INTRODUCTION:

Bacterial antimicrobial resistance has become a global issue. Antimicrobial resistance in bacteria, particularly in Gram-negative bacteria(GNB), is terrifying. The World Health Organization (WHO) produced a list of 12 bacteria that pose a hazard to human health in 2017, with gram-negative bacteria making up the bulk of those on the list.¹The majority of hospital-acquired and community-acquired infections are caused by Gram-positive (such as Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumonia, Bacillus subtilis, Enterococcus faecalis, and Enterococcus faecium) and Gram-negative (such as Escherichia coli and Pseudomonas aeruginosa) pathogens.

Every year, around 0.7 million fatalities are linked to drug-resistant infections throughout the world², with the figure rising to 10 million by 2050 if present trends continue.

As a result, novel antibacterial with outstanding efficacy against both drug-sensitive and drug-resistant microorganisms are urgently needed.³

Staphylococcus aureus was known to be capable of acquiring penicillin resistance early in the antibiotic era. The introduction of semisynthetic penicillinase-resistant penicillin-like methicillin and first-generation cephalosporins in the early 1960s broadened the therapeutic options.⁴As a result, the discovery of new antibacterial targets and the development of novel antibacterial drugs are critical. One promising target has been proposed: peptide deformylase (PDF), a metalloenzyme that is highly conserved in bacteria.⁵In the scenario, most of the drug’s isatin derivatives have been screened for their antibacterial activities, and some of them have demonstrated promising in vitro and in vivo potency. The isatin moiety is present everywhere in nature, and its derivatives have different pharmacological actions.

Furthermore, several isatin derivative compounds like indirubin and semaxanib have previously been utilized in clinics or in clinical studies to treat a variety of disorders. Despite their differences, the human and bacterial protein synthesis systems have a lot of molecular similarities. Blocking the particular stages involved in protein synthesis stops the translation process in bacteria.⁶

Peptide deformylase (PDF) is a metalloenzyme found in prokaryotes that is necessary for bacterial growth but not in human cells. As a result, it is a particular and probable target for the development of novel antibacterial drugs. Protein synthesis occurs in bacterial and human cells in very similar ways. Both use the same amino acids and codons, as well as the same elongation method. The use of N-formyl methionine as the initiator for the bacterial process represents a distinct distinction between bacterial protein synthesis and mammalian cytosolic protein synthesis.The enzyme belongs to the matrix metalloprotease (mmp) family and has three catalytic domains that are highly conserved. The only naturally occurring PDIs are actinonin and macrolactin N.^7-9

Isatin schiff based derivatives have wide pharmacological activity^10-19.We here report the design and antimicrobial potential of some new isatin schiff based derivatives 1-18 having different substituents on aromatic rings. All of those compounds were developed using computational approaches to determine their important drug-like features and docked in the native location of the PDF protein. Various aromatic amines were used to manufacture substituted isatin Schiff base derivatives from isatin derivatives. The addition of substituents to the 5^th position of ring B and various positions of ring C of the developed compounds revealed that these groups (hydrophobic/hydrophilic) had an impact on drug-like characteristics and antibacterial effectiveness.

MATERIAL AND METHODS:

1 Designing of isatin schiff base derivatives:

At the beginning of eighteen isatin Schiff base derivatives were designed by using chem draw 8.0 and molecular virtual docker (MVD). On the basis of molecular docking studies twelve potent compounds were selected for the advanced studies.

The SAR analysis revealed that the compounds possessing a nitro group at the R₃position of isatin moiety play an important role in increasing the activity against both Staphylococcus aureus and E. coli. As per the reported literature substitutions at R₂and R₃ positions with the electron-withdrawing group increased the potency. Similarly, substitution at ring B hydrophobic substitutions on favorable for biological activity.⁶

Based on the above considerations, eighteen Schiff base derivatives of isatin were designed by the substitution of different groups on R, R_1, R,_2,and R₃ positions respectively.

