1 -hydroperoxy-1 -hydroxy-2,5-dihydro

Other degradation products of the cytosine moiety were isolated and characterized. These include 5-hydroxy-2 -deoxycytidine (5-OHdCyd) (22) and 5-hydroxy-2 -deoxyuridine (5-OHdUrd) (23) that are produced from dehydration reactions of 5,6-dihydroxy-5,6-dihydro-2 -deoxycytidine (20) and 5,6-dihydroxy-5,6-dihydro-2 -deoxyuridine (21), respectively. MQ-photosen-sitized oxidation of dCyd also results in the formation of six minor nucleoside photoproducts, which include the two trans diastereomers of AT-(2-de-oxy-/j-D-eryf/iro-pentofuranosyl)-l-carbamoyl-4 5-dihydroxy-imidazolidin-2-one, h/1-(2-deoxy-J8-D-crythro-pentofuranosyl)-N4-ureidocarboxylic acid and the a and [5 anomers of N-(2-deoxy-D-eryfhro-pentosyl)-biuret [32, 53]. In contrast, formation of the latter compounds predominates in OH radical-mediated oxidation of the pyrimidine ring of dCyd, which involves preferential addition of OH radicals at C-5 followed by intramolecular cyclization of 6-hydroperoxy-5-hydroxy-5,6-dihydro-2 -deoxycytidine and subsequent generation of the 4,6-endoperoxides [53]. 

Dihydro-6-hydroperoxy-5-hydroxy-5-methyl-2,4(li/,3 )- pyiimidinedione (FUFDIT) 1.451 1.394 105.8 86... 

TABLE 1. Kinetic and thermodynamic parameters of the 8 ds and trans diastereomers of 6-hydroperoxy-5-hydroxy-5,6-dihydrothymidine (5) and 5-hydroperoxy-6-hydroxy-5,6-dihydro-thymidine (6) ... 

The A -(pyrrol-2-yl)carbamates 860 are oxidized smoothly by air to a mixture of the A -(5-hydroxy- 862 and 5-hydroperoxy- 863 -l,5-dihydro-2/7-pyrrol-2-yliden)carbamates (in 63% and 8% yield, respectively, when R = H, = Bn) (Scheme 166) <1997TL1293>. Oxidation with pure oxygen gives the same products in a yield of 47% and... 

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