4-Fluorobenzenesulfonyl chloride → (R)-2-(4-fluoro-benzenesulfonylamino)-4-methyl-pentanoic acid

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A mixture of 4-fluoro-benzenesulfonyl chloride (1.65 g, 0.00848 mol), (R)-2-amino-4-methyl-pentanoic acid (1.233 g, 0.009398 mol), and sodium carbonate (1.91 g, 0.0180 mol) in water (15 mL) was stirred at room temperature for 5 days. The solution was filtered, and the filtrate was acidified with concentrated hydrochloric acid to pH=4. The mixture was extracted with ethyl acetate. The extract was washed with saturated sodium chloride, dried (MgSO4), and rotary evaporated to a yellow oil. The oil was chromatographed on silica gel (320 g, 230-400 mesh) eluting with dichloromethane-methanol (10:1, 10×300 mL). Fractions containing product were combined and rotary evaporated to give a pale yellow oil. The oil was dried in vacuo; yield 1.44 g (59%). 1H-NMR (DMSO-d6): δ8.1 (br s, 1H), 7.80 (m, 2H), 7.38 (m, 2H), 3.55 (t, 1H), 3.33 (br s, H2O),1.56 (m, 1H), 1.36 (dd, 2H), 0.75 (dd, 6H).

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