Microcyclamide, a Cytotoxic Cyclic Hexapeptide from the Cyanobacterium Microcystis aeruginosa

Abstract
Microcyclamide (1), a cytotoxic cyclic hexapeptide, was isolated from the cultured cyanobacterium Microcystis aeruginosa (NIES-298). Its structure was elucidated to be 1 on the basis of two-dimensional 1H− 1H, 1H−13C, and 1H−15N NMR correlation experiments and the HRFABMS measurement. The absolute stereochemistry of the asymmetric centers was determined by the Marfey's method. This peptide showed a moderate cytotoxicity against P388 murine leukemia cells.