Corresponding Author:
N. C. Desai
Medicinal Chemistry Division, University Department of Chemistry, Bhavnagar University, Bhavnagar-364 002, India
E-mail: [email protected]
Date of Submission 7 April 2008
Date of Revision 27 August 2008
Date of Acceptance 14 February 2009
Indian J Pharm Sci, 2009, 71 (1): 90-94

Abstract

Several 4-arylidene-2-phenyl-1-(2,4,5-trichlorophenyl)-1H-imidazol-5(4H)-ones (4a-q), N-(4-benzylidene-5-oxo-2-phenyl-4,5-dihydroimidazol-1-yl)-4-chlorobenzamides (5a-o) and N-(4-benzylidene-5-oxo-2-phenyl-4,5-dihydroimidazol-1-yl)-2,4-dichlorobenzamides (6a-m) were prepared. All newly synthesized compounds have been tested for their antibacterial activity against gram (+)ve and gram (-)ve bacteria and also on different strains of fungi. Introduction of OH, OCH 3 , NO 2 , Cl and Br groups to the heterocyclic frame work enhanced antibacterial and antifungal activities.

Keywords

5-Imidazolinone, antibacterial activity, antifungal activity

Imidazolinone ring system is of biological and chemical interest since long. The imidazolinones [1] are associated with a wide range of therapeutic activities [2-7] such as anticonvulsant, sedative and hypnotic, potent CNS depressant, antihistamine, antifilarial, bactericidal, fungicidal, antiinflammatory, MAO inhibitory, antiparkinsonian, antihypertensive and anthelmintic. Recently some new imidazolinone derivatives have been reported as antiinflammatory, herbicidal and hypertensive activities. Some workers have recognized 5-imidazolone as having anticancer activity [8]. The therapeutic importance of the compounds inspired us to synthesize some potential imidazolinones [9-13].

Desai et al. [14] have synthesized 4-benzylidene-2-phenyloxazole-5-one based on the methods descried in the literature which is a special type of Perkin condensation in which reaction between aldehyde and benzoylglycine proceeds first followed by ring closer. It is observed that aldehyde condenses under the influence of a base with the reactive methylene group in the azalactone which is formed by the dehydration of benzoylglycine, when the latter reacts with Ac2O in presence of sodium acetate. In view of these observations, we have synthesized imidazol-5-ones (Scheme I, Table 1).

Figure

Scheme 1: Synthetic pathway for synthesis of 5-imidazolone derivatives.

