Isolation, structural elucidation, and synthesis of RA-XVII, a novel bicyclic hexapeptide from Rubia cordifolia, and the effect of side chain at residue 1 upon the conformation and cytotoxic activity

A novel antitumor bicyclic hexapeptide RA-XVII was isolated from the roots of Rubia cordifolia. By spectral studies and synthetic approach, its structure was determined to be [D-2-aminobutyric acid-1]deoxybouvardin. Studies on the effect of side chain at residue 1 on cytotoxic activity and conformation showed that although it had little effect on the conformation of the molecule, it decreased the activity as it grew longer. (C) 2003 Elsevier Ltd. All rights reserved.