New cytotoxic bicyclic hexapeptides, RA-XXIII and RA-XXIV, from Rubia cordifolia L.

Abstract

Two new bicyclic hexapeptides, RA-XXIII and RA-XXIV, were isolated from the roots of Rubia cordifolia L. (Rubiaceae). Their structures were determined by the analysis of their 2D NMR spectra, chemical methods, and X-ray crystallography. The IC50 values of RA-XXIII and RA-XXIV against P-388 leukemia cells were 0.16 and 0.48 μg/ml, respectively. © 2008 Pharmaceutical Society of Japan.