[H-].[Na+].[CH:3]1[N:7]2[C:8]3[CH2:19][C:18]4[CH:17]=[CH:16][CH:15]=[CH:14][C:13]=4[C:9]=3[NH:10][C:11](=[O:12])[C:6]2=[N:5][CH:4]=1.[N:20](OCCC(C)C)=[O:21].C>CS(C)=O.CN(C)C=O.C(O)(=O)C.O>[OH:21]/[N:20]=[C:19]1\[C:18]2[CH:17]=[CH:16][CH:15]=[CH:14][C:13]=2[C:9]2[NH:10][C:11](=[O:12])[C:6]3[N:7]([CH:3]=[CH:4][N:5]=3)[C:8]\1=2
0.4 g of 80% sodium hydride is added to a suspension of 1.1 g of 5H,10H-imidazo[1,2-a]indeno-[1,2-e]pyrazin-4-one in 10 ml of anhydrous dimethyl sulphoxide. After stirring for 10 minutes at a temperature in the region of 20° C., a solution of 0.7 g of isoamyl nitrite in 2 ml of anhydrous dimethyl sulphoxide is added dropwise over 5 minutes and the mixture is then stirred for 1 hour at the same temperature. 10 ml of distilled water are added slowly and the mixture is subsequently poured into 120 g of water and ice, acidified with 1 ml of acetic acid and then centrifuged. After removal of the supernatant solution, the solid is suspended in 25 ml of distilled water, filtered, washed with 10 ml of acetone and dried under reduced pressure (15 mmHg; 2 kPa) at 20° C. The product obtained (1.5 g) is dissolved in 100 ml of boiling dimethylformamide and, after 0.1 g of decolorizing charcoal has been added, the solution is filtered while hot, cooled, poured into 800 ml of distilled water and centrifuged. The solid is suspended in 20 ml of distilled water, filtered, washed with 20 ml of acetone and dried under reduced pressure (15 mmHg; 2 kPa) at 20° C. The product obtained (0.9 g) is dissolved in 75 ml of dimethyl sulphoxide at 20° C. and, after 0.1 g of decolorizing charcoal has been added, the solution is filtered. The filter is washed twice with 20 ml in total of dimethyl sulphoxide and the filtrate and the washings are then combined, 75 ml of distilled water are added and they are centrifuged. The solid is suspended in 25 ml of distilled water, filtered, washed twice with 50 ml in total of acetone and then dried under reduced pressure (1 mmHg; 0.13 kPa) at 60° C. 0.63 g of 10-(E-hydroxyimino)-5H,10H-imidazo[1,2-a]indeno[1,2-e]pyrazin-4-one is thus obtained, decomposing without melting above 300° C. [N.M.R. spectrum: (200 MHz; DMSO d6 ; δ in ppm): 7.40 and 7.48 (2t, J=7 Hz, 2H: --H7 and --H8); 7.60 and 8.00 (2s broad, 1H each: --H of the imidazole); 7.82 and 8.20 (2d, J=7 Hz, 1H each: --H6 and --H9); 12.70 and 13.00 (2 cplx, 1H each: --NH-- and --OH)].
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