Molecular structure determination, spectroscopic, quantum computational studies and molecular docking of 4-(E)-[2-(benzylamino)phenylimino) methyl-2]ethoxy phenol

Abstract A Schiff base compound 4-(E)-[2-(benzylamino)phenylimino)methyl-2]ethoxy phenol (4BPM2EP) was synthesized and spectroscopic characterization was performed using experimental methods such as FT-IR, FT-Raman and UV-Vis spectroscopy. Density functional theory (DFT/B3LYP/6-311++G(d,p)) computation was used to investigate the optimized molecular geometry, harmonic vibrational wavenumber, NMR chemical shifts, natural bond orbital (NBO) analysis, non-linear optical (NLO) properties, molecular electrostatic potential (MEP) map and Mulliken atomic charges of 4BPM2EP molecule. TD-DFT calculations have been carried out on the optimized geometry at gaseous phase, DMSO and ethanol to further understand the electronic transitions and solvents effect on the UV-Vis spectra of the compound. The assignments of vibrational modes were performed on the basis of total energy distribution (TED) using VEDA 4 program and were compared with experimental data. Molecular docking study was performed using Glide program to establish the information about the interactions between the topoisomerase DNA gyrase enzymes and the novel compound in order to explore the biological behaviour of the examined compound. The compound screened against four pathogens two gram positive, two gram negative and two fungal strains had shown good anti-bacterial and antifungal behaviour. Furthermore the compound was subjected to in-silico ADMET studies. Communicated by Ramaswamy H. Sarma


Introduction
Azomethines known as Schiff bases, consisting of imine groups (CH ¼ N) and benzene rings in the main chain alternatively and being p-conjugated, exhibit interest as materials for wide spectrum applications, particularly as corrosion inhibitors (Emregul et al., 2006), catalyst carriers (Drozdzak et al., 2005;Sessler et al., 2006), thermo-stable materials (Bk et al., 2017;Destri et al., 1998;Grigoras et al., 2001), a metal ion complexing agents (Kaya et al., 2001), medicinal and pharmaceutical fields due to broad spectrum of biological activities like anti-tumor (Ren et al., 2002),, anti-bacterial (Sharma et al., 2016), anti-fungal, anti-viral, anti-tubercular, insecticidal, bacteriostatic, in vitro cytotoxic, anti-inflammatory, analgesic and anti-pyretic agents (Andiappan et al., 2018;Bagihalli et al., 2008;Gopi et al., 2017;Jarrahpour et al., 2007;Murtaza et al., 2017;Qin et al., 2013;Shen et al., 2016;Zhu et al., 2000). The Schiff base compounds have been investigated during past years because they have vital importance in optical communications and many of them have NLO behaviour (Jalali-Heravi et al., 1999;Unver et al., 2004). On the basis of their high molecular hyperpolarizabilities, organic materials possess a number of significant NLO properties. NLO materials have been attractive in recent years with respect to their future potential applications in the field of optoelectronics such as optical communication, optical computing, optical switching and dynamic image processing (Kanis et al., 1994;Pn & Williams, 1991). Molecular docking methods are extremely significant and generally accepted for drug design and discovery initiatives (Di Muzio et al., 2017;Lopez-Camacho et al., 2015;Yuriev et al., 2015). Docking methods provides relatively fast and economical alternative to standard experimental techniques (Pereira et al., 2016;Sousa et al., 2010). They predict the experimental binding modes and affinities of small molecules within the binding site of receptor targets. Important goals in docking studies are to find the correct binding poses and to predict accurately the binding affinity. More accurate predictions of binding poses and binding affinities can suggest candidates for active compounds with higher true positive rates and can considerably reduce expensive experimental efforts (Shin et al., 2013). The quality of molecular docking depends on two factors: the optimization search method and the scoring function (Bazgier et al., 2016;Guo et al., 2014;Heo et al., 2014). An optimization algorithm mainly detects docking conformations with minimum binding energies. The scoring function is used to evaluate the results obtained from the search. In the present study, the crystal structure of protein was downloaded from Protein Data Bank (PDB ID: 2XCT) with resolution 3.35 Å to understand an interaction with the ligand. The docking was performed using Glide program (Halgren et al., 2004).
In recent years, density functional theory (DFT) has become important for theoretical modelling. Literature survey revealed that DFT has a great accuracy in reproducing the experimental values in geometry, dipole moment and vibrational frequency (Andzelm & Wimmer, 1992;Dickson & Becke, 1993;Fitzgerald & Andzelm, 1991;Johnson et al., 1993;Oliphant & Bartlett, 1994;Scuseria, 1992;Ziegler, 1991). The aim of present work is to investigate the energetic and structural properties of the Schiff base compound 4BPM2EP using DFT calculations. This study, presents the molecular structure, MEP, NLO property, frontier molecular orbitals (FMOs) of 4BPM2EP. These calculations are valuable for providing insight into molecular properties of Schiff base compounds.

