[CH3:1][N:2]([CH3:14])[C@H:3]([C:11]([OH:13])=[O:12])[CH2:4][C:5]1[CH:10]=[CH:9][CH:8]=[CH:7][CH:6]=1.Cl.[CH3:16]O>>[CH3:16][O:12][C:11](=[O:13])[C@H:3]([CH2:4][C:5]1[CH:6]=[CH:7][CH:8]=[CH:9][CH:10]=1)[N:2]([CH3:1])[CH3:14]100 ml of methanol and 10 g (0.05 mol) of N,N-dimethylphenylalanine (prepared in accordance with Y. Ikutani, Bull. Chem. Soc. Jpn. 41, 1679 (1968)) are placed in a 350 ml sulfonating flask having an anchor mixer, thermometer, reflux condenser and gas introduction tube and, with stirring, saturated with HCl gas. The solution is stirred at reflux for 8 hours, then cooled, and the solvent is evaporated in a rotary evaporator. The residue is taken up in 250 ml of methylene chloride and washed first with 10% aqueous NaHCO3 solution and then with H2O until neutral. The reaction mixture is then dried over MgSO4, filtered and concentrated by evaporation. The residue is purified by flash chromatography (hexane/ethyl acetate=7:3), yielding 5.0 g of N,N-dimethylphenylalanine methyl ester in the form of a slightly yellow liquid. NMR analysis and IR spectrum agree with the said structure.
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