2 Chemistry:

All chemicals and reagents were of synthetic grade. All reactions were carried out in oven-dried equipment using distilled and dried solvents. Thin layer chromatography (TLC) was used to track the reaction's progress and visualized by ultraviolet light at 254 nm. Melting points of synthesized compounds were recorded on digital Veego Model VMP-D melting point apparatus.

3 Synthesis:

In an ice bath, 12 mL of H₂SO₄ was added dropwise over a 5-minute period with stirring to a combination of isatin (2.94 g, 20 mmol) and 9 mmol of (Trichloroisocynauric acid)(2.09 g, 9 mmol) for the synthesis of 5-choloroisatin Schiff base. For 15 minutes, the mixture was held in an ice bath with constant stirring. After that, the mixture was poured over split ice. After collecting the crystals and washing them with cold water, 3.51 g (97 percent) of 5-chloroisatin as an orange solid was obtained.

1–3 substituted(5-Chloroisatin and 5-Fluroisatin) isatin was treated with commercially available various aromatic amines (1:1) in ethanol (30mL) including a few drops of glacial acetic acid to synthesise Schiff base.The resultant reaction mixture was heated for 3–4 hours at 40°-50°C. TLC was used to monitor the reaction's development. After the reaction was completed, the reaction mixture was cooled to room temperature, concentrated, poured into ice-cold water, and basified with 2 M NaOH (pH 10) to create a precipitate. To get the crude product, the precipitate was filtered, washed with water, and dried on CaCl2 in a vacuum chamber. The product was then purified using column chromatography before being crystallised in ethanol.

2.3.1(Z)-3-(2,4-dichlorophenylimino)-5-chloroindoline-2-one

Darkmaroon solid, yield (25.94%), M.p 110⸰-114⸰C; IR (KBr) cm^-1 IR 3174.1(benzene),650.9 (C-Cl),2150.3 (C=N),1785.7(C=O),1597(NH)¹HNMRδ_ppm,7.1;7.3(t,1H,Benzylidenimin),7.27(s,1H,1benzene),7.3(t,1H,Benzylidenimin),7.61(d,1H,Benzylidenimin), 8.0(s,1H,N-H); MS m/z C₁₄H₇Cl₃N₂O (M⁺) 323.96

2.3.2 (Z)-3-(2-nitrophenylimino)-5-chloroindoline-2-one

Dark maroon solid, yield (49%), M.p 120⸰-124⸰C; IR (KBr) cm^-13015.1(benzene),640.9 (C-Cl),1659.3 (C=N),1718.7 (C=O),1567.9 (N-H)¹H NMR δ_ppm 7.1;7.2 (q,1H, 1benzene), 7.28 (t,1H,Benzylidenimin), 7.3 (s,1H,Benzylidenimin),7.61(t,1H,Benzylidenimin), 8.0 (t,1H,N-H) ;MS m/z C₁₄H₈ClN₃O₃ (M⁺) 290

2.3.3(Z)-3-(2-nitrophenylimino)-5-chloroindoline-2-one

Dark maroon solid, yield (66,44%), M.p 122⸰-126⸰C; IR (KBr) cm-¹619.9 (C-Cl) 2173.3 (C=N ) 1711.7 (C=O) 1504.5 (C-NO₂) 1567.9 (N-H);¹H NMR δ_ppm7.2(t,1H,Benzylidenimin), 7.5 (q,1H,1benzene), 7.61;7.61(d,1H,1benzene),7.7(s,1H,1benzene),8.2(t,1H,1benzene),8.0(t,1H,N-H); MS m/z C₁₄H₈ClN₃O₃ (M⁺) 301.03;

2.3.4 (Z)-3-(3,4-dichlorophenylimino)-5-chloroindoline-2-one

Red solid , yield (73.61%),M.p 130⸰-133⸰C ; IR (KBr) cm^-1751.0(C-Cl),2199.8 (C=N) ,1716.7 (C=O),1570.5 (N-H);¹H NMR δ_ppm7.28;7.28;7.57;7.54 (s,1H, Benzylidenimin), 7.38 (t,1H, Benzylidenimin), 7.16 (t,1H,1benzene), 8.13 (d,1H,N-H); MS m/z C₁₄H₇Cl₃N₂O (M⁺) 323.96;