Materials and methods
2.1. Synthesis procedure 0.01 M (1.66 g) 3-ethoxy 4-hydroxy benzaldehyde 0.01 M (1.0 g) 2-aminophenol and 0.01 M (1.0 mL) 1-phenylmethanamine were dissolved in 40 mL ethanol and the solution was taken in 100 mL round bottom flask. The reaction mixture was refluxed at 60-80 C. The completion of the reaction was ensured by TLC. After completion the reaction mixture was poured into crushed ice, crude solid formed was filtered, washed with water, dried in air and recrystallized using ethanol.

Instrumentation
The FT-IR spectrum was recorded in the spectral range of 4000-400 cm À1 using KBr pellet with FT-IR Shimadzu spectrometer at room temperature with a scanning speed of 10 cm À1 per minute at the spectral resolution of 2.0 cm À1 . The FT-Raman spectrum was recorded using the 1064 nm line of a Nd: YAG laser as excitation wavelength in the region 4000-50 cm À1 on Bruker IFS 66v spectrophotometer equipped with a FRA 106 FT-Raman module accessory with spectral resolution of 4 cm À1 . The UV-Vis absorption spectrum was recorded in the range of 200-800 nm using Shimadzu-2600 spectrometer.

Computational procedure
The theoretical calculations of the title molecule were performed using the Gaussian 03 W software program (Frisch, 2004). The input and output files were visualized by GaussView 5 visualization program (Dennington et al., 2009;Lee et al., 1988). The geometry optimization, structural properties, vibrational spectra and NLO properties of the title molecule were determined through the applications of B3LYP Becke's three-parameter hybrid model using the Lee-Yang Parr correlation (Becke, 1993;Frisch et al., 1984) with the 6-311þþG(d,p) basis set (Merrick et al., 2007). The optimized structure parameters of the title molecule were also calculated at DFT/B3LYP using 6-311þþG(d,p) basis set. The potential surface scan (PES) for the conformational analysis of the molecule was done by minimizing the potential energy using the same level of theory for all geometrical parameters by varying the torsion angles in steps of 10 in the range of 0 -360 rotation around the bond. Moreover, detailed assignments of vibrational modes for the title molecule were performed on the basis of TED by using VEDA 4 program (Jamroz, 2004) based on B3LYP/6-311þþG(d,p) level. Some discrepancies could be identified in between harmonic and observed frequencies, which are scaled down by proper scale factor (Radom & Pople, 1970) to neglect the vibrational anharmonicity. 1 H and 13 C NMR chemical shifts were calculated with Gauge Invariant Atomic Orbital (GIAO) method (Zeyrek et al., 2015) which is one of the most common methods for calculating nuclear magnetic shielding tensors. To investigate the reactive sites and to identify sites of intra-and inter-molecular interactions of the molecule, MEP surface was evaluated using same level of theory. The total molecular energies, HOMO, LUMO energies and HOMO-LUMO band gap energy were calculated at the same level. The chemical hardness, softness, electronegativity were calculated using HOMO and LUMO energies (Zeyrek et al., 2015). In addition, dipole moment (l), linear polarizability (a 0 ) and first-order hyperpolarizability (b 0 ) were calculated at B3LYP/6-311þþG(d,p) level for NLO properties. Furthermore, the biological parameters were carried out using an online tool preADMET (Lee et al., 2003).

