Selectively acidic hydrolysis of steroidal saponins

Steroidal saponins have been shown to exhibit a wide range of pharmacological activities.The biological activities of steroidal saponins are strongly dependent on the carbohydrate residues attached to the aglycon.In this paper,three steroidal saponins solamargine,solasonine and dioscin were isolated from nigrum(S.nigrum L.)fruits and the rhizomes of Dioscorea nipponica Makino.Selectively acidic hydrolysis of steroidal saponins was performed.Hydrolytic products were prepared and characterized by TLC and13C NMR spectrum.The results showed that partial acidic hydrolysis of α-solamargine can produce four products.The efforts to prepare β1-solasonine were unsuccessful.Acidi-catalyzed partial hydrolysis of carbohydrate groups of dioscin obtained four products.The optimal hydrolytic condition for preparation of γ-dioscin(trillin) was at 90℃ with 2%H2SO4-MeOH-H2O(2∶90∶10,V/V/V)in a reaction period of 75 min.For preparation of β-dioscin,the best condition was at 75℃ using 5%H2SO4-MeOH-H2O(5∶90∶10,V/V/V) for 75 min.