To a solution of the product from Example 9A (0.80 g, 6.8 mmol) and 1H-tetrazole (0.190 g) in THF (7.0 mL) at 0° C. was added dibenzyl diethylphosphoramidite (0.96 mL), and the solution was allowed to warm to room temperature and was stirred for 68 hours. To this solution was added dichloromethane (7.0 mL) and the mixture was cooled to −45° C., followed by addition of m-chloroperbenzoic acid (1.3 g). The mixture was stirred at −45° C. for 1 hour and at room temperature for 1 hour. 10% Na2CO3 was added and the reaction was extracted twice with chloroform. The combined organic layer was dried over MgSO4, filtered and evaporated. The residue was purified by chromatography on silica gel, eluting with a gradient of 50-100% ethyl acetate in chloroform, to give the title compound (0.396 g, 17%).