Vibrational assignments
The title molecule posses 48 atoms and hence 138 normal vibrational modes are possible, which belongs to C 1 point group symmetry. These modes are distributed as 93 A' (inplane vibrations) þ 45 A'' (out-of-plane vibrations). The measured and computed (unscaled and scaled) vibrational frequencies, IR, Raman intensities and vibrational assignments are given in Table 2. The calculated and observed FT-IR and FT-Raman spectra of 4BPM2EP are shown in Figure  2(a,b), respectively. Due to anharmonicity of incomplete treatment of electron correlation, the calculated harmonic vibrational wavenumbers are usually higher than the experimental vibrational wavenumbers (Szafran et al., 2007).
The calculated Raman intensities of the spectra were obtained using the equation (Lorenc, 2012) where 0 and i denote the wavenumber of exciting line and the i th normal mode and C is a normalization factor used for all peaks. The term S R i is the Raman scattering activity of the normal mode calculated by DFT method. B i is the temperature factor which accounts for the intensity contribution of excited vibrational states and is represented by the Boltzmann distribution: where h, k, c and T are fundamental Planck and Boltzmann constants, speed of light and temperature in Kelvin. I R i is given in arbitrary units. The values of correlation coefficients (r 2 ¼ 99921/FT-IR) and (r 2 ¼ 9997/FT-Raman) shows that there is good agreement between the experimental and the calculated wavenumbers are shown in Figure S1.

OH vibrations
The OH vibrations are most sensitive to the environmental factors and their vibrational positions change that depend upon hydrogen bonding interactions. The free hydroxyl stretching mode that do not exist an intra-and inter-molecular hydrogen bonding interactions gives rise a sharp absorption band near 3500 cm À1 (Bellamy, 1975;Colthup et al., 1964;Lambert et al., 1987;Pavia et al., 2014;Silverstein & Webster, 1998;Stuart, 2004). If hydrogen bonding occurs, this band appears in the region 3200-3550 cm À1 (Dabbagh et al., 2008). The OH band is observed at 3468 cm À1 in FT-IR spectrum and corresponding harmonic value is 3669 cm À1 (mode no: 1) with 100% contribution of TED. In our earlier studies, the OH was observed at 3450 cm À1 /FT-IR (Hajam et al., 2020). The OH in-plane bending vibration is observed at 1317 cm À1 in FT-IR, where as the corresponding band is calculated at 1326 cm À1 (mode no: 45). The band calculated at 349 cm À1 (mode no: 115) is assigned to OH out-of-plane bending vibration with 87% contribution of TED.

NH vibrations
The NH stretching vibrations generally occurs in the region 3200-3400 cm À1 (Lorenc, 2012) and the same mode is assigned at 3367 cm À1 in FT-IR spectrum (Bharanidharan et al., 2016). In agreement with these observations, the harmonic value 3420 cm À1 (mode no: 2) is designated as NH mode that is supported by the observed FT-IR/FT-Raman bands: 3280/ 3287 cm À1 , respectively. The harmonic wavenumbers for bH 39 N 33 C 2 /UN 33 C 2 C 31 H 39 are 1483/673 cm À1 (mode nos: 31/98) have considerable TED values (32/74%), respectively and also find support from FT-IR band: 1489 cm À1 .

CH 2 vibrations
There are basically six fundamental vibrations possible namely CH 2 asy stretch, CH 2 sym stretch, CH 2 scissoring and CH 2 rocking which falls under in-plane vibrations and two out-of-plane vibrations, viz., CH 2 wagging and CH 2 twisting modes, which are anticipate to depolarized. In the present study, there are two CH 2 groups from which 12 The sCH 2 /mode no: 44 appear at higher frequency, which may be due to the electron donating tendency of N 33 atom.

