To a solution of Example 46 (1.03 g, 2.65 mmol) in dimethylformamide (5 ml) was added imidazole (361 mg, 5.30 mmol), followed by tert-butyldimethylchlorosilane (600 mg, 3.97 mmol). The solution was stirred at room temperature for 4 days. The reaction mixture was partitioned between ethyl acetate and water and the aqueous phase was further extracted with ethyl acetate. The combined organic phases were dried over anhydrous magnesium sulphate, filtered and evaporated under reduced pressure to give a yellow oil. The crude product was purified by flash chromatography on silica gel eluting with cyclohexane:ethyl acetate (20:1, by volume), followed by cyclohexane:ethyl actetate (5:1, by volume) to afford the title compound (1.1 g) as a white powder, m.p. 83-84° C.
