Ureides cyclic, hydrolysis

Many kinds of enzymes with different substrate specificities are involved in hydantoin hydrolysis. Ogawa et al. [10] found two hydantoin-hydrolyzing enzymes in Blastobacter sp. A17p-4. These enzymes were purified to homogeneity and characterized (Table 1). One hydrolyzed dihydropyrimidines and 5-monosubstituted hydantoins to the corresponding AT-carbamoyl amino acids. Since the hydrolysis of 5-substituted hydantoins by this enzyme was D-stereo-specific, this enzyme was identified as D-hydantoinase, which is identical with dihydropyrimidinase. The other one preferably hydrolyzed cyclic imide compounds such as glutarimide and succinimide more than cyclic ureide compounds such as dihydrouracil and hydantoin. Because there have been no reports on enzymes which show same substrate specificity as this enzyme, it is considered to be a novel enzyme, which should be called imidase [10]. 

Our results provide a basis for predicting the relative hydrolytic tendencies of the cyclic ureides 25-32. Susceptibility toward hydrolysis is expected to increase roughly as Vs becomes more positive. However, we anticipate that the number of C=0 groups in the molecule is also an important factor in determining its reactivity, since each of them is a potential site for nucleophilic interaction. 

Parabanic acid is a cyclic ureide containing a five membered ring, which on hydrolysis by alkali may regenerate the corresponding acid and urea. The cyclic ureides are acidic owing to enolization and hence, they may form metallic salts by replacing the H atom of the -OH group as shown below ... 

Example. Phenobarbital [Gardinal ]. The following scheme vividly explains the base hydrolysis of phenobarbital wherein the cyclic ureide ring (in barbiturate) undergoes cessation. Besides, it may also be seen that the aforesaid cessation strategically takes place either between C-l/C-2 and/or C-l/C-6 locations in the structure of barbiturate. However, the cleavage between C-1 and C-6 is considered to be the most preferred pathway prevailing in the ionized barbiturates , such as aqueous solutions of sodium salts. 

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