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Studies on covalent adducts of dehydrouric acid

The structure of 5-chloro and 5-alkoxy-5, 7-dihydro-3H-purine-2, 4, 6-triones has been corroborated by their spectral properties and X-ray crystallography. The stereochemical model (R)-10 of the key uricolytic intermediate was prepared using menthol as chiral auxiliary. In acidic solutions, depending on the N-substitution, the ring cleavage occurred either at the 4, 9-bond or at the 3, 4-bond. Opening of the 1, 6-bond is the dominant process under alkaline conditions. Decarboxylative rearrangement into 1, 3-dimethylallantoin was specific for N(7)-unsubstituted derivatives. Evidence for intermediacy of the bicyclol tautomeric form was supplied by isolation of 1-menthoxy-2, 4-dimethyl-3, 7-dioxo-2, 4, 6, 8-tetraazabicyclo[3.3.0]octane ; fragmentation of 10 into 5-menthoxy-imidazolidin-2, 4-dione also takes place under forcing conditions. Conversely, no allantoin rearrangement was encountered in the R7 not-equal H cases ; 7d underwent the pyrimidine ring fragmentation to give 5-methoxy-1-methyl-4-methylimino-imidazolidine-2-one or 5-carboxamido-5-methoxy-1-methyl-4-methylimino-imidazolidine-2-one. A possible mechanism for these ring transformation reactions is discussed.

uric acid; mechanism; allantoin; degradation; conversion; purines

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