Design, synthesis, and biological evaluation of thiazole bioisosteres of goniofufurone through in vitro antiproliferative activity and in vivo toxicity

The synthesis of several new goniofufurone bioisosteres was achieved in which the phenyl residue was replaced by a thiazole ring. The key steps of the synthesis included the initial condensation of cyanohydrin benzoates with cysteine ethyl ester hydrochloride, followed by the subsequent reaction of resulting C-4' epimeric thiazolines with DBU, to introduce 5-deoxy functionality and to elaborate the thiazole ring in one step. Synthesized compounds showed potent growth inhibitory effects against selected human tumour cell lines, especially bioisostere 4, which in the culture of MCF-7 cells displayed the highest activity (IC₅₀ = 0.19 nM) of all compounds under evaluation. This molecule exhibited 64474-fold higher antiproliferative activity than lead 2 and was1053-fold more active than the commercial antitumour agent doxorubicin in the culture of MCF-7 cells. The structural features of the tested compounds responsible for their antiproliferative activity have been identified by preliminary SAR analysis. The toxicity of the most active compound 4 was assessed by an in vivo experiment in a zebrafish model (Danio rerio), whereupon it was found non-toxic at any of the tested concentrations up to 125 μM.