Hermitamides A and B, toxic malyngamide-type natural products from the marine cyanobacterium Lyngbya majuscula

A Papua New Guinea collection of the marine cyanobacterium Lyngbya majuscul a yielded two new and toxic natural products, hermitamides A (1) and B (2). The hermitamides were isolated using a brine shrimp (Artemia salina) toxic ity assay. Planar chemical structures of 1 and 2 were established through 1 D and 2D NMR, as well as FABMS data. Semisyntheses of hermitamides A (1) an d B (2) were achieved by coupling the acid chloride derivative of 7(S)-meth oxytetradec-4(E)-enoic acid (4), obtained from the same cyanobacterium coll ection, and the respective free amines, phenethylamine and tryptamine. Herm itamides A (1) and B (2) exhibited LD50 values of 5 mu M and 18 mu M in the brine shrimp bioassay, and an IC50 values of 2.2 mu M and 5.5 mu M to Neur a-2a neuroblastoma cells in tissue culture, respectively. Hermitamide A was mildly ichthyotoxic to goldfish, with an LD50 value of 19 mu M, while herm itamide B was inactive at 25 mu M.