Tetrahydrofuran → (1S)-(4-{[5-tert-butoxycarbonylamino-1-(diethoxyphosphoryloxymethyl)-pentyl]isobutyl-sulfamoyl}-phenyl)-carbamic acid tert-butyl ester

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Reaction Steps

2.00 g (3.7 mmol) (1S)-{4-[(5-tert-butoxycarbonylamino-1-hydroxymethyl-pentyl)-isobutyl-sulfamoyl]-phenyl}-carbamic acid tert-butyl ester (VII) (example 1, step D) is dissolved in 0.63 mL triethylphosphate and 10 mL THF at 0° C. under inert argon atmosphere. 0.63 mL (4.44 mmol) diethylchlorophosphate is added and then 0.25 g (6.2 mmol), NaH 60% in oil is added in portionwise. The mixture is allowed to warm to room temperature and left to stir for 2 h (LC-MS showed completion after 1 h). To the solution is added 20 mL of Amberlite XAD-2 resin and the slurry thoroughly mixed and added to 200 mL ice water. After stirring for 15 min. the resin suspension is filtered and the resin washed several times with distilled water (500 mL). The desired product is desorbed from the resin with acetone (5×50 mL), EtOAc (5×50 mL), the organic phase is then dried over Na2SO4. After evaporation of the solvent 2.66 g (89%) of clear oil is obtained. The crude product contains a fraction with two diethyl phosphates and is used as is in the next step.

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