New bis hydrazone: Synthesis, X-ray crystal structure, DFT computations, conformational study and in silico study of the inhibition activity of SARS-CoV-2

Graphical abstract

Abstract

The aim of this work was to synthesize new bis hydrazone derived from benzil in good yield, namely: (1Z,2Z)-1,2-bis (3-Chlorophenyl Hydrazino) Benzil, encoded by 3-Cl BHB. The benzil (or 1,2-diphenyl ethanedione) reacts with 3-Cl phenyl hydrazine by reflux method using ethanol as solvent to obtain the target compound. The obtained product is depicted by UV–Vis, IR spectroscopy and XRD-crystals analysis. All various contacts intra and intermolecular found in 3-Cl BHB were determined by the X-ray diffraction technique performed on single crystals. On the other hand, the optimized geometric structure of 3-Cl BHB was computed by the DFT/B3LYP method with 6–31 G (d, p) level. So, the bond lengths and angles, frontier molecular orbitals (FMO), surface electrostatic potential of the molecule (MEP), global reactivity descriptors, Mulliken atomic charges, computed vibrational analysis and electronic absorption spectrum were determined to get a good understanding of the electronic properties and the active sites of 3-Cl BHB, then to compare them with experimental data. Additionally, a conformational study was carried out using the same method (DFT). The structure-activity relationships established through molecular docking studies showed that 3-Cl BHB structure strongly binds to the receptors M^pro (-8.90 Kcal/mol) and RdRp (-8.60 Kcal/mol) which confirm its inhibition activity against COVID-19.

1. Introduction

COVID-19 is most common among older patients, particularly those with comorbidities such as diabetes, hypertension, obesity, and chronic kidney disease [1,2]. Despite significant progress in COVID-19 disease treatment tools, effective therapies for managing the novel coronavirus disease's long-term complications (COVID-19) are still lacking. COVID-19 is now found to affect other parts of the body in addition to the respiratory system [3]. In the meantime, the search for the appropriate vaccines and the effective drugs continues.

Due to the richness of many antiviral drugs on a significant number of nitrogen atoms and aromatic rings such as Merimepodib, Remdesivir and Mozenavir [4], we were motivated to synthesize a new bioactive compound of hydrazine derivatives called hydrazone. Because of its reaction efficiency and product stability, hydrazone formation, which is characterized by the formation of an R₁R₂C N—NH₂ bond, stands out in medicinal and combinatorial chemistry as a promising method for intermolecular conjugation [5,6].

Generally, hydrazones are a special class of Schiff bases containing azomethine group (C = N) and N—N bound. So, they have been used as possible ligands for metal complexes in organic synthesis [[7], [8], [9]–10], optoelectronic applications [11,12] and organo-catalysis [13]. Furthermore, due to their diverse pharmacological activities, hydrazone derivatives have recently attracted the attention of medicinal chemists. Many studies have found that these compounds have a wide range of biological activities, such as anticancer [14], antidiabetic [15], antioxidant [16], antimicrobial [17,18], antituberculosis [19], anticholinesterase [20], antifungal [21] and antiviral [22,23].

In the current work, novel bis-hydrazone was synthesized with a good yield. Single crystal X-ray diffraction (XRD), FT-IR, and UV–Vis spectroscopy were used to investigate the molecular structure and spectroscopic properties. As well, the Density Functional Theory (DFT) is used to gain a better understanding of the geometrical and electronic properties, then to compare them with the experimental data of the title compound. On the other hand, we wanted to see if the compound synthesized for the first time in this study could be antiviral agent candidate for use in the treatment of SARS-CoV-2 with an in silico study. Therefore, the molecular docking studies were carried out to know its interactions with the main protease (M^pro) and RNA dependent RNA polymerase (RdRp) of SARS-CoV-2.

2. Experimental section

2.1. Physical and material investigations

In this work, all the chemical reagents and solvents employed for the 3-Cl BHB ligand synthesis were available from commercial sources and used without any purification. The FT-IR in the range of 500–4000 cm⁻¹ was recorded in solid state (KBr disks) using a Shimadzu FTIR-8010 M spectrometer. Electrothermal melting point apparatus was utilized for measuring melting point, and then the UV–Vis spectrum of the synthesized product was obtained in the range of 200–800 nm by UV–Vis 1800 UNICAM.

