Synthesis, in vitro antimicrobial, antioxidant, and antidiabetic activities of thiazolidine–quinoxaline derivatives with amino acid side chains

Abstract

A novel protocol for the rapid assembly of a hybrid framework based on amino acid, thiazolidine and quinoxaline scaffolds has been demonstrated by microwave irradiation. The quinoxalines with amino acid side chains 5a–5c were prepared in three steps from 2,4-dinitrofluorobenzene and the amino acids, valine, methionine, and tyrosine and subsequently reacted with four different aldehydes and thioglycolic acid to produce thiazolidine–quinoxaline hybrids with amino acid side chains 6a–6l. All synthesized compounds were evaluated for their in vitro antimicrobial, antioxidant, and antidiabetic activities. Compounds 6f, 6j, and 6k showed broad spectrum antimicrobial activity against Gram +ve and Gram –ve bacteria, whilst 6h, 6k, and 6l showed the best antioxidant activity in the same order of magnitude to that of ascorbic acid. Four of the compounds, 5c, 6d, 6g, and 6k showed activity against α-glucosidase and α-amylase similar to acarbose. Those compounds showing antibacterial activity possessed 4-fluorophenyl and 4-methoxyphenyl groups along with methionine and tyrosine side chains while the compounds showing antioxidant, α-glucosidase, and α-amylase activity contained 4-nitrophenyl and 4-methoxyphenyl groups on the thiazolidine moiety with mainly methionine and tyrosine side chains. The α-glucosidase and α-amylase inhibitory compound 5c did not have a thiazolidine moiety and 6d was the only active compound with a valine amino acid side chain. Compound 6k with a tyrosine side chain and a 4-methoxyphenylthiazolidine moiety on the quinoxaline scaffold showed good bioactivity in all three assays.