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Issue 0, 1973
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Biosynthesis of rotenoids. Chalcone, isoflavone, and rotenoid stages in the formation of amorphigenin by Amorpha fruticosa seedlings

Abstract

[2′-14C]-7-Hydroxy-2′,4′,5′-trimethoxyisoflavone (2b) is shown to be excellently converted into [6-14C]-amorphigenin (1b) by Amorpha fruticosa seedlings, this being the first direct demonstration of the biosynthetic link between isoflavones and rotenoids. Isoflavones rather than isoflavanones are implicated and prenylation is evidently a post-rotenoid phase. In agreement, (±)-[6-3H]-9-demethylmunduserone (8a) is a good precursor for amorphigenin. This places 9-demethylmunduserone in a key biosynthetic position as parent of a sub-family of rotenoids, similar unprenylated rotenoids heading other sub-families. (±)-[6-3H]-8-Dimethylallyl-9-demethyl-munduserone and [6-3H]rotenone (as 6aS,12aS,5′R- and 6aR,12aS,5′S-diastereoisomers) are each satisfactorily incorporated into amorphigenin. Post-rotenoid stages are thus likely to be dimethylallylation, epoxidation, cyclisation to dalpanol (17), dehydration to rotenone (1a), and 8′-oxidation to amorphigenin. Administration of chalcones shows that the 2′,4,4′-trihydroxy-member is the most acceptable precursor and a mechanism for 2,3-aryl migration in biosynthesis takes account of the free 4-hydroxy-group requirement. The product from the rearrangement appears to be 7-hydroxy-4′-methoxyisoflavone rather than the 4′,7-dihydroxy-compound. Methylation accompanying rearrangement of a spirodienone intermediate (14) can accommodate this. Acetate is incorporated into rings D and E, but the radioactivity from serine and glycine is found in risic acid (16) obtained by degrading amorphigenin. This is discussed.

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Article information


J. Chem. Soc., Perkin Trans. 1, 1973, 1285-1294
Article type
Paper

Biosynthesis of rotenoids. Chalcone, isoflavone, and rotenoid stages in the formation of amorphigenin by Amorpha fruticosa seedlings

L. Crombie, P. M. Dewick and D. A. Whiting, J. Chem. Soc., Perkin Trans. 1, 1973, 1285
DOI: 10.1039/P19730001285

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