Synthesis, In silico Molecular Docking Study and Anti-bacterial Evaluation of some Novel 4-Anilino Quinazolines

 

K. Hemalatha¹*, Joseph Selvin², K. Girija¹

¹Department of Pharmaceutical Chemistry, College of Pharmacy, Mother Theresa Post Graduate and Research Institute of Health Sciences, (A Government of Puducherry Institution),

Indira Nagar, Gorimedu, Puducherry-06., India

²Department of Microbiology, School of Life Sciences, Pondicherry University, Kalapet, Puducherry.

 

ABSTRACT:

A series of some novel 4-anilino quinazoline derivatives have been synthesized from anthranilic acid in four steps via benzoxazinones, Quinazolin-4-ones and 4-Chloro quinazolines. The purity of the compounds was monitored by thin layer chromatography and melting point. The Structures of the newly synthesized compounds have been established on the basis of their FT-IR ¹H-NMR,¹³ C-NMR, Mass Spectral data and elemental analysis. The title compounds were subjected to drug likeliness study using Molinspiration software. Molecular docking study of synthesized derivatives was also performed to find out their interaction with the target site of DNA Gyrase enzyme using Autodock software. All the newly synthesized 4-anilino quinazoline derivatives were evaluated for their in vitro anti-bacterial activity by disc diffusion method by measuring the zone of inhibition and the results were compared to standard. Compound SMOQ2 showed good efficacy against tested strains. Further, docking results revealed that Nitrogen atom of quinazoline part of compound SMOQ2 showed the hydrophilic interaction at ASN 46 (A) amino acid residue, whereas the oxazole part of compound SMOQ2 showed the hydrophilic interaction at GLY 117(A) amino acid residue. The binding energy of SMOQ2 (-8.82 Kcal/mol) was significant when compared to standard drug ciprofloxicin (-5.36 Kcal/mol).

 

 

 

INTRODUCTION:

Microbial drug resistance is a serious issue, especially as increasing numbers of strains are becoming resistant to multiple antimicrobial agents, with some bacteria now being resistant to all available antibiotics. Thus there is a critical need to develop new drugs with novel mechanisms of action.

 

The development of new drug entities is hampered by several issues, notably the high cost and length of time required, as well as the logistical and regulatory challenges of performing the necessary clinical evaluations across multiple geographical areas. Therefore, a few new classes of antimicrobials have been developed since the late 1980s^1,2, and much research has focused only on the chemical modification of existing drugs to improve their potency and/or ability to overcome antibiotic resistance mechanisms. Quinazolines are classes of fused heterocycles that are of considerable interest because of the diverse range of their biological activities such as anti-cancer^3,4, anti-tubercular⁵, anti-bacterial⁶, anti-fungal⁷, anti-HIV⁸, anthelmintic⁹, analgesic¹⁰, anti-inflammatory¹¹, anti-hypertensive¹², anti-diabetic¹³ and anti-oxidant¹⁴activities.

 

DNA Gyrase is an enzyme that influences all metabolic processes involving DNA by regulating negative supercoiling of bacterial DNA and is essential for replication¹⁵. The enzyme gets inhibited by two classes of antimicrobials. This shows that its composition is from reversibly associated subunits¹⁶. Inhibition of Gyrase A subunit affects breakage and rejoining of DNA, thereby, affecting metabolic pathways in bacterial pathogen. In the present study, a series of some novel anilino quinazoline derivatives were synthesized and evaluated for in-vitro anti-bacterial activity against Gram negative bacterium and gram-positive bacterium by disc diffusion method. Molecular docking study of the synthesized derivatives was also performed to find out their interaction with the target site of the DNA Gyrase enzyme.

 

Experimental:

All the chemicals and solvents used were LR grade. The reactions were monitored with the help of thin-layer chromatography using pre-coated aluminum sheets with GF₂₅₄ silica gel, 0.2 mm layer thickness (E-Merck) and solvent system of n-Hexane: Ethyl acetate (5:5). The spots were visualized using UV chamber. Melting points of the synthesized compounds were recorded on the veego melting point apparatus. IR spectrum was recorded on a Shimadzu Infra red spectrometer (Model FT-IR-8400s). both ¹H-NMR (DMSO) spectra of the synthesized compounds were performed with Bruker Advance II 400 NMR Spectrometer operating at 400 MHz. chemical shifts were measured relative to internal standard TMS (δ:0). ¹³C-NMR spectra were recorded at 67.8 MHz on the same instrument with internal TMS (δ: 0, DMSO). Chemical shifts were reported in δ scale (ppm).