2.3.5 (Z)-3-(3-nitrophenylimino)-5-chloroindoline-2-one

Dark Maroon solid, yield (28.90%), M.p 122⸰-125⸰C;IR (KBr) cm^-1 548.3(C-Cl),2173.0 (C=N),1714.7 (C=O),(1616.0 N-H), 1519.3 (C-NO₂); ¹H NMR δ_ppm 7.28;7.57;7.54 (s,1H,Benzylidenimin),8.09(d,1H,N-H),8.22;8.22(d,1H,Benzylidenimin); MS m/z C₁₄H₈ClN₃O₃ (M⁺) 301.03;

2.3.6 (Z)-3-(3-nitrophenylimino)-5-chloroindoline-2-one

Dark maroon solid, yield (64.07%), M.p 152⸰-155⸰C ; IR (KBr) cm^-1750.3(C-Cl),2187.9 (C=N),1715.9 (C=O), 1611.4 (N-H),1095.2 (C-F);¹H NMR δ_ppm 7.28;7.2;7.33 (s,1H, Benzylidenimin), 7.62 (d,1H, Benzylidenimin),7.48;7.4 (s,1H, Benzylidenimin), 8.07 (s,1H,N-H); MS m/z C₁₄H₈BrClN₂O(M⁺) 335.95;

2.3.7(Z)-3-(4-chlorophenylimino)-5-chloroindoline-2-one

Red solid, yield (77.21%), M.p 162⸰-165⸰C; IR (KBr) cm^-13015.1(benzene),640.9 (C-Cl), 1659.3 (C=N),1718.7 (C=O),1567.9 (N-H);¹H NMR δ_ppm 7.1;7.2 (m,1H, Benzylidenimin), 7.28;7.28(s,1H, Benzylidenimin),7.3;7.3(d,1H, Benzylidenimin), 7.48 (s,1H,benzene), 8.01(s,1H,N-H); MS m/z C₁₄H₈Cl₂N₂O(M⁺) 290;

2.3.8 (Z)-3-(4-Fluorophenylimino)-5-chloroindoline-2-one

Dark maroon solid, yield(54.21%), M.p 102⸰-106⸰C, IR (KBr) cm^-13088.54(benzene),1689.9 (C=N), 1715.9 (C=O),1690.4,(N-H),1045.2(C-F),732.06(C-Cl);¹HNMRδ_ppm7.0(q,1H,Benzylidenimin),7.28(d,1H,Benzylidenimin), 7.2(s,1H,1benzene), 7.61;7.61(t,1H,Benzylidenimin), 8.01 (t,1H,N-H); MS m/z C₁₄H₈Cl₂N₂O(M⁺) 290;

2.3.9 (Z)-3-(4-nitrophenylimino)-5-chloroindoline-2-one

Dark maroon solid, yield (65.35%), M.p 122⸰-126⸰C; IR (KBr) cm^-13038.54(benzene),780.24(C-Cl),2187.9 (C=N),1715.9(C=O),1611.4,(NH),1095.2(NO₂)¹HNMRδ_ppm7.28;7.28(s,1H,Benzylidenimin),7.61;7.61(s,1H,Benzylidenimin),7.5(d,1H,1benzene), 8.28(t,1H,1benzene); MS m/z C₁₄H₈ClFN₂O(M⁺) 274.03

2.3.10 (Z)-3-(2,4-dichlorophenylimino)-5-fluoroindoline-2-one

Orange solid, yield (90.96%), M.p 124⸰-127⸰C ; IR (KBr) cm^-13342.78(benzene),650.03(C-Cl),1678.9 (C=N),1734.08(C=O),1549.16(NH),1125.33(CF)¹HNMRδ_ppm6.98(q,1H,Benzylidenimin),7.3(d,1H,Benzylidenimin),7.1(s,1H,Benzylidenimin),7.2(d,1H,1benzene), 7.3 (d,1H,1benzene)7.65(d,1H,Benzylidenimin),8.0 (t,1H,N-H); MS m/z C₁₄H₇Cl₂FN₂O(M⁺) 307.99;

