Ulongamides A−F, New β-Amino Acid-Containing Cyclodepsipeptides from Palauan Collections of the Marine Cyanobacterium Lyngbya sp.

Abstract

Six new β-amino acid-containing cyclic depsipeptides, termed ulongamides A−F (1−6), have been isolated from collections of apratoxin-producing cyanobacteria from Palau. Their planar structures have been determined by NMR spectroscopic techniques. The absolute stereochemistry of the hydroxy acid and all the α-amino acid-derived units was ascertained to be S by chiral HPLC analysis of degradation products. The stereochemistry of the β-amino acid moiety, 3-amino-2-methylhexanoic acid, was established by advanced Marfey analysis of the acid hydrolyzates and found to be 2R,3R in compounds 1−3 but 2S,3R in compounds 4−6. All compounds except 6, which lacks an aromatic amino acid moiety, were weakly cytotoxic against KB cells.