A solution of acrylic acid (1.19 g.) in anhydrous methylene chloride (10 cc.) followed by a solution of N,N'-dicyclohexylcarbodiimide (3.4 g.) in anhydrous methylene chloride (30 cc.) are added successively, at a temperature of about 20° C., to a suspension of 6-(5-chloropyrid-2-yl)-7-oxo-5-(piperazin-1-yl)carbonyloxy-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine (5.6 g.) in anhydrous methylene chloride (100 cc.). The mixture is stirred for 1 hour at a temperature of about 20° C. The insoluble product (dicyclohexylurea) is filtered off and washed with methylene chloride (2×10 cc.). The filtrate is concentrated to dryness under reduced pressure and then the residue obtained is taken up in ethyl acetate (25 cc.) and a small amount of insoluble matter is filtered off. The filtrate is left to stand for 18 hours at a temperature of about 20° C. and the product which has crystallised is filtered off and washed with ethyl acetate (3×2 cc.). After drying, the product obtained (4.9 g.) is dissolved in methylene chloride (100 cc.). The solution is filtered through silica gel (100 g.) contained in a column of diameter 3 cm. Elution is carried out using pure methylene chloride (400 cc.), a mixture of methylene chloride and methanol (99-1 by volume; 300 cc.) and a mixture of methylene chloride and methanol (98-2 by volume; 300 cc.). These eluates are discarded. Elution is then carried out using a mixture of methylene chloride and methanol (98-2 by volume; 200 cc.) and the corresponding eluates are combined and concentrated to dryness under reduced pressure (20 mm.Hg). After recrystallisation from acetonitrile and drying, a product (2.3 g.), which is solvated with acetonitrile, is obtained. This product is dissolved in dimethylformamide (37 cc.) at a temperature of about 50° C. and the solution is poured into ice-water (370 cc.). The insoluble product is filtered off and washed with water (3×10 cc.). After drying, 5-(4-acryloylpiperazin-1-yl)carbonyloxy-6-(5-chloropyrid-2-yl)-7-oxo-6,7-dihydro-5H-pyrrolo[3,4-b]pyrazine hydrate (2.08 g.), which melts at about 202°-204° C., is obtained.
