Isolation and Structures of Nostopeptolides A1, A2 and A3 from the Cyanobacterium Nostoc sp. GSV224

Abstract

The isolation and total structure determinations of nostopeptolides A1 ( 1), A2 ( 2) and A3 ( 3) are described. These cyclic depsipeptides, which are devoid of cytotoxic, antifungal and inhibition of protease activities, are characteristic constituents of the cryptophycin-producing cyanobacterium Nostoc sp. GSV224. Structure elucidation by NMR analysis was made more challenging by the existence of each nostopeptolide in three conformations. One-dimensional TOCSY experiments proved to be very useful in isolating and identifying the nine amino acid residues and the butyryl group in each compound. The absolute stereochemistries of 1– 3 were determined by comparing the amino acids in the acid hydrolyzates directly with authentic standards.