(2R)-2-[methyl-[(2-methylpropan-2-yl)oxycarbonyl]amino]butanoic acid

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: To a solution of N-Boc-D-Val-OH (0.678 g, 3.34 mmol) in THF (11.1 mL) at 0° C. was added MeI (2.09 mL, 33.4 mmol, 10.0 equiv). NaH (60%, 1.33 g, 33.4 mmol, 10.0 equiv) was added as a solid to the suspension over a period of 2 hours. After stirring for 12 hours at room temperature, the reaction mixture was diluted with diethyl ether and quenched with water slowly. Aqueous layer was extracted with diethyl ether followed by acidified to pH 3 with 10% citric acid and extraction with ethyl acetate. Combined organic layer was washed with brine, dried with Na2SO4, filtered and concentrated in vacuo to afford compound 3.1a (0.73 g) which was used for the next step without further purification. MS m/z (M+Na) 240.2. 1H NMR (400 MHz, CDCl3) 4.56 and 4.37 (br-s, 1H), 2.83 (br-s, 3H), 2.08-1.92 (m, 1H), 1.85-1.68 (m, 1H), 1.48 (br-s, 9H), 0.96 (t, J=7.38 Hz, 3H). quenched with water slowly Aqueous layer was extracted with diethyl ether by acidified to pH 3 with 10% citric acid and extraction with ethyl acetate Combined organic layer was washed with brine dried with Na2SO4 filtered concentrated in vacuo