[F:1][C:2]1[CH:9]=[CH:8][C:5]([CH:6]=O)=[CH:4][CH:3]=1.C([O-])(=O)C.[Na+].C([BH3-])#N.[Na+].Cl.[CH2:20]([O:22][C:23](=[O:31])[CH2:24][CH:25]([NH2:30])[CH2:26][CH:27]([CH3:29])[CH3:28])[CH3:21]>CO>[CH2:20]([O:22][C:23](=[O:31])[CH2:24][CH:25]([NH:30][CH2:6][C:5]1[CH:8]=[CH:9][C:2]([F:1])=[CH:3][CH:4]=1)[CH2:26][CH:27]([CH3:28])[CH3:29])[CH3:21]
4-Fluorobenzaldehyde (0.500 mL, 4.66 mmol), sodium acetate (0.766 g, 9.34 mmol), powdered/activated 4 Å molecular sieves (1.0 g) and sodium cyanoborohydride (0.587 g, 9.34 mmol) were added sequentially to a solution of racemic 3-amino-5-methyl-hexanoic acid ethyl ester hydrochloride (0.979 g, 4.67 mmol) in methanol (25 mL) at 25° C. The mixture was stirred at 25° C. for 22 h, and then was filtered through Celite. The Celite was washed with ethyl acetate (2×30 mL) and the combined filtrate and washings were partitioned between half-saturated aqueous sodium bicarbonate solution (150 mL) and ethyl acetate (2×150 mL). The combined organic layers were dried over sodium sulfate and were concentrated in vacuo. The residue was purified by flash column chromatography (Teledyne Isco RediSep column; 0-80% ethyl acetate in hexanes) to afford rac-3-(4-fluoro-benzylamino)-5-methyl-hexanoic acid ethyl ester (0.616 g, 2.19 mmol, 47%) as a pale yellow oil. 1H NMR (400 MHz, CDCl3) δ: 0.88 (3H, d, J=3.8 Hz), 0.90 (3H, d, J=3.4 Hz), 1.26 (3H, t, J=7.0 Hz), 1.43-1.49 (1H, m), 1.66-1.76 (1H, m), 2.48 (2H, d, J=6.3 Hz), 3.04-3.11 (1H, m), 3.76 (1H, d, J=13.6 Hz), 3.80 (1H, d, J=12.2 Hz), 4.10-4.18 (2H, m), 6.97-7.01 (2H, m), 7.29-7.32 (2H, m).
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