A suspension of 7-chloro-6-phenyl-1,2,3,4-tetrahydropyrrolo[1,2-a]pyrazine-8-carboxylic acid amide trifluoroacetic acid salt (100 mg, Reference Example 1) in dry dichloromethane (10 mL) was treated with dry triethylamine (0.11 mL), then with a solution of 3-cyclohexylpropionyl chloride (45 mg) in dry dichloromethane (5 mL). After stirring at room temperature overnight the reaction mixture was washed with water, then the organic phase was dried over magnesium sulfate and evaporated. The residue was subjected to column chromatography on silica eluting with a mixture of methanol and dichloromethane (1:19, v/v) to give 7-chloro-2-(3-cyclohexylpropionyl)-6-phenyl-1,2,3,4-tetrahydropyrrolo [1,2-a]pyrazine-8-carboxylic acid amide (80 mg) as a white solid, m.p. 181–182° C. MS: 416 [MH]+, 414 [MH]+.
