SYNTHESIS AND ANTIMICROBIAL EVALUATION OF 2-(2-(BENZO [D] OXAZOL-2-YL) PHENYLAMINO)-N-(SUBSTITUTED PHENYL) ACETAMIDES

Received on 05 February, 2014; received in revised form, 10 April, 2014; accepted, 30 May, 2014; published 01 August, 2014

SYNTHESIS AND ANTIMICROBIAL EVALUATION OF 2-(2-(BENZO [D] OXAZOL-2-YL) PHENYLAMINO)-N-(SUBSTITUTED PHENYL) ACETAMIDES

Priyanka*, N.K. Sharma, K. K. Jha and M. Vijaya Kumar

Teerthanker Mahaveer College of Pharmacy, Teerthanker Mahaveer University, Bagarpur, Moradabad, Uttar Pradesh, India

ABSTRACT: In the present work six new benzoxazole derivatives were synthesized adopting the suitably selected scheme. The synthetic methodology included the synthesis of 2-(2-aminophenyl) benzoxazole (D1) by the reaction of anthranilic acid with 2-aminophenol in poly phosphoric acid. Substituted chloroacetanilides (A1-A6) were synthesized by the reaction of substituted anilines with chloroacetyl chloride. Finally compound 2-(2-(benzo[d]oxazol-2-yl) phenylamino)-N-(substituted phenyl) acetamide (2A-2F) were synthesized by the fusion of 2-(2-aminophenyl) benzoxazole (D1) and substituted chloroacetanilides (A1-A6).  All the aynthesized compounds were subjected to antimicrobial screening against the bacterial strains i.e., Bacillus subtilis (MTCC-619), Streptococcus pneumonia (recultured), Escherichia coli (NCTC 6571) and Staphylococcus aureus (NCTC 7447). The compounds were also tested for antifungal potential against two fungal strains i.e. Aspergilus. Niger (NCIM NO. 618) and Candida albicans (NCYC 597). In all the testing a significant correlation existed between the antimicrobial potential and the concentration of test compound.

Heterocyclic, Benzoxazole, Acetanilides, Antimicrobial

INTRODUCTION: Various Heterocyclic compounds have received considerable attention during last few decades as they are endowed with variety of biological activities and have wide range of therapeutic properties. The earlier sources of drugs i.e. plant, animal and mineral sources, resulted somehow lesser therapeutic efficacy and even more toxicities comparatively. So the process of new drug discovery has been accelerated by the necessity of synthesizing compounds possessing better therapeutic and least possible toxicological parameters.

During recent years there have been some interesting developments in the pharmacology of benzoxazole derivatives. These compounds have special significance in the field of medicinal chemistry due to their remarkable pharmacological potentialities ¹.

It has been investigated in past decade that benzoxazoles possess a wide range of promising biological activities ². The substituted benzoxazoles have been shown to exhibit antitumor³, antioxidant, antihelmintic ⁴, cyclooxygenase inhibitory ⁵, antifungal ⁶, Antitubercular ⁷, 5HT₃ receptor antagonists ⁸, anti-inflammatory, analgesic & cyclin dependent kinase inhibitory ⁹, 5-lipoxygenase inhibitory ¹⁰, melatonin receptor agonist ¹¹, anticancer ¹², antibacterial ¹³ and anti-HIV-1¹⁴ activities.

Recent observations suggested that substituted benzoxazoles and related heterocycles possessed potential activities with lower toxicities chemo-therapeutically ¹⁵ e.g. benzoxazole derivative, Calcimycin, is a carboxylic polyether antibiotic isolated  from the culture of Streptomyces chartreusis (NRRL 3882). It was found to be very active against Gram-positive bacteria including some Bacillus and Micrococcus microbes. Two calcimycin analogues, Routiennocin ¹⁶ and Cezomycin ¹⁷ were found to be highly active against Bacillus cereus, Bacillus negaterium, Micrococcus luteus and Streptomyces rimosus. Additionally Frankamide ¹⁸ that is 11-demethyl cezomycin showed some activity against Bacillus subtilis, Staphylococcus aureus, Enterococcus faecalis and against several plant pathogenic fungal strains ¹⁹.

Keeping in view of the immense biological activities exhibited by the molecule, present investigation explores the possibility of antimicrobial potential of a series of suitably substituted benzoxazole moiety.

