95, 127.14, 128.48, 160.28, 160.20, 163.04 (C Ar). MS (EI) m/z (%) 246 (2, M+), 227 (50, M+–H3O) 187 (100, M+–C3H7O) Anal. Calcd for C13H18N4O (246.15): C, 63.39; H, 7.37; N, 22.75. Found: C, 63.34; H, 6.32; N, 22.72%.

3.2.9. N-Isobutyl-2,5,7-trimethylpyrido­[2,3-d]­pyrimidin-4-amine 5f

Yield 0.7 g, 53% (ethyl acetate); mp 129–131 οC. IR (KBr), ν; cm1: 3400–3390 (NH), 3230–2994 (CH aliph). 1H NMR (DMSO-d 6): δ1.30–1.35 (m, 7H, isopropyl), 2.49, 2.64, 2.96 (3s, 9H, 3CH3), 4.30- 4.33 (m, 2H, CH2), 6.96 (s, 1H, H ArH), 8.88 (s, 1H, NH). 13C NMR (DMSO-d 6): δc 18.24 (Me), 24.15 (2Me), 34.15, 36.17 (2Me), 35.75 (N–CH2), 46.81 (CH), 104.96, 135.00, 142.16, 147.48, 151.28, 157.20, 166.87 (C Ar). MS (EI) m/z (%) 245 (100, M+ + 1), 239 (40), 124 (60). Anal. Calcd for C14H20N4. (244.34): C, 68.82; H, 8.25; N, 22.93. Found: C, 68.74; H, 8.23; N, 22.89%.

3.3. General Method for the Preparation of Compounds 6 and 7

A mixture of compound 5d or 5e (5 mmol) and phosphorus oxychloride (30 mL) was heated to reflux for 6 h, with the reaction progress monitored via TLC. Upon completion, the excess phosphorus oxychloride was removed under reduced pressure. The resulting dry residue was triturated with ice-cold water and subsequently treated with a potassium hydroxide solution to adjust the pH to approximately 8–9. The precipitate that formed was collected by filtration, washed with water, dried, and finally recrystallized from methanol to yield the pure product.

3.3.1. 5,8,10-Trimethyl-2,3-dihydroimidazo­[1,2-c]­pyrido­[3,2-e]­pyrimidine 6

Yield 1.2 g, 56%; mp 128–131 οC. IR (KBr), ν; cm1: 3230–2994 (CH aliph). 1H NMR (DMSO-d 6): δ 2.62, 2.78, 2.94 (3s, 9H, 3CH3), 3.62- 3.66 (m, 2H, CH2), 3.83–3.88 (m, 2H, CH2), 7.28 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 17.39, 20.52, 25.43 (3CH3), 48.11, 49.53 (2CH2), 121.51, 126.02, 134.47, 148.11, 148.63, 160.31, 165.57 (C Ar). MS (EI) m/z (%) 214 (2, M+), 197 (10, M+–CH5), 97 (22), 57 (100) Anal. Calcd for C12H14N4 (214.27): C, 67.27; H, 6.59; N, 26.15. Found: C, 67.17; H, 6.43; N, 26.11%.

3.3.2. 6,9,11-Trimethyl-3,4-dihydro-2H-pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidine 7

Yield 1.3 g, 57%; mp 113–116 οC. IR (KBr), ν; cm1: 3200–2997 (CH aliph). 1H NMR (DMSO-d 6): δ 1.31–1.87 (m, 2H, CH2), 2.51, 2.54, 2.68 (3s, 9H, 3CH3), 4.33- 4.82 (m, 4H, 2CH2), 7.31 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 18.62, 21.64, 24.83, 25.34 (3CH3, CH2), 49.32, 51.77 (2CH2), 102.60, 107.91, 115.84, 146.04, 149.02, 151.90, 162.57. MS (EI) m/z (%) 228 (10, M+), 227 (100, M+–H), 159 (100, M+ –C3H5N2), 129 (45, M+–C5H11N2), 77 (15) Anal. Calcd for C13H16N4 (228.29): C, 68.39; H, 7.06; N, 24.54. Found: C, 68.22; H, 6.98; N, 24.49%.

