BIOSYNTHESIS OF PTEROCARPAN AND ISOFLAVAN PHYTOALEXINS IN MEDICAGO-SATIVA - BIOCHEMICAL INTERCONVERSION OF PTEROCARPANS AND 2'-HYDROXYISOFLAVANS

Feeding experiments have shown that 2′-7-dihydroxy-4′-methoxy-isoflavone-[Me-14C] and -isoflavanone-[Me-14C] are efficient precursors of the phytoalexins demethylhomopterocarpin, sativan and vesitol in CuCl2-treated lucerne (Medicago sativa) seedlings. Demethylhomopterocarpin-[Me-14C] was also incorporated into sativan and vestitol, and vestitol-[Me-14C] was incorporated into demethylhomopterocarpin and sativan. Thus, the pterocarpan demethylhomopterocarpin and the 2′-hydroxy-isoflavan vestitol are interconvertible in M. sativa, but incorporation data, and the results of kinetic feeding experiments with l-phenylalanine-[U-14C] suggest that these compounds are synthesized simultaneously from a common intermediate, which could be involved in the interconversion. A carbonium ion, derived from an isoflavanol, a likely intermediate in the biosynthetic reductive sequence from 2′,7-dihydroxy-4′-methoxy-isoflavone and -isoflavanone, is proposed as this common intermediate. 7-Hydroxy-2′,4′-dimethoxyisoflavone-[4′-Me-14C] was a very poor precursor of all three phytoalexins. Sativan, then, is most probably derived by methylation of vestitol. The incorporation of vestitol-[Me-14C] into demethylhomopterocarpin, but not into maackiain, pterocarpan phytoalexins of red clover (Trifolium pratense), is also demonstrated. © 1979.