Acetic Acid → (2R)-3-benzyloxy-2-(N-(4-fluorobenzyl)amino)propanoic acid methyl ester

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A solution of (2R)-3-benzyloxy-2-aminopropanoic acid methyl ester (19 g, 78 mmol) in methanol (350 mL) under N2 was cooled to 0° C. and acetic acid (2 g, pH 2) was added, followed by the addition of 4-fluorobenzaldehyde, a compound of formula (N) (12.5 mL, 117 mmol) and sodium cyanoborohydride (7.3 g, 117 mmol) and 3 A molecular sieves (15 g). The resulting mixture was stirred at ambient temperature for 3 hours, then filtered through Celite (MeOH). The filtrate was concentrated in vacuo to afford a clear liquid. This was taken up in ethyl acetate and washed sequentially with 10% aqueous Na2CO3 solution, water, then brine. The organic phase was then dried over MgSO4, filtered, and concentrated in vacuo. Purification by flash column chromatography on silica gel afforded 14.7 g (60% yield) of (2R)-3-benzyloxy-2-(N-(4-fluorobenzyl)amino)propanoic acid methyl ester, a compound of formula (O), as a clear, colorless oil; NMR (CDCl3) 7.4-7.2 (m, 7), 7.0 (dd, 2), 4.5 (d, 2), 3.9-3.5 (m, 8) ppm, MS (LSIMS) 317.

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