Cesium carbonate (29.3 mg, 0.090 mmol) was added to a stirred, room temperature mixture of chloromethyl methyl (3S,3aS,6R,6aS)-6-(nitrooxy)hexahydrofuro[3,2-b]furan-3-yl phosphate (30 mg, 0.090 mmol) and 2-butyl-4-chloro-1-{[2′-(1-trityl-1H-tetrazol-5-yl)biphenyl-4-yl]methyl}-1H-imidazole-5-carboxylic acid (Intermediate 4, 61.1 mg, 0.090 mmol) in N,N-dimethylformamide and the mixture was stirred at room temperature for overnight. The reaction was cooled, quenched with water and extracted with ethyl acetate. The organic phase was washed with saturated brine, dried (sodium sulfate), filtered and concentrated in vacuo. Chromatography over silica, eluting with 40-100% ethyl acetate/hexane afforded the separated diastereomers.