EXPERIMENTAL: All melting points were determined in open capillaries and are uncorrected. The progress of the reaction and the purity of compounds were checked by TLC on percolated silica gel plates using n-Hexane, ethyl acetate, chloroform & benzene in different ratio as mobile phase.Detection of compounds was made by treatment with iodine vapours. IR spectra of compounds were recorded on FTIR 4100 type A spectrophotometer and HNMR spectra (DMSO) on Bruker FTAC spectrometer with TMS as internal standard.

Synthesis of substituted chloroacetanilides (A1-A6): Substituted aniline (0.1mole) was dissolved in 50ml of glacial acetic acid containing 50ml of saturated solution of sodium acetate. In case the substance did not dissolve completely, the mixture was warmed. The solution was cooled in ice bath with stirring. To this stirred solution, about 1 ml of 2-chloroacetyl chloride was added drop wise so that the vigorous reaction could not take place. After half an hour, the white product formed was separated by filtration through Whatman filter paper.

The solid precipitate was washed with distilled water, dried and recrystalized from aqueous alcohol²⁰.

Synthesis of 2-(2-aminophenyl) benzoxazole (D1): Equimolar quantities (0.1 mole) of 2-aminophenol and anthranilic acid were refluxed in poly phosphoric acid at 190°-195°C for 4 hrs.  The completion of reaction was checked by thin layer chromatography (TLC) using benzene: chloroform (2:3) solvent system as mobile phase and iodine vapour as developing agent. The reaction mixture was poured into crushed ice, with vigorous stirring. Filtered, washed with cold water, dried and recrystalized from ethanol²¹.

Synthesis of 2-(2-(benzo[d]oxazol-2-yl)phenylamino)-N-(substituted phenyl)acetamides (2A-2F): Equimolar quantities (0.1mole) of compound 2-(2-aminophenyl) benzoxazole (D1) and substituted chloroacetanilide (A₁-A₆) were mixed in 25 ml of 1, 4-dioxane. To this 0.001 ml of triethylamine (TEA) was added and the reaction mixture was refluxed for 2 hours. The completion of reaction was checked by TLC using ethyl acetate: n-hexane (1:3) solvent systemin iodine vapour. It was then cooled and poured into crushed ice. The solid product thus obtained was filtered, washed with 1% potassium bicarbonate followed by distilled water, dried & recrystallized with ethanol ²⁰.

Reaction Scheme: (Given on the following page)

Yield = 69%, mp 115-120˚C. IR (KBr, cm^-1) υ; 1420 (Ar.C=C Str.); 3060(Ar.C-H Str.); 753 (Ar.C-H bend _{out plane}); 1152 (Ar.C-H bend _{in plane}); 1302 (Ar. C-N Str.); 1589 (Ar. C=N Str.); 1753 (Ar. C-O Str.); 3374 (Ali. 1° N-HStr.). ¹H NMR (400.13 MHz, DMSO) δ; 7.2057- 7.7392 (5H, m, Ar.H), 6.5177, 6.6812, 6.7392 (3H, s, Ar.H), 4.4257- 4.4976 (2H, d, Ali NH₂). Anal. for C₁₃H₁₀N₂O, Calcd (%) C C, 74.27; H, 4.79; N, 13.33; O, 7.61%, Found C, 74.25; H, 4.77; N, 13.31; O, 7.59%.

2-(2-(benzo[d]oxazol-2-yl)phenylamino)-N-(4-bromophenyl) acetamide (2A): Compound 2A was found as light brown solid. Yield = 63%, mp 150-160˚C. IR (KBr, cm^-1) υ; 1485 (Ar.C=C Str.); 3089 (Ar.C-H Str.); 741 (Ar.C-H bend _{out plane}); 1152 (Ar.C-H bend _{in plane}); 1320 (Ar. C-N Str.); 1614 (Ar. C=N Str.); 1740 (Ar. C-O Str.); 1550 (Ali. C=O Str.); 3370 (Ar. 2° N-H Str.); 2825 (Ali.C-HStr.); 531(Ar. C-Br. Str.). ¹H NMR (400.13 MHz, DMSO) δ; 7.29 (s, 5H, ArH ), 7.53 (d, 2H, CH), 7.41 (m, 2H, Ar-H), 6.64-6.69 (m, 2H, Ar-H), 4.13 (d, 3H CH₂NH), 8.0 (s, 1H, NH). Anal. for C₂₁H₁₆BrN₃O, Calcd (%) C, 59.73; H, 3.82; Br, 18.92; N, 9.95; O, 7.58%, Found C, 59.70; H, 3.79; Br, 18.89; N, 9.92; O, 7.55%

2-(2-aminophenyl) benzoxazole (D1): Compound D1 was found as Reddish brown solid.

