Synthesis and Structural Confirmation of the Thiazole Alkaloids Derived from Peganum harmala L.

Abstract

Peganumal A and B are thiazole alkaloids isolated from the seeds of Peganum harmala L. Thiazole moieties are rarely found in natural products, but diverse compounds possessing thiazole moieties have attracted attention owing to their broad range of biological activities. Peganumals are the first natural thiazole compounds isolated from the genus Peganum. It was difficult to define the exact structure of peganumal A via spectroscopic analysis. In this paper, we report the first total synthesis of peganumal A and B. The 5-benzylthiazole skeleton possessing methyl or hydrogen at the 2-position of the peganumals was efficiently constructed via the Hantzsch thiazole synthesis of the α-bromoaldehyde intermediate. Moreover, the spectral data of the synthetic 2H–thiazole compound were identical to those previously reported for peganumal A. The synthesis allowed the confirmation of the structure of peganumal A.