Synthesis of Biologically Active [4-(4-Bromophenyl)-2-thiazolyl]hydrazones and their D-Galactose Derivatives

Benzaldehyde [4‐(4‐bromophenyl)thiazol‐2‐yl]hydrazones 5a–5d were prepared by reacting the thiosemicarbazones 2a–2d with 2,4′‐dibromoacetophenone (1) in absolute ethanol. Acetylation of 5a and 5b with Ac2O/Py at room temperature gave the N‐acetyl derivatives 6a and 6b. 4‐Methyl‐2‐pentanone/cyclopentanone [4‐(4‐bromo‐phenyl)thiazol‐2‐yl]hydrazones (8a) and (8b) were similarly obtained from the reaction of 1 with the thiosemicarbazones 7a and 7b, respectively. Cyclization of D‐galactose thiosemicarbazone (9) and its tautomers 10 and 11 with 1 afforded an equilibrium mixture of the acyclic 2‐thiazolylhydrazone 12, together with its respective cyclic galactosyl derivatives 13 and 14, whose structures were studied by using 1H and 13C NMR spectra. The antimicrobial activity of the synthesized thiazole derivatives was evaluated in vitro by using an agar diffusion technique, and some of these compounds showed potential activity against Candida albicans.