2-(2-(benzo[d]oxazol-2-yl)phenylamino)-N-(4-chlorophenyl) acetamide (2B): Compound 2B was found as reddish brown solid. Yield = 62%, mp 135-140˚C. IR (KBr, cm^-1) υ; 1499 (Ar. C=C Str.); 3078 (Ar. C-H Str.); 821 (Ar.C-H bend _{out plane}); 1243 (Ar.C-H bend _{in plane}); 1282 (Ar. C-N Str.); 1590 (Ar. C=N Str.); 1755 (Ar. C-O Str.); 1544 (Ali. C=O Str.); 3299 (Ar. 2° N-H Str.); 2952 (Ali.C-HStr.); 1042 (Ar. C-Cl. Str.). ¹H NMR (400.13 MHz, DMSO) δ; 7.26 (s, 5H, C₆H₅), 7.25 (m, 2H, p-Cl Ar-H), 6.64-6.49 (d, 2H, ArH) 4.23 (d, 3H, CH₂NH) 8.23 (s, 1H, NH). Anal. for C₂₁H₁₆ClN₃O₂, Calcd (%)C, 66.76; H, 4.27; Cl, 9.38; N, 11.12; O, 8.47%, Found C, 66.72; H, 4.23; Cl, 9.34; N, 11.10; O, 8.44%.

2-(2-(benzo[d]oxazol-2-yl)phenylamino)-N-(2,4-dichloro phenyl) acetamide (2C): Compound 2C was found as reddish brown solid. Yield = 65%, mp 82-85˚C. IR (KBr, cm^-1) υ; 1508 (Ar.C=C Str.); 3046 (Ar.C-H Str.); 753 (Ar.C-H bend _{out plane}); 1254 (Ar.C-H bend _{in plane}); 1272 (Ar. C-N Str.); 1601 (Ar. C=N Str.); 1725 (Ar. C-O Str.); 1664 (Ali. C=O Str.); 3266 (Ar. 2° N-H Str.) 2952 (Ali.C-HStr.); 1089 (Ar. C-Cl. Str.). ¹H NMR (400.13 MHz, DMSO) δ; 7.32-7.37 (m, 5H, C₆H₅), 6.69-6.72 (d, 2H, ArH), 7.13 (s, 1H, p-Cl), 7.26 (s, 1H, O-Cl), 4.12 (s, 3H, CH₂NH), 8.32 (s, 1H, NH).  Anal. for C₂₁H₁₅Cl₂N₃O₂, Calcd (%)C, 61.18; H, 3.67; Cl, 17.20; N, 10.19; O, 7.76%, Found  C, 61.14; H, 3.64; Cl, 17.18; N, 10.18; O, 7.75%.

2-(2-(benzo[d]oxazol-2-yl)phenylamino)-N-(3-chlorophenyl) acetamide (2D): Compound 2D was found as reddish brown solid. Yield = 64%, mp 80-85˚C. IR (KBr, cm^-1) υ; 1507 (Ar.C=C Str.); 3045 (Ar C-H Str.); 753 (Ar.C-H bend _{out plane}); 1230 (Ar.C-H bend _{in plane}); 1299 (Ar. C-N Str.); 1582 (Ar. C=N Str.); 1702 (Ar. C-O Str.); 1633 (Ali. C=O Str.); 3350 (Ar. 2° N-H Str.) 2870 (Ali.C-HStr.); 1096 (Ar. C-Cl. Str.). ¹H NMR (400.13 MHz, DMSO) δ; 8.1104, 7.6054, 7.3046, 6.7778, 6.5540 (5H, s, Ar.H); 7.0475-7.0854 (2H, d, Ar.H); 4.0089-4.2089 (2H, d, Ar.NH); 7.4556-7.2431(6H, m, Ar.H). Anal. for C₂₁H₁₆ClN₃O₂, Calcd (%)C, 66.76; H, 4.27; Cl, 9.38; N, 11.12; O, 8.47%, Found C, 66.73; H, 4.25; Cl, 9.35; N, 11.11; O, 8.44%.

