(S)-mandelic acid → (1R,2S,3R,4S)-3-ethoxycarbonyl-bicyclo[2.2.1]hept-2-yl-ammonium (S)-alpha-hydroxyphenylacetate

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In order to determine the enantiomeric excess, (1S,2R,3S,4R)-3-amino-bicyclo[2.2.1]heptane-2-carboxylic acid ethyl ester was derivatized to the (S)-mandelate salt as follows: To a solution of (1S,2R,3S,4R)-3-amino-bicyclo[2.2.1]heptane-2-carboxylic acid ethyl ester (34.2 mg, 0.187 mmol) in ethyl acetate (1 mL) was added (S)-α-hydroxyphenylacetic acid (28.7 mg, 0.187 mmol) and the mixture was stirred at 25° C. for 0.5 h. The solid was filtered and dried under high vacuum to afford (1R,2S,3R,4S)-3-ethoxycarbonyl-bicyclo[2.2.1]hept-2-yl-aminium (S)-α-hydroxyphenylacetate (11.4 mg, 0.034 mmol, 18%, de=97%), as a white solid. 1H NMR (400 MHz, CDCl3) 1.08-1.20 (3H, m), 1.28 (3H, t, J=7.1 Hz), 1.50-1.59 (2H, m), 1.79 (1H, d, J=10.9 Hz), 2.23 (1H, s), 2.46-2.48 (2H, m), 3.04 (1H, d, J=7.8 Hz), 4.05-4.18 (2H, m), 4.89 (1H, s), 5.49 (3H, bs), 7.22-7.31 (3H, m), 7.43 (2H, d, J=6.9 Hz).

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