2.2. General procedure for the preparation of 3-Cl BHB

In a 100 ml flask, topped with a condenser, 1 g of benzil (4.76 mmol) is dissolved in 25 ml of ethanol and then mixed with this solution 1.36 g of 3-chlorophenylhydrazine (9.52 mmol), in order to speed up the reaction, a few drops of acetic acid were also added to the solution mixture. All were placed in the flask heater while stirring at a temperature of 80 °C for 7 h (Scheme 1), TLC was used to monitor the reaction until it was finished. At the end of the reaction and by cooling the reaction mixture, a light-yellow precipitate was obtained which was separated from the liquid phase by filtration (yellow 71%; m.p: 188 °C).The product was recrystallized by dimethylformamide (DMF).

Scheme 1.

The synthesis schematic for (1Z,2Z)−1,2-bis (3-Chlorophenyl Hydrazino) Benzil.

2.3. X-ray diffraction and refining of single crystals

The diffracted intensities were set to 150 K on a Bruker-diffractometer. Nonius with Kappa geometry was equipped with a two-dimensional CCD type detector, (Nonius Kappa CCD diffractometer). The diffractometer was also equipped with a system cryoscopic with liquid nitrogen and a monochromator with a graphite blade according to the ω/2θ scan, using the Kα radiation of Mo (λ = 0.71073 Å) at 150 K in a domain angular going from 2.93° to 27.48° The structures were solved by direct methods using the SHELXS-97 program and refined on F² by full matrix least squares [24]. Also, the crystalline structure was drawn using the Mercury and Ortep software [25,26]. The experimental data like the crystal system, conditions recording, mesh parameters, and others, are detailed in Table 1 . Thus, copies of these information may be obtained free of charge from http://www.ccdc.cam.ac.uk or by emailing data_request@ccdc.cam.ac.uk, because the crystallographic data on the structure of 3-Cl BHB have been deposited in the Cambridge Crystallographic Data centre, with CCDC No: 2,101,205.

Table 1.

Crystallographic data and structure refinement detail for 3-Cl BHB.

Compound	3-Cl BHB
Empirical formula	C26H20Cl2N4
Formula weight, g/mol	459.36
Crystal system	Triclinic
Space group	P-1
Temperature/Ka (Å)	150(2)7.8551(5)
b (Å)	8.5174(5)
c (Å)	16.9720(13)
α (°)	77.943(3)
β (°)	86.730(3)
γ (°)	89.118(3)
V (Å3)	1108.65(13)
Z	2
Crystal size/mm3Data / restraints / parametersCalculated density (mg/mm3)	0.3 × 0.22 × 0.174925 / 0 / 2951.376
Absorption coefficient(mm−1)Ɵ range for data collection (°)F (000)	0.3152.93 to 27.48476
Limiting indices(h,k,l)Absorption correction	−8 ≤ h ≤ 10, −8 ≤ k ≤ 11, −21≤l ≤ 21Semi-empirical from equivalents
Max./min. trans.	0.948 and 0.864
Wavelength (Å)	0.71073
Reflections collected/ unique	13,443 / 4925[R(int) = 0.0507]
Refinement methodFinal R indices [I>2σ(I)]	Full-matrix least squares on F2R1=0.0498, wR2 =0.1133
R indices (all data)S [Goodness of fit on F2]	R1 =0.0708, wR2 =0.12271.083
Largest diff. peak/hole/e Å−3	0.268 and −0.267

2.4. Computational methodology

Density functional theory (DFT) with Becke-3-Yang-Parr (B3LYP) hybrid parameter and standard basis sets 6–31 G (d, p) was used to calculate the optimized molecular structure of the title compound and their corresponding energies [27,28]. For a better study about our bis hydrazone and its active sites, bond lengths, bond angles, frontier molecular orbitals (FMO), surface electrostatic potential of the molecule (MEP), global reactivity descriptors and Mulliken atomic charges were carried out. The Gaussian 09 program package has been applied to perform all these calculations, while Gauss View was used for results visualizations and analysis [29,30]. Besides, the conformational analysis of synthesized compound has been investigated by this theory (DFT).