 

MATERIALS AND METHODS:

Chemistry:

2-amino benzoic acid (1) reaction with benzoyl chloride (2) yielded 2-phenyl-4H-3,1-benzoxazin-4-one (3) by N-acylation via dehydrative cyclization mechanism. Subsequently which was refluxed with formamide to obtain 2-phenyl quinazoline-4(3H)-one (4). 2-phenyl quinazoline-4(3H)-one (4) which was chlorinated using POCl₃/PCl₅ under reflux conditions and obtained respective 4-chloro quinazoline derivatives (5) which was followed by condensation with various amino group substituted compounds yield 4-anilino quinazolines (6). The  sequence of reaction was drawn in scheme 1 and the products were tabulated in table 1.

Scheme 1

 

Synthesis of 2-phenyl-4H-1, 3-benzoxazin-4-one:

2-amino benzoic acid (13.7 gms, 0.1 mole) was dissolved in minimum volume of dry pyridine (30 ml) by shaking. To this solution, benzoyl chloride (28 ml, 0.2 mole) taken in dry pyridine (30 ml) was added slowly with constant stirring. When the addition was completed (the operation of addition required half-an-hour). The resultant solution was subjected to vigorous stirring for one hour mechanically. Subsequently it was left as such for one hour at room temperature and treated with a solution of sodium bicarbonate (10%). White crystalline mass, Yield 95%, mp 165⁰C.

 

 

Synthesis of 2-phenyl quinazoline-4(3H)-one:

2-phenyl-4H-3,1-benzoxazin-4-one (0.01 mole, 2.18 gms) was heated under reflux in Formamide  for 3 Hrs. The solid obtained was filtered, dried and crystallized form ethanol. White crystalline mass, Yield 70%, mp 106⁰C.

 

Synthesis of 4-chloro quinazoline:

A mixture of 2-phenyl quinazoline-4(3H)-one 4 (0.01 mole), Phosphorous pentachloride (0.05 mole) and Phosphorous oxychloride (12 ml) were heated under reflux for 4 hr at 118⁰C. excess of phosphorous oxychloride was removed by distillation under reduced pressure. The crude product obtained was crystallized from ethyl acetate. Half-white crystalline powder, Yield 74%, mp 180⁰C.

General procedure for the synthesis of 4-anilino quinazolines:

A mixture of 4-chloro quinazoline 5 and different amino compounds in equimolar quantities in the presence of dimethyl formamide was heated under reflux for 3-4 hrs. The solution was cooled and poured carefully into crushed ice. A solid separated out which was allowed to settle down. It was filtered off, washed successively with water and dried. The solid obtained was recrystallized afforded the title compounds.

 

Table 1: Synthesized compounds

Sl.No.	Compound code	R	Title compounds
1	PNAQ1
2	SMOQ2
3	SNAQ3
4	SGQ4
5	DMUQ5
6	6AUQ6
7	4AAQ7
8	PTQ8
9	2APQ9
10	PABAQ10

 

Evaluation of Lipinski’s rule of five and Drug Likeliness properties:

Molinspiration Chemoinformatics was used for calculating important drug like properties like logP, Polar surface area, Number of hydrogen bond donors, Number of hydrogen bond acceptors, Number of rotatable bonds, Volume, Number of violations from rule of five. It was also used to predict bioactive scores against important drug targets like GPCR ligand, Kinase inhibitors, Ion channel modulators, nuclear receptors, Protease inhibitors, Enzyme inhibitors. The results were shown in table 2 and 3.

 

Molecular Docking Study:

The three dimensional structure of protein, DNA Gyrase (Fig 1) were retrieved from the RCSB Protein data bank (PDB ID: 1KZN). All the water molecules and ligands were removed from the PDB file prior to docking. The receptor molecule was prepared by adding missing hydrogen and side chain atoms, using the graphic user interface of Autodock Tools 4.2 (ADT). The active site were calculated using Pdbsum and the active site of the protein Biotin Carboxylase was found to be Leu 162 (A), Glu 164 (A). Grid maps were generated by Auto Grid program. Each grid was centered at the crystal structure of the corresponding 3JZI. Lamarckian Genetic Algorithm was employed as the docking algorithm. The grid dimensions were 60Å X 60Å X 60Å with generation:27,000 were used for this study. The structure with the lowest binding free energy and the most cluster members was chosen for the optimum docking conformation. Interactions of synthesized compounds with amino acids at the active site of the protein, DNA Gyrase were shown in table 4.

