Antitumor agents, 112.¹ emarginatine Β, a novel potent cytotoxic sesquiterpene pyridine alkaloid from maytenus emarginata

A new sesquiterpene pyridine alkaloid, emarginatine Β [2] has been isolated, along with maytansine [3], from Maytenus emarginata. Emarginatine Β showed potent cytotoxicity against human KB cells (ED₅₀ = 0.4 μg/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.