2.5. Molecular docking procedure

In this study, docking calculations of 3-Cl BHB ligand with SARS-CoV-2 main protease (M^pro) and RNA dependent RNA polymerase (RdRp) were used. They are generally used to predict the affinity of a ligand-protein and the most favorable position and orientation for a ligand interacting with a target protein. That is why, these simulations were performed by AutoDock software version 4.2.6, and a grid box size of 30Å × 30Å × 30Å centered at the pocket of protein at XYZ= (−10.85, 12.58, 68.72) was selected. In addition, the target proteins PDB structures were obtained from the RCSB protein data bank (Research Collaboratory for Structural Bioinformatics) with M^pro $\to id:6\text{LU}7\text{and}\text{RdRp}\to \text{id}:7\text{BV}2$, the polar hydrogen atoms were added to the amino acid residues, while the water molecules were discarded and all of the protein's atoms were given Gasteiger charges [31]. The 3-Cl BHB-M^pro and 3-Cl BHB-RdRp complexes were visualized using Accelry's Discovery Studio Visualizer as represented in Fig. 1 a and b, respectively.

Fig. 1.

Best docked model visualization of the studied molecule with SARS-CoV-2 main protease (a) and RNA dependent RNA polymerase (b).

3. Results and discussion

3.1. X-ray diffraction analysis

After a slow evaporation of our solution (3-Cl BHB in DMF), the structure and geometry of the obtained single crystals were analyzed by X-ray diffraction. This technique confirms exactly the molecular structure of the target compound. Fig. 2 shows the numbering scheme and a displacement ellipsoid plot of 3-Cl BHB, whereas the most important crystal properties are given in Table 1. Our bis-hydrazone crystallized in a triclinic system in P-1 space group and with a two molecules unit per cell (Z = 2) as displayed in Fig. 3 .

Fig. 2.

3-Cl BHB structure as seen by ORTEP at the 50% probability threshold, displacement ellipsoids are drawn.

Fig. 3.

Unit cell with the layered structure of the molecule in the crystal.

The 3Cl-pH—HN—N = C_9—C₂₉ N—NH-pH-3Cl moieties were found to be in the s-Trans conformation, this positioning has been defined by the contact interactions and steric effects which forced a rotation of the two hydrazone units relative to C9-C29 single bond axis [32]. These two moieties are nearly perpendicular to one another by the dihedral angle N₈C₉C₂₉N₂₈ (−80.80°). On the other hand, the two phenyl rings of the benzil makes dihedral angles of −81.2°, which confirms that the geometry of the target compound is not planar. Furthermore, the azomethine groups were noted to be in Z configuration, which is involved in the torsion angles N₇N₈C₉C₁₀ [178.06(15)°] and N₂₇N₂₈C₂₉C₃₀ [178.60 (15)°]. Concerning bonds distances, the C = N bond lengths are 1.299 (2) Å for N₈ C₉ and 1.297 (2) Å for N₂₈ C₂₉, while the N—N (hydrazine) distance is in a typical single bond range [1.360(2)−1.357(2) Å]. Additionally, the C_1—Cl₁ andC_21—Cl₂ bonds distances are 1.748(19) and 1.744(2) Å, respectively, close to that expected for C—Cl bond (Table 4, Supplementary Information). All the results realized herein are similar to those found in the previous studies [[33], [34]–35].

Table 4.

Selected bond distances (Å) and angles (°) from X-ray diffraction and DFT optimization for 3Cl-BHB.