2-(2-(benzo[d]oxazol-2-yl)phenylamino)-N-(3-nitrophenyl) acetamide (2E): Compound 2E was found as reddish brown solid. Yield = 63%, mp 150-155˚C. IR (KBr, cm^-1) υ; 1507 (Ar.C=C Str.); 3045 (Ar C-H Str.); 753 (Ar.C-H bend _{out plane}); 1230 (Ar.C-H bend _{in plane}); 1299 (Ar. C-N Str.); 1582 (Ar. C=N Str.); 1702 (Ar. C-O Str.); 1633 (Ali. C=O Str.); 3350 (Ar. 2° N-H Str.) 2870 (Ali.C-HStr.); 1096 (Ar. C-Cl. Str.). ¹H NMR (400.13 MHz, DMSO) δ; 8.6692, 7.227, 6.6586, 6.5272 (4H, s, Ar.H); 7.824-7.2272 (8H, m, Ar.H ); 4.9089-4.9557 (2H, d, Ar.NH). Anal. for C₂₁H₁₆ClN₃O₂, Calcd (%)C, 64.94; H, 4.15; N, 14.43; O, 16.48%, Found C, 64.92; H, 4.14; N, 14.40; O, 16.46%.

2-(2-(benzo[d]oxazol-2-yl)phenylamino)-N-phenylacetamide (2F): Compound 2F was found as reddish brown solid. Yield = 65%, mp 146-150˚C. IR (KBr, cm^-1) υ; 1520 (Ar.C=C Str.); 3051 (Ar. C-H Str.); 805 (Ar.C-H bend _{out plane}); 1176 (Ar.C-H bend _{in plane}); 1297 (Ar.C-N Str.); 1593, 1606 (Ar.C=N Str.); 1737 (Ar.C-O Str.); 1770 (Ali.C=O Str.); 3360 (Ar.2° N-H Str.); 2886 (Ali.C-HStr.).¹H NMR (400.13 MHz, DMSO) δ; 7.21-7.64 (9H, ArH), 6.64-6.69 (d, 2H, Ar NH), 4.29-4.32 (d, 3H, CH₂NH). Anal. for C₂₁H₁₆ClN₃O₂, Calcd (%) C, 73.45; H, 4.99; N, 12.24; O, 9.32%, FoundC, 73.42; H, 4.97; N, 12.23; O, 9.30%.

Biological Activity: Antibacterial activity of the compounds, 2A-2F was studied against Staphylococcus aureus (NCTC 7447), Bacillus subtilis (MTCC-619), Escherchia coli (NCTC 6571)and Streptococcus pneumonia (recultured) by disc-diffusion method and Ampicillin (100μg/ml) was used as the reference antibiotics^{22, 23}. Agar media was taken in the pre-sterilized petri-dishes and the microorganisms were grown. Each test compounds were dissolved in dimethyl formamide (DMF) to get a concentration of 10 mg/ml. The disc (6 mm in diameter) was impregnated with 200 μg/ml 100 μg/ml and 50 μg/ml of each test solution, placed on the seeded agar medium and the petri-dishes were incubated at 37˚C for 24 hr. DMF alone was used as control at the equal aforementioned concentration. Zone of inhibition of each compound in mm was recorded and the results were furnished in Table 1.

TABLE 1: SUBSTITUTION OF COMPOUNDS

In all the cases a significant correlation existed between the concentration of the tested compound and the inhibition of microbial intensification. As the concentration of the tested compound amplified, the growth of bacteria diminished. The antifungal activity of the compounds, 2A-2Fwas also determined against Aspergillus niger (NCIM NO. 618) and C.albicans (NCYC 597)by filter paper disc technique. The antifungal activity was studied by incubating for 48 hr at 22˚C and Fluconazole (100 μg/ml) was used as standard drug ²⁴.