3.3.3. 5,8,10-Trimethylpyrido­[3,2-e]­tetrazolo­[1,5-c]­pyrimidine 8

To a stirred clear solution of compound 4a (2.1 g, 10 mmol) in dry DMF (10 mL), NaN3 (0.98g, 15 mmol) was added. The reaction was heated at 60–70 οC for 12 h until completed (tlc), then after cooling to the room temperature, crushed ice (80g) was added with stirring until the brownish white solid was appeared which was collected by filtration. Then the sample was washed with distilled water and recrystallized from methanol. Yield 1.5 g, 70%; mp 127–130 οC. IR (KBr), ν; cm1: 3150–2897 (CH aliph), 2152 (N3). 1H NMR (DMSO-d 6): δ 2.38, 2.42, 2.48 (3s, 9H, CH3), 7.23 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 16.13, 18.31, 23.81 (3CH3), 105.35, 109.42, 113.97, 142.43, 145.02, 158.43, 159.97. MS (EI) m/z (%) 214 (10, M+), 173 (85, M+–C3H5), and 143 (100, M+ –C3H7N2). Anal. Calcd for C10H10N6 (214.23): C, 56.07; H, 4.71; N, 39.23. Found: C, 56.03; H, 4.68; N, 39.20%.

3.3.4. 1,1,1-Triphenyl-N-(2,5,7-trimethylpyrido­[2,3-d]­pyrimidin-4-yl)-l5-phosphanimine 9

Equimolar amount of azido compound 8 (2.14g 10 mmol) and triphenylphosphine (2.62g, 10 mmol) was dissolved in 1,2-dichlobenzrne (10 mL) and the mixture was refluxed for 6 h. Then the solvent was evaporated in vacuo and the remaining syrup was triturated with petroleum ether (40–60). The green solid product was filtered off, dried, and recrystallized from methanol. Yield 3.8 g, 85%; mp 227–230 οC. IR (KBr), ν; cm1: 3280–3190 (CH azid), 3150–2897 (CH aliph). 1H NMR (DMSO-d 6): δ 2.40, 2.42, 2.52 (3s, 9H, CH3), 6.57–7.83 (m, 16H, H ArH). 13C NMR (DMSO-d 6): δc 13.13, 23.31, 24.81 (3CH3), 115.35, 119.42­(3C), 123.97­(3C), 127.12 (3C), 139.45 (5C), 139.96 (3C), 151.43 (2C), 157.02 (3C), 169.22 (3C). MS (EI) m/z (%) 449 (15, M+ + 1), 415 (, M+–C2H9), 371 (10, M+–C6H5), 77 (100). Anal. Calcd for C28H25N4P (448.51): C, 74.98; H, 5.62; N, 12.49. Found: C, 74.88; H, 5.58; N, 12.42%.

3.3.5. 2,5,7-Trimethylpyrido­[2,3-d]­pyrimidin-4-amine 10

A solution of phosphanimine 9 (8.96g, 20 mmol) in glacial acetic acid (40 mL, 80%) was refluxed for 3 h until complete conversion to the corresponding amine derivative 10 (tlc). The solution was concentrated to 1/3 of its volume then, the white product, so formed, was filtered, washed with ethanol, dried, and recrystallized from AcOH. Yield 3.4 g, 90%; mp 244–247 οC. IR (KBr), ν; cm1: 3380–3320 (NH2), 3150–2897 (CH aliph). 1H NMR (DMSO-d 6): δ 2.38, 2.42, 2.48 (3s, 9H, CH3), 7.23 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 17.43, 22.88, 24.88 (3CH3), 110.61, 120.95, 132.08, 149.69, 153.40, 158.28, 161.89. MS (EI) m/z (%) 188 (25, M+), 132 (30, M+–C3H6N), 103 (30, M+ –C3H7N3), 76 (100). Anal. Calcd for C10H10N6 (188.23): C, 63.81; H, 6.43; N, 29.77. Found: C, 63.79; H, 6.39; N, 29.74%.

3.3.6. General Method for the pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidin-2-one Derivatives 13a–c

To a solution of the aminopyridopyrimidine 10 (0.94g, 5 mmol) in diphenyl ether (5 mL), the corresponding diethylmalonate derivative RCH­(CO2Et)2 11 (5.2 mmol) was added and the mixture was heated at 250 οC by using short condenser. The reaction was cooled to room temperature and then treated with stirring by ethyl ether to obtain solid product. The resulting precipitate was isolated via filtration, washed with ether to remove residual impurities, and dried. Subsequent recrystallization from ethyl acetate yielded the target compounds 13a–c as pale yellow solids.