2.3.11 (Z)-3-(2-chlorophenylimino)-5-fluoroindoline-2-one

Dark brown solid, yield (89.33), M.p 147⸰-149⸰C IR (KBr) cm^-1 3342.78(benzene),659.06(C-Cl),16907.9 (C=N), 1734.08(C=O),1465.16(NH),15340.33(CF);¹HNMRδ_ppm6.98(q,1H,Benzylidenimin),7.31(d,1H,Benzylidenimin),7.65(q,1H,Benzylidenimin, 7.2;7.2 (d,1H,1benzene), 7.1(t,1H,1benzene), 7.3 (d,1H,1benzene),8.0(t,1H,N-H); MS m/z C₁₄H₈Cl₁FN₂O(M⁺) 274.03;

2.3.12(Z)-3-(2-nitrophenylimino)-5-fluoroindoline-2-one

Orange solid, yield (90.54%), M.p 125⸰-127⸰C; IR (KBr) cm^-1 3342.78(benzene),2187.9 (C=N),1734.08 (C=O), 1569.16 (N-H),1130.33 (C-F);¹HNMRδ_ppm6.84(d,1H,Benzylidenimin),7.37(t,1H,Benzylidenimin),8.14 (d,1H,N-H); MS m/z C₁₄H₈FN₂O₃(M⁺) 285.05

2.3.13(Z)-3-(3,4-dichlorophenylimino)-5-fluoroindoline-2-one

Orange solid, yield (26.71%), M.p 135⸰-138⸰C; IR (KBr) cm^-1 750.3(C-Cl),2187.9 (C=N), 1711.9 (C=O),1627.4 (N-H),1179.2 (C-F),3075.63(Benzene);¹H NMR δ_ppm 6.93(d,1H,Benzylidenimin), 7.31(t,1H,Benzylidenimin), 7.51 (d,1H, Benzylidenimin), 7.19 (d,1H,1benzene),7.28 (s,1H,1benzene), 7.98 (s,1H,N-H); MS m/z C₁₄H₇Cl₂FN₂O(M⁺) 307.99

2.3.14(Z)-3-(3-nitrophenylimino)-5-fluoroindoline-2-one

Orange solid, yield (66.43%), M.p 165⸰-168⸰C; IR (KBr) cm^-11520.94(NO₂),2187.9 (C=N),1716.9 (C=O),1616.42 (N-H),1235.46 (C-F);¹H NMR δ_ppm 6.97 (d,1H,Benzylidenimin), 7.31 (q, 1H,Benzylidenimin), 7.66 (t,1H, Benzylidenimin), 7.50;7;57 (d,1H,1benzene), 7.7(t,1H,1benzene), 8.07(d,1H,N-H), 8.19 (d,1H,1benzene); MS m/z C₁₄H₈ClFN₃O₃(M⁺) 307.99

2.3.15(Z)-3(4-bromophenylimino)-5-fluoriindoline-2-one

Green solid, yield (45.56%), M.p 192⸰-195⸰C; IR (KBr) cm^-1750.3(C-Cl),2187.9 (C=N),1715.9 (C=O), 1611.4 (N-H), 1095.2 (C-F),639.43(C-Br);¹H NMR δ_ppm 6.98 (d,1H,Benzylidenimin), 7.31 (q, 1H,Benzylidenimin), 7.66 (t,1H,Benzylidenimin), 7.50;7;57 (d,1H,1benzene), 7.7(t,1H,1benzene), 8.07(t,1H,N-H), 8.19 (d,1H,1benzene);MS m/z C₁₄H₈BrFN₂O(M⁺) 317.98

2.3.16 (Z)-3-(4-chlorophenylimino)-5-fluoroindoline-2-one

Orange solid, yield (69.59%), M.p 120⸰-124⸰C; IR (KBr) cm^-13248.27(benzene),2126.9 (C=N),1719.61 (C=O),1571.09 (N-H),1208.46 (C-F);¹H NMR δ_ppm 6.98 (q,1H,Benzylidenimin), 7.34 (d,1H,Benzylidenimin), 7.28 (s,1H,1benzene), 7.36 (d,1H,1benzene), 8.08 (s,1H,N-H); MS m/z C₁₄H₈ClFN₂O(M⁺) 274.03

