Two new malyngamides from a Madagascan Lyngbya majuscula

The lipid extract of a Madagascan Lyngbya majuscula has yielded malyngamides Q and R, both amides of 7-methoxytetradec-4-enoic acid. The isolation of these metabolites was accomplished using preparative liquid chromatography, with final purification through repetitive reversed-phase HPLC. Structure elucidation was accomplished utilizing 1D and 2D NMR spectroscopic characterization of the natural products and comparisons with malyngamides A and B. DPFGSE 1D NOE data suggested a different geometrical stereochemistry at C-6 in malyngamides Q and R from that observed for malyngamide A, as well as the other known malyngamides. The Z stereochemistry was confirmed for malyngamide R by measurement of key diagnostic (3)J(CH) couplings utilizing the HSQMBC pulse sequence. The absolute stereochemistry of C-4' ' of the pyrrolidone ring was defined by chiral GCMS analysis of serine released by ozonolysis and acid hydrolysis.