 

Table 2: Lipinski rule of Five properties for the designed compounds

Sl.No.	Compound Code	Log p	TPSA	M.W. (gms)	nON	nOHNH	nrotb	M.V.
1	PNAQ1	5.73	83.64	342.36	6	1	4	298.28
2	SMOQ2	5.36	110.01	457.51	8	2	6	384.16
3	SNAQ3	4.46	97.98	376.44	6	3	4	317.66
4	SGQ4	3.71	136.36	432.51	8	5	6	369.04
5	DMUQ5	3.41	81.82	359.39	7	1	3	316.76
6	6AUQ6	3.28	103.53	331.33	7	3	3	282.88
7	4AAQ7	5.67	54.88	339.40	4	1	4	310.49
8	PTQ8	6.22	37.81	311.39	3	1	3	291.50
9	2APQ9	4.87	50.70	298.35	4	1	3	270.79
10	PABAQ10	5.68	75.11	341.37	5	2	4	301.94

TPSA – Topological Polar Surface Area                   M.V – Molar Voume

M.W – Molecular Weight                                         n rotb – Number of Rotatable bonds

 nON- No. of Hydrogen Bond acceptors

nOHNH- No. of Hydrogen bond  donors

 

Table 3: Drug likeliness properties of the designed compounds

Sl. No.	Compound Code	GPCR Ligand	Ion Channel Modulator	Kinase Inhibitor	Nuclear Receptor Ligand	Protease Inhibitor	Enzyme Inhibitor
1	PNAQ1	-0.02	-0.12	0.31	-0.22	-0.41	0.11
2	SMOQ2	-0.01	-0.04	0.15	-0.14	-0.33	0.01
3	SNAQ3	0.03	-0.17	0.41	-0.34	-0.12	0.32
4	SGQ4	0.10	-0.13	0.15	-0.41	-0.16	0.25
5	DMUQ5	0.12	-0.37	0.12	-0.36+	-0.60	0.17
6	6AUQ6	0.01	-0.42	0.36	-0.22	-0.66	0.36
7	4AAQ7	0.05	-0.16	0.29	-0.20	-0.36	0.13
8	PTQ8	0.09	-0.15	0.45	-0.16	-0.38	0.16
9	2APQ9	0.27	0.07	0.68	-0.19	-0.34	0.40
10	PABAQ10	0.14	-0.09	0.40	0.20	-0.25	0.26

Table 4: Interactions of synthesized compounds with amino acids at the active site of the protein, DNA Gyrase

Sl.No.	Compound code	No. of hydrogen bond formed	Amino acid involved in Hydrogen bond interactions	Distance between Donor and Acceptor  (Å)	Binding Energy
1	PNAQ1	0	……	……	-7.98
2	SMOQ2	2	Asn 46 (NH) Gly 117 (NH)	2.072 2.103	-8.82
3	SNAQ3	1	Asn 46 (NH)	1.843	-7.87
4	SGQ4	1	Asn 46 (NH)	2.21	-8.45
5	DMUQ5	0		……	-8.10
6	6AUQ6	1	Asn 46 (NH)	2.233	-8.27
7	4AAQ7	1	Asn 46 (NH)	1.868	-8.09
8	PTQ8	1	Asn 46 (NH)	2.127	-8.35
9	2APQ9	0	……	……	-5.8
10	PABAQ10	0	……	……	-7.23
11	Standard (Ciprofloxazin)	1	Thr 163 (NH)	1.775	-5.36

 

 

Fig. 1: Crystal structure of DNA Gyrase (PDB ID: 1KZN)

 

 

Fig. 2: Docking pose of compound SMOQ2 in the active site of the target Protein DNA Gyrase

 

Fig. 3: Docking pose of Ciprofloxazin in the active site of the target Protein DNA Gyrase

 

