5-N-Carboxyimino-6-N-chloroaminopyrimidine-2,4(3H)-dione as a hypochlorite-specific oxidation product of uric acid

Although uric acid is known to react with many reactive oxygen species, its specific oxidation products have not been fully characterized. We now report that 5-N-carboxyimino-6-N-chloroaminopyrimidine-2,4(3H)-dione (CCPD) is a hypochlorite (ClO(−))-specific oxidation product of uric acid. The yield of CCPD was 40–70% regardless of the rate of mixing of ClO(−) with uric acid. A previously reported product, allantoin (AL), was a minor product. Its yield (0–20%) decreased with decreasing rate of mixing of ClO(−) with uric acid, indicating that allantoin is less important in vivo. Kinetic studies revealed that the formation of CCPD required two molecules of ClO(−) per uric acid reacted. The identity of CCPD was determined from its molecular formula (C(5)H(3)ClN(4)O(4)) measured by LC/time-of-flight mass spectrometry and a plausible reaction mechanism. This assumption was verified by the fact that all mass fragments (m/z −173, −138, −113, and −110) fit with the chemical structure of CCPD and its tautomers. Isolated CCPD was stable at pH 6.0–8.0 at 37°C for at least 6 h. The above results and the fact that uric acid is widely distributed in the human body at relatively high concentrations indicate that CCPD is a good marker of ClO(−) generation in vivo.