To a stirred solution of 3-{[isobutyl(methyl)amino]methyl}-5-methylbenzoic acid (110 mg, 0.48 mmol) in methylene chloride (3 mL) is added HBTU (273 mg, 0.72 mmol), HOBt (97 mg, 0.72 mmol), and N,N -diisopropylethylamine (0.243 mL, 1.44 mmol), followed by (2R,3S)-3-amino-4-(3,5-difluorophenyl)-1-[(3-ethylbenzyl)amino]butan-2-ol prepared by the method of Example SP-272 (196 mg, 0.48 mmol), and the reaction mixture is stirred for 12 h at room temperature. The reaction mixture is diluted with methylene chloride, washed with water, and saturated sodium bicarbonate, dried (magnesium sulfate), filtered, and concentrated under reduced pressure. Purification by flash column chromatography (silica, 10% methanol/chloroform) affords a clear oil, which is dissolved in methanol (2 mL). To this solution is added hydrochloric acid (5 mL, 4 N dioxane, 20 mmol), and the reaction mixture is stirred for 1 h at room temperature. The reaction mixture is then diluted with ethyl ether (10 mL). The precipitate that is formed is collected by filtration to provide the title compound. ESI MS m/z 552.5 [M+H]+.
