in DMSO (8 mL). The reaction mixture was stirred at r.t. for 20 hours. The mixture was poured into a separating funnel and water (100 mL) was added. The mixture was extracted with diethyl ether (3 × 50 mL), the organic layer was dried over MgSO4. The residue was purified using silica gel column chromatography (hexane:EA, 9:1) to afford the desired compound 3 as a white solid (360 mg, 50 %). The protected DL-Tfm (500 mg, 1.27 mmol) was dissolved in DCM (25 mL). TFA (5 mL) was added dropwise to the solution and the reaction mixture was stirred at r.t. for 3 hours. After the completion of reaction, the solvent was removed under reduced pressure to yield a white powder. This was redissolved in THF (12.5 mL) and water (12.5 mL). Lithium hydroxide monohydrate (2.08 g) was added to the solution and the reaction mixture was stirred at r.t. for 3 hours, after which the solution was neutralized with DOWEX 50WX8 (H+) until pH < 3. The suspension was poured into an empty column and washed with water (5 CV, gravity flow). The flow-through was discarded and the column was eluted with 5% NH4OH. The eluent fractions containing the product were pooled and concentrated under reduced pressure. The compound was dissolved in water and lyophilized to afford the desired compound 4 as a white powder (233 mg, 90 % yield). Method B: Synthesis of L-Tfm from L-homocystine using Togni's reagent