RESULTS AND DISCUSSION: Substituted chloroacetanilides (A₁-A₆) were prepared by suitably substituted aromatic amine and chloroacetyl chloride in glacial acetic acid, as catalyst. 2-(2-aminophenyl) benzoxazole (D1)was synthesized according to illustrated procedure ²⁵ and was used as preparatory material. It was reacted with substituted α-chloro acetanilides (A₁-A₆) in the existenceof dioxane and Tri ethyl amine (TEA) as catalyst to attain the title compounds i.e. 2-(2-(benzo[d]oxazol-2-yl)phenylamino)-n-(substituted phenyl) acetamides (2A-2F). All the synthesized compounds were obtained in adequate yield. The structures of the synthesized compounds were assigned on the bases of their spectral data and elemental analysis.

In the IR spectra of 2-(2-aminophenyl) benzoxazole (D1), occurrence of absorption band at 1302 cm^-1 and  at 3374 cm^-1 strappingly recommended the existence of C-N and NH group respectively in the molecule, while the bands at 1420-1589 cm^-1 recommended the company of C=C and C=N ring stretching respectively. Other significant peaks were observed at 1753 cm^-1 for C-O and 3060 cm^-1 for C-H stretching bands. The emergence of absorption band in the IR spectrum of the compound 2Afor 2° N-H and C-Br were observed at 3370 cm^-1 and 531 cm^-1 respectively. The appearance of absorption band in IR spectrum of compound 2Aappears for (C=O) and (C=N) at 1550 cm^-1 & 1614 cm^-1 respectively. Spectra of all the other compounds were found to be in full consignment with the assigned structure.

Antimicrobial activity: All compounds were screened at the concentrations of 50 μg/ml, 100 μg/ml and 200 μg/ml. The results of antimicrobial screening are presented in Tables 2 and 3.

TABLE 2: ANTIBACTERIAL ACTIVITY OF BENZOXAZOLE COMPOUNDS

TABLE 3: ANTIFUNGAL ACTIVITY OF BENZOXAZOLE COMPOUNDS

From the data presented, it is clear that 2E is the highly active amongst the synthesized compounds, as it displayed better inhibition against E. coli, S. aureus and S. pneumonia compared to others.In the case of B. subtilis compound 2B was proved to be very effectivewhile 2C displayed least activity. The compound 2F and 2Cexhibited significant activity against Candida albicans and Aspergillus niger respectively.

FIGURE 1: ANTIMICROBIAL ACTIVITY OF BENZOXAZOLES AT 50μg/ml

FIGURE 2: ANTIMICROBIAL ACTIVITY OF BENZOXAZOLES AT 100μg/ml

FIGURE 3: ANTIMICROBIAL ACTIVITY OF BENZOXAZOLES AT 200μg/ml

CONCLUSION

The benzoxazole moiety independently has been reported to possess potent antimicrobial activity. In the present work authors have provided a convenient synthetic method for the synthesis of newer benzoxazole compounds by utilizing various substituted anilines imparting condensation of these with 2-(2-aminophenyl) benzoxazole.

The results of antimicrobial screening were encouraging. Further investigations with appropriate structural modifications of title compounds may result in therapeutically useful outcomes for future researchers.

The above results established the fact that benzoxazole derivatives could be a rich source of potential entities in search of new generation of biologically active compounds and be worthwhile to explore the possibility in this area by fusing differently substituted moieties which may result in better pharmacological activities.

ACKNOWLEDGEMENTS: Authors are very thankful to Shri Suresh Jain, Hon’ble chancellor of the Teerthanker Mahaveer University for his invariable encouragement and endowing us with facilities necessitated for successful completion of the study.

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25. Saravanan G, Alagarsamy V and Pavitra TGV: Synthesis, Characterization and Antimicrobial Activities of Novel thiazole derivatives. Inter. J. Pharm. Biosciences 2010; 1(3):1-8.How to cite this article:Priyanka, Sharma NK, Jha KK and Kumar MV: Synthesis and antimicrobial evaluation of 2-(2-(benzo [d] oxazol-2-yl) phenylamino)-n-(substituted phenyl) acetamides. Int J Pharm Sci Res2014; 5(8): 3260-66.doi: 10.13040/IJPSR.0975-8232.5(8).3260-66All © 2014 are reserved by International Journal of Pharmaceutical Sciences and Research. This Journal licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 3.0 Unported License.