CH 3 vibrations
The present molecule has a CH 3 assembly in the side substitution of the chain. It confines one methyl group, having nine fundamental vibrations, namely the symmetrical (sym) stretch, asymmetrical (asy) stretch, in-plane stretching, outof-plane stretching, symmetrical (sym) deformations, asymmetrical (asy) deformations, in-plane rocking, out-of-plane rocking and twisting bending modes. For the methyl group, it is generally referred as electron donating group in the aromatic ring system. The methyl hydrogen atoms are exposed simultaneously to hyper assemblage and back donation, which motive the reduction in stretching wavenumbers and IR intensities. The CH methyl assembly stretching vibrations are highly localized and collectively observed in the region 2800-3000 cm À1 (Dollish et al., 1997). In the present study, the harmonic wavenumbers 3014, 3007 and 2935 cm À1 (mode nos: 15, 16 and 19) are assigned to asymmetric and symmetric CH 3 vibrations, respectively. The mode nos: 15 and 16 are in good agreement with the observed FT-IR bands: 3025, 3005 cm À1 . The b asy /b sym HCH modes of CH 3 group were observed in the regions of 1440-1465/ 1370-1398 cm À1 , respectively (Socrates, 2001). Based on the above literature, the harmonic frequencies: 1458, 1438 and 1354 cm À1 with TED values (>32%) are certainly assigned to b asy and b sym HCH modes of CH 3 group. These assignments are agreeable with the above literature and also find support from the observed bands: 1439/1440; 1362/1355 cm À1 (FT-IR/ FT-Raman). According to Dolish et al. (Dollish et al., 1997), the vibrational absorption assigned in the region 900-1070 cm À1 are due to qCH 3 mode, whereas in the present study, the mode nos: 65/62 are designated as in-plane rocking/twisting modes of CH 3 group. The observed Raman band: 249 cm À1 and its corresponding harmonic frequency 247 cm À1 /mode no: 121 belong to out-of-plane qCH 3 mode. These assignments have considerable TED values (>14%).

CO vibrations
Silverstein and Webster (Silverstein & Webster, 1998) suggested that the CO stretching bands in phenol compounds could be observed in the regions 1330-1390 and 1180-1260 cm À1 . According to Hajam et al. (Hajam et al., 2020;2021), the CO is observed at 1238/1239 cm À1 and means energy of hyper conjugative interaction (stabilization energy). b Energy difference between donor (i) and acceptor (j) nbo orbitals. c F(i, j) is the Fock matrix element between i and j nbo orbitals. 1228/1224 cm À1 in FT-IR/FT-Raman spectra. In the present work, C 26 -O 36 is assigned to 1277/1278 cm À1 in FT-IR/FT-Raman spectra and its corresponding harmonic value is 1282 cm À1 (mode no: 49

NMR Spectral analysis
NMR spectroscopy is the key to reveal the structural and functional group determination of the molecules. The 1 H and 13 C NMR chemical shifts of 4BPM2EP are given in Table 3. 1 H and 13 C NMR chemical shifts were computed using Gauge Invariant Atomic Orbital (GIAO) method. The 1 H NMR chemical shifts have been calculated from 1.037 to 8.384 ppm. Similarly, 13 C NMR chemical shifts are calculated in the region 15.995-161.834 ppm. The large chemical shift of 1 H and 13 C are calculated for H 40 and C 32 atoms. This is due to the combined effect of electron-withdrawing nature of electronegative N 34 and its presence near to C 32 and H 40 atoms. These atoms experience the reduced electron density and therefore the nucleus is deshielded, that lead to the higher chemical shifts for H 40 (8.384) and C 32 (161.834 ppm) atoms, respectively. The shielding effect produced due to the presence of methyl group lead to lower the 1 H and 13 C NMR chemical shifts for H 43 and C 38 atoms as 1.037 and 15.995 ppm, respectively.

