Aspidofractinine and Eburnane Alkaloids from a North Borneo <i>Kopsia</i>. Ring-Contracted, Additional Ring-Fused, and Paucidactine-Type Aspidofractinine Alkaloids from <i>K. pauciflora</i>

Eleven new indole alkaloids (1–11) comprising seven aspidofractinine
and four eburnane alkaloids, were isolated from the stem-bark extract
of Kopsia pauciflora occurring in Malaysian Borneo.
The aspidofractinine alkaloids include a ring-contracted, an additional
ring-fused, a paucidactine regioisomer, two paucidactine, and one
kopsine alkaloid. The structures of several of these alkaloids were
also confirmed by X-ray diffraction analyses. The bisindole alkaloids
isolated, norpleiomutine and kopsoffinol, showed in vitro growth inhibitory
activity against human PC-3, HCT-116, MCF-7, and A549 cells and moderate
effects in reversing multidrug-resistance in vincristine-resistant
human KB cells.