Hydrochloric Acid → (2R)-2-Phenylcarbonyloxypropyl (2S)-2-Amino-3-(3,4-dihydroxyphenyl)propanoate Hydrochloride

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A solution of (2R)-2-phenylcarbonyloxypropyl (2S)-2-(tert-butoxycarbonyl)amino-3-(3,4-dihydroxyphenyl)propanoate 1c (6.3 g, 13.7 mmol) in 50 mL of 4N HCl in dioxane was stirred at room temperature for 30 min. The mixture was concentrated to dryness under reduced pressure. The resulting residue was dissolved in ca. 20 mL of anhydrous acetonitrile and 4 mL of ether. The solution was refrigerated, and the resulting white precipitate was filtered, washed with ether, and dried under vacuum to afford 4.7 g (87% yield) of the hydrochloride salt 1d as a white solid. 1H NMR (400 MHz, CD3OD): δ 1.40 (d, J=6.4 Hz, 3H), 2.99 (dd, J=7.6, 14.4 Hz, 1H), 3.10 (dd, J=5.6, 14.4 Hz, 1H), 4.24 (dd, J=6, 8 Hz, 1H), 4.38 (dd, J=6.8, 11.6 Hz, 1H), 4.52 (dd, J=3.2, 11.6 Hz, 1H), 5.40 (m, 1H), 6.52 (dd, J=2.2, 8.4 Hz, 1H), 6.66 (d, J=2.2 Hz, 1H), 6.69 (d, J=8.2 Hz, 1H), 7.47 (t, J=7.6 Hz, 2H), 7.60 (t, J=7.6 Hz, 1H), 8.02 (d, J=7.6 Hz, 2H). MS (ESI) m/z 360.15 (M+H)+ and 358.09 (M−H)−.

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