NBO analysis
NBO analysis (Glendening et al., 1998) was performed using NBO 3.1 program package at DFT/B3LYP/6-311þþG(d,p) method. It offers an evidence for exploring charge transfer or conjugative interaction in the molecular system and is an efficient method for interactions among bonds. It is evident that NBO analysis is an important tool to interpret the hyperconjugative interaction and electron density transfer from the filled lone pair electrons. The hyperconjugative interaction energy was deduced from the second-order perturbation approach.
Where q i is the donor orbital occupancy, e j and e i are diagonal elements and F(i,j) is the off diagonal NBO Fock matrix element. In NBO analysis large E (2) value shows the intensive interaction between electron-donors and electron-acceptors and greater the extent of conjugation of the whole system. The most important possible intensive interactions are given in Table 4. As can be seen from the Table 4, NBO analysis revealed that p(C 25 -C 28 )!p Ã (C 23 -C 24 ), p(C 2 -C 3 )!p Ã (C 4 -C 5 ), p(C 23 -C 24 )!p Ã (C 26 -C 29 ), p(C 26 -C 29 )!p Ã (C 25 -C 28 ) interactions gives a strong stabilization to the title compound as 89.54, 90.79, 91.84, 95.27 kJ/mol, respectively. The hyperconjugation interaction energy from p(C 2 -C 3 )!p Ã (C 32 ¼N 34 ) and from p(C 25 -C 28 )!p Ã (C 32 ¼N 34 ) are 35.82 and 79.20 kJ/mol, respectively. This may be due to the presence of more electronegativities (CH 3 , CH 2 O, OH) at ring R 3 compare to ring R 1 . The interaction between lone pair n(N 34 ) and the anti-bonding orbital r Ã (C 31 -H 47 ) shows the existence of intra-molecular hydrogen bonding with stabilization energies 9.71 kJ/mol. Likewise, n(N 33 )!r Ã (C 2 -C 3 ), n(O 35 )!r Ã (C 26 -C 29 ), n(N 34 )! p Ã (C 32 -H 40 ) and n(O 36 )! p Ã (C 26 -C 29 ) interactions shows stabilization energy values: 101.00, 35.15, 52.80 and 110.96 kJ/mol, respectively. The interactions p(C-C) and their anti-bonding p Ã interactions are responsible for conjugation of respective p-bonds in benzene rings. The movement of p-electron cloud from donor to acceptor i.e. ICT can make the molecule more polarized and must be responsible for the NLO properties of the molecule. The interactions of r(H 22 -C 23 )! r Ã (C 25 -C 28 ), r(C 4 -H 8 )! r Ã (C 2 -C 3 ), r(C 17 -H 20 )! r Ã (C 12 -C 14 ), r(H 11 -C 12 )! r Ã (C 14 -C 17 ) and r(N 33 -H 39 )! r Ã (C 2 -C 3 ) give stabilization energy values as 18.58, 18.66, 19.46, 19.71 and 20.08 kJ/mol, respectively.

Molecular electrostatic potential
The MEP is generally used as a reactivity map to display the most probable regions for electrophilic and nucleophilic attack of charged point-like reagents on organic molecules as well as used in molecular modeling studies. MEP contour map gives a prediction how different geometries could interact. The MEP of 4BPM2EP compound is obtained based on B3LYP with 6-311þþG(d,p) basis set. The different electrostatic potential values are represented by different colors. Potential increases in the order red < orange < yellow < green < blue. The importance of MEP is that it simultaneously displays molecular size, shape as well as positive, negative and neutral electrostatic potential regions in terms of color grading and is very useful in research of molecular structure with its physiochemical property relationship ( Politzer & Murray, 2002;Politzer & Truhlar, 2013;Scrocco & Tomasi, 1973). The color code of the map is in the range between À4.073e À2 (deepest red) and þ4.073e À2 (deepest blue) in the compound. The positive (blue) regions of MEP are related to electrophilic reactivity and negative (red) regions are related to nucleophilic reactivity is shown in Figure 3. As can be seen from the MEP map the regions around azomethine (C ¼ N) and ethoxy groups are negative whereas the region around phenol is positive.

