[NH:1]1[CH2:6][CH2:5][NH:4][CH2:3][CH2:2]1.[Cl:7][C:8]1[CH:9]=[CH:10][C:11]([N:14]2[CH:22]([O:23][C:24]([O:26]C3C=CC=CC=3)=O)[C:21]3[C:16](=[N:17][CH:18]=[CH:19][N:20]=3)[C:15]2=[O:33])=[N:12][CH:13]=1>C(#N)C.C(Cl)Cl>[Cl:7][C:8]1[CH:9]=[CH:10][C:11]([N:14]2[CH:22]([O:23][C:24]([N:1]3[CH2:6][CH2:5][NH:4][CH2:3][CH2:2]3)=[O:26])[C:21]3[C:16](=[N:17][CH:18]=[CH:19][N:20]=3)[C:15]2=[O:33])=[N:12][CH:13]=1Anhydrous piperazine (86 g.) is added to a suspension of 6-(5-chloropyrid-2-yl)-7-oxo-5-phenoxycarbonyloxy-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine (76.4 g.) in acetonitrile (760 cc.). The reaction mixture is stirred for 5 hours at a temperature of about 20° C. and then the insoluble product is filtered off, washed with acetonitrile (3×25 cc.) and with diisopropyl ether (50 cc.). After drying, a product (30.8 g.) is obtained and is dissolved in methylene chloride (750 cc.). A small amount of insoluble matter is removed by treating the solution with decolourising charcoal (2 g.). After filtration, the solution is concentrated to dryness under reduced pressure. 6-(5-Chloropyrid-2-yl)-7-oxo-5-(piperazin-1-yl)carbonyloxy-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine (28.3 g.), which melts at 205° C., is thus obtained.
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