2.3.17(Z)-3-(4-fluorophenylimino)-5-fluoroindoline-2-one

Orange solid, yield (62.10%), M.p 157⸰-160⸰C; IR (KBr) cm^-13200.78(benzene),1678.9 (C=N),1714.08 (C=O),1589.16 (N-H),1152.33 (C-F);¹H NMR δ_ppm 6.98 (d,1H,Benzylidenimin), 7.31 (q, 1H,Benzylidenimin), 7.66 (t,1H,Benzylidenimin), 7.50;7;57 (d,1H,1benzene), 7.7(t,1H,1benzene), 8.07(t,1H,N-H), 8.19 (d,1H,1benzene); MS m/z C₁₄H₈F₂N₂O(M⁺) 258.06

2.3.18(Z)-3-(4-nitrophenylimino)5-fluoroindoline-2-one

Orange solid, yield (74.90%), M.p 73⸰-75⸰C; IR (KBr) cm^-1 3066.95(Benzene),2345.09 (C=N),1734.08 (C=O),1597.13 (N-H),1094.23 (C-F),1421.93(NO₂); ¹H NMR δ_ppm 6.93 (q,1H,Benzylidenimin), 7.31 (d,1H,Benzylidenimin), 7.43 (d,1H, Benzylidenimin), 8.09 (d,1H,N-H), 8.29;8.29 (d,1H,1benzene); MS m/z C₁₄H₈FN₂O₃(M⁺) 285.03

4. MOLECULAR DOCKING:

Molecular docking is a type of bioinformatic modelling in which two or more molecules combine to generate a stable adduct. It predicts the three-dimensional structure of any complex based on the binding characteristics of the ligand and target. A molecular docking study was done using molecular virtual docker software (MVD 6.0). PDF enzymes of E. coli (PDB code :1BSJ) and S. aureus (PDB code-1LMH) respectively was chosen as a target and its x–ray crystal structure was downloaded from protein data bank.^20,21The rsults of molecular docking analyses are displayed in table 1 and 2.

Table 1: Mol Dock and rerank score of designed compounds in the active site of PDF ofE. coli.

S. No	Compounds	MolDock Score	Rerank Score
1.	Compound 1	-100.743	-79.3279
2.	Compound 2	-104.115	-83.5387
3.	Compound 3	-111.791	-89.3411
4.	Compound 4	-128.781	-99.5429
5.	Compound 5	-129.445	-105.012
6.	Compound 6	-121.508	-94.9224
7.	Compound 7	-122.659	-96.0572
8.	Compound 8	-103.32	-81.9816
9.	Compound 9	-114.352	-93.3773
10.	Compound 10	-99.1097	-76.3498
11.	Compound 11	-108.19	-86.7292
12.	Compound 12	-116.543	-89.995
13.	Compound 13	-110.524	-85.5122
14.	Compound 14	-141.89	-114.89
15.	Compound 15	-113.531	-90.3199
16.	Compound 16	-123.755	-96.6208
17.	Compound 17	-116.839	-92.8048
18.	Compound 18	-114.713	-93.365
Ref. Compound	Actinonin	-112.438	-97.955
Ref. Compound	Quercetin	-107.591	-94.478

Table 2: Mol Dock and rerank score of designed compounds in the active site of PDF ofS. Aureus

S. No	Compounds	MolDock Score	Rerank Score
1.	Compound 1	-100.928	-78.1143
2.	Compound 2	-100.723	-80.2922
3.	Compound 3	-106.288	-87.6825
4.	Compound 4	-97.9189	-75.0737
5.	Compound 5	-133.241	-111.115
6.	Compound 6	-109.287	-61.2601
7.	Compound 7	-110.129	-76.3816
8.	Compound 8	-111.957	-82.9494
9.	Compound 9	-121.648	-94.2105
10.	Compound 10	-106.007	-78.9876
11.	Compound 11	-111.372	-73.1836
12.	Compound 12	-125.644	-97.1299
13.	Compound 13	-116.677	-73.4114
14.	Compound 14	-132.966	-110.772
15.	Compound 15	-109.864	-70.0943
16.	Compound 16	-111.073	-62.449
17.	Compound 17	-112.182	-70.8311
18.	Compound 18	-121.643	-94.1535
Ref. Compound	Actinonin	-107.64	-76.9405
Ref. Compound	Quercetin	-105.581	-85.482

