Three novel indole alkaloids from Kopsia officinalis.

Three new indole alkaloids, named kopsioffines A-C (1-3), possessing relatively novel ten-membered lactam ring, and one known compound (11,12-demethoxy-16-deoxypauciflorine, 4) were isolated from the leaves and stems of Kopsia officinalis. Their structures were elucidated by means of spectroscopic methods. The absolute configuration of 1 was determined by calculated electronic circular dichroism data. The hypothetical biosynthetic pathway of 1 was postulated. All these isolates were evaluated for their inhibitory effects on α-glucosidase. None of them showed activity with IC50 far beyond 50μM.