"Photoclick" Postsynthetic Modification of DNA

A new DNA building block bearing a push-pull-substituted diaryltetrazole linked to the 5-position of 2'-deoxyuridine through an aminopropynyl group was synthesized. The accordingly modified oligonucleotide allows post-synthetic labeling with a maleimide-modified sulfo-Cy3 dye, N-methylmaleimide, and methylmethacrylate as dipolarophiles by irradiation at 365 nm (LED). The determined rate constant of (23 +/- 7) m(-1) s(-1) is remarkably high with respect to other copper-free bioorthogonal reactions and comparable with the copper-catalyzed cycloaddition between azides and acetylenes.