Bond lengths (Å)	Exp.	Calc.	Bond angles (°)	Exp.	Calc.
C1-Cl1C9-C10C9-C29C29-C30C5-N7N7-H7N7-N8N8-C9N27-N28N27-H27N28-C29C25-N27C21-Cl2C21-C26C30-C31C30-C35	1.748(19)1.474(2)1.500(3)1.475(3)1.394(2)0.89(2)1.360(2)1.299(2)1.357(2)0.86(2)1.297(2)1.399(2)1.744(2)1.390(3)1.392(3)1.394(3)	1.8321.4961.4661.4961.3971.0151.3581.3131.3581.0151.3121.3971.8321.3881.4071.409	C6-C1-Cl1C6-C5-N7C6-C5-C4C4-C5-N7N8-N7-H7C9-N8-N7N8-C9-C10N8-C9-C29N28-C29-C9C29-N28-N27N28-N27-H27C24-C25-N27C26-C25-N27C26-C21-Cl2C29-C30-C35C31-C30-C35	118.72(15)118.08(17)120.12(16)121.76(17)120.2(14)116.96(16)118.57(17)122.20(16)122.31(16)117.46(16)119.8(16)118.18(18)121.20(18)118.47(17)119.95(17)118.31(18)	118.21118.36119.88121.76120.18120.36123.63116.24116.39120.44120.29118.98121.09118.16120.14118.82

The atoms with a high electronegativity like Cl and N play a crucial role in most interactions; this is confirmed by the short contacts in our bis-hydrazone, which are summarized in two categories. The first is intramolecular contacts, depicted in Fig. 4 a and Table 2 a, where four interaction types are found π(C = N)….H_Ph(N8…H4, N8…H11, N28…H26 and N28…H31), two corresponding N = C…HN (C9…H27, C29…H7) and others like H_Ph….π(pH) where they enhance the toughness of the compound. Concerning the second category called intermolecular contacts as represented in Fig. 4 b and Table 2 b, most of them were of the type H_Ph….π(pH) like (C5…H34 × 2 and C35…H14 × 2). Besides, there are a lot of H-bonds in the title product, which would control the conformation of 3-Cl BHB compound as mentioned earlier and make it more stable. Where N and Cl atoms acts as potent acceptor for H-bond in which atoms N7 and N27 donates a proton, as shown in Fig. 5 a and Table 3 . The crystal structure in 3-Cl BHB is oriented head to tail along the a-axis direction, in parallel columns driven by H-bonds (N—H…Cl) interactions, resulting in limitless chains, as seen in the Fig. 5 b.

Fig. 4.

(a). Contact intramolecular in 3-Cl BHB. (b). Contact intermolecular in 3-Cl BHB.

Table 2.

(a). Contact intramolecular.

Number	Atom1	Atom2	Length (Å)
123456789101112	H4H6H7N8C9C9C10C10H15H24H26N28	N8H7C29H11H27H35C35H35C29H27N28H31	2.5182.3612.3542.5622.3662.5093.3512.7472.5262.3462.5492.561

(b). Contact intermolecular.
Number	Atom 1	Atom2	Length (Å)
12345678	C35H14C5H34Cl2H33H4H12	H14C35H34C5H33Cl2H12H4	2.8892.8892.7132.7132.9022.9022.3562.356

Fig. 5.

(a)The hydrogen bonds (dashed lines), (b) a view along the a-axis in the crystal structure of 3-Cl BHB.

Table 3.

3-Cl BHB H-bond angles (°) and distances (Å).

D-H … A	d(D-H)	d(H … A)	d(D-A)	D-H-A
InterN7-H7…Cl2 $\times 2$N27-H27…Cl1 $\times 2$IntraN7-H7…N27N7-H7…N28N27-H27…N8N27-H27…N7	0.8890.8610.8890.8890.8610.861	3.2152.9933.1852.7832.7853.166	4.0293.7813.3563.2313.2373.356	153.28153.1493.31112.60114.4195.22

