Astins K–P, six new chlorinated cyclopentapeptides from Aster tataricus

During further investigation on the methanol extract of roots and rhizomes of Aster tataricus, six new chlorinated cyclopentapeptides, designated as astins K–P (9–14), together with eight known derivatives, astins A–H (1–8), were isolated. Structures of the new cyclopeptides were established using extensive spectroscopic methods, and the absolute configurations were determined by the advanced Marfeyʹs method. Astin P (14) represents a unique cyclopentapeptide linking as cyclo-(l-Pro (Cl2)1-l-allo-Thr2-l-Ser3-l-β-Phe4-l-Ava5). Astin B (2) showed cytotoxicity against BGC-823 cell with IC50 value of 19.2 μg/ml. Astin C (3) exhibited cytotoxicity on HCT-116 and BGC-823 cells with IC50 values of 13.4 and 3.3 μg/ml, respectively.