Evaluation of Anti-microbial Activity:

All the synthesized compounds were screened for their anti-bacterial activity against Staphylococcus aureus, Bacillus substilis (Gram positive bacteria) and Escherichia coli, P.aeruginosa (Gram negative bacteria) by paper disc diffusion technique using Ciprofloxacin as a standard. The sterilized Mueller-Hinton agar (autoclaved at 120◦C for 30 min) medium was inoculated with the suspension of the microorganism and poured into a petridish to give a depth of 3-4 mm. The paper impregnated with the test compounds (50, 100, 250 and 500 microgram per ml in DMSO) was placed on the solidified medium. The plates were pre-incubated for 1 hr at room temperature and incubated at 37°C for 24 hrs using Ciprofloxacin as standard at a concentration of 20 microgram per ml. The antimicrobial activity of the synthesized compounds was recorded in table 5 and its zone of inhibition were shown in figure 4.

 

 

Table 5: Anti-Bacterial Activity of the Synthesized compounds against E. Coli, B. Substilis, P.aeruginosa, S.aureus

11.5	Compound code	Organism tested	Zone of Inhibition (mm)
			Std	50mg	100mg	250mg	500mg
1.	PNAQ1	E.coli	10	13	14	15	22
		B.substilis	26	-	-	-	10
		P.aeruginosa	26	-	-	-	-
		S.aureus	20
2.	SMOQ2	E.coli	18	11	14	20	23
		B.substilis	27	19	20	23	27
		P.aeruginosa	27	19	20	22	25
		S.aureus	20	-	-	-	-
3.	SNAQ3	E.coli	19	-	-	-	-
		B.substilis	29	-	-	9	10
		P.aeruginosa	27	-	-	-	-
		S.aureus	20	-	-	-	-
4.	SGAQ4	E.coli	19	-	-	-	-
		B.substilis	26	-	9	10	15
		P.aeruginosa	27	8	9	10	13
		S.aureus	20	-	-	-	-
5.	DMUQ5	E.coli	10	-	-	-	-
		B.substilis	27	-	-	-	10
		P.aeruginosa	26	-	-	-	10
		S.aureus	19	-	-	-	-
6.	6AUQ6	E.coli	17	-	-	-	-
		B.substilis	19	-	-	-	9
		P.aeruginosa	29	-	-	-	9
		S.aureus	11	-	-	-	-
7.	4AAQ7	E.coli	20	-	-	-	-
		B.substilis	19	-	-	-	-
		P.aeruginosa	25	-	-	-	-
		S.aureus	20	14	15	16	21
8.	PTQ8	E.coli	20	-	-	-	-
		B.substilis	21	-	-	-	-
		P.aeruginosa	17	-	-	-	-
		S.aureus	21	-	-	-	-
9.	2APQ9	E.coli	20	-	-	-	-
		B.substilis	13	-	-	-	-
		P.aeruginosa	30	-	-	-	7
		S.aureus	20	14	15	16	21
10.	PABAQ10	E.coli	29	-	-	-	-
		B.substilis	22	-	-	-	-
		P.aeruginosa	25	-	-	-	-
		S.aureus	20	-	-	-	-

 

 

 

 

 

 

 

Fig 4: Anti-bacterial Activity Compound SMOQ2 against the tested bacterial strain E.coli, B.substilis, p.aeruginosa, S.aureu

 

N-(4-nitrophenyl)-2-phenylquinazolin-4-amine (PNAQ1):

Yield 70 %; mp 136 ⁰C; R_f value 0.6; IR (KBr, cm^-1): ¹H-NMR (CDCl₃): 8.72 – doublet (2H) in benzene C1 and C6 proton / 8.70 – singlet (1H) C8 proton in quinazoline/ 7.95 – doublet (2H) C5 and C7 proton in quinazoline/ 7.58 – doublet (2H), in benzene C5 and C3 proton / 7.56 – singlet (1H) benzene C4 proton /7.58 – singlet (1H) C6 in quinazoline/ 8.06 – doublet (2H) C5 and C3 proton in nitro benzene/ 7.18  - doublet (2H) C2 and C6 proton in nitro benzene/ 3.51 – singlet (1H) secondary amine proton.¹³C-NMR: δ = 170.11, 164.78, 155.76, 127.08, 116.51, 132.25, 134.39, 131.36, 129.05, 126.46, 141.18, 135.68, 123.02, 119.94. MS: m/z:  342 (M⁺)  Anal. Calcd for C₂₀H₁₄N₄O₂ : C(70.17%) H(4.12%) N(16.37%) O(9.35%).

