New 6-O-acyl isoflavone glycosides from soybeans fermented with Bacillus subtilis (natto). I. 6-O-succinylated isoflavone glycosides and their preventive effects on bone loss in ovariectomized rats fed a calcium-deficient diet.

Three new 6-O-acylated isoflavone glycosides were isolated from soybeans fermented with Bacillus subtilis (natto) and identified as daidzein 7-O-beta-(6''-O-succinyl)-D-glucoside (1), genistein 7-O-beta-(6''-O-succinyl)-D-glucoside (2), and glycitein 7-O-beta-(6''-O-succinyl)-D-glucoside (3) on the basis of spectral data and chemical transformations. During fermentation, the content of the isoflavone glycosides first decreased and then increased, whereas the corresponding 6''-O-succinyl derivatives first accumulated and then decreased, in either soybeans or soybean cooking solution. These changes suggest that enzymatic interconversion of isoflavone glycosides and the corresponding 6''-O-succinylated derivatives occurs in these media during fermentation. The 6-O-succinylated isoflavone glycosides 1, 2 and 3 accounted for 4.8, 7.2 and 0.6%, respectively, of the total isoflavones in commercial fermented soybeans (Japanese natto). Oral administration of 1 or 2 alone for 4 weeks at a dose of 50 mg/kg/d prevented bone loss in ovariectomized (ovx) rats fed a calcium-deficient diet, being as effective as the positive controls, daidzin and genistin, respectively. Compound 1 seems to be proestrogenic, like daidzin, which suppresses bone resorption to prevent bone loss after ovariectomy by directly acting on bone sites, while 2 appears to have a different mechanism of action, like that of genistin.