Two cytotoxic stereoisomers of malyngamide C, 8-epi-malyngamide C and 8-O-acetyl-8-epi-malyngamide C, from the marine cyanobacterium Lyngbya majuscula.

Two epimers of malyngamide C, 8-O-acetyl-8-epi-malyngamide C (1) and 8-epi-malyngamide C (3) have been isolated along with known compounds 6-O-acetylmalyngamide F (5), H (6), J (7) K (8), and characterized from a Grenada field collection of the marine cyanobacterium Lyngbya majuscula. The structures of these compounds were deduced by 1D and 2D NMR spectroscopic and mass spectral data interpretation. Absolute configurations were determined by a combination of CD-spectroscopy, chemical degradation and the variable temperature Mosher's method. Compounds 1-5, 7 and 8 displayed moderate cytotoxicity to NCI-H460 human lung tumor and neuro-2a cancer cell lines, with IC(50) values ranging between 0.5 and 20 microg/mL.