Chemoselective modification of vinyl DNA by triazolinediones

A new method for post-synthetic modification of nucleic acids has been developed by mixing a phenyl triazolinedione (PTAD) derivative with DNA containing a vinyl nucleobase. The resulting reactions proceeded via step-wise mechanisms, giving either a formal 4 + 2 cycloaddition product, or, depending on the context of nucleobase, PTAD addition + solvent trapping to give a secondary alcohol in water. Catalyst-free addition between PTAD and the terminal alkene of 5-vinyl-2'-deoxyuridine (VdU) was exceptionally fast, with a second-order rate constant of 2000 M-1s-1. PTAD derivatives selectively reacted with VdU-containing oligonucleotides in a conformation-selective manner, with higher yields observed for G-quadruplex versus duplex DNA. These results demonstrate a new strategy for copper-free bioconjugation of DNA that can potentially be used to probe nucleic acid conformations in cells.