The structure of Palau'amide, a potent cytotoxin from a species of the marine cyanobacterium Lyngbya.

Bioassay-guided fractionation of the extract of a species of Lyngbya from Palau has yielded Palau'amide (1), which had an IC(50) value of 13 nM against KB cells. The structure of 1 was elucidated by NMR analysis in a variety of solvents. In particular, a gradient-enhanced band-selective HMBC experiment allowed unambiguous assignment of HMBC correlations to carbon signals that were separated by 0.1 ppm. The relative stereochemistry and the absolute configurations of all but one (C-37) of the nine chiral centers were determined by NMR analysis of the alpha-methoxyphenylacetic acid (MPA) derivatives and chiral HPLC of the degradation products of 1. The assignment of S rather than R stereochemistry at C-37 is discussed in detail.