1 Department of Chemistry and Biochemistry, Concordia University 7141 Rue Sherbrooke Ouest Montréal Québec H4B 1R6 Canada chris.wilds@concordia.ca.
2 School of Chemistry, The University of Sydney Sydney NSW 2006 Australia.
3 Australian Research Council Centre of Excellence for Innovations in Peptide and Protein Science, The University of Sydney Sydney NSW 2006 Australia richard.payne@sydney.edu.au.

A breadth of strategies are needed to efficiently modify oligonucleotides with peptides or lipids to capitalize on their therapeutic and diagnostic potential, including the modulation of in vivo chemical stability and for applications in cell-targeting and cell-permeability. The chemical linkages typically used in peptide oligonucleotide conjugates (POCs) have limitations in terms of stability and/or ease of synthesis. Herein, we report an efficient method for POC synthesis using a diselenide-selenoester ligation (DSL)-deselenization strategy that rapidly generates a stable amide linkage between the two biomolecules. This conjugation strategy is underpinned by a novel selenide phosphoramidite building block that can be incorporated into an oligonucleotide by solid-phase synthesis to generate diselenide dimer molecules. These can be rapidly ligated with peptide selenoesters and, following in situ deselenization, lead to the efficient generation of POCs. The diselenide within the oligonucleotide also serves as a flexible functionalisation handle that can be leveraged for fluorescent labelling, as well as for alkylation to generate micelles.