(2R)-3-(tert-butyldisulfanyl)-2-[(2-methylpropan-2-yl)oxycarbonylamino]propanoic acid

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: N-Boc-Cys(StBu)-OH 9 (1.00 g, 3.23 mmol) was dissolved in dry dichloromethane (25 mL) followed by the addition of EDC (0.75 g, 3.87 mmol), HOBt (0.53 g, 3.87 mmol), NMM (1.77 mL, 16.15 mmol) and glycine methyl ester hydrochloride (0.61 g, 4.84 mmol) at 0° C. under argon. The reaction mixture was then allowed to warm to room temperature and stirred overnight. After evaporation of solvent, the residue obtained was taken in EtOAc (35 mL), washed with 20% citric acid solution (2 30 mL), sat. NaHCO3 (20 mL), brine and dried over MgSO4. The EtOAc layer was evaporated in vacuo and resulting crude product was purified by flash silica gel column chromatography to get the dipeptide product 12 as white foam (1.09 g, 89% yield). 1H NMR (300 MHz, CDCl3) δ7.35, 5.81 (2H), 4.44 (1H), 3.82 (2H), 3.61 (3H), 3.02-2.83 (2H), 1.43, 1.28 (18H); 13C NMR (75 MHz, CDCl3) δ171.2, 169.9, 155.5, 80.0, 53.5, 52.3, 48.0, 41.4, 37.9, 30.0, 28.5; ESI-LRMS m/z 380.5 (M+H)+. After evaporation of solvent the residue obtained washed with 20% citric acid solution (2 30 mL), sat. NaHCO3 (20 mL), brine dried over MgSO4 The EtOAc layer was evaporated in vacuo resulting crude product was purified by flash silica gel column chromatography

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: O-(7-Azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU) (2.52 g, 6.62 mmol), benzylamine (0.723 ml, 6.62 mmol) and N,N-diisopropylethylamine (1.153 ml, 6.62 mmol) were added to a solution of (R)-2-((tert-butoxycarbonyl)amino)-3-(tert-butyldisulfanyl)propanoic acid (Compound tk91) (1.95 g, 6.30 mmol) in tetrahydrofuran (20 ml), and the reaction solution was stirred at room temperature for 2 hours. The reaction solution was concentrated under reduced pressure, and the resulting residue was purified by normal-phase silica gel column chromatography (hexane/ethyl acetate) to afford (R)-tert-butyl(1-(benzylamino)-3-(tert-butyldisulfanyl)-1-oxopropan-2-yl)carbamate (Compound tk92) (2.357 g, 5.91 mmol, 94%). The reaction solution was concentrated under reduced pressure the resulting residue was purified by normal-phase silica gel column chromatography (hexane/ethyl acetate)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: 2-Bromoacetonitrile (0.473 ml, 6.78 mmol) and N-ethyl-N-isopropylpropan-2-amine (0.444 ml, 2.49 mmol) were added to a solution of (R)-2-((tert-butoxycarbonyl)amino)-3-(tert-butyldisulfanyl)propanoic acid (Compound 2k-A) (700 mg, 2.26 mmol) in DMF (5 ml), and the mixture was stirred at room temperature for 10 minutes. A saturated aqueous ammonium chloride solution (1 ml) was added to the reaction mixture, after which the mixture was extracted with ethyl acetate and the organic layer was washed with water. The organic extract was then dried over magnesium sulfate. Following concentration under reduced pressure, the resulting residue was purified by silica gel column chromatography (hexane/ethyl acetate=100/0→70/30) to afford (R)-cyanomethyl 2-((tert-butoxycarbonyl)amino)-3-(tert-butyldisulfanyl)propanoate (Compound 21-A) (748 mg, 95%). after which the mixture was extracted with ethyl acetate the organic layer was washed with water The organic extract was then dried over magnesium sulfate concentration under reduced pressure the resulting residue was purified by silica gel column chromatography (hexane/ethyl acetate=100/0→70/30)

Conditions: temp:0.00; pressure:0.00; stir:; See reaction.notes.procedure_details.

Procedure: N-Boc-Cys(StBu)-OH 9 (1.00 g, 3.23 mmol) was dissolved in dry dichloromethane (25 mL) followed by the addition of EDC (0.75 g, 3.87 mmol), HOBt (0.53 g, 3.87 mmol), NMM (1.77 mL, 16.15 mmol) and glycine methyl ester hydrochloride (0.61 g, 4.84 mmol) at 0° C. under argon. The reaction mixture was then allowed to warm to room temperature and stirred overnight. After evaporation of solvent, the residue obtained was taken in EtOAc (35 mL), washed with 20% citric acid solution (2 30 mL), sat. NaHCO3 (20 mL), brine and dried over MgSO4. The EtOAc layer was evaporated in vacuo and resulting crude product was purified by flash silica gel column chromatography to get the dipeptide product 12 as white foam (1.09 g, 89% yield). 1H NMR (300 MHz, CDCl3) δ7.35, 5.81 (2H), 4.44 (1H), 3.82 (2H), 3.61 (3H), 3.02-2.83 (2H), 1.43, 1.28 (18H); 13C NMR (75 MHz, CDCl3) δ171.2, 169.9, 155.5, 80.0, 53.5, 52.3, 48.0, 41.4, 37.9, 30.0, 28.5; ESI-LRMS m/z 380.5 (M+H)+. After evaporation of solvent the residue obtained washed with 20% citric acid solution (2 30 mL), sat. NaHCO3 (20 mL), brine dried over MgSO4 The EtOAc layer was evaporated in vacuo resulting crude product was purified by flash silica gel column chromatography