Convergent synthesis of (-)-mirabazole B using a chloroimidazolidium coupling reagent, CIP

(-)-Mirabazole B (1), an alkaloid consisting of four successive thiazoline/thiazole rings, has been synthesized in a convergent route. The key intermediate, a linear tripeptide amide 13 composing of three S-benzyl-2-methylcysteine residues, was prepared using 2-chloro-1,3-dimethyl-imidazolidium hexafluorophosphate (CIP) in the presence of 1-hydroxy-7-azabenzotriazole (HOAt) as a coupling agent. The successive thiazoline/thiazole rings were constructed by TiCl4-mediated cyclization followed by Hantzsch reaction without difficulty. (C) 1997 Elsevier Science Ltd.