Biosynthesis of Methylcyclopentane Monoterpenoids

Studies on the biosynthesis of actinidine, the steam-volatile alkaloid of Actinidia polygama Miquel, show that radioactivity from mevalonate-2-14C, acetate-2-14C, and geranyl pyrophosphate-1-14C is incorporated into the alkaloid. Radioactivity from lysine-2-14C and quinolinic acid-2,3,5,7-14C is not incorporated. Radioactivity from uniformly labeled aspartic acid-14C is incorporated only during experiments of long duration. The results provide evidence for the isoprenoid origin of actinidine and show that lysine and quinolinic acid do not serve as precursors of the pyridine ring of actinidine; they thus demonstrate the existence of a third biosynthetic pathway for the formation of pyridine compounds in plants.