3.2. Computational analysis

3.2.1. Optimized molecular structure

To optimize the structure and establish key geometric parameters, the DFT approach was employed at the B3LYP level using the 6–31 G (d, p) basis set. The optimized molecular geometry (the most stable structures correlate to the lowest energy) of the 3-Cl BHB is shown in Fig. 6 . Furthermore, the calculated total energy for this molecule in the best structure was −58,281.69 eV, which represents the energy of the more stable conformation of the analyzed ligand. The DFT gaseous state optimization revealed the 3-Cl BHB configuration with E-isomer in the two imine groups, rather than Z as in the crystalline structure. This is not surprising because in the gaseous state, E-isomers have a lower internal repulsion energy than Z-isomers [36]. Following this optimization, we conducted a comparison study with the XRD data. Table 4 lists the selected bond length (DRX/DFT) and bond angle (DRX/DFT) values, it was discovered that they are well matched, with correlation coefficients of R² = 0.9859 and 0.9861, respectively, as displayed in Fig. 7 a and b.

Fig. 6.

Optimized structure of 3-Cl BHB.

Fig. 7.

DFT/XRD-graphical correlation for bond lengths (a) and bond angles (b).

3.2.2. Electronic properties and frontier molecular orbitals (FMO) analysis

The information regarding electrical and optical properties, as well as UV–Vis spectra and quantum chemistry, is provided by the frontier molecular orbital HOMO (Highest Occupied Molecular Orbital) and LUMO (Lowest Unoccupied Molecular Orbital), the gap between them, known as the orbital energy gap, is crucial in defining the molecule's electron transport capability. A greater orbital energy gap indicates that the molecule is chemically hard, stable, and unreactive, whereas a lower orbital energy gap indicates that the molecule is soft, unstable, and reactive [37].

The quantum molecular descriptors of 3-Cl BHB such as ionization potential (I), electron affinity (A), global hardness (η), electronegativity (χ), electronic chemical potential (μ), electrophilicity (ω), and chemical softness (S) were calculated and summarized in Table 5 and they have helped in many ways to understand the structure of molecules and their reactivity. Ionization potential (I) and electron affinity (A) are the negative energies of HOMO and LUMO, respectively. The global hardness (η) corresponds to the energy gap between HOMO and LUMO. Also, the ability to give an electron orto accept an electron is represented by the HOMO and LUMO, respectively [38,39]. The ΔE_Gap value denotes the minimum amount of energy required for electronic excitation, which is mostly associated with the π-π* transition [40].

Table 5.

Calculated quantum chemical parameters of 3-Cl BHB using DFT/B3LYP 6–31 G (d,p) method.

Molecular energy (eV)	3-Cl BHB
EHOMOELUMOIonization Potential (I)Electron affinity (A)Chemical potential(µ)Electronegativity (ᵡ)Chemical hardness (ɳ)Softness (S)Electrophilicity index (ω)	−5.1462−1.55875.14621.5587−3.35253.35251.79380.27873.1328

I= -E_HOMO, A= -E_LUMO, $\mu =\frac{E_{HOMO}+E_{LUMO}}{2}$,$x=\frac{-\left(E_{LUMO}+E_{HOMO}\right)}{2}$

$\omega =\frac{{\mu }^2}{2\eta }$, $S=\frac{1}{2\eta }$, $\eta =\frac{1}{2(E_{\mathit{LUMO}}-E_{\mathit{HOMO}})}$

At the B3LYP/ 6–31 G (d,p) level, the HOMO and LUMO in the stable conformer of 3-Cl BHB were determined and the 3D plots generated from the calculations are depicted in Fig. 8 , their energies are equal to −5.1462 and −1.5587 eV, respectively. Therefore, ΔE_Gap value will be 3.5875 eV. In our compound, the HOMO is mainly focused over the two phenyl hydrazyl moieties; conversely the LUMO is projected over both of the molecule. There are two hues that stand out: green and red. Green indicates the negative phase, while red represents the positive phase. The query molecule's low energy gap (3.58 eV) indicates that it has higher chemical reactivity, lower dynamic stability, softness, and more polarizability, which means that the charge is easily transferred between the HOMO and LUMO orbitals of 3-Cl BHB [41]. We can divide organic compounds in to three categories based on their electrophilicity index values: marginal electrophiles with a value less than 0.8 eV, moderate electrophiles with a value between 0.8 and 1.5 eV, and strong electrophiles with a value greater than 1.5 eV [42]. Consequently, our bis-hydrazone will be strong electrophiles (3.13 eV). In the meantime, a nucleophilic attack on the 3-Cl BHB would be energetically advantageous and has good biological activity [43,44].

