Design and synthesis of a bis(cycloisodityrosine) analogue of RA-VII, an antitumor bicyclic hexapeptide

An analogue of an antitumor bicyclic hexapeptide RA-VII was prepared, in which the Ala-2 and Tyr-3 residues of RA-VII were replaced by a cycloisodityrosine unit. In the crystalline state, the peptide backbone structures and the side-chain conformations at Tyr-3, Tyr-5, and Tyr-6 of this analogue and of RA-II were very similar. This analogue, however, showed much weaker cytotoxicity against P-388 leukemia cells than parent RA-VII.