[C:1]([O:5][C:6]([NH:8][C@H:9]([CH3:12])[CH2:10][OH:11])=[O:7])([CH3:4])([CH3:3])[CH3:2].C(N(C(C)C)CC)(C)C.[CH3:22][S:23](Cl)(=[O:25])=[O:24]>ClCCl>[C:1]([O:5][C:6]([NH:8][C@H:9]([CH3:12])[CH2:10][O:11][S:23]([CH3:22])(=[O:25])=[O:24])=[O:7])([CH3:4])([CH3:3])[CH3:2]A solution of 22.0 gm (125.6 mMol) (R)-N-tert-butoxycarbonyl-2-amino-1-propanol and 19.5 gm (150.7 mmol) diisopropylethylamine in 450 mL dichloromethane was cooled to 0° C. To this solution was added dropwise 10.7 mL (138.2 mMol) methanesulfonyl chloride at a rate to maintain the temperature of the reaction mixture at from 0° C. to 10° C. Once the addition was complete the reaction mixture was stirred at 0° C. for about one hour. The reaction mixture was washed twice with 200 mL portions of water, once with 200 mL saturated aqueous sodium chloride, dried over magnesium sulfate and concentrated under reduced pressure. The residue was subjected to silica gel chromatography, eluting with 1:1 hexane:ethyl acetate. Fractions containing product were combined and concentrated under reduced pressure. The residue was crystallized from hexane and ethyl acetate to provide 19.4 gm (61%) of the desired compound in two crops (m.p.=65–68° C.)
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