Bistratamides E-J, modified cyclic hexapeptides from the Philippines ascidian Lissoclinum bistratum

The Philippines ascidian Lissoclinum bistratum contained the known metabolites bistratamides C and D, together with six novel modified cyclic hexapeptides, bistratamides E-J. The structures of bistratamides E-J were elucidated by interpretation of spectral data, and the absolute stereochemistry of the constituent amino acids was determined after ozonolysis and acid-catalyzed hydrolysis. Bistratamides E-J were moderately cytotoxic in the HCT-116 cell line assay.