The reactions of thymine and thymidine with ozone

摘要: The ozonolysis of thymine and thymidine has been investigated by a product study complemented kinetic studies using spectrophotometry, conductometry stopped-flow with optical conductometric detection. Material balance obtained. Ozonolysis (k = 3.4 × 104 dm3 mol−1 s−1) leads to the formation acidic (pKa = 4) hydroperoxide 1-hydroperoxymethylene-3-(2-oxopropanoyl)urea 5 (∼34%), neutral hydroperoxides (possibly mainly 1-hydroperoxyhydroxymethyl-3-(2-oxopropanoyl)urea 6, total ∼41%) H2O2 (25%, corresponding 1-formyl-5-hydroxy-5-methylhydantoin 11). organic decay (∼1.1 10−3 s−1 at 20 °C, 1.3 10−4 at 3 °C) releasing formic acid (formation 5-hydroperoxy-5-methylhydantoin 18) also some extent (and After 100 min, yield is 75%. Upon treatment high pH, it increases 100%. Reduction bis(2-hydroxyethyl) sulfide 50 11 whose subsequent base yields 5-hydroxy-5-methylhydantoin 13 in 100% yield. It suggested that Criegee ozonide formed upon reaction ozone C(5)–C(6) double bond opens heterolytically two directions opening bond. In preferred route (75%), positive charge resides C(6). Deprotonation N(1) gives rise 5, while its water 6. Loss 18. 6 11. minor (25%), positive charge remains C(5) followed water. resulting α-hydroxy rapidly loses basic solution, singlet dioxygen (8%). concomitant product, 5,6-dihydroxy-5,6-dihydrothymine detected. thymidine, rapid conductance 0.55 due release acetic acid (18%). this short-lived destroyed. As consequence this, 25 s after only ∼78% (including 8% H2O2). products acetic are be CO2 N-(2-deoxy-β-D-erythropentofuranosyl)formylurea 22. A number have detected HPLC post-column derivatisation iodide. An such as case not among products. reduction, (43–50%) N1-(2-deoxy-β-D-erythropentofuranosyl)-5-hydroxy-5-methylhydantoin 23. reasons for striking differences ozonolyses discussed.