Fig. 8.

HOMO and LUMO frontier orbitals of 3-Cl BHB.

3.2.3. Surface electrostatic potential of the synthesized molecule (MEP)

The molecular electrostatic potential (MEP) is a three-dimensional map that depicts a molecule's charge distribution. It is a visual tool that can be used to determine the relative polarity of molecules and their negative and positive electrostatic potentials [45]. Generally, the MEP is used to gain a better understanding of active sites and to pinpoint the location of chemical reactivity in molecules. The colors scheme for the MEP of 3-Cl BHB is scaled from the deepest red maximum electron concentration (−4.443 10⁻² a.u.) to the deepest blue maximum electron deficient (+4.443 10⁻2 a.u.) for 3-Cl BHB. Therefore, the MEP calculation surface of our compound as shown in Fig. 9 , with different colors: the orange-colored high e-rich locations that covered the N of the imine functional group (nucleophilic site), then a relatively larger region around the chloro atoms of the phenyl hydrazyl, reflects by the yellowish blobs, represents e-riche locations (halogen with high electronegativity). On the other hand, the hydrogen atom of the NH group has the most positive potential region characterized by deep blue color (e-poor), corresponding to the nucleophilic reaction sites. Whereas the H atoms of aromatic rings found in zone blue sky carry positive charges. All of this is confirmed by the contacts intra and intermolecular present in our DRX analysis.

Fig. 9.

Molecular electrostatic potential map of 3-Cl BHB.

3.2.4. Analysis of the Mulliken atomic charges population

Many properties of molecular systems like dipole moment, polarizability, refractivity, and electronic structure are all influenced by the charge diffusion of donor and acceptor atoms in molecules [46]. For this purpose, the Milliken population charges were carried out through B3LYP/6–31 G (d, p) level and are presented in Fig. 10 a, the bar diagrams of atomic charges are shown in Fig. 10 b. Generally, the calculation revealed the presence of several atoms with nucleophilic and electrophilic properties. From this study, we found that both nitrogen atoms possess negative Mulliken charges. Furthermore, all carbon atoms have a negative charge except for the carbon atoms which are attached directly to the nitrogen atom (C12, C13, C31, C41). Concerning the H and Cl atoms are all electropositives, however the H atoms coupled to nitrogen atoms have larger positive atomic charges than the other hydrogen atoms (+0.320, +0.321 a.u) with high electrophilic properties indicate the ability to form H-bonds like as founded in our DRX analysis.

Fig. 10.

(a). Mulliken atomic charges of 3-Cl BHB calculated at B3LYP/6–31 G (d,p) level. (b). The Mulliken atomic charge distribution of 3-Cl BHB.

3.2.5. FT-IR analysis

For the purpose of confirming the expected formula and to discover the vibrational frequencies of the characteristic groups in our compound, it was depicted by IR analysis in the region of 500 and 4000 cm⁻¹. Fig. 11 shows the experimental and calculated IR spectra of 3-Cl BHB in which we find that our bis-hydrazone exhibit a new strong band assigned to azomethine υ(C = N) stretching vibration around 1597 cm⁻¹ [47], besides one peak at higher wavenumbers (3420 cm⁻¹) is due to the stretching of the υ(N—H) vibrations. Concerning the υ(C—H_Ar) stretching in the phenyl rings, it is located at 3311 cm⁻¹ [48], while the strong absorption peaks at 1240, 1134 and 754 cm⁻¹ are assigned to the stretching modes of υ(C—N), υ(N—N) and υ(C—Cl) [49], respectively. A good agreement has been obtained between DFT(B3LYP/6–31 G) and experimental spectra as noticed (Table 6 ), which means that the experimental values have a better correlation with the calculated values.

Fig. 11.

Experimental and theoretical FT-IR spectra of 3-Cl BHB.

Table 6.

