Quinoline alkaloids. Part 28. The biosynthesis of furoquinolines and other hemiterpenoids in Ptelea trifoliata

Feeding experiments with doubly labelled 4-methoxy-3-prenyl-2-quinolones have shown that the biosynthesis of kokusaginine 8 and maculosidine 9 in P. trifoliata also involves a myrtopsine-like derivative. Contrary to our proposed pathways, the biosynthesis of hemiterpenoid olefines such as ptelefoline 15, in the same plant species, does not appear to involve directly platydesminium salt but possibly also a myrtopsine derivative. On the basis of the results obtained, alternative biosynthetic pathways to these alkaloids are discussed.