Ac2O (377 mg, 1.5 eq) was added dropwised into the solution of (1R,2R,3S,4R,5R,6S)-4-(4-chloro-3-(4-ethylbenzyl)phenyl)-6-(hydroxymethyl)cyclohexane-1,2,3,5-tetraol (5, R=Et, 1 g, 2.46 mmol) and DMAP (cat.) in CH2Cl2 (10 mL) at 0° C. followed by pyridine (292 mg, 1.5 eq), and the mixture was stirred overnight at rt. The reaction mixture was washed with 3N HCl, and the organic layer was combined, dried over Na2SO4, filtered, and the filtrate was evaporated to dryness. The residue was purified by preperative HPLC to give target compound (566 mg, white solid, yield of 50.4%). 1H-NMR (400 MHz, CD3OD): δ 7.32 (1H, d, J=8.4 Hz), 7.06-7.14 (6H, m), 4.37 (2H, ddd, J=2.0, 10.8, 16.8 Hz), 4.04 (2H, s), 3.57 (1H, t, J=10.8 Hz), 3.40-3.47 (1H, m), 2.49-2.60 (3H, m), 2.04 (3H, s), 1.60-1.66 (1H, m), 1.18 (3H, t, J=8.0 Hz); MS (ESI+): 449 [M+H]+, 466 [M+NH4]+, 897 [2M+H]+, (ESI−): 492 [M+HCOO]−, 941 [2M+HCOO]−.