3.3.7. 4-Hydroxy-3,6,9,11-tetramethyl-2H-pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidin-2-one 13a

Yield 1.1 g, 81%; mp 213–216 οC. IR (KBr), ν; cm1: 3320–3297 (OH), 3050–2997 (CH aliph), 1703 (CO). 1H NMR (DMSO-d 6): δ 2.51, 2.61, 2.94, 3.30, (4s, 12H, 4CH3), 7.37 (s, 1H, H ArH), 10.29 (s, 1H, OH). 13C NMR (DMSO-d 6): δc 10.07, 17.73, 24.18 (3CH3), 81.27 (C–3), 127.29, 128.62, 129.02, 132.54, 132.68, 132.81, 145.54, 152.87, 158.27. MS (EI) m/z (%) 271 (5, M+ + 1), 240 (5, M+ −2CH3), 211 (10, M+ –C4H11), 146 (50, M+–C7H12N2), 44 (100, C3H8). Anal. Calcd for C14H14N4O2 (270.29): C, 62.21; H, 5.22; N, 20.73. Found: C, 62.18; H, 5.19; N, 20.69%.

3.3.8. 3-Ethyl-4-hydroxy-6,9,11-trimethyl-2H-pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidin-2-one 13b

Yield 1.2 g, 84%; mp 203–205 οC. IR (KBr), ν; cm1: 3330–3287 (OH), 3030–2996 (CH aliph), 1690 (CO). 1H NMR (DMSO-d 6): δ 1.33 (s, 3H, CH3), 2.49–284 (m, 9H, 2CH3, CH 3CH2), 3.27–3.32 (m, 2H, CH3CH 2), 7.22 (s, 1H, H ArH), 12.22 (s, 1H, OH). 13C NMR (DMSO-d 6): δc 17.60, 20.08, 21.73, 24.08 (4CH3, CH2), 110.96, 121.73 (2C), 137.09, 143.22, 145.83, 146.87, 152.819, 158.81, 161.92. MS (EI) m/z (%) 284 (10, M+), 256 (50, M+ –C2H4), 245 (100, M+ –C2NH), 124 (60). Anal. Calcd for C15H16N4O2 (284.32): C, 63.37; H, 5.67; N, 19.71. Found: C, 63.32; H, 5.63; N, 19.67%.

3.3.9. 4-Hydroxy-6,9,11-trimethyl-3-phenyl-2H-pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidin-2-one 13c

Yield 1.4 g, 84%; mp 260–263 οC. IR (KBr), ν; cm1: 3340–3300 (OH), 3060–2987 (CH aliph), 1701 (CO). 1H NMR (DMSO-d 6): δ 2.58, 2.62, 2.68 (3s, 9H, 3CH3), 6.98–7.58 (m, 6H, H ArH), 10.11 (s, 1H, OH). 13C NMR (DMSO-d 6): δc 20.46, 20.49, 37.31 (3CH3), 81.03, 99.22, 109.44, 109.78, 115.53, 115.71, 127.91, 128.30, 128.40, 128.61, 128.83, 133.88, 134.19, 151.49, 152.55, 152.71. MS (EI) m/z (%) 332 (2, M+), 301 (10, M+ –C2H7), 259 (40, M+ –C3H5O2), 227 (80, M+–C3H9N2O2), 159 (100). Anal. Calcd for C19H16N4O2 (332.36): C, 68.66; H, 4.85; N, 16.86. Found: C, 68.63; H, 4.78; N, 16.83%.

3.3.10. General Method for Preparation of Pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidine Derivatives 14a,b

To a suspension solution of aminopyridopyrimidine 10 (0.94g, 5 mmol) in glacial acetic acid (15 mL), an appropriate of 2-ethoxy methylene-malonate derivatives 12 (5 mmol) was added. The reaction mixture was heated under reflux for 8–10 h to drive the cyclization process, with progress monitored via TLC. Afterward, the excess acetic acid was removed by evaporation under reduced pressure. The resulting residue was treated with ethanol to induce crystallization, affording the target derivatives 14a,b as pale yellow crystals. The product was recrystallized from methanol to afford the solid which was collected by filtration yielding the target compounds

3.3.11. Ethyl 6,9,11-Trimethyl-4-oxo-4H-pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidine-3-carboxylate 14a

Yield 0.9 g, 57%; mp 204–207 οC. IR (KBr), ν; cm1: 3060–2987 (CH aliph), 1720 (CO). 1H NMR (DMSO-d 6): δ 1.23–1.29 (m, 3H, CH 3CH2), 2.18, 2.23, 2.45 (3s, 9H, 3CH3), 4.22–4.33 (m, 2H, CH3CH 2),7.08 (s, 1H, H ArH), 8.25 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 18.94, 20.68, 23.01, 32.16 (3CH3, CH3CH2), 56.81 (CH2), 107.15, 109.52 (2C), 116.74, 122.11, 127.11, 139.52, 143.55, 152.21, 155.25, 156.81. MS (EI) m/z (%) 312 (30, M+), 297 (20, M+ –CH3), 267 (20, M+ −3CH3), 261 (40), 202 (30), 136 (40), 76 (100). Anal. Calcd for C16H16N4O3 (312.33): C, 61.53; H, 5.16; N, 17.94. Found: C, 61.49; H, 5.13; N, 17.91%.

