Study On Biotransformation Of Steroidal Saponins And Its Specific Glycosidase

Steroidal saponin is one kind of important substances of bioactivity, which is widespread in traditional Chinese medicine ( herbs ), such as Rhizoma Paridis, Rhizoma Polygonati, Rhizoma Dioscorea Nipponica, Liriope Spicata, Paris Polyphylla, etc. Steroidal saponins show a vary of pharmacological activities of anti-cancer, anti-dementia, inhibiting platelet aggregation, and anti-diabete, etc.Biotransformation is a kind of synthesis or structure modification methods using dissociated enzyme, microorganism or cultureal plant cells as catalyst, which has highly selectivity, mild reaction condition and reaction versatility, etc. It has potentially wide applications and market value for increasing natural products diversity, searching for lead compounds, enhancing the sustainability of the rare species of natural resources, improving preparation efficiency and reducing the costs, etc. There is just few reports on steroidal saponin biotransformation and its regularity.Five steroidal saponins were isolated from Rhizoma Paridis and their structures were elucidated as polyphyllin Ⅰ (1a), polyphyllin Ⅲ (2a), polyphyllin Ⅴ(3a), polyphyllin VI (4a) and diosgenin-3-O-α-L- rhamnopyranosyl (1→4)-β-D-glucopyranoside (2b). These compounds, together with timosaponin AⅢ (5a) and timosaponin BⅡ (6a) were used as substrates for biocatalyst screening and selectivity study.Rhizopus nigricans ( 3.2050, S01)and Curvularia lunata (3.4381, S02), used for 11β-hydroxylation of steroids, were tried to used as biocatalysts of hydroxylation of steroidal saponins and aglycones. However, they showed the negative result. Rhizopus nigricans can isomerize a steroidal saponin at C22 position. The biotransformed product of C22 β isomer, which is very rare in nature, was purified and elucidated as 3 - O -β-D-glucopyranosyl- (1-2 )-β- D - galactopyranoside of...