İlkay Ören

Synthesis and antimicrobial activity of some novel 2,5- and/or 6-substituted benzoxazole and benzimidazole derivatives.

A new series of 2,5- and/or 6-substituted benzoxazoles (7a-f), benzimidazoles (8a-g) holding cyclohexyl or cyclopentyl moieties at position 2 and 5- or 6-substituted-2-cyclohexylaminomethylbenzoxazoles (9a, b) was synthesized in order to determine their antimicrobial activities and feasible structure-activity relationships. The synthesized compounds were tested in vitro against three Gram-positive, two Gram-negative bacteria and the yeast Candida albicans in comparison with several control drugs. Microbiological results showed that the synthesized compounds were possessing a broad spectrum of antibacterial activity against the tested microorganisms. 5-Chloro-2-(2-cyclohexylethyl)benzimidazole (8g) was found as the most active compound against the screened Gram-positive bacteria strains at a minimum inhibitory concentration (MIC) value of 12.5 microg/ml. However, it exhibited lower antibacterial potency than the compared control drugs. On the other side, compounds 7-9 indicated significant antibacterial activity against the Gram-negative enterobacter Pseudomonas aeruginosa having MIC values of 50 microg/ml, providing either the same effect as tetracycline or higher activity than streptomycin, but showing less potency than the compared control drug gentamycin. Moreover, the synthesized compounds also possessed antimycotic activity against the yeast C. albicans showing MIC values between 25-50 microg/ml.

The synthesis and the structure−activity relationships of some substituted benzoxazoles, oxazolo(4,5-b)pyridines, benzothiazoles and benzimidazoles as antimicrobial agents

Abstract The synthesis of a new series of 2,5-disubstituted benzoxazoles 4a–f , 2-substituted oxazolo(4,5- b )pyridines 5a, b , benzothiazoles 6a, b and benzimidazoles 7a, b is described in order to determine their antimicrobial activities and feasible structure-activity relationships (SAR). The synthesized compounds were tested in vitro against 3 Gram-positive, 3 Gram-negative, and a fungus Candida albicans , 4b, 4e and 4f were found to be more active than the others against Klebsiella pneumoniae at a MIC value of 12.5 μg/ml. All the derivatives 4–7 exhibited significant antimycotic activity against C albicans . The antibacterial and antimycotic activities of 4–7 are also compared with several standard drugs.

Synthesis and microbiological activity of some novel 5- or 6-methyl-2-(2,4-disubstituted phenyl) benzoxazole derivatives

The synthesis of a new series of 5-or 6-methyl-2-(2,4-disubstituted phenyl) benzoxazoles (4, 5) is described in order to determine their antimicrobial activities and feasible structure-activity relationships. The synthesized compounds were tested in vitro against three Gram-positive bacteria, three Gram-negative bacteria and the yeast Candida albicans, in comparison with several control drugs. Microbiological results exhibited that the synthesized compounds possess a broad spectrum of antibacterial activity against the tested microorganisms. The compounds 4b and 4c indicated some antibacterial activity against Staphylococcus aureus having a minimum inhibitory concentration (MIC) of 12.5 micrograms/ml. Moreover, the compound 5a revealed a significant antibacterial activity against the enterobacter Pseudomonas aeruginosa showing a MIC value of 25 micrograms/ml, i.e. more potent than the control drugs tetracycline and streptomycin. For the antimycotic activity against the yeast C. albicans, the derivative 4c was found to be more active than the other synthesized compounds with a MIC value of 12.5 micrograms/ml, but one-fold less potent than the control drugs oxiconazole and haloprogin.

Synthesis and microbiological activity of some N-(o-hydroxyphenyl)benzamides and phenylacetamides as the possible metabolites of antimicrobial active benzoxazoles: part II

The synthesis of some N-(o-hydroxyphenyl)benzamides and benzacetamides (2a-2p) in order to determine their in vitro antimicrobial activity against two Gram-positive bacteria, three Gram-negative bacteria and the fungus Candida albicans is described. The new compounds were compared with several control drugs. The derivative 2g, 4-amino-N-(o-hydroxyphenyl)benzamide, was found active at an MIC value of 25 microg/ml against the Gram-negative microorganism Klebsiella pneumoniae. Most of the compounds exhibited antibacterial activity at an MIC value of 25 microg/ml against Pseudomonas aureginosa. For the antifungal activity against C. albicans, compounds 2e, 2h and 2m were found more active than the other derivatives (MIC 12.5 microg/ml). The antimicrobial activity of some of these benzamide and phenylacetamide derivatives (2a, 2b, 2f, 2g, 2h and 2k), possible metabolites of benzoxazoles, was also compared with that of the cyclic analogues 3-8. Compound 2f possesses two dilutions better antifungal activity than its cyclic analogue the benzoxazole derivative 5 against C. albicans, while having one dilution better antibacterial activity against Streptococcus faecalis and K. pneumoniae.

Synthesis and antimicrobial activity of some novel 2-(p-substituted-phenyl)-5-substituted-carbonylaminobenzoxazoles

A series of 2-(p-substituted-phenyl)-5-substituted-carbonylamino benzoxazole derivatives (5-22) was synthesized and their antimicrobial activities determined in comparison to several control drugs. The synthesized compounds were tested in vitro against Staphylococcus aureus, Streptococcus faecalis and Bacillus subtilis as Gram-positive, Pseudomonas aeruginosa and Escherichia coli as Gram-negative bacteria and the yeast Candida albicans. Microbiological results showed that the compounds possessed a diffuse spectrum of antibacterial activity against these microorganisms. Compound 9 which bears a phenylacetamido moiety at position 5 and a 4-fluorophenyl group at the 2-position of benzoxazole ring was the most active derivative against S. aureus, S. faecalis and P. aeruginosa with a MIC value of 12.5 microg/ml. Compound 11 provided higher potency than the other tested compounds against B. subtilis at a MIC value of 12.5 microg/ml. Compounds 5-22 showed antifungal activity against C. albicans with MIC values between 50 and 12.5 microg/ml.

Structure-activity relationships of some antimicrobial 5-substituted 2-(3-pyridyl) benzoxazoles using quantum-chemical calculations

The synthesis and in vitro antimicrobial activity of 5-substituted 2-(3-pyridyl)benzoxazoles (3–7) is described for some Gram-positive and Gram-negative bacteria and the yeast Candida albicans. The compounds 3–7 exhibited significant activity against the screened microorganisms, having MIC values between 25 and 12.5 μg/ml. Quantum-chemical calculations were performed for the compounds 1–10, in order to observe some feasible structure-activity relationships. These theoretical observations, calculated for the description of the mechanism of interactions at the molecular level, revealed that the electrophilic superdelocalizability of the nitrogen atom (SNE) in the oxazolo moiety of the benzoxazole ring is related to the activity. The results obtained from the theoretical calculations and the observed MIC values show that 2-(3-pyridyl)- and 2-phenylbenzoxazole derivatives exhibit bio-isosteric effects for antimicrobial activity. Additionally, substituents at position 5 on the fused heterocyclic system contribute to the activity constructively or destructively depending on the type of microorganism screened.