The general procedure for the synthesis of benzophenone, (R)-2-amino-3-(2-bromophenyl)propionic acid and (S)-2-amino-3-(2-bromophenyl)propionic acid from 3-(2-bromophenyl)-2-oxopropionic acid and 2,2-diphenylglycine is as follows: to a 5 mL reaction vial equipped with a magnetic stirrer, 3-(2-bromophenyl)-2-oxopropionic acid (0.0510 g , 0.30 mmol), 2,2-diphenylglycine (0.0681 g, 0.30 mmol), chiral pyridoxamine 6 g (0.0195 g, 0.030 mmol), and MeOH-H2O (8:2, 3.0 mL). The reaction mixture was stirred at 20 °C for 3 days. Subsequently, the reaction mixture was transferred to a 25 mL round-bottomed flask and MeOH was added until all solids were completely dissolved. Next, silica gel (0.50 g) was added. After the solvent was removed by concentration under reduced pressure at 20 °C, the resulting residue was separated by silica gel column chromatography (eluent ratio EtOH/Ethyl acetate/25-28% ammonia = 100:58:16) to afford compound 3j (0.0401 g, 78% yield, 52% ee) as a white solid. To determine the enantiomeric excess of 3b-k, it was treated by thionyl chloride in methanol and subsequently converted to N-benzoylmethyl ester by reaction with benzoyl chloride and finally analyzed by HPLC. For the determination of the enantiomeric excess of 3a, it was converted to methyl ester by treatment with CH2N2 in methanol and then analyzed by HPLC.
