Chemistry of the 2-deoxyribonolactone lesion in oligonucleotides: cleavage kinetics and products analysis

Deoxyribonolactone in DNA is an oxidized abasic site damage that is produced by a variety of physical and chemical agents such as gamma-irradiation and ene-diyne antibiotics. The extent and biological significance of the lesion are poorly documented due to the high lability of the damaged DNA. The chemistry of degradation of deoxyribonolactone-containing DNA was investigated using oligonucleotides of different length (5-, 11-, 23-, 34-mers) in which the lactone was photochemically generated, as already reported, from oligonucleotide precursors containing a photoactive nitroindole residue. The procedure was successfully extended to double-strand synthesis by irradiation of the preformed duplex in which one strand contained the nitroindole residue. The degradation kinetics were investigated as a function of pH, temperature, length, and ionic strength. The cleavage fragments resulting from beta- and delta-eliminations were isolated and identified by (1)H NMR. It was found that the lesion is extremely sensitive to pH and temperature while slightly dependent upon ionic strength, length, and sequence. The cleavage rates for the beta- and delta-elimination steps are of the same order of magnitude. The deoxyribonolactone site leads to greater instability of DNA than the "regular" deoxyribose abasic site.