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.