Furoquinoline alkaloids and cytotoxic constituents from the leaves of Melicope semecarpifolia.

Three new furoquinoline alkaloids, melicarpine, semecarpine, and (+/-)-8-methoxyplatydesmine, together with a known flavone, ayanin, were isolated from the leaves of Melicope semecarpifolia. The structures of the three alkaloids were determined through spectral analyses. Of the nineteen isolates obtained here and during earlier work, twelve exhibited cytotoxic activity against P-388, HT-29, or A549 cell lines in vitro. Among them, confusameline is the most cytotoxic isolate, and exhibited more potent cytotoxicity (ED 50 value = 0.03 microgram/mL) against the P-388 cell line than the reference compound mithramycin (ED 50 value = 0.06 microgram/mL).