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 2 (6.3 g, 13.7 mmol) in 50 mL of 4N HCl in dioxane was stirred at room temperature for 30 min. The reaction mixture was concentrated to dryness under reduced pressure. The resulting residue was dissolved in about 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 3 as a white solid. 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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