Synthesis of [Gly-1]RA-VII, [Gly-2]RA-VII, and [Gly-4]RA-VII. Glycine-Containing Analogues of RA-VII, an Antitumor Bicyclic Hexapeptide from Rubia Plants
journal contributionposted on 05.03.2004, 00:00 by Yukio Hitotsuyanagi, Tomoyo Hasuda, Takayuki Aihara, Hiroshi Ishikawa, Kentaro Yamaguchi, Hideji Itokawa, Koichi Takeya
Three analogues of RA-VII (1), an antitumor bicyclic hexapeptide from Rubia plants, were synthesized. Three analogues, [Gly-1]RA-VII (4), [Gly-2]RA-VII (5), and [Gly-4]RA-VII (6), in which one of the three alanine residues in 1 was replaced by a glycine residue, were prepared by linking of the cycloisodityrosine unit, obtained by degradation of 1, to three different glycine-containing tetrapeptides followed by macrocyclization. Of these three analogues, analogue 4 showed the highest cytotoxic activity. The NMR study revealed that in solution the conformer structures and their ratios of analogue 4 were very similar to those of natural peptide 1, suggesting that the methyl groups at Ala-2 and Ala-4 should be essential for producing the bioactive conformation, whereas that at d-Ala-1 is not essential.