4,5-Diaminouracils

The readiness of amidine formation in reactions of lactim ethers with amines has been used in the synthesis of 8,9-poly methylene-purines.97 Attempts to condense 2 (R = Me) with uramil and l,3-dimethyl-4,5-diaminouracil failed.97 Lactim ethers were also found not to react with derivatives of 5-aminouracil, probably due to the low basicity of the latter.97... 

A transribosylase which exchanges the hypoxanthine of inosine with adenine, guanine, xanthine, thymidine, 4,5-diaminouracil, 5-bromouracil, and 4,6-diaminouracil has been found in Escherichia coli. - ... 

Use of alkyl (or aryl) isocyanates in the same way offers a useful route to 9-alkyl (or aryl)-8-oxopurines. 9-Phenyluric acid is produced in this way by the reaction of 4,5-diaminouracil with phenyl isocyanate and cyclization of the intermediate phenyl-ureidopyrimidine with hydrochloric acid (Scheme 89) (23LA(432)266). It is noteworthy that the cyclization results in loss of ammonia and not aniline. In contrast to this reaction, fusion of the Vmethylphenylureidopyrimidine (270) resulted in loss of aniline rather than ammonia (Scheme 90) (66JCS(C)10). 

Analogously, 4,5-diaminouracil (483) and 405 give rise to 2,4,5,6- tetrakis(TMS)-4,5-diaminouracil (484) in 90% yield including both N- and O-silylation (equation 231)245. 

The synthesis of uric acid by cyclization of 4,5-diaminouracil with ethyl chloroformate according to Traube is more convenient. 

Diaminouracil in 2%-sulfuric acid heated slowly to 90, an aq. soln. of chloral hydrate added, and stirring continued 15 min. at 90 2,4,6-trihydroxy-pteridine. Y 88%.— All three Gl-aloms are readily eliminated in this condensation. F. e. s. F. Bergmann, M. Tamari, and H. Ungar-Waron, Soc. 196A, 565. 

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