Near ultraviolet radiation-mediated reaction between N-nitrosoproline and DNA: Isolation and identification of two new adducts, (R)- and (S)-8-(2-pyrrolidyl)-2′-deoxyguanosine

To explore possible genotoxicity of N-nitrosoproline (NPRO), we investigated near-ultraviolet radiation (UVA)-mediated chemical reaction of NPRO with 2′-deoxyguanosine (dG). An acidic solution containing NPRO and dG was irradiated with UVA and products were analyzed by HPLC. In addition to the three known modified guanine nucleosides, i.e., 2′-deoxyxanthosine, 8-oxo-7,8-dihydro-2′-deoxyguanosine and 2′-deoxyoxanosine, we found two products. These new products were isolated and identified as (R)- and (S)-8-(2-pyrrolidyl)-2′-deoxyguanosine (G1 and G2, respectively). Experiments using monochromatic UVA in the range 300–400 nm were performed to determine the relation between products-yield and wavelength, and the highest yields of both G1 and G2 were found to occur at 340 nm. This wavelength coincided with the absorption maximum of NPRO. We propose that the NO radical produced from NPRO by photolysis triggers the formation of these products. Further investigation using calf thymus DNA showed that G1 and/or G2, probably both, could be produced by UVA irradiation of DNA + NPRO as well.