N-(5-methyl-1, 2-oxazol-3-yl)-4-{(2-phenyl quinazolin-4-yl) amino] benzene-1-sulphonamide (SMOQ2)

Yield 85 %; mp 144 ⁰C; R_f value 0.56; IR (KBr, cm^-1):   ¹H-NMR (CDCl₃): 8.70 doublet (2H) aromatic/ 8.05 singlet (1H) aromatic/ 7.75 doublet (2H) aromatic/ 7.58, 7.56, 7.54 triplet (3H) aromatic/ 7.21 doublet (2H) aromatic/ 2.24 – triplet (3H) methyl/ 6.53 – singlet (1H) isoxazole/ 4.72 – doublet (2H) secondary amine. ¹³C-NMR: δ = 170.16, 169.97, 153.36, 95.35, 12.15, 164.77, 141.25, 134.61, 132.39, 131.39, 129.05, 127.10, 122.9, 119.92, 116.53. MS: m/z: 457 (M⁺) . Anal. Calcd. for C₂₄H₁₉N₅O₃S:   C(63.01%) H(4.19%) N(15.31%) O(10.49%) S(7.01%)

 

4-[(2-phenylquinazolin-4 yl) amino] benzene sulfonamide (SNAQ3):

Yield 73 %; mp 170 ⁰C; R_f value 0.62; IR (KBr, cm^-1):   ¹H-NMR (CDCl₃): 8.06 doublet (2H) aromatic/ 8.04 – singlet (1H) aromatic/ 7.94 – doublet (2H) aromatic / 7.66 – triplet (3H) aromatic/ 7.64 – doublet (2H) aromatic/ 7.62 – singlet (1) aromatic/ 7.20 – doublet (2H)/ 2.50 – singlet (1H) secondary amine/ 2.06 – doublet (2H) primary amine. ¹³C-NMR: δ = 116.53, 119.92, 122.9, 127.10, 129.05, 131, 132.39, 132.24, 134.24, 141.25, 164.77, 170.16. MS: m/z:  376.0 (M⁺). Anal. Calcd. for C₂₀H₁₆N₄O₂S : C(63.81%) H(4.28%) N(14.88%) O(8.50%) S(8.52%)

 

N-(diaminomethylidene)-4-[(2-phenylquinazolin-4-yl)amino]benzenesulfonamide (2SGQ4):

 Yield 75 %; mp 158 ⁰C; R_f value 0.59; IR (KBr, cm^-1): 3397.96 (N-H), 3050.83 (CH-arom), 1566.88 (C=N), 1155.2 (S=O str), 814.0 (C-S str), 932.5 (S-N str);   ¹H-NMR (CDCl₃): 8.72  - quartet (4H) two primary amine/ 8.70 – doublet (2H) in benzene C1 and C6 proton / 8.07– singlet (1H) C8 proton in quinazoline/ 7.95 – doublet (2H) C5 and C7 proton in quinazoline/ 7.58 – doublet (2H), in benzene C5 and C3 proton / 7.56 – singlet (1H) benzene C4 proton /7.59 – singlet (1H) C6 in quinazoline/ 4.7 - singlet (1H) secondary amine proton/ 7.61 – doublet (2H) 3^rd and 5^th carbon next to sulfonyl group in sulfanilamide ring/ 7.21 – doublet (2H) 2^nd and 6^th carbon in sulfanilamide ring. ¹³C-NMR: δ = 170.20, 164.76, 157.86, 141.47, 134.17, 132.47, 131.39, 130.84, 129.06, 127.10, 122.9, 117.92, 112.53. MS: m/z: 418 (M⁺). Anal. Calcd. for C₂₁H₁₈N₆O₂S: C(60.27%) H(4.34%) N(20.08%) O(7.65%) S(7.66%)

 

1,3-dimethyl-6-[(2-phenylquinazolin-4-yl)amino]pyrimidine-2,4(1H,3H)-dione (DMUQ5):

