Z. Kazimierczuk, D. Shugar
Dec 16, 1971
Citations
0
Influential Citations
8
Citations
Journal
Biochimica et biophysica acta
Abstract
Abstract The monoanionic, but not the neutral, form of 6-chlorouracil in aqueous medium undergoes quantitative photochemical transformation to barbituric acid. Similarly, 1-methyl-6-chlorouracil and 3-methyl-6-chlorouracil monoanions are transformed to 1(3)-methylbarbituric acid, and 5-ethyl-6-chlorouracil to 5-ethylbarbituric acid, all in quantitative yield. The quantum yields for these reactions are quite high, 0.05 to 0.09, and unaltered over the wavelength range 254–280 nm, or by a 10-fold change of concentration of the initial substances. The rates of photochemical transformation are independent of the OH− concentration, but exhibit a marked deuterium isotope effect. A reaction scheme consistent with the foregoing, and other, data is the photohydration of the 5,6 bond of the excited singlet state of the chlorouracil monoanion, followed by the very rapid dark climination of Cl− to give barbituric acid. The findings are discussed in relation to the photochemistry of 5-halogeno analogues of thymine.