Reaction Steps
A solution of the alcohol 50 (424 mg, 0.401 mmol) and 2,3,4,6-tetra-O-benzoyl-α-D-mannopyranosyl trichloroacetimidate (357 mg, 0.481 mmol, 1.2 eq) in anhydrous DCM (7.5 mL) was stirred with powdered molecular sieves 3 Å (50 mg) at 0° C. for 1 h. A solution of TMSOTf (15 μL, 0.0802 mmol, 0.2 eq) in DCM (0.5 mL) was added dropwise via a syringe. The mixture was stirred at 0° C. for 2 h and TLC indicated complete conversion. Et3N (100 μL) was added. Pyridine (65 μL, 0.802 mmol) and benzoyl chloride (47 μL, 0.401 mmol) were added. The mixture was stirred at room temperature o/n and evaporated onto silica gel. Purification by column chromatography (silica 2.5×17 cm, gradient elution with hexane-EtOAc 210:30, 200:50, 180:60, 160:80 and 150:100) gave the trisaccharide 51 as a colourless gum (392 mg, 60%). 1H NMR (CDCl3, 400 MHz) δ 8.19-7.89 (m, 16H, Ph), 7.68-7.63 (m, 4H, Ph), 7.61-7.15 (m, 35H, Ph), 6.00 (dd or t, 1H, JH3-H4=10.7, JH4-H5=9.8, H4), 5.98 (dd or t, 1H, JH3-H4=9.8, J=9.8, H4), 5.92 (dd or t, 1H, J=10.7, J=9.8, H4), 5.72 (dd, 1H, JH1-H2=2.0, JH2-H3=3.9, H2), 5.56 (dd, 1H, JH2-H3=2.9, H3), 5.33 (d, 1H, J=2.0, H1), 5.26 (dd, 1H, J=2.0, H2), 5.19 (d, 1H, J=2.0, J=3.9, H2), 5.16 (d, 1H, J=2.0, H1), 4.90 (d, 1H, H1), 4.78 and 4.62 (AB quartet, 2H, Jgem=11.7, CH2), 4.65-4.56 (m, 3H), 4.45 (dd, 1H, Jgem=12.7, JH5-H6=3.9, H6), 4.35 (dd, 1H, H3), 4.34-4.28 (m, 2H), 4.24 (dd, 1H, J=12.7, JH5-H6=2.9, H6), 4.10 (dt or dm, 1H, H5), 4.01 (dd, 1H, J=12.7, H6), 3.95 (dd, 1H, JH5-H6=2.0, H6).
