Isolation, Structure Elucidation, and Synthesis of Cytotoxic Tryptanthrin Analogues from Phaius mishmensis

Bioassay-guided chromatographic separation of the cytotoxic MeOH extract of Phaius mishmensis led to the isolation of two known and six new indoloquinazolinones, phaitanthrins A−E (1−5) and methylisatoid (6). The structures of the new compounds were elucidated by spectroscopic analysis. Phaitanthrin A (1) and tryptanthrin (7) showed moderate cytotoxicity against MCF-7, NCI-H460, and SF-268 cell lines. A series of ketone adducts of tryptanthrin were prepared and tested initially for anticancer activity in vitro against MCF-7, NCI-H460, and SF-268 human cancer cell lines. The 3-pentanone adduct 13 showed activity similar to tryptanthrin.