| Popis: |
The glycosylation of cholesterol, β-sitosterol, 28- O -acetylbetulin, and betulin with acylated glycosyl halides in the presence of Hg(OAc) 2 , Hg(CN) 2 , CdCO 3 , Ag 2 O, Ag 2 CO 3 , and HgO + HgBr 2 , usually gives acylated αβ-glycosides accompanied by acetates, ethers, and bromo and unsaturated derivatives of the initial alcohols. The use of Hg(CN) 2 gave mainly β anomers (40–87%), whereas α anomers preponderated when Hg(OAc) 2 was the catalyst. When there was a deficiency of hydrogen halide acceptor and in the presence of the acidic catalyst HgBr 2 · HBr, the β anomer, produced initially, underwent anomerisation. Cholesteryl α- D -gluco-pyranoside tetra-acetate (48 %) was obtained by anomerisation of the β anomer. |
