Limonin biosynthesis from obacunone via obacunoate in Citrus limon

Radioactive tracer work showed that [14C]obacunone was converted to at least four metabolites in Citrus limon. Two were identified as obacunoate and limonin. When [14C]methyl obacunoate was fed, limonin was found to be one of the metabolites. Based on these results and data accumulated thus far, biosynthetic pathways of limonoids in citrus are proposed.