Dissolve 2-(S)-(2-cyclohexylethyl)-5-(S)-hydroxymethylmorpholine-4-carboxylic acid tert-butyl ester (165 mg, 0.50 mmol) in dimethylsulfoxide (2 mL), and cool to 10° C. Add triethylamine (0.28 mL, 2.02 mmol) followed by pyridine sulfur trioxide complex and stir for 30 min. Dilute with ethyl acetate and pour into cold water. Wash with 5% citric acid (50 mL), saturated aqueous sodium chloride (50 mL) and dry (sodium sulfate), filter and concentrate give the desired compound as an oil which is used without further purification.