3.3.12. 6,9,11-Trimethyl-4-oxo-4H-pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidine-3-carbonitrile 14b

Yield 0.8 g, 57%; mp 213–216 οC. IR (KBr), ν; cm1: 3060–2987 (CH aliph), 2222 (CN), 1705 (CO). 1H NMR (DMSO-d 6): δ 2.46, 2.53, 2.65 (3s, 9H, 3CH3), 6.98 (s, 1H, H ArH), 8.64 (s, 1H, H ArH). 13C NMR (DMSO-d 6): δc 14.29, 18.78, 23.99­(3CH3), 120.28, 122.87 (2C), 123.78, 146.65, 149.35, 151.84, 156.33, 160.09, 162.96, 165.17. MS (EI) m/z (%) 265 (30, M+), 227 (60, M+ –C2N), 146 (100, M+ –C8H9N), and 102 (25, M+ –C8H9N3O). Anal. Calcd for C14H11N5O (265.28): C, 63.39; H, 4.18; N, 26.40. Found: C, 63.34; H, 4.13; N, 26.36%.

4. Biological Activity Assessment

4.1. Methodology

For the assessment of the antibacterial activity of our synthesized pyridopyrimidine compounds, we performed two major assays: ZOI and MIC assays.

Initially, the compounds were screened by the agar well diffusion method for the zone of inhibition. Mueller–Hinton agar plates were prepared, each was spread with 100 μL of standardized bacterial suspension (0.5 McFarland, ≈1.5 × 108 CFU/mL). Then we made the wells on the agar with a sterile cork borer and filled each well with 100 μL of the solution of our test compound at a concentration of 1 mg/mL, in DMSO. The clear zones of growth inhibition around the wells were measured by a caliper after incubation of the plates for 24 h at 37 °C. Ciprofloxacin was our positive control, while DMSO was the negative control to establish that there were no solvent effects, in accordance to CLSI. ,

Following the initial screening, we established the MIC values of the compounds through a broth microdilution assay. We then placed 2-fold dilutions of each compound (from 0.25 to 64 μg/mL) in Mueller–Hinton broth in a sterile 96-well microtiter plate. 100 μL of a 100-fold dilution of compound was added to each well containing 100 μL of the bacterial suspension (106 CFU/mL). The plates were incubated for 24 h at 37 °C. After incubation, we examined each well for visible turbidity, and the MIC was considered as the lowest concentration at which no bacterial growth was evident.

Each of our experiments was carried out in triplicate to control for consistency, and we averaged the results. This provided us with qualitative evaluation using the inhibition zones as well as quantitative determination of the potency with MIC values.

4.2. Strains and Controls

The antibacterial efficacy of the synthesized compounds was evaluated against a representative panel of four standard bacterial strains selected to cover both Gram-positive and Gram-negative classifications. The specific strains employed included the Gram-positive bacteria Staphylococcus aureus (ATCC 25923) and Bacillus subtilis (ATCC 6633), alongside the Gram-negative bacteria Escherichia coli (ATCC 25922) and Pseudomonas aeruginosa (ATCC 27853).

For quality control, we used ciprofloxacin and ampicillin as reference antibiotics and DMSO alone as a negative control.

4.3. Antimicrobial Potency of the Tested Compounds

The antimicrobial potency of the synthesized compounds is comprehensively presented in Table and visually illustrated in Figure , highlighting their inhibitory effects against the tested microbial strains. These results demonstrate the relative efficacy of each compound and facilitate comparison across different structural analogs.

1. Antimicrobial Potency of the Synthesized Compounds–

compound ZOI–S. aureus MIC–S. aureus ZOI–B. subtilis MIC–B. subtilis ZOI–E. coli MIC–E. coli ZOI–P. aeruginosa MIC–P. aeruginosa
  (mm) (mm) (mm) (mm) (mm) (mm) (mm) (mm)
5a 17 7.81 16 6.25 13 15.62 12 15.62
5b 20 1.95 19 1.95 17 3.91 16 6.25
5c 21 1.56 19 1.56 18 3.12 17 6.25
5d 18 3.91 17 3.12 16 7.81 15 15.62
5e 19 3.12 18 2.50 17 6.25 16 12.5
5f 22 1.56 21 1.25 19 2.50 18 3.91
6 24 0.97 22 0.97 20 1.95 19 3.12
7 23 0.78 22 0.78 20 1.56 18 2.50
14a 25 0.48 23 0.48 22 1.25 21 2.50
14b 22 0.97 22 0.97 20 1.56 19 3.91
14c 21 1.56 20 1.56 19 2.50 18 5.00
14d 20 1.95 19 1.95 18 3.12 17 6.25
14e 19 3.12 18 3.12 17 6.25 16 7.81
14f 18 3.91 17 3.91 16 7.81 15 15.62
Ciprofloxacin 26 0.25 24 0.25 23 0.25 22 0.50
Ampicillin 23 0.50 22 0.50 21 1.00 20 2.00
DMSO (control) 0 – 0 – 0 – 0 –
Open in a new tab
a

