Gelstriamine A, a Triamino Monoterpene Indole Alkaloid with a Caged 6/5/7/6/6/5 Scaffold and Analgesic Alkaloids from Stems.

A novel triamino monoterpene indole alkaloid with an unprecedented skeleton, gelstriamine A (), four new monoterpene indole alkaloids (-), and 12 known analogues (-) were isolated from . The structures of - were established using extensive spectroscopic techniques, NMR calculations with i/d-DP4 and 2D C-H COSY ANNs analysis, ECD calculations, chemical methods, and single crystal X-ray diffraction analysis. Gelstriamine A () possesses an unprecedented 6/5/7/6/6/5 heterohexacyclic scaffold bearing a unique hexahydrooxazolo[4,5-]pyridin-2(3)-one motif, and a plausible biosynthetic pathway was proposed. All the isolated alkaloids - showed discernible analgesic activities in an acetic acid-induced writhing test in mice, and -desmethoxyhumantenine -oxide () exhibited more potent analgesic activities than those of morphine at doses of 0.04 and 0.2 mg/kg.