Sr No Ar- Molecular Formula M.P. Yield (%) Elemental Analysis
% Carbon % Nitrogen
Cal. Found Cal. Found
4a C6H5 C22H13Cl3N2O 173 65 61.78 61.69 6.55 6.41
4b 2-OH-C6H4 C22H13Cl3N2O2 170 60 59.55 59.47 6.31 6.25
4c 4-OCH3-C6H4 C23H15Cl3N2O2 160 55 60.35 60.28 6.12 6.03
4d 3-Cl-C6H4 C22H12Cl4N2O 185 54 57.17 57.06 6.06 6.01
4e 3-OCH3-C6H4 C23H15Cl3N2O2 190 50 60.35 60.21 6.12 6.03
4f 2-Cl-C6H4 C22H12Cl4N2O 195 53 57.17 57.06 6.06 5.98
4g 4-Cl-C6H4 C22H12Cl4N2O 210 54 57.17 57.05 6.06 6.01
4h 2-NO2-C6H4 C22H12Cl3N3O3 180 57 55.9 55.79 8.89 8.8
4i 3-NO2-C6H4 C22H12Cl3N3O3 230 55 55.9 55.74 8.89 8.78
4j 3-OCH3-4-OH-C6H3 C23H15Cl3N2O3 170 65 58.31 58.21 5.91 5.7
4k 5-Br-3OCH3-4-OH-C6H2 C23H14BrCl3N2O3 235 68 49.99 49.85 5.07 4.98
4l 4-OH-C6H4 C22H13Cl3N2O2 145 57 59.55 59.36 6.31 6.21
4m 5-Br-2OH-C6H 3 C22H12BrCl3N2O2 175 50 50.56 50.45 5.36 5.22
4n 3-OC6H5-C6H4 C28H17Cl3N2O2 160 48 64.7 64.64 5.39 5.34
4o 2,4,5 (OCH3)3-C6H2 C25H19Cl3N2O4 198 45 57.99 57.9 5.41 5.33
4p 3,4,5 (OCH3)3-C6H2 C25H19Cl3N2O4 185 45 57.99 57.89 5.41 5.35
4q 3-OH-C6H4 C22H13Cl3N2O2 165 58 59.55 57.47 6.31 6.26
5a C6H5 C23H16ClN3O2 233 60 68.74 68.62 10.46 10.35
5b 2-OH-C6H4 C23H16ClN3O3 235 65 66.11 66.05 10.06 9.97
5c 3-Cl-C6H4 C23H15Cl2N3O2 237 66 63.32 63.2 9.63 9.51
5d 3-OCH3-C6H4 C24H18ClN3O3 246 55 66.75 66.66 9.37 9.29
5e 2-Cl-C6H4 C23H15Cl2N3O2 212 62 63.32 63.19 9.63 9.51
5f 4-Cl-C6H4 C23H15Cl2N3O2 214 64 63.32 63.23 9.63 9.54
5g 2-NO2-C6H4 C23H15ClN4O4 248 50 61.82 61.73 12.54 12.45
5h 3-NO2-C6H4 C23H15ClN4O4 223 56 61.82 61.69 12.54 12.47
5i 3-OCH3-4-OH-C6H3 C24H18ClN3O4 226 45 64.36 64.25 9.38 9.25
5j 4-OH-C6H4 C23H16ClN3O3 231 47 66.11 66.01 10.06 9.98
5k 3-OC6H5-C6H4 C29H20ClN3O3 186 48 70.52 70.4 8.51 8.39
5l 2,4,5 (OCH3)3-C6H2 C26H22ClN3O5 245 46 63.48 63.4 8.54 8.47
5m 3,4,5 (OCH3)3-C6H2 C26H22ClN3O5 210 50 63.48 63.41 8.54 8.45
5n 3-OH-C6H4 C23H16ClN3O3 182 57 66.11 66.02 10.06 9.98
5o 4-N(C2H5)2-2-OH-C6H3 C27H25ClN4O3 176 43 66.21 66.21 11.46 11.4
6a 2-OH-C6H4 C23H15Cl2N3O3 175 60 61.08 61.01 9.29 9.93
6b 3-Cl-C6H4 C23H14Cl3N3O2 208 58 58.68 58.61 8.39 8.88
6c 3-OCH3-C6H4 C24H17Cl2N3O3 202 55 61.82 61.7 9.01 5.9
6d 2-Cl-C6H4 C23H14Cl3N3O2 205 56 58.68 58.58 8.93 8.85
6e 4-Cl-C6H4 C23H14Cl3N3O2 244 55 58.68 58.59 8.93 8.87
6f 2-NO2-C6H4 C23H14Cl2N4O4 216 58 57.4 57.31 11.64 11.55
6g 3-NO2-C6H4 C23H14Cl2N4O4 233 60 57.4 57.32 11.64 11.56
6h 3-OCH3-4-OH-C6H3 C24H17Cl2N3O4 237 48 59.77 59.65 8.74 8.65
6i 4-OH-C6H4 C23H15Cl2N3O3 236 45 61.08 61.01 9.29 9.22
6 j 3-OC6H5-C6H4 C29H19Cl2N3O3 224 48 65.92 65.8 7.95 7.81
6k 2,4,5 (OCH3)3-C6H2 C26H21Cl2N3O5 238 43 59.33 59.27 7.98 7.9
6l 3,4,5 (OCH3)3-C6H2 C26H21Cl2N3O5 212 45 59.33 59.26 7.98 7.88
6m 3-OH-C6H4 C23H14Cl2N3O3 190 48 61.08 61.01 9.29 9.2

Table 1: Physical constants and elemental analysis of 5-imidazolnes4a-q, 5a-o and 6a-m.

