Hoiamide A, a Sodium Channel Activator of Unusual Architecture from a Consortium of Two Papua New Guinea Cyanobacteria

Hoiamide A, a novel bioactive cyclic depsipeptide, was isolated from an environmental assemblage of the marine cyanobacteria. Lyngbya majuscula and Phormidium gracile collected in Papua New Guinea. This stereochemically complex metabolite possesses a highly unusual structure, which likely derives from a mixed peptide-polyketide biogenetic origin, and includes a peptidic section featuring an acetate extended and S-adenosyl methionine modified isoleucine moiety, a triheterocyclic fragment bearing two alpha-methylated thiazolines and one thiazole, and a highly oxygenated and methylated C15-polyketide substructure. Pure hoiamide A potently inhibited [H-3]batrachotoxin binding to voltage-gated sodium channels (IC50 = 92.8 nM), activated sodium influx (EC50 = 2.31 mu M) in mouse neocortical neurons, and exhibited modest cytotoxicity to cancer cells. Further investigation revealed that hoiamide A is a partial agonist of site 2 on the voltage-gated sodium channel.