For the synthesis of compounds 2a, 2c-2g, a slightly modified literature method [1] was used. The procedure was as follows: (S)-2-amino-3-cyclohexylpropanoic acid hydrochloride (32.2 mmol) was dissolved in anhydrous methanol (100 mL) under stirring conditions, and the temperature of the reaction system was maintained between -10 and -5 °C, and thionyl chloride (64.4 mmol) was added slowly dropwise. After the dropwise addition, the reaction mixture was stirred continuously at room temperature for 16 hours. After completion of the reaction, the reaction solution was concentrated to dryness by rotary evaporator. The resulting crude product was dissolved with ethyl acetate (EtOAc) and the solid product was subsequently collected by filtration. The collected solid was dried under reduced pressure to afford (S)-methyl 2-amino-3-cyclohexylpropanoate hydrochloride as a white crystalline powder, all in higher than 80% yield. The melting point of the product and the 1H and 13C NMR spectroscopic data in D2O were in agreement with those reported in the literature [20] for the characterization of the compound.
