PNA Molecular Beacons Assembled by Post-Synthetic Click Chemistry Functionalization

To avoid the tedious synthesis of functionalized peptide nucleic acid (PNA) monomers for probe development, we proposed a simple approach to modify PNA oligomers by post-synthetic on-resin click chemistry. PNA molecular beacons (MBs) were prepared by incorporation of azide-containing monomers into the oligomer by automatic solid-phase peptide synthesis and subsequent derivatization with pyrene moieties by copper-catalyzed azide-alkyne cycloaddition. Two pyrene-based quencher-free PNA molecular beacons, a stemless MB and one possessing a stem-loop structure, targeting a portion of the cystic fibrosis gene, were successfully synthesized by using this method. Fluorescence studies showed that the stem-loop MB exhibited better discrimination of changes in excimer/monomer ratios as compared to the stemless MB construct.