The calculated and experimental vibrational assignments of 3-Cl BHB.

Major Assignments	Exp wavenumbers (cm−1)	Calc wavenumbers (cm−1)
N-H stretching vibrationC—H (aromatic) stretching vibrationC—H (aliphatic) stretching vibrationC = N stretching vibrationC = C in phenyl ring (stretching)C—N stretching vibrationN—N (hydrazine) stretching vibrationC—Cl stretching vibration	3420331129251597153412401134754	35013209-1608152712831086780

3.2.6. UV–Vis analysis

In order to have a better understanding of the electronic structure in the desired ligand, the experimental absorption behavior and TD-SCF CAM-B3LYP/6–31 G (d,p) computation were performed in the DMSO solvent, as shown in Fig. 12 . The experimental spectrum of 3-Cl BHB showed two absorption bands, one located at λ_max= 299 nm and the other at λ_max= 392 nm, which may be attributed to π → π^∗ transition due to a conjugation in an unsaturated system and n → π^∗ excitation of the conjugation between the lone pair of electrons (N) and the others conjugated bond in 3-Cl BHB, respectively [50]. The absence of visible region absorption and the diversity of absorption peaks in the UV band ensure that the material is suitable for optical and photonic applications [51]. Conversely, the calculated spectrum founded through TD-SCF CAM-B3LYP/6–31 G (d,p) method for 3-Cl BHB compound showed a good resemblances in the shape and the band positions with the experimental UV–Vis spectrum in DMSO solvent. In which two broad peaks were detected by TD-DFT, the first is localized around 291 nm with Δλ= 8 nm shift, while the second peak at 401 nm due to HOMO→LUMO electron transfer which was in a good agreement with the n → π^∗ transition of the experimental UV–Vis spectrum (Δλ= 9 nm) [52].

Fig. 12.

Experimental and calculated electronic spectra (CAM-B3LYP) of 3-Cl BHB.

3.2.7. Conformational study

According to the relative orientation of the two unsaturated bonds (C = N) around a single bond (C9–C29) in 3-Cl BHB compound predisposes the existence of several conformational isomeric structures. In order to obtain additional information on this stereochemical aspect, the potential energy surface (PES) for internal rotation around the N8-C9-C29-N28 dihedral angle was calculated using the B3LYP/6–31 G (d,p) level of approximation [53,54]. The PES was created by varying this dihedral angle from 0° to 180° with a step of 15° to determine the more stable conformer of our bis hydrazone. Fig. 13 shows the results of the PES scan for the selected dihedral angle. It seems that there are three conformers were detected: the least stable conformer namely s-cis is located at the point with the highest energy value of −58,281.97 eV, then another one has less energy than the first isomer at −58,282.03 eV corresponding to pseudo s-cis conformer, while the minimum energy conformation is attributed to an angle of −80° corresponding to s-trans form with relative energy value of −58,282.12 eV, we explain this more stable positioning by the intramolecular hydrogen bonds formed in 3-Cl BHB which we discovered through the DRX analysis [55], all of these conformers are depicted in Fig. 14 . We observe that the molecular structure computed for the most stable conformer (s-trans) agrees very well with the structure experimentally determined from the single crystal X-ray diffraction analysis in solid state.

Fig. 13.

Scan of total energy of N8-C9-C29-N28 dihedral angle calculated by B3LYP/6–31 G (d,p) method.

Fig. 14.

Optimized structures of possible conformers of 3-Cl BHB.

3.3. Molecular docking analysis

The molecular docking of 3-ClBHB ligand with the M^pro and RdRp receptors becomes completed to outline the precise conformation of the title compound in the receptor and the secondary forces resulting between 3-Cl BHB and the lively amino acids of the receptor.