Various 4-arylidene-2-phenyl-1-(2,4,5-trichlorophenyl)- 1H-imidazol-5(4H)-ones (4a-q) were prepared by the reaction of 2,4,5-trichlorobenzenamine with 4-arylidene-2-phenyloxazol-5(4H)-ones (3a-q). N-(4- benzylidene-5-oxo-2-phenyl-4,5-dihydroimidazol- 1-yl)-4-chlorobenzamide (5a-o) were synthesized by the reaction of 4-chlorobenzohydrazide and 4-arylidene-2-phenyloxazol-5(4H)-ones (3a-q). N-(4- benzylidene-5-oxo-2-phenyl-4,5-dihydroimidazol-1- yl)-2,4-dichlorobenzamides (6a-m) were obtained by the reaction of 2,4-dichlorobenzohydrazide with 4-arylidene-2-phenyloxazol-5(4H)-ones (3a-q).

Melting points were taken in open capillaries using paraffin bath and are uncorrected. IR spectra were recorded on FTIR-Perkin-Elmer spectrometer (Vmax cm-1); 1H NMR spectra were recorded on Bruker Avance 300 FT-NMR spectrometer using CDCl3 as a solvent and mass spectra carried out on JEOL SX 102/DA-600 mass spectrometer, respectively. All the compounds were analyzed for carbon, hydrogen and nitrogen and the results were within ±0.4% of theoretical values. Purity was checked by TLC using TLC aluminum sheets silica gel 60, supplied by E. Merck, Mumbai, India. The spots were located by keeping the plates in iodine vapor and 2,4,5-trichlorobenzenamine was supplied by S. D. Fine Chem Limited, Mumbai, India. 4-Chlorobenzohydrazide, 2,4-dichlorobenzo hydrazide and 4-arylidene-2-phenyloxazol-5(4H)-one (3a-q), were prepared as given in literature method [15-20].

4-Arylidene-2-phenyl-1-(2,4,5-trichlorophenyl)-1H-imidazol- 5(4H)-one (4) were synthesized as follows; A mixture of 2,4,5-trichloroaniline (0.01 mol) and 4-(arylidene)-2-phenyloxazol-5(4H)-ones (0.01 mol) was placed in a round bottom flask and 10 ml of pyridine were added to it. The reaction mixture was refluxed on a sand bath for 6 h. (scheme I) and the mixture was poured into ice-cold water and then a required amount of conc. hydrochloric acid was added to neutralize the reaction mixture. The progress of the reaction and the purity of compounds were routinely checked on TLC. The solid obtained was left overnight, filtered and washed with water. The product was dried and recrystallized from ethanol (99%). m.p.195° Yield 53% anal. found: C, 57.06; N, 5.98; calc for C22H12Cl4N2O: C, 57.17; N, 6.06%.

Compound 4f: IR (KBr): 3062 cm-1 (-C-H str., aromatic), 1643 cm-1 (>C=O str., cyclic ring), 1359 cm-1 (>C=N str., imidazol ring), 1284 cm-1 (-C-N tertiary amine), 1074 cm-1 (-C-Cl str., aromatic), 744 cm-1 (>C=CH medium), 704, 688, 613 cm-1 (trisubstituted aromatic). 1H NMR (CDCl3): δ7.2 (s, 1H, -CH), 7.26-8.54 (m, 11H, Ar-H, C=C-Ar) ppm. MS: m/z 461 with 62% relative intensity (base peak) & 462 with 47% relative intensity (M+). Other compounds of the series were prepared by using a similar method and their physical data are recorded in Table 1.

N-(4-benzylidene-5-oxo-2-phenyl-4,5-dihydroimidazol-1-yl)-4-chlorobenzamides (5)/N-(4-benzylidene-5-oxo-2-phenyl-4,5-dihydroimidazol- 1-yl)-2,4-dichlorobenzamides (6) were prepared using the following procedure; A mixture of 4-chlorobenzohydrazide/ 2,4-dichlorobenzohydrazide (0.01 mol) and 4-(arylidene)-2-phenyloxazol-5(4H)- ones (0.01 mol) was placed in a round bottom flask and 10 ml of pyridine was added to this mixture. The reaction mixture was refluxed on a sand bath for 6 h (Scheme I). The mixture was poured into ice-cold water and then required amount of con. hydrochloric acid was added to neutralize the reaction mixture. The solid obtained was left overnight, filtered and washed with water. The product was dried and recrystallized from ethanol (99%).

