An Efficient Preparation of Acetyl Isoflavone Glucoside

Minor components of isoflavones in soybeans, 7-(6-O-acetyl-beta-D-glucopyranosyl)-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one (6 "-O-acetyldaidzin, 5) and 7-(6-O-acetyl-beta-D-glucopyranosyl)-5-hydroxy-3-(4-hydroxyphenyl)-4H-1-benzopyran-4-one (6 "-O-acetylgenistin, 6), were efficiently prepared from 6 "-O-malonyldaidzin (3) or 6 "-O-malonylgenistin (4) by decarboxylation in N,N-dimethylformamide at 60 degrees C in 46% or 57% yield, respectively, This reaction may explain the increase in the amount of the acetate during toasting of soybeans.