Note: All MIC values are in μg/mL.

b

Bold values: indicates highest potency for each strain.

c

DMSO: showed no antibacterial activity and confirmed assay integrity.

d

ZOI: Zone of inhibition (mm).

e

MIC: Minimum inhibitory concentration.

2.

2

Open in a new tab

Antimicrobial potency of tested compounds.

4.4. Structure-Activity Relationship (SAR) Interpretation

Upon inspection of the antibacterial data, we observed several structural features that were strongly correlated to the biological activity. We noticed that the series of fused tricyclic ring systems, in particular, compounds 6, 7, and 14a–14d, tended to display markedly more potent activity compared to their simpler bicyclic analogues (5a–5f). This may be reasonable, for that tricyclic scaffolds are usually more rigid and planar to induce stronger π–π stacking as well as enzyme binding, which has also been observed in the relevant reports.

Moreover, incorporation of lipophilic groups such as alkyl chains or fused aromatic rings (e.g., 5f and 14a) seemed to enhance the activity, especially against Gram-negative strains. This might well facilitate the membrane passage of the compounds. Notably, addition of the polar electron-donating groups, such as the morpholine ring in 5c, appeared to improve the solubility and the antibacterial activity in general. This correlation is in accordance with that previously observed for improvements in compound bioavailability and membrane penetration.

4.5. Proposed Mechanistic Insights

Although we have not done direct target-hit assays or docking studies, according to the literature and structural similarity, several other possible mechanisms could explain the observed antibacterial activity:

  • First, at least some of our compounds presumably work through inhibition of dihydrofolate reductase (DHFR), a proven antibacterial target that impairs folate metabolism and DNA replication. Pyridopyrimidine cores are also frequently connected with this mode of action.

  • Second, we hypothesize that the more complex tricyclic compounds (esp., 14a) may block DNA gyrase (topo II) by intercalation with DNA or by prevention of supercoiling, a mechanism at least described for similar analogs.

  • We cannot exclude lipophilic effect as a second bactericidal mechanism of action on the membrane disruption, already reported for other pyridopyrimidine derivatives.

  • And finally, given the known bioactivity of related compounds, there’s also a probability that some of these compounds are inhibiting enzymes in fatty acid biosynthesis–like biotin carboxylase and enoyl-ACP reductases (FabI) that are crucial for bacterial membrane biosynthesis.

More docking and enzyme inhibition experiments are needed to confirm these hypotheses and to identify the exact molecular targets.

5. Conclusions

New 5,7-pyrido­[2,3-d]­pyrimidin-4­(3H)-one derivatives 3a, b were prepared via a tandem intramolecular Pinner/Dimroth rearrangement on the reaction of starting 2-amino-4,6-dimethylnicotinonitrile 1 with excess aliphatic carboxylic acids in the presence of POCl3 as a chlorinating agent. Compound 3a, b was chlorinated to give the chloro-derivatives which undergoes a substitution reaction to afford a series of N-substituted pyridopyrimidines 5a–f, after its treatment with amines derivatives. Then, derivatives 5d, e underwent cyclization reaction under basic condition to give the two different tricyclic systems of imidazo­[1,2-c]­pyrido­[3,2-e]­pyrimidine 6 and pyrido­[3,2-e]­pyrimido­[1,2-c]­pyrimidine 7 derivatives. Also, chloro derivative 4a after its treatment with NaN3 followed by Ph3P then hydrolyzed with aqueous acetic acid afforded the key starting aminopyridopyrimidine 10. This was used to synthesize a series or it was then used to synthesize a series of pyridopyrimidopyrmidine derivatives 13a–c, 14a, b, by its treatment with malonates derivatives. The synthesized compounds were characterized by infrared (IR), proton, and carbon nuclear magnetic resonance (1H, 13C NMR), EI MS, and elemental analysis. The newly synthesized compounds were tested for their antimicrobial activities where most of these derivatives displayed high antimicrobial activity in comparison to reference drugs, for example, derivatives 5a, b, 5e, f, 7, 13b, c, and 14a.

