Hydrochloric Acid → (S)-2-(dibenzylamino)pentanoic acid

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The crude (S)-benzyl 2-(dibenzylamino)pentanoate (3) (2.2 Kg) was dissolved in methanol (5.5 L). A previously prepared, cold (0-5° C.) solution of sodium hydroxide (568 g; 14.2 mol) in water (6 L) was added to the solution of (3), and the resulting mixture heated at 90° C. for 20 hours. The reaction mixture was then allowed to cool to ambient temperature, and the methanol evaporated under reduced pressure. The residue was diluted with water (25 L), and extracted with methyl t-butyl ether/hexane (1:1; 2×5 L) to remove the benzyl alcohol formed in the hydrolysis. The basic aqueous layer was acidified to pH 2 with 6M aqueous hydrochloric acid (4 L), then extracted with ethyl acetate (2×8 L). The combined organic extracts were dried over sodium sulfate and the solvent removed under reduced pressure, to afford a semi solid, which was washed with hexanes (8 L) to provide 1.12 Kg of (S)-2-(dibenzylamino)pentanoic acid, a compound of formula (4), as a white solid.

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