| Popis: |
The title disaccharide ( 16 ) has been synthesized in 50% overall yield by way of condensation of 4,6-di- O -acetyl-2,3- O -carbonyl-α- D -mannopyranosyl bromide 5 with methyl 2,3- O -isopropylidene-α- L -rhamnopyranoside ( 1 ) in chloroform solution, in the presence of silver oxide. The disaccharide was characterized as the crystalline isopropyl alcoholate of methyl 4- O -β- D -mannopyranosyl-α- L -rhamnopyranoside ( 11 ) and as 1,2,3-tri- O acetyl-4- O - (2,3,4,6-tetra- O -acetyl-β- D -mannopyranosyl)-α- L -rhamnopyranose ( 15 ). Methyl β- D -mannopyranoside isopropyl alcoholate 7 was readily obtained in 85% yield via the reaction of bromide 5 with methanol. Reduction of 2,3-di- O -methyl- L -rhamnose with sodium borohydride, followed by acetylation, may result in the formation of an appreciable proportion of a boric ester, namely 1,5-di- O -acetyl-4-deoxy-2,3-di- O -methyl- L -rhamnitol-4-yl dimethyl borate, depending on the procedure used. |
