Antidesmone (3), known from several species of Antidesma and Hyeronima (Euphorbiaceae), is a quinoline alkaloid with an unusual substitution pattern. It carries a linear aliphatic side chain that indicates an at least partially acetogenic origin of the carbon skeleton. Feeding experiments with 13C and 15N labeled precursors administered to cell cultures of Antidesma membranaceum yielded antidesmone, which was investigated by NMR spectroscopy. Accordingly, antidesmone is built up from a linear C16-polyketide chain and a C2 unit derived directly from glycine. It is thus the first representative of a biosynthetically novel class of alkaloids.