3.3.1. SARS-CoV-2 main protease and 3-Cl BHB interaction

The detailed presentation of the binding modes of the studied molecule in the receptor M^pro as illustrated in Fig. 15 a. With a view to this diagram, we observe that the title compound connects through van der Waals bond with the ASN142 amino acid, through Pi-sulfur interaction between the phenyl ring of the ligand and sulfur atom ofMET49 amino acid. In addition, it interacts through just one hydrogen bond with GLN189. Also, Pi-alkyl interactions are formed between Cl atoms in our bis hydrazone and LEU27, HIS41, HIS164 and MET165 amino acids residues of M^pro. All calculated lengths of these interactions are displayed in a 2D diagram, whereas the total binding energy of this complex is −8.90 Kcal/mol.

Fig. 15.

3D and 2D Binding-interaction diagrams of the studied molecule with SARS-CoV-2 main protease (a) and RNA dependent RNA polymerase (b).

3.3.1. RNA dependent RNA polymerase and 3-Cl BHB interaction

Our present ligand has a good binding interaction with RdRp (−8.60 Kcal/mol). Fig. 15 b represents the important interactions in the 3-Cl BHB-RdRp complex. According to the 2D diagram, we find that the 3-Cl BHB interacts with ALA547 and ARG555 by Pi-alkyl bonds, and then it was able to establish one Pi-cation interaction between A19 and N⁺ of the title compound. In general, hydrogen bonds develop when hydrogen is bonded to a more electronegative atom, such as sulfur, nitrogen or oxygen, and another atom with a single pair of electrons [56], as illustrated in the case of our compound with the LYS545amino acid. Besides, the Pi-Pi stacking could be another hydrophobic interaction between the drug and the receptors, as in the aromatic rings of 3-Cl BHB with U20 and U18 nucleotides.

When we look at Table 7 which contains the values of binding energy of our molecule and other published inhibitors such as: HDZPA [57], M1BZP [58], Hydroxychloroquine [59] and moroxydine [4] with the same receptors. We find that these results give a clear view that 3-Cl BHB has the lowest values of the bending energy compared to the rest of the drugs, which confirms that our ligand have the stronger binding affinity towards M^pro and RdRp of SARS-CoV-2. This harmonious bonding may be due to the abundance of electron density (four aromatic rings, 2 atoms of Cl and 4 atoms of N) in 3-Cl BHB and the flexibility of its structure.

Table 7.

Docking score results of 3—Cl BHB and some drugs with M^pro and RdRp.

Compounds	Mpro Binding energy in Kcal/mol	RdRp Binding energy in Kcal/mol
3-Cl BHB (the studied molecule)HDZPAM1BZPHydroxychloroquineMoroxydine	−8.90−6.00− 6.5−5.5−5.7	−8.60−7.70−7.4−5.6−5.8

According to the findings of our research, we can consider 3-Cl-BHB as a potent inhibitor against corona virus and more effective along with other compounds having similar activity. However, there must be other studies and experiments on this compound to develop its activity.

4. Conclusion

We have successfully completed an efficient and convenient synthesis of new bis hydrazone derived from benzil in good yield, called (1Z,2Z)−1,2-bis (3-Chlorophenyl Hydrazino) Benzil and encoded by 3-Cl BHB. UV–Vis, IR spectroscopy, and XRD-mono crystal were used to investigate the structure of the title compound. As well, DRX analysis enabled us to study the various contacts intra and intermolecular found in our bis hydrazone. Whereas, the Density Functional Theory (DFT) at the B3LYP/6–31 G (d,p) level was utilized to determine the active sites, electronic properties, quantum parameters and the most stable conformer of the examined molecule. Finally, after calculating the binding energies of M^pro-3-Cl BHB and RdRp-3-Cl BHB complexes by molecular docking and comparing it with other drugs having similar activity, we believe that our compound 3-Cl BHB can be a good inhibitor against SARS-CoV-2 main protease and RNA dependent RNA polymerase responsible for Coronavirus disease.

CRediT authorship contribution statement

Abdelkader Tabbiche: Investigation, Formal analysis, Methodology, Software, Resources, Writing – original draft. Abdelaziz Bouchama: Conceptualization, Methodology, Validation. Nadjib Chafai: Methodology, Software, Validation. Farouk Zaidi: Supervision. Chaabane Chiter: Supervision. Messaoud Yahiaoui: Supervision. Abdellah Abiza: Supervision.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.