Catha edulis (Forsk) (Celastraceae) is a small tree, widely cultivated in East Africa and areas of the Middle East to provide, from fresh leaves and young shoots, a drug known as khat. The drug acts as a stimulant and suppresses appetite. The physiological effects are in part due to the cathine [(+) norpseudoephedrine] and cathinone content, but other constituents may also be active. To assist accurate understanding of the pharmacology we have made a detailed examination of the constituents of khat, which has revealed a group of alkaloids with molecular weights ca. 600-ca. 1200 daltons, all containing sesquiterpene polyol cores. Neutral terpenoids and phenylalkylamines have also been investigated, as well as the root-bark pigments. Full background literature is given in ref. 1. We have continued work on the alkaloids of khat and in this paper report the structures of three new compounds, cathedulin-K17, -K19, and -K20, all from plant material collected in Kenya. The constitutions of three new sesquiterpene alkaloids, cathedulin-K19 (1) (C54H58N2O23, M 1102), cathedulin-K17 (6) (C59H62N2O23, M 1166), and cathedulin-K20 (8) (C59H62N2O23, M 1166), obtained in small quantities from stems and leaves of Catha edulis (khat), have been demonstrated by spectroscopic examination. Alkaloids K17 and K19 contain a novel diester bridge derived from (Z)-4-(3-carboxy-2-pyridyl)-2-methylbut-3-enoic acid.