Alloxan, tautomerism

Allomaltol, methyl — see Pyran-4-one, 5-methoxy-2-methyl-Allopurinol applications, 5, 343 metabolism, 1, 237 synthesis, 5, 316, 340 tautomerism, 5, 308 xanthine oxidase inhibition by, 1, 173 Allopurinol, oxy-applications, 5, 343 synthesis, 5, 316 Alloxan... 

The various tautomers and rotamers of alloxan have been examined in detail by the MNDO method and it is predicted that the keto form is most important in the gas phase, although in solution the monohydroxy forms are also thought to contribute. A mass spectral study has been used to investigate the enol-keto tautomeric equilibria of a series of substituted salicylaldehyde and 2-hydroxynaphthaldehyde Schiff bases. In neutral, ethanolic solutions, the cis- and trans-tm forms of 4,5-dimethyl-2-(2 -hydroxyphenyl)imidazoles (393) and (394) have been found to exist in equilibrium in the ground state. However, in neutral aqueous solutions, the trans-eao and keto forms (394) and (395) were the only species detected. Deuterium isotope effects on... 

The significant difference in energy between 165a and other tautomers excluding the possibility of tautomerism in the gas phase was confirmed by the ab initio STO-3G, 3-21G, and 6-31G calculations. The population analysis of the alloxan anion gives evidence that the preferred protonation site is offered by the central oxygen... 

Alloxazine 18 is formed by the cyclocondensation of o-phenylenediamine with alloxan (Kuhling 1891). The tautomeric isalloxazin 19 (flavin) is the parent compound of the 10-substituted derivatives. 

We have found that the action of nitrous acid on isobarbituric add (IV) leads to the formation of an isomer of violuric acid which we term iso-violuric acid (VI). Since the phenolic character of isobarbituric add has been established by its behavior toward acetic anhydride, hydroxylamine, hypobromous acid, diazomethane and potassium ferricyanide, it was anticipated that 5-hydroxy-6-nitrosouracil (V) would be obtained. The behavior of the product, however, indicated it to be the tautomeric form (VI) (alloxan-6-oxime). 

Deamination of amino acids by carbonyl compounds has long been known in organic chemistry. Classical instances are the Strecker reaction of amino acids with alloxan and rimilar reactions with o-quinones, isatin, ninhydrin, methylglyoxal, and the like. In such cases deamination is usually associated with decarboxylation of the amino acid. Condensation of the amino and carbonyl groups to yield SchiiTs bases, and tautomeric transformation of these, are generally assumed as intermediary steps. 

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