Reaction Steps
The trichloroacetimidate 62 (300 mg, 0.221 mmol), cholestanol (2 eq, 172 mg, 0.442 mmol) and 3 Å molecular sieves (100 mg) were stirred in dry DCM (1.5 mL) for 0.5 h. A solution TMS-triflate in dry DCM (0.5 eq., 0.4 M, 0.275 mL, 0.11 mmol,) was added dropwise at 0° C. After 30 min at r.t. another portion of TMS-triflate in dry DCM (0.36 eq., 0.4 M, 0.2 mL, 0.08 mmol) was added and stirring continued for 30 min at r.t. The reaction was quenched by adding Et3N (0.025 mL) at 0° C. for 10 min, filtered through a plug of celite (0.5 cm), washed with DCM (5×25 mL) and EtOAc (3×25 mL). Both organic phases were washed separately with satd. NaHCO3-solution (3×25 mL) and brine (25 mL). Aqueous extracts were combined and re-extracted with EtOAc (3×30 mL), washed with brine (30 mL), combined with the other organic extracts, dried (Na2SO4) and concentrated in vacuo to afford the crude yellow foam (480 mg). The product was purified on a column of silica gel (30×5 cm, toluene:EtOAc 3:2→1:1→1:2→EtOAc, containing 0.2% Et3N (v/v)). The purification resulted in the desired β-linked glycoside 63 in fraction A as a white foam (81 mg, 23%) and fraction B containing 77% partially deacetylated α-linked glycoside and 23% partially deacetylated β-linked glycoside (118 mg). 1H NMR (CDCl3, 400 MHz) δ 5.24-5.45 (m, 7H, 3×H1,4×H3), 5.08 (t, 3H, JH3-H4=JH4-H5 9.80, H4III,) 4.86 (dd, 1H, JHI-H2=4.1, JH2-H3=10.4, H2IIII), 4.70-4.80 (m, 3H, 3×H2), 4.63 (d, 1H, JHI-H2=7.7, H1I), 4.33-4.54 (m, 4H, 4×H6), 3.86-4.31 (m, 10H, 3×H4, 3×H5, 4×H6), 3.70 (ddd, 1H, H5I), 3.56 (m, 1H, cholesteryl-H3), 2.20, 2.19, 2.16, 2.11, 2.07, 2.04, 2.03, 2.02, 2.015, 2.010, 2.00, 1.99 (s, 39H, 13×Ac), 0.55-2.00 (m, 33H, 12CH2, 9CH), 0.90 (d, 3H, J=6.6, cholestanyl-CH3), 0.871 (d, 3H, J=6.6, cholestanyl-CH3), 0.867 (d, 3H, J=6.6, cholestanyl-CH3), 0.78 (s, 3H, cholestanyl-CH3), 0.65 (s, 3H, cholestanyl-CH3).