The docking method was validated by doing control docking of reference compounds. Reference compounds actinonin and quercetin were docked into the active sites of PDF of E.coli and S. aureus respectively. The reference compound actinonin and quercetin in the conformation found in the crystal structures of PDF of E.coli and S. aureus respectively was extracted and docked back into the corresponding binding pocket to determine the ability of MVD 6.0 to reproduce the orientation and positions of the reference compounds in the crystal structure. The RMSD value between actual and docked pose was found to be 0.3Ǻ.

Antibacterial Assay:

The compounds (4, 5, 7, 9, 12, 14, 16, 18 and 13) with good binding interaction in the active sites of PDF of E. coli and S. aureus were selected for in vitro evaluation. The minimum inhibitory concentration (MIC) was determined by broth dilution method.

1 Determination of MIC by the broth dilution method:

To estimate MIC using the broth dilution technique, different concentrations (100, 50, 25, 12.5 and 6.25µg/mL) of all drugs were produced in sterile dry test tubes using dimethylsulphoxide (DMSO) as solvent. Nutrient broth media was used and 4.9mL of it was placed in each test tube and sterilized after plugging. After chilling, 0.1mL of each dilution of compounds was added to the test tube, bringing the total amount to 5.0mL. The test tubes were shaken to ensure that the inoculum was evenly mixed with the soup. The tubes were incubated at 37^⸰C for 48 hours. The presence of any turbidity indicated that the chemical was unable to prevent bacterial growth.²²

RESULTS AND DISCUSSION:

The isatin Schiff base derivatives were designed as antimicrobial agents using computation approach. There were eighteen compounds was designed based on a literature review and docked against peptide deformylase of E. coli (PDB code-1BSJ). In E. coli peptide deformylase the compound-14 (having fluoro group at R position and nitro group at R₂position) showed a higher mol dock score than actinonin. Most active compound-14 showed interaction with catalytic site residues Gln-50, Leu-91, and Cys-90 in the enzyme peptide deformylase.However, compound-1 having chloro group at R, R₁and R₃respectively showed lowest docking score among all synthesized compounds.The oxygen atom of the nitro group showed bifurcated hydrogen bonds with Leu91 and the side chain of Gln50 respectively.¹²The oxygen atom of the nitro group of compound-14 mimics the carbonyl oxygen of the formyl group of natural substrate N-formyl-L-methionyl peptide of peptide deformylase (enzyme-substrate complex). Hence compound-14 can prevent the binding of natural substrate to the catalytic site of the enzyme.

In S. aureus peptide deformylase (PDB code-1LMH) compound-5 showed a higher moldock score than actinonin. Most active compound-5 showed interaction with catalytic site residues Leu112(A), Gln65(A), and Cys111(A). However, compound-1 is having a chloro group at R, R_1,and R₃respectively showed the lowest docking score among all synthesized compounds.

1. Antibacterial activity of compounds:

The broth dilution technique was used to assess the antibacterial activity of all compounds. The compounds (4, 5, 7, 9, 12, 14, 16, 18 and 13) with good binding interaction in the active sites of PDF of E. coli and S. aureus were selected for in vitro evaluation. MIC was measured using actinonin and quercetin as reference drugs, some of the compounds having better antibacterial activity in comparison to the reference drugs. Compounds having higher moldock scores showed excellent activity against bacterial strain S. aureus and moderate activity against E. coli. In the case of E. coli, compounds 4, 5, 14, and 16(MIC- 50µ/ml) showed higher inhibitory activity as compared to reference compounds quercetin and actinonin respectively. However, compounds 5, 12, 14, 16, and 18(MIC-25µg/ml) showed higher activity against S. aureus as compared to reference compounds actinonin and quercetin respectively (Table-3). Compound 14 has 5- Fluoro group on ring B and a Nitro group at R₃ on ring C possessing higher antibacterial activity compared with compound 5 having a 5-chloro group on ring B and a Nitro group at R₂ on ring C. In general, it was investigated that compounds possessing a small hydrophobic group on ring B while an electron-withdrawing group on ring C were found to be more potent among all synthesized compounds.

