The structure of cotyledoside, the active toxic principle of Tylecodon wallichii (Harv.) Toelken subs.wallichii was assigned as 7fA8-epoxy-1 4-hydroxy-2a,3P -(tetra hydro-3,5 -di hydroxy-4-met hoxy-6methyl-2H-pyran-2,4-diyldioxy)-5abufa-20,22-dienolide. The structure is based on a detailed study of the high-field H and 3C n.m.r. spectra of cotyledoside. The relative configuration of the metabolite was deduced from the observed proton-proton nuclear Overhauser effects and the magnitude of the proton-proton coupling constants.Members of the genera Cotyledon, Tylecodon, and Kalanchoe (Crassulacea) cause annual stock losses in South Africa through cotyledonosis, an intoxication affecting the nervous and muscular systems. ' The active principle of Tylecodon wallichii (Harv.) Toelken subs. waZlichii,2 called cotyledoside, was first isolated by van Rooyen and Pieter~e.~ van Wyk4 studied the structure of cotyledoside, C3 1H42010, and observed the formation of a chlorohydrin aglycane upon treatment of the substance with hydrogen chloride in dry chloroform. This compound was subsequently treated with thionyl chloride in pyridine to produce the disulphite (1). Structure (2) was proposed for the aglycone of cotyledoside.We now report a revised structure for cotyledoside, including the nature, stereochemistry, and mode of attachment of the carbohydrate moiety to the aglycone. The structure of cotyledoside is based mainly on the analysis of the high-field 'H and 13C n.m.r. spectra. Extensive 'H-{ 'H) homonuclear decoupling experiments enabled us to assign the 'H n.m.r. spectrum. The 3C n.m.r. spectrum was assigned on the basis of broad-band proton-decoupled and single-frequency offresonance proton-decoupled experiments as well as the reported 13C n.m.r. chemical shifts of related compounds. The residual splittings observed in a series of off-resonance protondecoupled 13C n.m.r. experiments enabled us to correlate the signals of the proton-bearing carbon atoms with specific carbon resonance^.^ The 'H and 13C n.m.r. data of cotyledoside are collated in Tables 1 and 2, respectively.Well-resolved signals at 6,7.399 (dd, J 2.7 and 0.9 Hz, 21-H), 7.848 (dd, J9.8 and 2.6 Hz, 22-H), and 6.171 (dd, J9.8 and 0.8 Hz, 23-H) were assigned to the protons constituting the pyrone ring. The presence of the epoxide moiety in cotyledoside was evident from the proton resonance, tiH 3.300 (d, J 5.5 Hz), and the carbon resonances, 63.28 (s) and 51.34 p.p.m. [d, ' J(CH)