FORMATION OF N-CARBAMOYLASPARTIC ACID AND ITS CYCLIZATION TO OROTIC-ACID

The stereochemistries of the reactions between cyanate and aspartic ac id and 3-methylaspartic acid have been examined. The product of the fi rst reaction, N-carbamoylaspartic acid 3, can cyclise to give either d ihydroorotic acid 5 or 5-carboxymethylhydantoin 4. Acid catalysed cycl isation gives the latter while catalysis by the enzyme dihydroorotase gives the former. Introduction of a double bond into 3 changes the cou rse of, non-enzymatic cyclisation and a six-membered ring compound oro tic acid 1 is the product. It is proposed that the double bond prevent s intramolecular hydrogen bonding.