The results of in vitro antibacterial activity comply with that of the output of the molecular docking study. Analysis of antibacterial activity results revealed that compounds 5, 12, 14, 16 and 18 showed higher antibacterial activity (MIC 25µg/ml or 50µg/ml) among all synthesized compounds. The SAR investigation revealed that the compounds possessing nitro and chloro group at the R₃position of isatin moiety play an important role in the inhibitory activity against both S. aureus and E. coli. The significant antibacterial activity of compounds was presumably due to the presence of small hydrophobic groups on ring B and electron-withdrawing group on ring C.

Table-3: In vitro antibacterial activity of higher moldock score compounds against gram positive and gram negative bacterial strains

Compounds	(Wild strain) Gram+ve Gram –ve S. aureus E.coli	Drug Resistant Strain E. coli
Compound 4	50µg 25µg	100 µg
Compound 5	25µg 50µg	50 µg
Compound 7	50µg 25µg	25 µg
Compound 9	50µg 50µg	50 µg
Compound 12	25µg 25µg	50 µg
Compound 13	50µg 50µg	100 µg
Compound 14	50µg 25µg	25 µg
Compound 15	25µg 50µg	50 µg
Compound 16	12.5µg 50 µg	100 µg
Compound 18	50µg 25 µg	50 µg
Quercetin	100µg 50µg	25 µg
Actinonin	50µg 50 µg	100µg

CONCLUSION:

In this research work we have successfully employed the drug designing technique such as molecular docking for the designing of Schiff base derivatives of isatin. The results of docking study comply with the results of in vitro evaluation of the antibacterial study. Compounds 4, 5, 12, 14, 16 and 18 showed promising antibacterial activity. Among all synthesized compounds compound 14 possessing small hydrophobic fluoro group on R position of ring B while electron withdrawing nitro group on R₃ position of ring C found to be most active.The results of this study may be helpful in further drug discovery paradigm.

REFERENCES:

1. Sharma R. Sharma C L. Kapoor B. Antibacterial resistance: current problems and possible solutions. Indian Journal of Medical Science. 2005; 59(3): 120-9.

2. Sharma R. Panigrahi D. Mishra G.P. QSAR studies of 7-methyljuglone derivatives as antitubercular agents. Medicinal Chemistry Research. 2012; 21: 2006–2011.

3. Kim WJ. Park SC. Bacterial resistance to antimicrobial agents: an overview from Korea. Yonsei Medical Journal. 1998; 39(6): 488-94.

4. Ragusa S, Blanquet S, Meinnel T. Control of peptide deformylase activity by metal cations. Journal of Molecular Biology. 1998, 280(3): 515-523.

5. Baldwin ET. Harris MS. Yem AW. Wolfe CL. Vosters AF. Curry KA. Murray RW. Bock JH. Marshall VP. Cialdella JI. Merchant MH. Choi G. Deibel MR. Jr. Crystal structure of type II peptide deformylase from Staphylococcus aureus. Journal of Biology and Chemistry. 2002; 23(34): 31163-31171.

6. Bing Gong H. Rajagopalan W. Ravi PT. Ying Z. Dehua P. Chan MK. Structural Basis for the Design of Antibiotics Targeting Peptide Deformylase. Biochemistry.1999; 38(15): 4712–4719.

7. Clements JM. Beckett RP. Brown A. Catlin G. Antibiotic Activity and Characterization of BB-3497, a Novel Peptide Deformylase Inhibitor. Antimicrob Agents Chemother. 2001; 45(2): 563–570.

