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General procedure for the synthesis of Z-L-methionine from D-methionine and benzyl chloroformate: (2R)-2-Amino-4-(methylthioalkyl)butyric acid (4.90 g, 32.84 mmol) and sodium carbonate (16.91 g, 159.54 mmol) were dissolved in water (100 mL) at room temperature. Subsequently, a solution of benzyl chloroformate (5.59 g, 32.74 mmol) in dioxane (50 mL) was added slowly and dropwise over 10 minutes. The resulting reaction mixture was stirred at room temperature for 5 hours. Upon completion of the reaction, the reaction was quenched by the addition of water (100 mL). The reaction mixture was extracted with ethyl acetate (300 mL x 3) and the organic phases were combined, washed with brine and dried over anhydrous sodium sulfate. The solvent was removed by concentration under reduced pressure and the residue was purified by chromatography on a C18 reversed-phase column using gradient elution with aqueous acetonitrile (0 to 50% acetonitrile, 30 min) to afford (2R)-2-[[(benzyloxy)carbonyl]amino]-4-(methylsulfanyl)butanoic acid as a yellow oil (3.48 g, 36% yield).