| Popis: |
A series of N-substituted 8-aminoxanthines (=8-amino-3,7(or 3,9)-dihydro-1H-purine-2,6-diones) 8–16 and 34–37 were synthesized from the corresponding 8-nitroxanthines 1–7, 30–33, and 8-(phenylazo)xanthines 17 and 18 by catalytic reduction. Another approach was derived from 6-amino-5-(cyanoamino)uracils (=N-(6-amino-1,2,3,4-tetrahydro-2,4-dioxopyrimidin-5-yl)cyanamides) 23, 24, and 27 by base-catalyzed cyclization yielding 25–28. All 8-aminoxanthines 8–29 and 34–37 were acetylated to the corresponding 8-(acetylamino)xanthines 40–57, and prolonged heating led to 8-(diacetylamino)xanthines 58 and 59. Several 8-aminoxanthines 8–13 were diazotized forming 8-diazoxanthines 60–64. Coupling reactions of isolated 62 and 64 and intermediary formed 8-diazoxanthines with 1,3-dimethylbarbituric acid (=1,3-dimethylpyrimidine-2,4,6(1H,3H,5H)-trione; 66) resulted in 5-[(xanthin-8-yl)diazenyl]-1,3-dimethylbarbituric acids=3,7(or 3,9)-dihydro-8-[2-(1,2,3,4-tetrahydro-1,3-dimethyl-2,4-dioxopyrimidin-5-yl)diazenyl]-1H-purine-2,6-diones) 67–80. The newly synthesized xanthine derivatives were characterized by the determination of their pKa values, the UV- and NMR spectra, as well as elemental analyses. |
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