The product of Step A (204 mg, 1 mmol) is dissolved in toluene (10 mL) with N-trityl-2-aminoimidazole (357 mg, 1.1 mmol) and heated to reflux with a Dean-Stark trap. Four aliquots of toluene (3 mL each) are removed via distillation at 1.5 hour intervals, being replaced by dry toluene each time, and then the solution is left to reflux for 18 hours. The reaction is cooled to room temperature and sodium triacetoxyborohydride (1 gram, 5 mmol) is added in one portion. The reaction is stirred at room temperature for 24 hours, poured into water, and the layers separated. The aqueous layer is extracted with ethyl acetate and the combined organic layers are washed with saturated bicarbonate, water, and brine, dried over magnesium sulfate, concentrated, and purified by flash chromatography to afford the product.
