Cyclic peptides from higher plants. XXVIII. Antitumor activity and hepatic microsomal biotransformation of cyclic pentapeptides, astins, from Aster tataricus

Antitumor activities on Sarcoma 180A of a series of cyclic pentapeptides, astins, isolated from the roots of Aster tataricus, were examined. The activities on various congeners of the dichlorinated proline residues prepared by chemical conversion and a hepatic microsomal biotransformation in rats suggested that 1,2-cis dichlorinated proline residues of astins A, B and C play an important role in the antitumor activity of astins.