Cytotoxic alkaloids from the roots of Tylophora atrofolliculata.

Four new phenanthroindolizidine alkaloids, tylophoridicines C-F, together with three known ones, R-(+)-deoxytylophorinidine, tylophorinine and tylophorinidine, were isolated from the roots of Tylophora atrofolliculata. The structures were determined on the basis of spectral evidence. These alkaloids exhibited cytotoxic activity in vitro on HCT-8 cell (with IC50 values in the range 0.083 to 18.99 microM) and KB cell (in the range 3.56 to 18.22 microM) lines.