H-1-NMR CHEMICAL-SHIFT VALUE OF THE ISOFLAVONE 5-HYDROXYL PROTON AS A CONVENIENT INDICATOR OF 6-SUBSTITUTION OR 2'-HYDROXYLATION

H-1 NMR examination of a range of simple and complex isoflavones has shown that the presence or absence of a 2'-hydroxyl group can be deduced from the chemical shift value of the 5-hydroxyl proton determined in acetone-d6. The data can also be used to establish if a methoxyl group or an alkyl side structure is present at C-6, and distinguishes between prenylation at C-6 and C-8. The application of this H-1 NMR technique to the identification of Piscidia-derived isoflavones is discussed.