The Kinetics of the Rearrangement of Some Isopyrimidines to Pyrimidines studied by Pulse Radiolysis

Article abstract of DOI:10.1039/P29840001777

Isopyrimidines are formed as a result of the oxidation of the 6-yl radicals derived by ^.OH attack on pyrimidines and dihydropyrimidines.The kinetics of the rearrangement of the isopyrimidines into the corresponding pyrimidines has been followed by pulse radiolysis.The rearrangement of isouracil into uracil is proton-catalysed (k 1.8E7 l mol^-1 s^-1).Around pH 7 a spontaneous reaction, k 3000 s^-1, is observed.On increasing the pH the isouracil deprotonates at N(3) (pK_a ca. 9.4).The spontaneous rearrangement of the isouracil anion is considerably slower (k -1).At pH > 10.5 an OH(1-)-catalysed reaction sets in (k 4.9E5 l mol^-1 s^-1) which involves a second deprotonation, at C(5).Similar results have been obtained for the rearrangement of 5-hydroxyisouracil into isobarbituric acid.On blocking the N(3) position as in 3-methylisouracil, the OH(1-)-induced rearrangement sets in at a much lower pH (pH-1 s^-1) than that observed in the other two systems.

Full text of DOI:10.1039/P29840001777

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