Example 5 Synthesis of L-2-tert-butoxycarbonylamino-3,3-diphenylpropionic acid: L-2-amino-3,3-diphenylpropionic acid (0.10 g, 0.28 mmol, 92.9% ee) was dissolved in water, and the pH was adjusted to 8-9 with sodium bicarbonate. ethyl acetate (1.0 mL) and di-tert-butyl dicarbonate (0.1 g, 0.45 mmol) were added and the reaction mixture was stirred at 37°C for 16 hours. Upon completion of the reaction, it was cooled to room temperature, the pH was adjusted to 2 with 6N hydrochloric acid, and partition extraction was performed to transfer N-tert-butoxycarbonyl-3-phenyl-L-phenylalanine to the organic layer. The organic layer was concentrated and heptane was added to the residue and stirred overnight to promote crystallization. The crystals were collected by filtration and dried to give N-Boc-3-phenyl-L-phenylalanine (97% ee, chiral column SUMICHIRAL OA-4100, mobile phase: hexane: methanol: 2-propanol: trifluoroacetic acid = 98:1:1:0.1, detection wavelength 220 nm, flow rate 1.0 mL/min, room temperature).
