Biosynthesis of Aloenin in Aloe arborescens var. natalensis

Abstract The 14C- and 3H-labeling patterns in aloenin biosynthesized by uptake of acetate-1-14C, malonate-2-14C, phenylalanine-1-14C and -3-14C, methionine-methyl-14C, and glucose-3-3H to Aloe arborescens var. natalensis demonstrated that the carbon skeleton of aloenin is arisen via a biological polyketide by the acetate-malonate pathway and the O-methyl group originates from methionine. Further, feeding experiments of 3H/14C-doubly labeled 4-methoxy-6-(2,4-dihydroxy-6-methylphenyl)-2-pyrone and 5-(2-β-d-glucopyranosyloxy-4-hydroxy-6-methylphenyl)-3,5-dioxopentanoic acid in the Aloe plant revealed that an immediate intermediate is the pyrone derivative and not the dioxopentanoic acid derivative. Aloenin was demonstrated to be biosynthesized in such a way that the first formation of the pyrone by cyclization of the biological polyketide and then O-methylation of the cyclized intermediate is followed by introduction of a glucose molecule into the pyrone derivative.