RA-dimer A, a novel dimeric antitumor bicyclic hexapeptide from Rubia cordifolia L.

A novel antitumor bicyclic hexapeptide dimer, RA-dimer A (3), was isolated from the roots of Rubia cordifolia L. The structure of 3 was determined by analysis of spectroscopic data and chemical correlations. Peptide 3 is the first example of the RA congeners having a dimeric structure.