Hydantoin from allantoin

The same authors elucidated the origin of allantoin from hy-droxonic acid on which the original hydantoin structure (5) was based and which was formulated as shown in Scheme 2. 

Urea, methylurea, and dimethylureas react with glyoxylic acid and its methyl ester to give a-substituted hydantoic acid derivatives (16) and substituted allantoic acid derivatives (17), which can be cyclized to 5-substituted hydantoins (18). Although allantoin (18) formation from urea and... 

The first hydantoin racemase acting on a cyclic amide substrate reported in the literature was the allantoin racemase (E.C. 5.1.99.3) (Fig. 12.4-4). This enzyme enables several bacteria to use both allantoin enantiomers as substrates120-221. Racemic mixtures of allantoin, e. g. from plant materials, can be completely metabo-... 

Uric acid 33 (2,6,8-trihydroxypurine) was isolated from urinary calculi by Scheele (1774). After ascertaining its molecular formula (Liebig and Mitscherlich 1834), its structure was established by oxidative degradation and structural correlation with barbituric acid, alloxan, allantoin and hydantoin (Liebig, Wohler, Baeyer) ... 

There is evidence that the first product of uricase oxidation is not HDC, but an unknown compound which contains the same number of carbon atoms as uric acid 266-269). HDC and the unknown compound had different ultraviolet absorption spectra the unknown compound was quite unstable and yielded allantoin more readily than HDC. It is possible that this unknown compound (X) had the structure shown in Fig. 14, and that it is converted to allantoin without preliminary hydration to HDC 261). Although X per se is not symmetrical, a tautomeric shift of the double bond to the other ring would result in equivalent structures and explain the equal labeling found in both the urea and hydantoin moieties of allantoin derived from uric-1,3-Ni acid 202). However, hydration of X at the 3 4 double bond could have also produced HDC, which would be converted subsequently to allantoin. Thus, both X and HDC might have been intermediates in the oxidation of uric acid. 

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