Synthesis of Triazole-linked Homonucleoside Polymers through Topochemical Azide-Alkyne Cycloaddition

There is a great deal of interest in developing stable modified nucleic acids for application in diverse fields. Phosphate-modified DNA analogues, in which the phosphodiester group is replaced with a surrogate group, are attractive because of their high stability and resistance to nucleases. However, the scope of conventional solution or solid-phase DNA synthesis is limited for making DNA analogues with unnatural linkages. Other limitations associated with conventional synthesis include difficulty in making larger polymers, poor yield, incomplete reaction, and difficult purification. To circumvent these problems, a single-crystal-to-single-crystal (SCSC) synthesis of a 1,5-triazole-linked polymeric ssDNA analogue from a modified nucleoside through topochemical azide-alkyne cycloaddition (TAAC) is reported. This is the first solvent-free, catalyst-free synthesis of a DNA analogue that proceeds in quantitative yield and does not require any purification.