Configuration and Conformation of Dihydroflavonols from Acacia Melanoxylon

Article abstract of DOI:10.1016/S0031-9422(00)84793-7

The isolation of two novel dihydroflavonols, namely (-)2,3-cis-3',4',7,8-tetrahydroxydihydroflavonol and (+/-)2,3-trans-3',4',7-trihydroxy-5-methoxydihydroflavonol together with the known (+/-)2,3-trans-3',4',7,8-tetrahydroxydihydroflavonol from Acacia melanoxylon is described. 1H NMR study shows the aryl substituent at C-2 in the 2,3-trans compounds is in the normal equatorial conformation but the 2,3-cis isomer, in contrast, has the aryl substituent in the unusual axial conformation.The elucidation of the 2,3-cis configuration of the dihydroflavonol and its co-occurrence with the metabolically related 2,3-cis-leucoanthocyanidins or flavan-3,4-diols provide the first evidence that the biosynthesis of flavan-3-ols and proanthocyanidins with the 2,3-cis configuration occur in a parallel pathway to that of the 2,3-trans compounds.Key Word Index - Acacia melanoxylon; Leguminosae; heartwood; 2,3-cis-3',4',7,8-tetrahydroxydihydroflavonol; 2,3-trans-3',4',7,8-tetrahydroxydihydroflavonol; 2,3-trans-3',4',7-trihydroxy-5-methoxy-dihydroflavonol; configuration; conformation; biogenesis.