反应详情

A mixture of α-L-glucopyranose (5.4 g.), methanol (30 ml.) and cation-exchange resin [(2 g., Dowex® 50W-X8 (H+), 50-100 mesh, previously prepared by treatment with methanol] was stirred magnetically at reflux temperature for 24 hours in a 50-ml. round-bottomed flask. The solution, which gave a negative test, was then cooled and filtered. The resin was washed several times with methanol and the filtrate and washings were evaporated at reduced pressure to a syrup (5.63 g., 96%) containing no L-glucose (paper chromatography, n-butanol/ethanol water v/v 40:11:19). A sample (1.0 g.) was dissolved in boiling methanol (2 ml.) and the mixture was allowed to slowly cool to room temperature to give crystalline methyl L-glucopyranoside. The crystals were suspended in enough ethanol to make a 10% (w/v) mixture, and this mixture was boiled to effect dissolution. On cooling of the mixture pure methyl α-L-glucopyranoside was obtained, m.p. 166.5°-168°, [α]D -156° (c 2.5, water). These values compare favourably with those for methyl α-D-glucopyranoside, m.p. 167°-169°, [α]D +157° (c 2, water).

1. temperatureat reflux temperature for 24 hours in a 50-ml
2. customThe solution, which gave a negative test
3. temperaturewas then cooled
4. filtrationfiltered
5. washThe resin was washed several times with methanol
6. customthe filtrate and washings were evaporated at reduced pressure to a syrup (5.63 g., 96%)
7. additioncontaining no L-glucose (paper chromatography, n-butanol/ethanol water v/v 40:11:19)
8. dissolutionA sample (1.0 g.) was dissolved