New antitumor bicyclic hexapeptides, RA-XI, -XII, -XIII and -XIV from Rubia cordifolia.

Four new bicyclic hexapeptides, named as RA-XI, -XII, XIII and -XIV were isolated from Rubia cordifolia and showed potent antitumor activities against P-388. The structures were elucidated from spectroscopic and chemical evidences. RA-XII, XIII and -XIV were proved to be unique bicyclic hexapeptidic glucosides.