Astins A and B, antitumor cyclic pentapeptides from Aster tataricus.

Two novel antitumor chlorine- and alloThr-containing cyclic pentapeptides, named astins A and B, both of which were isomers and took a cis configuration in one of the amide bonds, were isolated from Aster tataricus together with astin C. Their structures were solved by spectroscopic analysis and chemical degradation.