Hexamollamide, a hexapeptide from an Okinawan ascidian Didemnum molle

The bioassay-guided fractionation of the cytotoxic constituents of the Okinawan ascidian Didemnum molle led to the isolation of hexamollamide (1), a hexapeptide. The gross structure and relative stereostructure of 1 were established by spectroscopic analysis including 2D NMR techniques and single-crystal X-ray diffraction analysis. The absolute stereostructure was determined by chiral HPLC analysis of acid hydrolysates of 1. Hexamollamide (1) exhibits moderate cytotoxicity against HeLa S3 cells.