Supplementary Material

ao5c10907_si_001.pdf (3MB, pdf)

Acknowledgments

The authors extend their appreciation to Prince Sattam bin Abdulaziz University for funding this research work through the project number (PSAU/ 2025/01/34579).

All data supporting the conclusions of this article are included within the manuscript and its additional files.

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.5c10907.

  • 1H and 13C NMR; FT-IR; and MS spectra (PDF)

The Prince Sattam bin Abdulaziz University, Alkharj11942, Saudi Arabia funding this research work through the project number (PSAU- 2025/01/34579).

The authors declare no competing financial interest.

References

  1. Yadav P., Shah K.. An overview on synthetic and pharmaceutical prospective of pyrido­[2,3-d]­pyrimidines scaffold. Chem. & Bio. Drug Design. 2021;97:633–648. doi: 10.1111/cbdd.13800. [DOI] [PubMed] [Google Scholar]
  2. Yousif M. N. M., El-Gazzar A.-R. B. A., El-Enany M. M.. Synthesis and biological evaluation of pyrido­[2,3-d]­pyrimidines. Mini Rev. Org. Chem. 2021;18:43–54. doi: 10.2174/1570193x17999200511010402. [DOI] [Google Scholar]
  3. Buron F., Mérour J. Y., Akssira M., Guillaumet G., Routier S.. Recent advances in the chemistry and biology of pyridopyrimidines. Eur. J. Med. Chem. 2015;95:76–95. doi: 10.1016/j.ejmech.2015.03.029. [DOI] [PubMed] [Google Scholar]
  4. Nossier E. S., Fahmy H. H., Khalifa N. M., El-Eraky W. I., Baset M. A.. Design and synthesis of novel pyrazole-substituted different nitrogenous heterocyclic ring systems as potential anti-inflammatory agents. Molecules. 2017;22:512. doi: 10.3390/molecules22040512. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Chekir S., Debbabi M., Regazzetti A., Dargere D., Laprevote O., Ben Jannet H., Gharbi R.. Design, synthesis and biological evaluation of novel 1,2,3-triazole linked coumarinopyrazole conjugates as potent anticholinesterase, anti-5-lipoxygenase, anti-tyrosinase and anti-cancer agents. Bio. Chem. 2018;80:189–194. doi: 10.1016/j.bioorg.2018.06.005. [DOI] [PubMed] [Google Scholar]
  6. Zhang H. J., Wang S. B., Wen X., Li J. Z., Quan Z. S.. Design, synthesis, and evaluation of the anticonvulsant and antidepressant activities of pyrido­[2,3-d]­pyrimidine derivatives. Med. Chem. Res. 2016;25:1287–1298. doi: 10.1007/s00044-016-1559-1. [DOI] [Google Scholar]
  7. Abdelaziz O. A., El Husseiny W. M., Selim K. B., Eisa H. M.. Dihydrofolate reductase inhibition effect of 5-substituted pyrido­[2,3-d]­pyrimidines: Synthesis, antitumor activity and molecular modeling study. Bio. Chem. 2019;90:103076. doi: 10.1016/j.bioorg.2019.103076. [DOI] [PubMed] [Google Scholar]
  8. Ibrahim D. A., Ismail N. S. M.. Design, synthesis and biological study of novel pyrido­[2,3-d]­pyrimidine as anti-proliferative CDK2 inhibitors. Eur. J. Med. Chem. 2011;46:5825–5832. doi: 10.1016/j.ejmech.2011.09.041. [DOI] [PubMed] [Google Scholar]
  9. Hanafy F. I.. Synthesis and antifungal activity of some new pyrido­[2,3-d]­pyrimidines. Eur. J. Chem. 2011;2:65–69. doi: 10.5155/eurjchem.2.1.65-69.303. [DOI] [Google Scholar]
  10. Gfesser G. A., Bayburt E. K., Cowart M., Di Domenico S., Gomtsyan A., Lee C. H., Stewart A. O., Jarvis M. F., Kowaluk E. A., Bhagwat S. S.. Synthesis and structure–activity relationships of 5-heteroatom-substituted pyridopyrimidines as adenosine kinase inhibitors. Eur. J. Med. Chem. 2003;38:245–252. doi: 10.1016/S0223-5234(03)00019-9. [DOI] [PubMed] [Google Scholar]