Yield 80 %; mp 168 ⁰C; R_f value 0.78; IR (KBr, cm^-1): 3354.57 (N-H), 3276.47 (CH-arom), 1642.1 (C=O), 1571.7 (C=N)’   ¹H-NMR (CDCl₃): 8.71 – doublet (2H) in benzene/ 8.69 – singlet (1H) C8 proton in quinazoline/ 7.93 – doublet (2H) C5 and C7 proton in quinazoline/ 7.57 – doublet (2H), in benzene/ 7.55 – singlet (1H) benzene/7.59 – singlet (1H) C6 in quinazoline/ 4.70–  singlet (1H) CH proton in uracil/ 4.00 – singlet (1H) NH proton in b/w quinazoline and uracil/ 3.17 – triplet (3H)  N methyl proton present in b/w two carbonyl group/ 3.06 – tiplet (3H) N methyl in uracil ring. ¹³C-NMR: δ = 170.14, 141.19, 119.85, 116.68, 132.25, 127.67, 134.55, 131.36, 129.04, 164.72. MS: m/z: 359 (M⁺). Anal. Calcd. for C₂₀H₁₇N₅O₂: C(66.84%) H(4.77%) N(19.49%) O(8.90%)

 

6-[(2-phenylquinazolin-4-yl)amino]pyrimidine-2,4(1H,3H)-dione (6AUQ6)

Yield 79 %; mp 162 ⁰C; R_f value 0.72; IR (KBr, cm^-1):  3395.07 (N-H), 2920.66 (CH-arom), 1642.1 (C=O), 1623.77 (C=N)

 

¹H-NMR (CDCl₃): 10.17 – singlet (1H) NH proton present in between two carbonyl carbon/  8.71 – doublet (2H) in benzene/ 8.16 – singlet (1H) C8 proton in quinazoline/ 7.95 – doublet (2H) C5 and C7 proton in quinazoline/ 7.60 – triplet (3H), in benzene/ 7.20 – singlet (1H) C6 in quinazoline/ 6.22 – singlet (1) NH proton in uracil/ 4.42 –  singlet (1H) CH proton in uracil/ 4.18 – sinlet (1H) NH proton in b/w quinazoline and uracil. ¹³C-NMR: δ = 170.12, 151.06, 132.26, 128.67, 127.82, 116.68, 134.59, 131.36, 129, 127.08, 164.77, 155.25, 74.18. MS: m/z:  331 (M⁺); Anal. Calcd. For C₁₈H₁₃N₅O₂: C(65.25%) H (3.95%) N (21.14%) O(9.66%)

 

1-{4-[(2-phenylquinazolin-4-yl)amino]phenyl}ethanone (4AAQ7):

Yield 75 %; mp 150 ⁰C; R_f value 0.52; IR (KBr, cm^-1): 3322.75 (N-H), 2921.63 (CH-arom), 1573.63 (C=N). Anal. Calcd. for  C₂₂H₁₇N₃O:  C(77.86%) H(5.05%) N(12.38%) O(4.71%).

 

N-(4-methylphenyl)-2-phenylquinazolin-4-amine (PTQ8):

Yield 76 %; mp 156 ⁰C; R_f value 0.28; IR (KBr, cm^-1): 3322.75 (N-H), 2921.63 (CH-arom), 1573.63 (C=N).  ¹H-NMR (CDCl₃): 8.73 – doublet (2H) in benzene/ 8.71 – singlet (1H) C8 proton in quinazoline/ 7.95 – doublet (2H) C5 and C7 proton in quinazoline/ 7.67 – doublet (2H), in benzene/ 7.56 – singlet (1H) benzene/7.59 – singlet (1H) C6 in quinazoline/ 7.21 – doublet (2H) in C2 and C6 proton in toluene/ 7.17 – doublet (2H) in C3 and C5 in toluene/4.0 - singlet (1H) NH proton in b/w quinazoline and toluene/ 2.22 – triplet (3H) methyl proton in toluene

¹³C-NMR: δ = 170.14, 164.74, 141.20, 119.89, 116.61, 132.22, 127.07, 134.59, 134.59, 134.33, 129.25, 131.36, 129.05, 122.96. MS: m/z: 311 (M⁺): Anal. Calcd. for C₂₁H₁₇N₃: C(81.00%) H(5.50%) N(13.49%)

 

