Mitsoamide: A cytotoxic linear lipopeptide from the Madagascar marine cyanobacterium Geitlerinema sp.

A new cytotoxic and linear peptide (IC50 460 nM to NCI-H460 human lung tumor cells) was isolated from the marine cyanobacterium Geitlerinema sp. The planar structure of mitsoamide was deduced by 1D and 2D NMR experiments in combination with MS analyses. The structure of mitsoamide contains an unusual polyketide unit (3,7-dimethoxy-5-methyl-nonanedioic acid, DMNA), incorporates a homolysine (HomoLys) residue and possesses a highly unusual piperidine aminal moiety. The configurations of the relatively common amino acids present in mitsoamide (Ala, Ile, N-Me-Ile, Phe, Val) were determined by chiral HPLC analysis of the acid hydrolysate.