The deuteration flask (6 mL) was charged with intermediate 3 (0.101 mmol, 28 mg), 10% Pd/C (14 mg), Et3N (0.151 mmol, 21 µL, 1.5 eq.), and MeOD-d4 (2 mL). The flask was connected to a deuteration manifold, and the mixture was degassed three times using the freeze-thaw method. Deuterium gas (390 mbar) was introduced into the reaction flask. The frozen solution was warmed to room temperature (1150 mbar). The reaction was stirred vigorously at room temperature for 6 h. Then, the catalyst was removed by a syringe PTFE filter, and the solvent was evaporated under vacuum. The reaction was repeated six times. All reaction mixtures were mixed, and the crude product was purified by reverse phase flash chromatography (a gradient from 5% to 60 % of MeCN during 25 min). The solvent was evaporated, and the white solid 95 mg (78.7%) was isolated. The pure product was dissolved in EtOH (10 mL) and HCl was added gradually. The temperature of the solution was kept at 5 °C throughout. HCl was added until the pH of the solution was 3. The reaction mixture was stirred for 5 min. The solvent was evaporated under reduced pressure. The desired product 7 was identified by 1 H and 13 C NMR and by MS. Deuterium enrichment (> 0.97 atom D per molecule) was determined from the mass spectrum.