The Acetylation Modification Of Ginenoside Rg2 And The Optimization Of Reaction Conditions

Ginsenoside Rg2 is one of protopanaxatriol rare saponins,which possesses a variety of pharmacological activities.To date,the research about structural modification of Rg2 is still in its infancy.To systematacially study the relationship between the structure and pharmacological activities of Rg2,ginsennoside Rg2 prepared by biotransformation was modified by acetylation under different reaction conditions in this thesis.Three acetylated derivatives of Rg2 with different substitution degree were obtained after separation and purification.The structure and the acetyl substitution sites of each product were determined by mass spectrometry?MS?,nuclear magnetic resonance spectroscopy?NMR?,infrared spectroscopy?IR?,etc.Thereafter,the optimal reaction conditions of these three acetylated derivatives of Rg2 were optimized by regulating the acetylation reaction conditions of Rg2.The main contents and results of this thesis are listed as follows:1.Two types of Rg2 derivatives?Compound a and b?with a high degree of acetyl substitution were synthesized in the pyridine/acetic anhydride system.After purification,their structures were characterized and analyzed,respectively.Characterization results indicate that compound a is an octasubsitituted Rg2 acetylated derivative with an unsubstituted hydroxyl group in the C-20 position,named as Rg2-ac8.Compoud b is a heptasubsitituted Rg2 acetylated derivative with unsubstituted hydroxyl groups at the C-20 and C-3' positions,named as Rg2-ac7.2.The optimal synthesis conditions of the Rg2-ac8 and Rg2-ac7 were further optimized by single factor experiments,including of the reaction temperature,reaction time,catalyst,solvent,etc.The results demonstrate that the optimal synthesis conditions of Rg2-ac8 are found as follows: the reaction system is pyridine?py?as solvent and DMAP as catalyst,the molar ratio of Rg2 and acetic anhydride?Ac₂O?is 1:27,the reaction temperature and time is 25 oC and 30 min,respectively.Moreover,the optimal conditions for the synthesis of Rg2-ac7 are as follows: pyridine?py?is used as solvent,the molar ratio of Rg2 and acetic anhydride?Ac₂O?is 1:315,the reaction temperature and time is 50 oC and 5 h,respectively.3.To obtain more Rg2 derivatives with a low degree of acetyl substitution,another Rg2 acetylated derivative was synthesized by changing the reaction system.Characterization results indicate that this new product is a monosubstituted Rg2 derivative whose hydroxyl group at the C-12 position is replaced by acetyl group.By optimizing the reaction conditions,the optimal synthesis conditions of Rg2-ac1 are as follows: DMF is used as the solvent,the molar ratio of Rg2 and Ac2 O is 1:225,the reaction temperature and time is 25 oC and 5 h,respectively.