Stepwise click functionalization of DNA through a bifunctional azide with a chelating and a nonchelating azido group.

A stepwise chemoselective click reaction was performed on nucleosides and oligonucleotides containing 7-octadiynyl-7-deaza-2'-deoxyguanosine and 5-octadiynyl-2'-deoxycytidine with unsymmetrical 2,5-bis(azidomethyl)pyridine using copper(II) acetate. The reaction is selective for the chelating azido group, thereby forming monofunctionalized adducts still carrying the nonchelating azido functionality. The azido-functionalized adduct was applied to a second click reaction, now performed in the presence of reducing agent, to generate cross-linked DNA or a pyrene click conjugate. The chelate-controlled stepwise click reaction is applicable to alkynylated nucleosides and oligonucleotides.