[C:1]([O:5][C:6]([NH:8][CH:9]([C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)[CH2:10][C:11](O)=[O:12])=[O:7])([CH3:4])([CH3:3])[CH3:2].ClC(OC)=O.[BH4-].[Na+].Cl>O1CCCC1.C(N(CC)CC)C>[C:1]([O:5][C:6](=[O:7])[NH:8][CH:9]([C:14]1[CH:19]=[CH:18][CH:17]=[CH:16][CH:15]=1)[CH2:10][CH2:11][OH:12])([CH3:4])([CH3:2])[CH3:3]
To a 17.9 mmol suspension of 3-(tert-butoxycarbonylamino)-3-phenylpropanoic acid (Formula 10) in tetrahydrofuran (THF) at 0° C. was added 2.74 mL of triethyl amine and 1.52 mL of methyl chloroformate. The mixture was stirred at 0° C. for 15 minutes. Next, the white solid formed was filtered off and washed with 10 mL of THF. The filtrate was added drop-wise to 8.4 mL of 26.8 mmol sodium borohydride at 0° C. and stirred for 30 min. The mixture was then stirred at room temperature for 2 hr. Ten percent hydrochloric acid (HCl) was added until a pH of 2 was reached, and then was extracted using ethyl acetate. The resulting combined ethyl acetate layers were washed with sodium carbonate, water, brine, and concentrated. Column chromatography (50% ethyl acetate/hexane) gave 1.63 g (36%) of the title compound as a colorless oil. The aqueous phase was acidified with HCl and extracted with ethyl acetate to recover 2 g of 3-(tert-butoxycarbonylamino)-3-phenylpropanoic acid. 1H NMR (300 MHz, CDCl3) δ 1.45 (s, 9H), 1.62-1.63 (m, 1H), 1.79-1.87 (m, 1H), 3.68-3.74 (m, 2H), 5.23 (br, 1H), 5.32 (br, 1H), 7.26-7.38 (m, 5H).
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