Preparation of a Convertible Spacer Containing a Disulfide Group for Versatile Functionalization of Oligonucleotides

Abstract

The protocols described in this article provide details regarding the synthesis and characterization of a disulfide containing linker phosphoramidite for terminal functionalization of synthetic oligonucleotides. The linker is first synthesized from 6-mercaptohexanol in two steps and is incorporated at the 5 end of short DNA oligonucleotides using automated solid-phase synthesis. The linker contains a terminal tosylate group which is post-synthetically displaced by altering the deprotection conditions to yield a variety of functional handles (N 3 , NH 2 , OMe, SH) or alternatively, the tosylate can be displaced directly with primary amines such as tert-butylamine. The linker system is also compatible with RNA oligonucleotides enabling the introduction of various functional handles (N 3 , NH 2 ). The protocol outlined in this procedure provides access to a versatile linker for the terminal functionalization of oligonucleotides containing a disulfide bond which may serve useful in the synthesis of reduction-responsive oligonucleotide conjugates. As a proof of concept, in this protocol the linker is used to modify a dT 10 oligonucleotide and then conjugated by copper(I)-mediated azide-alkyne cycloaddition (CuAAC) to an alkyne-modified poly(ethylene glycol) which shows concentration dependent release of the oligonucleotide upon treatment with 1,4-dithiothreitol, a reducing agent.