Chemistry of ecteinascidins. Part 3: preparation of 2'-N-acyl derivatives of ecteinascidin 770 and evaluation of cytotoxicity

A three-step transformation of ecteinascidin 770 (1b) into 2'-N-indole-3-carbonyl derivative 3 via 18,6'-O-bisallyl-protected derivative 4a, which was shown to have higher cytotoxicity than 1b, is presented. In addition, a number of 2'-N amide derivatives of 1b have been prepared from 4a and their in vitro cytotoxicity were determined by measuring IC₅₀ values against human cell lines HCT116, QG56, and DU145. Benzoyl amide derivatives 7a-c showed similar in vitro cytotoxicity to 1b, whereas the nitrogen-containing heterocyclic derivatives 7d-h and cinnamoyl derivatives 9a-b showed higher cytotoxicity than 1b. In contrast, the 18,6'-O-bisallyl protected derivatives 4a-c, 6a-h, and 8a-b showed dramatic decreases in cytotoxicity relative to 1b.