HOMO-LUMO analysis
The FMOs are important to study the electric and optical properties of the organic molecules. The overlapping of molecular orbitals shows the stabilization of bonding orbitals and destabilization of the anti-bonding orbitals. Stabilization of bonding and destabilization of anti-bonding orbitals increases on the increase of overlap (Jean & Volatron, 2005). In the molecular interaction, two important orbitals that interact with each other are HOMO and LUMO orbitals. The interaction between them is much stable and is called as filled empty interaction. The electron density will occupy at the region between two nuclei when two same sign orbitals overlap to form a molecular orbital. The molecular orbitals formed from in-phase interactions are defined as the bonding orbitals which have lower energy than the original atomic orbitals. The out of-phase interaction forms the anti-bonding molecular orbital with higher energy than the original atomic orbital. The orbital interaction depends upon their symmetry. It is stated that the orbital interactions are allowed if the symmetries of the atomic orbitals are compatible with one another. The calculated HOMO, LUMO and energy gap between them are À5.089, À1.333 and 3.375 eV, respectively. The HOMO, LUMO plots along with density of states (DOS) spectrum are shown in Figures 4 and S2, respectively. In the present study, HOMO orbitals are localized over the whole molecule except ethoxy group, where as LUMO orbitals are localized over the whole molecule except ethoxy group and phenyl ring attached with C-N group. The physico-chemical properties and FMO values are given in Tables S1 and S2. The calculated value of electrophilicity index 2.745 describes the biological activity of the title compound.  The electronic absorption spectrum of the 4BPM2EP compound was recorded within 200-800 nm range in DMSO solvent. Generally in Schiff base compounds the bands are observed at 300-400 nm that indicates the excitation of electrons of azomethine C ¼ N group. In the present study, the experimentally observed spectrum showed band at 486.85 nm assigned to n ! p Ã transition within azomethine C ¼ N group. Electronic absorption spectra of 4BPM2EP were calculated by the time-dependent density functional theory (TD-DFT) method with B3LYP/6-311þþG(d,p) basis set. The calculated k max is obtained at 395.89 nm in gas phase, 397.29 nm in ethanol and 398.40 nm in DMSO. It is evident from the k max values shown in Figure 5 that there is a red shift (bathochromic shift) of spectra. These shifts are due to the stabilization of the ground state or excited electronic states, thus resulting in change in energy gap between the energy levels involved in the transition. The shifts are due to increasing solvent polarity. The calculated and the experimental values are given in Table 5.

Nonlinear optical properties
In order to investigate the relationships among the molecular structure, NLO properties and molecular properties, the polarizabilies & first-order hyperpolarizabilities of 4BPM2EP are calculated using DFT/B3LYP method with 6-311þþG(d,p) basis set. The mean polarizability (a 0 ) dipole moment (l) and average value of the first hyperpolarizability (b 0 ) can be calculated using the equations: It is well known that, molecule with high values of dipole moment, molecular polarizability and first-order hyperpolarizability have more active NLO properties. The first-order hyperpolarizability (b 0 ) and the components of hyperpolarizability b x, b y and b z of 4BPM2EP along with related properties (l, a 0 ) are reported in Table 6. The calculated value of dipole moment is found to be 0.9489 Debye. The highest value of dipole moment is observed in the component of l z which is 0.8400 D and lowest value in l x as À0.4422 D. The polarizability (a 0 ) is found to be 0.5980Â10 À30 esu, respectively. The magnitude of the molecular hyperpolarizability (b 0 ) is one of the important key factors in an NLO system. The first-order hyperpolarizability (b 0 ) value which is calculated at B3LYP/6-311þþG(d,p) is 3.797Â10 À30 esu. The calculated first-order hyperpolarizabilty is ten times higher than urea, whose standard value is 0.3728Â10 À30 esu.

