Isolation and Structure Elucidation of Three New Lipopeptides from the Marine Cyanobacterium Symploca sp.

Marine cyanobacteria are prolific producers of biosynthetically intriguing natural products. Lipopeptides constitute one of the larger classes of cyanobacterial metabolites, and consist of both structurally diverse and biologically exciting compounds. Recently, utilizing bioassay-guided fractionation with an H460 (human lung cancer cell line) cytotoxicity assay, three new metabolites were purified and their planar structures determined by the combination of MSⁿ and 2D NMR spectroscopy, and were identified as linear lipopeptides. Each of these new metabolites contains several post-translational modifications, including O- and N-methylation and the incorporation of hydroxy acids. The absolute configuration of each of these new metabolites was determined by chiral GCMS analysis for both the hydroxy acids and for a selection of the amino acids (Gln and Ile), while Marfey's analysis was used for the remaining residues. These new metabolites resemble two previously identified families of compounds, the grassystatins and the tasiamides, both of which are known to possess moderate to potent cytotoxic activity. The biological properties of these new metabolites will be reported.