Spirostanols obtained by cyclization of pseudosaponin derivatives and comparison of anti-platelet agglutination activities of spirostanol glycosides

Naturally occurring saponins 3 and 4 have a normal type F ring and alpha-ar ranged CH3-21 group. Treatments of pseudosaponin peracetates 18 and 19 deri ved from 3 and 4, respectively, with alcoholic KOH, followed by acidificati on with acetic acid, gave spirostanols 20 and 22 having iso type F rings as major products. Structural analyses of sapogenins and saponins derived fro m pseudo derivatives 11, 12, 18 and 19 were performed by comparisons of the ir H-1-NMR spectral data and the X-ray analytical data of 3-O-p-bromobenzoy l sarsasapogenin 7, 3-O-acetyl diosgenin 13 and saponin 20. The mechanisms of ring-closure reaction of the side chain at C-22 of pseudosapogenins and pseudosaponins were deduced using stereomodels of the spirostanols derived from 11 under various reaction conditions. Inhibitory activities of saponin diglycosides 3, 4, 20, 21 and 25 on human platelet agglutinations induced by ADP and ristocetin were compared. (C) 2000 Editions scientifiques et med icales Elsevier SAS.