BIOSYNTHESIS OF PTEROCARPAN, ISOFLAVAN AND COUMESTAN METABOLITES OF MEDICAGO-SATIVA - CHALCONE, ISOFLAVONE AND ISOFLAVANONE PRECURSORS

Comparative feeding experiments in CuCl2,- and UV-treated lucerne (Medicago sativa) seedlings have shown that 2′,4,4′-trihydroxychalcone-[carbonyl-14C] and formononetin-[Me-14C] but not 2′,4′-dihydroxy-4-methoxychalcone-[carbonyl- 14C] or daidzein-[4-14C] were incorporated into the phytoalexins demethylhomopterocarpin, sativan and vestitol, and also into 9-O-methylcoumestrol. The synthesis of 9-O-methylcoumestrol is greatly stimulated by this abiotic treatment but coumestrol production is not noticeably affected. Daidzein and the trihydroxychalcone were precursors of coumestrol. The results are interpreted in favour of a mechanism in which methylation is an integral part of the aryl migration process associated with the biosynthesisof 4′-methoxyisoflavonoids. Formononetin, 2′,7-dihydroxy-4′-methoxyisoflavone-[Me-14C], 7-hydroxy-4′-methoxyisoflavanone-[Me-14C] and 2′,7-dihydroxy-4′-methoxyisoflavanone-[Me-14C] were all excellent precursors of demethylhomopterocarpin, sativan, vestitol and 9-O-methylcoumestrol, and thus a metabolic grid may be involved in their biosynthetic origin. © 1979.