Synthesis of 2'-deoxyoxanosine from 2'-deoxyguanosine, conversion to its phosphoramidite, and incorporation into oxanine-containing oligodeoxynucleotides.

Oxanine (Oxa, O) is one of the damaged bases produced from guanine (G) through nitrosative deamination induced by nitric oxide (NO) or nitrous acid (HNO(2)). Large-scale preparation of Oxa-containing oligodeoxynucleotide (Oxa-ODN) with the desired base sequence is a prerequisite for exploring detailed properties of Oxa in DNA. This can be accomplished by incubation of G nucleosides with NaNO(2) in acetic acid buffer (pH 3.5) to produce Oxa nucleosides (e.g., 2'-deoxyoxanosine or dOxo), conversion of dOxo to DMT-dOxo-amidite by tritylation and conventional phosphoramidation, and subsequent synthesis of Oxa-ODN. The presence of Oxa in the synthetic ODN is confirmed by enzymatic digestion. Oxa-ODN is useful for analyzing the biochemical and biophysical properties of Oxa in DNA, which is believed to be involved in NO-induced genotoxicity and cytotoxicity. In addition, since Oxa possesses the carbodiimide-activated carboxylate function (O-acylisourea structure), Oxa-ODN can be used as a functional DNA oligomer that makes covalent cross-linkages with amine or amine-containing biomolecules and amine-modified solid surfaces.