Figure 13.

Oxidation pathways of s²c⁵Ura and se²c⁵Ura (Y = S or Se). Here each derivative is abbreviated as UraYH. The uracil derivatives could be oxidized via a direct oxidation pathway (red) to produce either the sulfinic/seleninic acids or the sulfonic/selenonic acids, which could eliminate sulfur dioxide/selenium dioxide or sulfite/selenite, respectively, to produce uracil-5-carboxylate (Ura). A second pathway (green) involves oxidation of the disulfide/diselenide to form a thiosulfinate/selenoseleninate, which can undergo hydrolysis to the parent compound and the sulfinic/seleninic acid. The parent uracil derivative can then reenter the cycle from multiple entry points. Alternatively, the sulfenic acid/selenenic acid could disproportionate (blue), resulting in production of the disulfide/diselenide and the sulfinic/seleninic acid. This figure is adapted from [37].