Hydrochloric Acid → (R)-7-[3-tert-butoxycarbonylamino-4-(2,4,5-trifluoro-phenyl)-butyryl]-3-trifluoromethyl-5,6,7,8-tetrahydro-imidazo[1,5-a]pyrazine-1-carboxylic acid

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(R)-7-[3-tert-Butoxycarbonylamino-4-(2,4,5-trifluoro-phenyl)-butyryl]-3-trifluoromethyl-5,6,7,8-tetrahydro-imidazo[1,5-a]pyrazine-1-carboxylic acid methyl ester 1n (2.0 g, 3.5 mmol) was dissolved in 50 mL of methanol under stirring, and 4 N sodium hydroxide solution (30 mL) was added to the solution. The reaction mixture was reacted at room temperature for an hour until thin lay chromatography showed the starting material disappeared, and was adjusted to pH 3 with a 2 N hydrochloric acid solution. The reaction mixture was extracted with ethyl acetate (50 mL×4), and the combined organic phase was dried over anhydrous magnesium sulfate, filtered, and concentrated under reduced pressure to obtain the title compound (R)-7-[3-tert-butoxycarbonylamino-4-(2,4,5-trifluoro-phenyl)-butyryl]-3-trifluoromethyl-5,6,7,8-tetrahydro-imidazo[1,5-a]pyrazine-1-carboxylic acid 2a (1.9 g) as a light yellow solid.

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