Mulliken atomic charges
The charge distribution on the molecule plays an important role on vibrational spectra. The atomic charge on all the exocyclic atoms are in accordance with their electronegativity whereas the charge on all carbon atoms of the ring are in accordance with the net flow of p electrons (delocalization of electron density) (Mukherjee et al., 2011). Mulliken atomic charges are calculated at DFT level with 6-311þþG(d,p) basis set in gas phase. The atomic charges are shown in Figure S3. From the Table S3 all the hydrogen atoms have a net positive charge. Moreover, Mulliken atomic charges reveal that H 46 has higher positive atomic charge (0.275 a.u) than other hydrogen atoms in 4BPM2EP. This is due to the presence of electronegative O 36 atom with H 46 drags more positive charge from it. The lowest positive charge of hydrogen atoms is shown at H 47 (0.015 a.u). The atomic charges at C 14 / C 28 : 0.882/À0.783 a.u are more positive/negative among all carbon atoms which are due to the substitution of C 31 -N 33 at C 14 that leads to the redistribution of electron density and substitution of ethoxy group at C 29 also redistributes the electron density of the ring.

PES scan
The conformational analysis of the compound 4BPM2EP is carried out with B3LYP functional at 6-311þþG(d,p) basis set using scan option. During the scan, the dihedral angle C 26 -C 29 -O 35 -C 37 is varied in steps of 10 for the angle 0-360 to get the stable geometry of the molecule. The conformational energy profile shows two maxima with energy values 0.0249065, 0.0247521 (Hartrees) and three minima with energy values 0.018756, 0.0220037, 0.0230307 (Hartrees) respectively, obtained from the potential energy curve is shown in Figure S4. The most stable conformer (I) is obtained at scan coordinate 0.49 that possess minimum energy (0.018756 Hartrees).

Biological evaluation
The present molecule has been studied in the context of drug-likeness, ADME and toxicity. These biological parameters were obtained using an online tool preADMET (Lee et al., 2003) (preadmet.bmdrc.kr). The compound is appropriate for Lipinski rule of five. The computed BBB, CYP inhibition, buffer solubility, skin permeability and SK log (D,P,S) etc, values are given in Table 7. These results revealed that the molecule 4BPM2EP is biologically active drug.

Antibacterial activity
The antibacterial activity of 4BPM2EP was screened against Gram positive Bacillus subtillis, Staphyloccus aureus and Gram negative Escherchia coli, Pseudomonas aereuginosa bacteria using diffusion method. The synthesized compound was tested against fungal isolates such as Candida albicans, Aspergillus niger. The test microorganisms were obtained from National Chemical Lab Pune and were maintained by periodical sub culturing on nutrient agar and Sabouraud dextrose bath, incubated at 37 and 25 C for 18 hours, respectively. The effect produced by the sample was compared with the effect produced by the positive control (Reference standard amoxicillin 100 ll/disc for bacteria; Nystanin 100 ll/disc for fungi) solvent DMSO. Antibacterial and antifungal activity of 4BPM2EP by bacterial pathogens and fungal strains are shown in Figure 6. It is revealed from the Table 8 that the title compound has better activity against Bacilus subtillis, E.Coli and fungal strain Aspergillus niger at 100 ll.

Docking studies
The molecular docking is carried out to explore the binding sites of the present compound. To understand the interaction of the synthesized compound 4BPM2EP with topoisomerase DNA gyrase enzymes, the crystal structure of topoisomerase was downloaded from Protein Data Bank (PDB ID: 2XCT) and the molecular docking is performed using the Glide program. The atomic coordinates of the protein with pdb code 2XCT was imported into the Maestro module available in the Schrodinger package (Schrodinger, 2013). The protein was further optimized using the protein preparation wizard (Schrodinger, 2013). The protein ligand interaction plays an important role in structural based drug designing. The 2 D and 3 D interactions of ligand with the protein are shown in Figure 7. Docking results show the pipi interactions of ligand with the active sites of deoxyguanosine and thymidine nucleotides. In this approach, H-bonding, Glide energy score, Emodel and G-score are kept as a support for the present work. The prepared ligand has a G-score of À4.809 kcal/mol whereas the standard compound (norfloxacin) has À7.9 kcal/mol. The Glide energy required for the formation of complex between ligand and the receptor indicates excellent binding affinity. Very low energy indicates that the ligand is buried in the cavity of the receptor (Daisy et al., 2012). The Glide binding energy, Emodel values of 4BPM2EP of ligand is found to be À45.294, À64.133 kcal/mol and norfloxacin posses Glide energy, Emodel À54.23, À83.073 kcal/mol.