A combination of configurational analysis based on coupling constants (JBCA) and Marfey's aminoacid derivatization allowed us to distinguish between the different possible diastereoisomers of threonines in cyclopeptides, when potentially some of the amino acids could be racemized/epimerized during the acid hydrolysis process. The strategy was applied to a new cyclic depsipeptide having an unusual chloropyrrol ring, gunungamide A (2), isolated from a marine sponge belonging to the genus Discodermia. Further validation of this approach was demonstrated with the peptide stellatolide (1), where epimerization of a threonine residue during hydrolysis in the Marfey's analysis resulted in a mistaken configuration. This approach can be extended to elucidate the absolute stereochemistry of peptides bearing amino acids with two or more contiguous chiral centers.

PM742 (1), a new chemical entity, has been isolated from the sponge Discodermia du Bocage collected in the Pacific Ocean. This compound showed strong in vitro cytotoxicity against several human tumor cell lines as well as a tubulin depolymerization mechanism of action, which led us to conduct an extensive Structure-Activity-Relationship study through the synthesis of different analogs. As a result, a derivatively named PM534 (2) is currently in its first human Phase I clinical trial. Herein, we present a comprehensive review of the isolation, structural elucidation, and antitumor activities of the parent compound PM742.