Aminobarbituric acid

Uramll (aminobarbituric acid) (III) may be prepared by the oxidation of barbituric acid (I) to nitrobarbiturlc acid (II), followed by reduction of the latter ... 

Urea may be recognised as a structural feature in the triketo form disconnection then reveals diethyl malonate as the other reagent. The synthesis of barbituric acid is therefore effected (Expt 8.36) by condensation of diethyl malonate with urea in the presence of sodium ethoxide. Barbituric acid undergoes nitration in the 5-position on treatment with fuming nitric acid, and reduction of the nitro derivative (98) yields 5-aminobarbituric acid (99) (uramil). 

Few examples of N-amination of azines have been reported. The use of such reagents as 0-mesitylenesulfonylhydroxylamine has led to the direct synthesis of /V-aminopyridazinium, -pyrimidinium, and -pyrazinium salts (80CPB2676), and 1-aminobarbituric acids (72CPB1814), while 0-(2,4-dinitrophenyl)hydroxylamine was a useful amino-transfer reagent in the direct synthesis of 1 -amino-6-methylthio-1,2,4-triazin-4( 17/)-ones from 2-methylthio-1,2,4-triazin-5( 1H)-ones (82JHC1583). 

Reactions of 5-nitrosobarbituric acids with aminoguanidine, of 5-phen-ylazobarbituric acids with phenethylamine, and of 5-arylmethylene-aminobarbituric acid with NBS or thionyl chloride afford isofervenu-lins, 8-phenyl-xanthines, and oxazolo[5,4-t/]pyrimidines, respectively [75BCJ725, 75BCJ1679 77H(6)689, 77H(6)1901, 77H(6)1919 78CPB765] (Scheme 75). 

Alkyl isothiocyanates also afford alkythioureidopyiimidines, usually by reaction in aqueous alkali, and these may be cyclized by hydrochloric acid to produce 9-alkyl-8-thioxopurines. In this manner 5-aminobarbituric acid furnished 9-alkyl-8-thiouric acids (2lLA(423)242). 8-Thiouric acid (300) was also obtained by formation of a thioureido-pyrimidine in situ from the cyanamidopyrimidine (301 Scheme 112) (02CB2563). 

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