Syntheses of new tetrasubstituted thiophenes as novel anti-inflammatory agents

Abstract

A series of new tetrasubstituted thiophenes ( 4a– 4i, 5a– 5i and 6a– 6f) have been synthesized as novel anti-inflammatory agents and were evaluated for their anti-inflammatory activity in carrageenin-induced rat hind paw oedema model at the doses of 10, 20 and 40 mg/kg body weight. Among ester series, the best compound 4c showed 71% protection at 10 mg/kg, 72% at 20 mg/kg, and 76% at 40 mg/kg to inflamed paw; while in acid series 5a showed 79% protection at 10 mg/kg, 80% at 20 mg/kg, and 70% at 40 mg/kg, and 5c showed 72% protection at 10 mg/kg, 75% at 20 mg/kg, and 69% at 40 mg/kg, to inflamed paw. In case of oxime series 6a– 6f, the anti-inflammatory activities of the candidates were found to be poor as compared to acid and ester series. It was found on the basis of SAR studies of target compounds, that the presence of OCH 3 at R 2 position and H, OCH 3 at R 1 are one of the requirements for eliciting comparable anti-inflammatory activity in both tetrasubstituted thiophenes' ester and acid series. Compounds 4a– 4i, 5a– 5i were investigated for their analgesic activity in acetic acid induced writhing response model at 10 mg/kg dose. Among the ester series compound 4e showed maximum protection of 60%, while 4a, 4b, and 4i exhibited 55%, 45%, and 43% protection, respectively. The result showed that presence of H, Cl at R 1 and OCH 3, CH 3 at R 2 in tetrasubstituted thiophene ester series enhances their analgesic activity. The candidates of acid series 5a– 5i showed poor analgesic activity as compared to the standard drug ibuprofen. Compounds 4a– 4i, 5a– 5i were evaluated for their in vitro antioxidant nitric oxide radical scavenging assay. Among the ester series 4a showed maximum in vitro nitric oxide radical scavenging activity having IC 50 value 30.08 μg/ml while in acid series 5a has IC 50 value 25.20 μg/ml. The results showed that the presence of R 1 = H, R 2 = OCH 3 and R 1 = R 2 = OCH 3 enhances nitric oxide radical scavenging property in tetrasubstituted thiophenes' acid series.