4.12. Symplocin A
Symplocin A is a new N,N-dimethyl-terminated peptide extracted from the Bahamian cyanobacterium Symploca sp. The complete absolute configuration of symplocin A, including the unexpected D configurations of the terminal N,N-dimethylisoleucine and valic acid residues, was assigned by chiral-phase high-performance liquid chromatography of the corresponding 2-naphthacyl esters, a highly sensitive, complementary strategy for assignment of N-blocked peptide residues where Marfey's method is ineffectual or other methods fall short. Symplocin A exhibits potent activity as an inhibitor of cathepsin E. 34