Synthesis
The general procedure for the preparation of 4,6-O-benzylidene-D-galactose in DMF (11 mL) from (3R,4S,5S,6R)-6-(hydroxymethyl)tetrahydro-2H-pyran-2,3,4,5-tetraol (D-glucose, 1.00 g, 5.55 mmol) and benzaldehyde dimethylacetal (1.24 mL, 8.33 mmol) was as follows: firstly a suspension of D-glucose in DMF was heated to 60 °C until the solid was completely dissolved. Benzaldehyde dimethyl acetal and p-toluenesulfonic acid monohydrate (10 mg) were subsequently added. The reaction mixture was stirred continuously at 60 °C for 6 h, during which time it was depressurized for 10 min every hour to remove the MeOH generated.After completion of the reaction, the mixture was concentrated under vacuum. The residue was purified by silica gel column chromatography (eluent: methanol/ethyl acetate, 1:10, v/v) to afford the target product glucopyranose 2 (799.5 mg, 2.98 mmol, 53.7% yield) as a white solid. The product characterization data were as follows:[α]20D +12.9 (c 0.20, MeOH); 1H-NMR (400 MHz, CD3OD) δ 7.46-7.42 (m, 2H), 7.38-7.35 (m, 3H), 6.31 (d, J=4.1 Hz, 0.5H), 5.79 (d, J=7.8 Hz, 0.5H), and 5.60 (t, J=9.9Hz, 0.5H), 5.52 (s, 0.5H), 5.51 (s, 0.5H), 5.37 (t, J=9.2Hz, 0.5H), 5.17-5.10 (m, 1H), 4.39 (dd, J=10.3,4.6Hz, 0.5H), 4.32 (dd, J=10.5,5.0 Hz, 0.5H), 4.08-4.00 (m, 0.5H), 3.80-3.63 (m, 2.5H), 2.19 (s, 1.5H), 2.11 (s, 1.5H), 2.08 (s, 1.5H), 2.06 (s, 1.5H), 2.05 (s, 1.5H), 2.04 (s, 1.5H); 13C-NMR (100 MHz, CD3OD) δ 139.2, 139.1, 129.9, 129.0, 127.5, 103.0, 102.9, 99.0, 94.7, 83.1, 82.4, 77.2, 74.7, 74.4, 71.8, 70.3, 69.8, 67.7, 63.5; HRMS (ESI) m/z Calculated value C13H16O6Na [M+Na]+ 291.0845, measured value 291.0842.
References
[1] Carbohydrate Research, 2005, vol. 340, # 18, p. 2812 - 2815
[2] Chemical and Pharmaceutical Bulletin, 2001, vol. 49, # 11, p. 1503 - 1505
[3] Journal of Organic Chemistry, 1998, vol. 63, # 23, p. 8491 - 8509
[4] Australian Journal of Chemistry, 1988, vol. 41, # 1, p. 91 - 102
[5] Tetrahedron Letters, 1998, vol. 39, # 16, p. 2299 - 2302
