Synthesis of Thiazole Derivatives and Evaluation of Their Antiamoebic Activity and Cytotoxicity

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Five ethyl (5-alkyl-2-amino-1,3-thiazol-4-yl) acetates (designated compounds 4a-e) incorporating octyl, decyl, dodecyl, tetradecyl, and hexadecyl alkyl chains, respectively, were prepared by reacting 4-alkyl-4-bromo-3-oxobutyric acid ethyl esters (3a-e) with thiourea in dried acetonitrile. Compounds 3a-e were synthesized by reacting alkylated ethyl acetoacetates with bromine. The newly synthesized compounds were characterized by mass spectrometry, NMR, and elemental analysis. Compounds 4a-c demonstrated good in vitro antiamoebic activity against Acanthamoeba polyphaga exposed to 10 mg L-1 for 6 h at 28 °C. Compound 4b showed the highest antiamoebic activity among the tested compounds, comparable to that of chlorhexidine dihydrochloride (CHX), decreasing the number of viable cells to below the detection limit of 1 cell mL-1. The activity of compounds 4a and 4c was similar to that of the commercial antifungal agent fluconazole (Flu). The cytotoxic and hemolytic activity of the compounds was assayed against human neonate dermal fibroblasts and sheep erythrocytes, respectively. Compounds 4a-c were less cytotoxic than Flu and CHX. Our results suggest that compound 4b, which is composed of a 2-amino-thiazole attached to a decyl group and an ethyl ester moiety, is a particularly safe and effective alternative amoebicidal agent.