Lundurines A–D, cytotoxic indole alkaloids incorporating a cyclopropyl moiety from Kopsia tenuis and revision of the structures of tenuisines A–C

The leaf extract of the Borneo Kopsia, K. tenuis, provided several new indoles with a novel hexacyclic carbon skeleton, incorporating a cyclopropyl moiety. Two of these, displayed appreciable in vitro cytotoxicity against B16 melanoma cells, as well as the circumvention of drug-resistance in drug-resistant KB cells. The structures of tenuisines A–C were revised from a dimeric to a monomeric structure, based on new LSIMS data, and in conjunction with the preparation of the methyl iodide salt of tenuisine A.