A Versatile and Convenient Synthesis of 34S-Labeled Phosphorothioate Oligonucleotides

Abstract

A synthetic protocol for 34S-labeled phosphorothioate oligonucleotides (PS ONs) was developed to facilitate MS-based assay analysis. This was enabled by a highly efficient, two-step, one-pot synthesis of 34S-labeled phenylacetyl disulfide (34S-PADS), starting from 34S-enriched elemental sulfur (34S8). 34S-PADS was subsequently used for stable isotope labeling (SIL) of oligonucleotides containing a phosphorothioate backbone. The 34S-SIL PS ONs are shown to retain the same melting temperature, antisense activity, and secondary structure as those of the corresponding unlabeled 32S PS ONs.