To a 1000 ml round bottom flask under N2 was added (5S)-1-{(2R)-2-(cyclopentylmethyl)-4-[(1,1-dimethylethyl)oxy]-4-oxobutanoyl}-4,5-dihydro-1H-pyrazole-5-carboxylic acid (27.7 g, 79 mmol) in dichloromethane (DCM) (700 mL) at 0° C., followed by 2-pyridinamine (14.79 g, 157 mmol), DIPEA (68.6 mL, 393 mmol), 3H-[1,2,3]triazolo[4,5-b]pyridin-3-ol (21.40 g, 157 mmol) and EDC (30.1 g, 157 mmol). The mixture was allowed to warm up to room temperature and stirring continued overnight. LCMS showed that the desired product was ˜56%. After another 24 h, LCMS indicated no starting material left. The organic solution was washed with water (300 mL), 10% citric acid (2×300 mL) and brine, dried (Na2SO4), filtered, and concentrated to afford 1,1-dimethylethyl (3R)-3-(cyclopentylmethyl)-4-oxo-4-{(5S)-5-[(2-pyridinylamino)carbonyl]-4,5-dihydro-1H-pyrazol-1-yl}butanoate (29.1 g, 58.4 mmol, 74% yield) as a brown gummy solid. LCMS: [M+H]+: 429.2.