Compound 5f: IR (KBr): 3249 cm-1 (medium –CONH-), 3033 cm-1 (-C-H str., aromatic), 1656 cm-1 (>C=O str., cyclic ring), 1625 cm-1 (>C=N str., imidazol ring), 1490 cm-1 ( >NH weak), 1299 cm-1 (-C-N tertiary amine), 1095 cm-1 (-C-Cl str., aromatic), 754 cm-1 (>C=CH medium ), 707 cm-1 (monosubstituted aromatic). 1H NMR (CDCl3): δ7.28 (s, 1H, -CH), 7.26-8.54 (m, 13H, Ar-H, -C=C-Ar), 10.02 (s, 1H, -NH-CO-) ppm. MS: m/z 436 with 45% relative intensity (base peak) & 437 with 32% relative intensity (M+).

Compound 6e: IR (KBr): 3213 cm-1 (medium, –CONH-), 2993 cm-1 (-C-H str., aromatic), 1662 cm-1 (>C=O str., cyclic ring), 1635 cm-1 (>C=N str., imidazol ring), 1473 cm-1 (>NH weak), 1305 cm-1 (-C-N tertiary amine), 1109 cm-1 (-CCl str., aromatic), 925 cm-1 (>C=CH medium), 825, 713 cm-1 (disubstituted aromatic), 707 cm-1 (monosubstituted aromatic). 1H NMR (CDCl3): δ7.2 (s, 1H ,-CH), 7.32-8.05 (m, 12H, Ar-H,C=C-Ar), 10.02 (s,1H, -NH-CO-) ppm. MS: m/z 471 with 79% relative intensity (base peak) and 472 with 51% relative intensity (M+). Other compounds of the series were prepared by using a similar method and their physical data are recorded in Table 1.

Antibacterial activity was carried out by broth dilution method [21]. The strains used for the activity were procured from Institute of Microbial Technology, Chandigarh. The compounds 4a-q, 5a-o and 6a-m were screened for their antibacterial activity against Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa and Staphylococcous pyogenes at concentrations of 1000, 500, 200, 100, 50, 25, 12.5 μg/ml respectively (Table 2). Same compounds were tested for antifungal activity against C. albicans, A. niger and A. clavatus at concentrations of 1000, 500, 200, and 100 μg/ml respectively (Table 2). The results are recorded in the form of primary and secondary screening.

Sr. No. Minimal bactericidal concentration (MBC) in μg/ml Minimal fungicidal concentration (MFC) in μg/ml
E. coli P. aeruginosa S. aureus S. pyogenus C. albicans A. niger A. clavatus
MTCC-443 MTCC-1688 MTCC-96 MTCC-442 MTCC-227 MTCC-282 MTCC-1323
4a 25
4b 25 50
4f 100 100 100 100
4i 25
4j 25
4k 50 100 50
4q 50 100
5b 100 100 100
5e 50 50
6f 100 100 100 100
6j 100
6l 100 100
6m 100

Table 2: Antibacterial and antifungal activities of the synthesized compounds*.

The synthesized compounds found to be active in the primary screening were further tested in a second set of dilution against all microorganisms. The compounds found active in primary screening were similarly diluted to obtain 100, 50, 25 μg/ml concentrations. Ten microlitres suspensions from each well were further inoculated on appropriate media and growth was noted after 24 and 48 h. The lowest concentration, which showed no growth after spot subculture was considered as MBC/MFC for each drug. The highest dilution showing at least 99% inhibition was taken as MBC/MFC. The result of this test is affected by the size of the inoculums. The test mixture should contain 108 organisms/ml. For antibacterial activity, in present protocol 50 μg/ml is considered as active as compared to the standard drug gentamycin. For antifungal activity, 100 μg/ml is considered as active as compared to standard nystatin. Compounds 4a, 4b, 4i, 4j, 4k, 4q and 5e are active on E. coli where as 4b and 5e are active on P. aeruginosa. Compound 4k is active on S. aureus and 6m is also active on S. pyogens. Compounds 4f, 5b, 6f, 6l, and 6m are active on fungi strains. On the basis of biological activity results, it may be concluded that the introduction of OH, OCH3, NO2, Cl and Br groups to the heterocyclic frame work enhanced antibacterial and antifungal activities.

Acknowledgements

The Authors are thankful to the Bhavnagar University for providing research facilities. Authors are also thankful to director, FSL Gandhinagar for the spectral data.

References