Antitumor Agents, 112. Emarginatine B, a Novel Potent Cytotoxic Sesquiterpene Pyridine Alkaloid from Maytenus emarginata

Abstract
A new sesquiterpene pyridine alkaloid, emarginatine B [2] has been isolated, along with maytansine [3], from Maytenus emarginata. Emarginatine B showed potent cytotoxicity against human KB cells (EC50 = 0.4 .mu.g/ml). Spectral correlations established its structure as a 9-benzoate and C-8 epimer of emarginatine A [1]. The conformational aspect of the latter compound was elucidated by nmr studies, including the use of 2D-nmr techniques and difference nOe methods.