AbstractThe possibility that 1,4‐dihydro‐1‐methyl‐4‐oxonicotinonitrile (V) is an intermediate in the biosynthesis of the alkaloid ricinine from nicotinic or quinolinic acid in Ricinus communis L. led to our interest in preparing the carbon‐14 labeled compound. The 4‐oxonicotinonitrile (V) and the corresponding 6‐oxonicotinonitrile were shown to be oxidation products of nicotinonitrile methiodide by a crude enzyme preparation from castor seedlings (1, 2). The 6‐oxonicotinonitrile was shown to be identical to the alkaloid nudiflorine isolated fromTr