The Convergent Synthesis Study On The Characteristic Steroid Saponins

Steroid saponins are largely distributed in terrestrial plants and some marine organnisms with significant pharmacological activities. Many Chinese traditional herbs contain saponins as the major biologically active ingredients. A lot of research results have implied that not only the sapogenin's structures, but also the sugar chain's structures in medicinal saponins had notable effect on their biological activities. Because of the lack of stable and large-scale acquisition of pure saponins from natural sources, it is a realistic way to get the naturally and artificial saponins by chemical synthesis.The research topic in the thesis was focused on the total synthesis of the bioactive steroid saponins which had the characteristic structures of the sugar moieties.1. The synthesis study on polyphyllin C and ophiopogonin C' and an improved glycosylation of spirostanols.The glycosylation of highly hindered sapogenins remained a great problem for chemists for many years. A facile glycosylation for the synthesis of spirostanol glycosides was disclosed. Using the acetoglycosyl bromides as the donors and cadmium carbonate as the promoter in CH3CN, a series of saponins were synthesized efficiently in satisfactory yields. Based on the method, two saponins, polyphyllin C and ophiopogonin C, which had the (1→2) or (1→3) glycosyl linkage respectively, had been synthsised by this glycosylation method. The in vivo biological tests of saponins: diosgenyl β-D-cellobioside, hecogenyl β-D-cellobioside and 11-ketotigogenyl β-D-cellobioside obtained in cholesterol absorption inhibition showed 11-ketotigogenyl β-D-cellobioside had the better bioactivity.2. The synthesis study on dioscin and gracillinDioscin and gracillin are structurally representative spirostanol saponins with a lot of bioactivities. They exist widely in the natural plants used in traditional Chinese herbal medicine. A mutually shared sugar fragment, neohesperidose [α-L-Rhap-(1→2)-D-Glcp] for both saponins was fabricated first. Then we attached it to diosgenin to get a protected saponin, diosgenyl 2,3,4-tri-O-benzoyl-α-L-rha-mnopyranosyl-(1→2)-3,4,6-tri-O-acetyl-...