8. Mishra R. Chaurasia H. Singh VK. Naaz F. Singh RK. Molecular modeling, QSAR analysis and antimicrobial properties of Schiff base derivatives of isatin. Journal of Molecular Structure. 2021(1243), 130763.

9. Beula SJ. Reddy RM. Suthakaran R. Suneetha K.A Review an Isatin, Isatin Derivatives and their Pharmacological Activity. Research Journal of Pharmacology and Pharmacodynamics. 2021; 13(2): 59-2.

10. Valli.G. Mareeswari P. Ramu K. Thanga T A. Analgesic, antipyretic, CNS and pass prediction Activities of 4-(4-hydroxy benzylidene amino) phenol Schiff base. Research Journal of Science and Technology. 2012; 4(5): 192-196.

11. Eberendu KO. Otuokere IE. Complexation Behavior of 1-Phenyl-2,3-dimethyl-4-(benzylamino) pyrazol-5-one Schiff Base Ligand with Manganese ion. Research Journal of Science and Technology. 2016; 8(4):199-203.

12. Eberendu KO. Onwu FK. Synergistic Effect of Halide Ions on the Corrosion Inhibition of Zinc in Hydrochloric Acid using Schiff base compound, 1-phenyl-2,3-dimethyl-4-(benzylamino) pyrazole-5-one. Research Jornal of Science and Technology. 2017; 9(2): 244-248.

13. Patil CJ. Patil CM. Patil MC. Studies on Synthesis of Aromatic Schiff Bases. Part-V. Evaluation of Antifungal Potential of Ketimines from 5-Chloro-2-hydroxy-4-methyl-acetophenone. Research Journal Science and Technology. 2018; 10(2):125-130.

14. Patel UY. Patel RN. Sen DJ. Badmanaban R. Structure Activity Relationship Studies of Synthesised Schiff Bases and Mannich Bases of Substituted 5-Methyl-1, 2-Dihydro-3H-Pyrazol-3-One Derivatives Having Variable Electronegative Atoms for Antioxidant Screening. Research Journal of Science and Technology. 2011; 3(2): 99-110.

15. Valli.G. Mareeswari P. Ramu K. Thanga Thirupathi A. Analgesic, antipyretic, CNS and pass prediction Activities of 4-(4-hydroxy benzylidene amino) phenol Schiff base. Research Journal of Science and Tech. 2012; 4(5): 192-196.

16. Kumar R. Sharma S. Synthesis, Spectroscopic, Thermal studies and Biological activity of a new Schiff base and its Copper Complexes. Research Journal of Science and Technology. 2020; 12(4): 251-256.

17. Eberendu KO. Spectrophotometric study of Stability Constants of 2-z-2–Benzylidene hydrazine carbothioamide -Mn Schiff Base Complex at Different Temperatures. Research Journal of Science and Technology. 2017; 9(2): 249-252.

18. Silva BV. Esteves PM. Pinto AC. Chlorination of isatins with trichloro isocyanuric acid. Journal of the Brazilian Chemical Society. 2011; 22(2), 257–263.

19. Mishra, GP. Sharma R. Jain, M. Syntheses, biological evaluation of some novel substituted benzoic acid derivatives bearing hydrazone as linker. Research on Chemical Intermediates. 2021; 47: 5061–5078.

20. Dar AM. Mir S. Molecular Docking: Approaches, Types, Applications and Basic Challenges. Journal of Analytical and Bioanalytical Technology. 2017; 8: 356-363.

21. Mishra GP. Sharma R. Identification of Potential PPAR γ Agonists as Hypoglycemic Agents: Molecular Docking Approach. Interdisciplinary Science Computational Life Sciences. 2016; 8: 220–228.

22. Kumari G. Singh RK. Synthesis and in vitro antibacterial activity of Schiff base of N- substituted isatins as effective scaffolds, Medicinal Chemistry Research. 2013; 22 (2): 927-933.

Received on 01.09.2022 Modified on 03.05.2023

Research J. Pharm. and Tech 2023; 16(11):5323-5328.

DOI: 10.52711/0974-360X.2023.00862