Bicyclic and tricyclic fused pyrimidine derivatives have received much attention in connection with biologically significant systems such as purines, 1-7 pteridines 8-14 and alloxazines. The synthesis of the above categories has been accomplished by the cyclisation of 6-aminouracil derivatives and ring transformation of other fused pyrimidine-2,4diones. 15,16 In extending our recent work on simple bicyclic xanthines, 6,7 tricyclic alloxazines 17,18 and pyridodi pyrimidines 19 this paper reports a novel synthesis of 3-benzyl-9-methylxanthine (5), 3,9-dimethyl-8-phenylxanthine (7), 7 dipyrimidopyridines 10a-f and pyrimido [4,5-d]pyrimidines 11a-d via Mannich reactions.The synthesis of 3,9-disubstituted xanthines 5,7 has been performed by various approaches [20][21][22] and we report a more favoured sequence from the 1-substituted-6-chlorouracils 1a, b 23,24 (Scheme 1) by reaction with methylamine and N-methyl benzylamine respectively where the 6-amino compounds 2 and 6 were obtained in a good yield. Nitrosation of 2 afforded the 5-nitroso compound 3, which underwent reductive formylation to 4 which readily undergoes intramolecular cyclization with formamide to furnish the xanthine 5 or refluxing the tertiary amine 6 with sodium nitrite in the presence of acetic acid resulted in ring closure in one step giving the 3,9-dimethyl-8-phenylxanthine (7), probably via a 5-nitroso compound 6a and its tautomer 6b. All the products were assigned by 1 H NMR, UV spectra and microanalysis.It was found that the intramolecular cyclisation of 6-(Nalkylanilino)uracils with dimethylformamide (DMF)-POCl 3 25

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The reactions of enaminones (6-aminouracils) 1a±c and 4 with cyano olefins 2a±b and 5a±f led to the formation of pyrido[2,3-d ]pyrimidines 3a±f and 6a±f in good yield, while the treatment of 4-amino-2-thiouracil 4 with aromatic aldehydes afforded pyridodipyrimidines 7a±c.

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Purine derivatives R 0540Synthesis of 3-Benzylxanthine and Lumazine Analogues. -Xanthine and lumazine derivatives exhibit a wide range of biological activities and they are potential anti-HIV drugs. -(EL ASHRY, E. S. H.; YOUSSIF*, S.; EL AHWANY, M.; EL SANAN, M.; J. Chem. Res. 2005, 4, 262-266; Dep. Chem., Fac. Sci., Zagazig Univ., Zagazig, Egypt; Eng.) -K. Woydowski 45-180

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Several xanthines (7–13) are prepared by the cyclisation of 1-benzyl-5,6-diaminouracil with single-carbon inserting agents such as aromatic aldehydes, formamides, acetic anhydride, carbon disulfide, and nitrous acid. Treatment of 6-amino-1-benzyl-5-nitrosouracil with anilinobenzylidene derivatives (14–18) affords 7-hydroxyxanthines (19–23). Cyclisation of the diaminouracil 3 with glyoxal, benzil, and diethyl oxalate leads to lumazines (25–28).

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