STUDIES ON COVALENT ADDUCTS OF DEHYDROURIC ACID

The structure of 5-chloro and 5-alkoxy-5,7-dihydro-3H-purine-2,4,6-tri ones (6 and 7-9) has been corroborated by their spectral properties an d X-ray crystallography. The stereochemical model (R)-10 of the key ur icolytic intermediate was prepared using menthol as chiral auxiliary. In acidic solutions, depending on the N-substitution, the ring cleavag e occurred either at the 4,9-bond 6b --> 13 (R1 = Me) or at the 3,4-bo nd 6c --> 14 (R1 = H). Opening of the 1,6-bond is the dominant process under alkaline conditions. Decarboxylative rearrangement into 1,3-dim ethylallantoin (15) was specific for N(7)-unsubstituted derivatives. E vidence for intermediacy of the bicyclol tautomeric form was supplied by isolation of hyl-3,7-dioxo-2,4,6,8-tetraazabicyclo[3.3.0]octane (16 ); fragmentation of 10 into 5-menthoxy-imidazolidin-2,4-dione (17) als o takes place under forcing conditions. Conversely, no allantoin rearr angement was encountered in the R7 not-equal H cases; 7d underwent the pyrimidine ring fragmentation to give methoxy-1-methyl-4-methylimino- imidazolidine-2-one (18) or methoxy-1-methyl-4-methylimino-imidazolidi ne-2-one (19). A possible mechanism for these ring transformation reac tions is discussed.