Polypeptides. Part XXV. Synthesis of isariin

Abstract

O-(Glycyl-L-valyl-D-leucyl-L-alanyl-L-valyl)-D- and L-3-hydroxydodecanoic acids (D- and L-isoisariic acids) have been synthesised and their cyclisation has been studied. D-Isoisariic acid was converted through its acid chloride into a cyclopeptolide indistinguishable from isariin, a metabolite of Isaria cretacea. High pressure liquid chromatography was necessary for the isolation of the product from the reaction mixture and facilitated comparison with the natural material. Attempts to cyclise D-isoisariic acid by other methods were unsuccessful.