[C:1](Cl)(=[O:5])[O:2][CH2:3][CH3:4].[C:7]([O:11][C:12]([N:14]1[CH2:21][C:20]2[C:19]([NH2:22])=[N:18][NH:17][C:16]=2[CH2:15]1)=[O:13])([CH3:10])([CH3:9])[CH3:8].CCN(C(C)C)C(C)C>C1COCC1>[CH2:3]([O:2][C:1]([N:17]1[C:16]2[CH2:15][N:14]([C:12]([O:11][C:7]([CH3:9])([CH3:8])[CH3:10])=[O:13])[CH2:21][C:20]=2[C:19]([NH2:22])=[N:18]1)=[O:5])[CH3:4]A solution of ethyl chlorocarbonate (8.9 ml, 93 mmol) in THF (250 ml) was added slowly to a mixture of 3-amino-4,6-dihydro-1H-pyrrolo[3,4-c]pyrazole-5-carboxylic acid tert-butyl ester (20 g, 89 mmol) and DIEA (92 ml, 528 mmol) in THF (500 ml) at 0-5° C. The reaction was kept at the same temperature for two hours then allowed to reach r.t. and stirred overnight. The obtained mixture was evaporated to dryness under vacuum. The resulting residue was extracted with AcOEt and water. The organic phase was separated, dried over sodium sulfate and evaporated to dryness. The mixture was purified by flash-chromatography (eluent: ethyl acetate/cyclohexane 4/6 to 7/3) to give 19 g (72% yield) of the title compound as a white solid.
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