Glycosylation Synthetic Study Of Steroidal Saponins

Steroidal saponins are complex glycosides of steroids and widely distributed in nature, especially in the plant kingdom. They are the active ingredients in many medicinal plants. However, the amount of steroidal saponins in plant is rather limited, hindering its large scale of industrial production. On the other hand, the current documented production of the synthetic steroidal saponins has employed expensive reagents and multiple-step processes, which is unfavorable in terms of green industrial production. Therefore, enzymatic synthesis of steroidal saponins should be a way out. To face the lag of adequate research in this area, the main task of this thesis is to explore the synthesis of steroidal saponins in two sections: 1) Chemical synthesis of Steroidal sapogenins; 2) Exploration of enzymatic synthesis of steroidal sapogenins.1. Chemical synthesis of steroidal sapogenins:Six common glycosyl donors and three aglycone receptors have been chosen, and a series of monosaccharides steroidal sapogenins have been synthesized based on classical Koenigs-Knorr glycosylational methods. All synthesized steroidal saponins have been characterized, including three compounds not appeared in the previous literature.2. Exploration of enzymatic synthesis of steroidal sapogenins:In this paper, our main concern is to explore rhamnosidase in the synthesis of steroidal saponins, after meticulous experiment exploration, we found rhamnosyl can not be transferred to trillin by -rhamnosidase that from plants or microorganisms. In enzymatic synthesis process, we quantitative characterize the activity of the plant rhamnosidase under the organic solvent conditions for the first time, meanwhile, we also confirmed by experiments the plant rhamnosidase can not transfer glycosyl to macromolecules such thillin, but can shift to small molecule alcohol, and indirectly confirmed the specific of the plant rhamnosidase. Of course, our work about the enzymatic synthesis of steroidal saponins is preliminary; thus the research in this area requires further be explorated. We hope that the completed research can enlighten other members in this group.