New diarylheptanoids from the rhizomes of Dioscorea spongiosa and their antiosteoporotic activity.

Bioassay-guided fractionation of the water extract of the rhizomes of Dioscorea spongiosa led to the isolation and identification of new diarylheptanoids, diospongins A - C, together with three known lignans. Their structures, including absolute stereochemistry, were determined by analyses of NMR data, chemical conversions and CD spectrum. The isolated compounds, except for diospongin A, exerted potent inhibitory activities on bone resorption induced by parathyroid hormone in a bone organ culture system.