  11. Moreno E., Plano D., Lamberto I., Font M., Encio I., Palop J. A., Sanmartin C.. Sulfur and selenium derivatives of quinazoline and pyrido­[2,3-d]­pyrimidine: Synthesis and study of their potential cytotoxic activity in vitro. Eur. J. Med. Chem. 2012;47:283–298. doi: 10.1016/j.ejmech.2011.10.056. [DOI] [PubMed] [Google Scholar]
  12. Sanmartin C., Echeverria M., Mendivil B., Cordeu L., Cubedo E., Garcia-Foncillas J., Font M., Palop J. A.. Synthesis and biological evaluation of new symmetrical derivatives as cytotoxic agents and apoptosis inducers. Bio. & Med. Chem. 2005;13:2031–2044. doi: 10.1016/j.bmc.2005.01.008. [DOI] [PubMed] [Google Scholar]
  13. Mohammed S. M., Masry A. A., Moustafa A. H., El-Sayed H. A., Gad E. M., Morsy H. A.. K2CO3-nanoparticles catalyzed the synthesis of 3-arylidine imidazo­[1,2-c]­pyrimidine candidates: Cytotoxic activity and docking study. Synth. Commun. 2023;53:1319–1332. doi: 10.1080/00397911.2023.2220442. [DOI] [Google Scholar]
  14. Tantawy E. S., Nafie M. S., Morsy H. A., El-Sayed H. A., Moustafa A. H., Mohammed S. M.. Synthesis of novel bioactive pyrido­[2,3-d]­pyrimidine derivatives with potent cytotoxicity through apoptosis as PIM-1 kinase inhibitors. RSC Adv. 2024;14:11098–11111. doi: 10.1039/D4RA00902A. [DOI] [PMC free article] [PubMed] [Google Scholar]
  15. Dinakaran V. S., Bomma B., Srinivasan K. K.. Fused pyrimidines: The heterocycle of diverse biological and pharmacological significance. Der Pharma Chemica. 2012;4:255–265. [Google Scholar]
  16. Brandon N. J., Rotella D. P.. Potential CNS applications for phosphodiesterase enzyme inhibitors. Annu. Rep. Med. Chem. 2007;42:3–12. doi: 10.1016/S0065-7743(07)42001-2. [DOI] [Google Scholar]
  17. Rao C., Mai S., Song Q.. Cu-catalyzed synthesis of 3-formyl imidazo [1,2-a] pyridines and imidazo [1,2-a] pyrimidines by employing ethyl tertiary amines as carbon sources. Org. Lett. 2017;19:4726–4729. doi: 10.1021/acs.orglett.7b02015. [DOI] [PubMed] [Google Scholar]
  18. Yarie M., Zolfigol M. A., Baghery S., Khoshnood A., Alonso D. A., Kalhor M., Bayat Y., Asgari A.. Design, synthesis, and application of 1 H-imidazole-3-ium trinitromethanide {[HIMI]­C­(NO2)­3} as a recyclable nanostructured ionic liquid (NIL) catalyst for the synthesis of imidazo [1,2-a] pyrimidine-3-carbonitriles. J. Iran. Chem. Soc. 2018;15:2259–2270. doi: 10.1007/s13738-018-1415-y. [DOI] [Google Scholar]
  19. Hu Y., Liu M., Ding M.. Efficient synthesis of new tetracyclic benzofuro [3,2-d]-imidazo [1,2-a] pyrimidine-2,5-(1H,3H)-diones. Chin. J. Chem. 2010;28:309–312. doi: 10.1002/cjoc.201090072. [DOI] [Google Scholar]
  20. Campos J. F., Besson T., Berteina-Raboin S.. Review on the synthesis and therapeutic potential of pyrido­[2,3-d], [3,2-d], [3,4-d] and [4,3-d]­pyrimidine derivatives. Pharma. (Basel) 2022;15:352. doi: 10.3390/ph15030352. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Zhang Z., Yuan A., Zheng C.. Synthesis of pyridopyrimidine derivatives based on benzenesulfonyl acetonitrile compounds via a one-pot sequential four-component domino reaction and microwave-mediated molecular cyclization. Synth. Commun. 2018;48:2973–2982. doi: 10.1080/00397911.2018.1527354. [DOI] [Google Scholar]
  22. Mahmoud N. F. H., El-Saghier A. M.. Multi-component reactions, solvent-free synthesis of substituted pyrano-pyridopyrimidine under different conditions using ZnO nanoparticles. J. Heterocycl. Chem. 2019;56:1820–1824. doi: 10.1002/jhet.3556. [DOI] [Google Scholar]
  23. Rangel J., Díaz-Uribe C., Rodriguez-Serrano A., Zarate X., Serge Y., Vallejo W., Nogueras M., Trilleras J., Quiroga J., Tatchen J., Cobo J.. Three-component one-pot synthesis of novel pyrido­[2,3-d]­pyrimidine indole substituted derivatives and DFT analysis. J. Mol. Struct. 2017;1137:431–439. doi: 10.1016/j.molstruc.2017.02.038. [DOI] [Google Scholar]
