Ulongapeptin, a cytotoxic cyclic depsipeptide from a Palauan marine cyanobacterium Lyngbya sp.

Ulongapeptin (1), a cyclic depsipeptide, was isolated from a Palauan marine cyanobacterium Lyngbya sp. The gross structure was elucidated through one-dimensional TOCSY experiments and other spectroscopic techniques. The absolute and relative stereochemistry of the b-amino acid, 3-amino-2-methyl-7-octynoic acid (AMO), in 1 was determined by synthesis of the saturated a-alkyl-b-amino acid and Marfey's analysis of the acid hydrolysate of tetrahydro-1. Ulongapeptin (1) was cytotoxic against KB cells at an IC50 value of 0.63 mM.