To a solution of 1-(((5S,7S)-3-(5-(2-hydroxypropan-2-yl)pyrazin-2-yl)-7-methyl-2-oxo-1-oxa-3-azaspiro[4.5]decan-7-yl)methyl)-1H-benzo[d]imidazole-6-carbonitrile (500 mg, 1.086 mmol, example 147) in ethylene glycol (4.93 mL) was added concentrated H2SO4 (0.5 mL, 9.38 mmol) at RT and heated at 60° C. overnight. The reaction mixture was cooled to RT, diluted with water, and extracted 5×DCM. The combined DCM layers were washed with brine, concentrated, and purified by reverse phase HPLC (Waters Sunfire 30×150 mm column, acetonitrile:water 0.1% TFA long 20-60%, 50 mL/min, 15 min). The product was free based with PL-HCO3 resin SPE to yield 1-(((5S,7S)-3-(5-(2-(2-hydroxyethoxy)propan-2-yl)pyrazin-2-yl)-7-methyl-2-oxo-1-oxa-3-azaspiro[4.5]decan-7-yl)methyl)-1H-benzo[d]imidazole-6-carbonitrile as a white solid (121 mg, 21%). MS (m/z) 505.3 (M+H+).