2-phenyl-N-(pyridin-2-yl)quinazolin-4-amine (2APQ8):

Yield 81 %; mp 148 ⁰C; R_f value 0.28; IR (KBr, cm^-1):   ¹H-NMR (CDCl₃): 7.5 triplet (3H), 7.6 singlet (1H), 7.6 singlet (1H), 7.9 doublet (2H), 7.9 singlet (1H), 8.7 doublet (2H), 7.1 singlet (1H), 7.1 singlet (1H), 8.7 S (1), 4.0 S (1H) amine.¹³C-NMR: δ = 116.68, 119, 122, 127, 129, 131, 132, 134, 141, 164, 170. MS: m/z:  298 (M⁺): Anal. Calcd. for C₁₉H₁₄N₄: C(76.49%) H(4.73%) N(18.78%)

 

4-[(2-phenylquinazolin-4-yl)amino]benzoic acid (PABAQ10)

Yield 85 %; mp 172 ⁰C; R_f value 0.64; IR (KBr, cm^-1):   ¹H-NMR (CDCl₃): 8.72 – doublet (2H) in benzene C1 and C6 proton / 8.70 – singlet (1H) C8 proton in quinazoline/ 7.95 – doublet (2H) C5 and C7 proton in quinazoline/ 7.58 – doublet (2H), in benzene C5 and C3 proton / 7.56 – singlet (1H) benzene C4 proton /7.58 – singlet (1H) C6 in quinazoline/ 12.2 –  singlet (1H) may be Acid proton not confirm (11.00)/ 7.94 – doblet (2H) C5 and C3 proton in PABA/ 7.89  - doublet (2H) C2 and C6 proton in PABA/ 3.72 – singlet (1H) secondary amine proton. ¹³C-NMR: δ = 170.12, 164.79, 141.18, 127.09, 116.51, 132.51, 134.58, 134.40, 129.05, 119.94, 131.37. MS: m/z: 341 (M⁺);  Anal. Calcd. for C₂₁H₁₅N₃O₂: C(73.89%) H(4.43%) N(12.31%) O(9.37%)

 

RESULTS AND DISCUSSION:

In the present study, ten novel 4-anilino quinazoline derivatives synthesized and characterized using FT-IR, ¹H-NMR, ¹³C-NMR, Mass spectra and Elemental analysis. Lipinski's rule of five was calculated for all the synthesized compounds (Table 2) that satisfy the 'rule of- 5' and it was found that all the compounds satisfied the rule for potent promotors. The synthesized compounds were evaluated for the drug likeness score using Molinspiration software (www.molinspiration.com). The derivatives were act as a ligand for various receptors like G-Protein Coupled Receptor (GPCR), Ion Channel Modulator, Kinase receptor and neuron receptor. The results were within the limits (-3 to +3). (Table3). Molecular docking study of the synthesized derivatives was performed to identify their interaction with the target site of DNa Gyrase enzyme and the results were shown in table 4 and figure 2 and 3. The synthesized compounds were screened for in vitro antibacterial activity at a concentration of 100, 150, 200 and 500 μg/ml in DMSO by paper disc diffusion method E.coli, B.substilis, P.aeruginosa, S.aureus. (Table 5).

 

CONCLUSION:

Among the tested compounds, compound SMOQ2 showed significant anti-bacterial activity compared to standard Ciprofloxacin (20 μg/ml). These in-vitro results showed good correlation with molecular docking studies. Compounds SMOQ2 showed good efficacy against tested strains. Further, docking results revealed that Nitrogen atom of quinazoline part of compound SMOQ2 showed the hydrophilic interaction at ASN 46 (A) amino acid residue, whereas the oxazole part of compound SMOQ2 showed the hydrophilic interaction at GLY 117(A) amino acid residue. The binding energy of SMOQ2 (-8.82 Kcal/mol) was significant when compared to standard drug ciprofloxicin (-5.36 Kcal/mol). Compound SMOQ2 with isooxazole substituent at 4^th position showed the highest potency as well as binding affinity with target site among synthesized compounds.

 

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Received on 27.05.2018          Accepted on 15.07.2018        

© Asian Pharma Press All Right Reserved

Asian J. Pharm. Res. 2018; 8(3):  125-132.

DOI: 10.5958/2231-5691.2018.00022.9