Versatile 5‘-Functionalization of Oligonucleotides on Solid Support:  Amines, Azides, Thiols, and Thioethers via Phosphorus Chemistry

Although the preparation of conjugates of oligonucleotides is by now commonplace, existing methods (usually utilizing thiols or primary amines) are generally expensive, and often require postsynthetic reaction with the DNA followed by a separate purification. Here we describe simple procedures for a broad set of direct 5‘-end (5‘-terminal carbon) functionalizations of DNA oligonucleotides while they remain on the synthesizer column. 5‘-Iodinated oligonucleotides (prepared by an automated cycle as previously reported) are converted directly to 5‘-azides, 5‘-thiocarbamates, and alkyl and aryl 5‘-thioethers in high yields. Further, we demonstrate high-yielding conversions of DNA-azides to 5‘-amines, and of thiocarbamates to 5‘-thiols. Finally, we report a new, one-pot conversion of naturally substituted 5‘-OH oligonucleotides (again on the solid support) to 5‘-amino-oligonucleotides. All of the above reactions are demonstrated in multiple sequence contexts. Most of the procedures are automatable.