| Popis: |
Glycosylation of the dammar-24-ene-3,12β,20( S )-triols with 2,3,4,6-tetra- O -acetyl-α- d -glucopyranosyl bromide ( A ) in the presence of silver oxide in dichloro-methane gives a mixture of the acetylated 3-, 12-, 20-, 3,12-di-, and 3,20-di- O -β- d -glucopyranosyl derivatives in a total yield of 83–84.5%. Under similar conditions, the 3- O -acetyl derivatives of dammar-24-ene-3,12β,20( S )-triols give a mixture of 12- and 20- O -β- d -glucopyranosyl derivatives. Condensation of betulafolienetriol [dammar-24-ene-3α,12β,20( S )-triol] both with the glycosyl bromide A in the presence of mercuric cyanide in nitromethane and with 3,4,6-tri- O -acetyl-β- d -glucopyranose 1,2-( tert -butyl orthoacetate) in the presence of 2,4,6-trimethyl-pyridinium perchlorate in chlorobenzene under azeotropic distillation results in dehydration and 20-dehydroxyglucosides are formed. |