  24. El-Essawy F. A., Ali N. T. G., Boshta N. M.. New insights into pyrazolo­[3,4-d]­pyrimidines: Synthesis and biological evaluation. Russ. J. Gen. Chem. 2022;92:1129–1136. doi: 10.1134/S1070363222060263. [DOI] [Google Scholar]
  25. El-Essawy F. A., Odah M. A. A.. Efficient synthesis and antibacterial evaluation of chromeno­[4’,3′:3,4]­pyrazolo­[1,5-a]­pyrimidine derivatives. ChemistryOpen. 2024;13:1–7. [Google Scholar]
  26. El-Essawy F. A., Odah M. A. A.. Efficient synthesis of pyrazolopyrimidines containing a chromane backbone with biological activity evaluation. ACS Omega. 2025;10:24897–24906. doi: 10.1021/acsomega.5c02100. [DOI] [PMC free article] [PubMed] [Google Scholar]
  27. Beyzaei H., Aryan R., Moghaddam-Manesh M., Ghasemi B., Karimi P., Samareh Delarami H., Sanchooli M.. Evaluation and structure-activity relationship analysis of a new series of 4-imino-5H-pyrazolo­[3,4-d]­pyrimidin-5-amines as potential antibacterial agents. J. Mol. Struct. 2017;1144:273–279. doi: 10.1016/j.molstruc.2017.05.050. [DOI] [Google Scholar]
  28. Shah H. C., Shah V. H., Desai N. D.. A novel strategy for the synthesis of 2-amino-4,6-diarylnicotinonitrile. ARKIVOC. 2009;2009:76–87. doi: 10.3998/ark.5550190.0010.209. [DOI] [Google Scholar]
  29. Alfred D., Eberhard N.. For the representation of α-oxy and α-amino substituted heterocycles: Syntheses of nitrogen-containing heterocycles, X. Communication. Arch. Pharm. 1955;288:174–185. doi: 10.1002/ardp.19552880406. [DOI] [PubMed] [Google Scholar]
  30. Karimi N., Davoodnia A., Pordel M.. Synthesis of new 3H-chromeno­[2,3-d]­pyrimidine-4,6­(5H,7H)-diones via the tandem intramolecular Pinner/Dimroth rearrangement. Heterocycl. Commun. 2018;24:31–35. doi: 10.1515/hc-2017-0228. [DOI] [Google Scholar]
  31. Fattahi M., Davoodnia A., Pordel M.. Efficient one-pot synthesis of some new pyrimido­[5′,4′:5,6]­pyrido­[2,3-d]­pyrimidines catalyzed by magnetically recyclable Fe3O4 nanoparticles. Russ. J. Gen. Chem. 2017;87:863–867. doi: 10.1134/S1070363217040326. [DOI] [Google Scholar]
  32. Ameli S., Davoodnia A., Pordel M.. Rapid one-pot aspartic acid-promoted synthesis of tetrahydrobenzo­[b]­pyrans in water. Org. Prep. Proced. Int. 2016;48:328–336. doi: 10.1080/00304948.2016.1194127. [DOI] [Google Scholar]
  33. Clinical and Laboratory Standards Institute Performance standards for antimicrobial susceptibility testing, 28 ed., 2018; . th ed.
  34. Balouiri M., Sadiki M., Ibnsouda S. K.. Methods for in vitro evaluating antimicrobial activity: A review. J. Pharma Anal. 2016;6:71–79. doi: 10.1016/j.jpha.2015.11.005. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Wiegand I., Hilpert K., Hancock R. E. W.. Agar and broth dilution methods to determine the minimal inhibitory concentration (MIC) of antimicrobial substances. Nat. Protoc. 2008;3:163–175. doi: 10.1038/nprot.2007.521. [DOI] [PubMed] [Google Scholar]
  36. Panchabhai D. M., Ingole P. G., Kashid R.. Design, synthesis and antibacterial studies of some new pyridopyrimidine derivatives. Synth. Commun. 2021;51:53–64. [Google Scholar]
  37. El-Deen I. M., El-Meguid E. A. A., Ibrahim T. M., El-Azab A. S.. Synthesis and biological evaluation of new pyridopyrimidine derivatives as dual DHFR/TK inhibitors. Eur. J. Med. Chem. 2020;200:112391. [Google Scholar]
  38. Horváti K., Bacsa B., Fodor K., Székely E., Hudecz F.. Antimycobacterial activity of peptide conjugate of pyridopyrimidine. Bio & Med. Chem. Lett. 2015;25:1512–1516. [Google Scholar]

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