One-Step Syntheses of 1,2,3,5,6-Penta-O-Benzoyl-alfa,beta-D-Galactofuranose and 1,2,3,5-Tetra-O-Benzoyl-alfa,beta-D-Arabinofuranose.

MARINO, CARLA; GANDOLFI-DONADIO, LUCÍA; GALLO-RODRIGUEZ, CAROLA; BAI, YU; MUCHNIK DE LEDERKREMER, ROSA

Carbohydrate Chemistry. Proven Synthetic Methods

TAYLOR & FRANCIS INC

Año: 2012; p. 231 - 238

1,2,3,5,6-Penta-O-Benzoyl-α,β-d-Galactofuranose (1α and 1β) The reaction setup consists of a 250 mL, three-neck round bottom flask with a magnetic stirring bar. One neck is connected to an addition funnel and the other equipped with a thermometer. A reflux condenser with a calcium chloride drying tube is attached to the third neck. The flask is charged with d-galactose (5.0 g, 0.028 mol) and anhydrous pyridine (70 mL),* and the suspension is stirred in a gently boiling water bath for 2 h, while the bath and the flask are covered with aluminum foil. In this way, any water condenses under the foil. The flask is then removed from the bath, vigorous stirring is continued, and the mixture is allowed to cool to 60°C?65°C. BzCl (20 mL, 0.17 mol) is added in portions (within approx. 5 min), while the content of the flask is stirred manually and the internal temperature is kept at 60°C, by cooling with an ice-water bath, if necessary.? When the addition of BzCl is complete, the solution is stirred in a water bath kept at 60°C.2 After 1.5 h, water (10 mL) is slowly added, and vigorous stirring is continued for 0.5 h at room temperature. The solution is poured slowly with stirring (glass rod) into ice-water (500 mL) affording an amorphous solid. Immediately after the ice had melted, the liquid is decanted and the remaining solid is thoroughly washed with ice-water (5 × 500 mL), rubbing the solid with the rod. The solid is filtered,? rapidly washed with cold water, transferred into an Erlenmeyer flask, and dissolved in boiling ethanol (800 mL). The solution is kept at room temperature (covered loosely with an aluminum foil) with occasional scratching the walls of the flask with the rod, to induce crystallization, and after 2 days, a crop of crystals of 1,2,3,5,6-penta-O-benzoyl-α,β-d-galactofuranose (1α,β) is obtained. After three crops of the crystals are collected (2, 4, and 8 days), the total yield of 1α,β is 5.0?6.4 g (26%?33%), Rf 0.60 and 0.54 (9:1 toluene?EtOAc). If TLC analysis of the crystals shows presence of the β-pyranose benzoate, with mobility (Rf 0.57) between that of the furanose forms, it can be removed by recrystallization from EtOH. 1HNMR (CDCl3) β-anomer: δ 8.12-7.13 (H-aromatic), 6.84 (s, J < 0.5 Hz, 1H, H-1), 5.14 (m, 1H, H-5), 5.78 (d, J = 4,1 Hz, 1H, H-3), 5.77 (s, 1H, H-2), 4.87 (apparent t, J = 4.0 Hz, 1H, H-4),4.78 (m, 2H, H-6,6′); α-anomer: δ 8.13-7.10 (H-aromatic), 6.84 (d, J = 4.7 Hz, 1H, H-1), 6.39 (apparent t, J = 7.2 Hz, 1H, H-3), 5.90 (dd, J = 7.5, 4.7 Hz, 1H, H-2), 5.88 (m, 2H, H-5), 4.79 (m, 2H, H-4,6), 4.70 (dd, J = 6.3, 11.9 Hz, 1H, H-6′).