Peptide nucleic acid (PNA) monomers with an orthogonally protected ester moiety

This application pertains to orthogonally protected esters of peptide nucleic acid (PNA) monomers, which ester groups can be removed under conditions that permit typical backbone and side chain acid- and base-labile protecting groups to remain substantially intact thereby permitting the high yield of PNA monomer carboxylic acids that are suitable for use in PNA oligomer synthesis. Exemplary ester groups include, but are not limited to, 2,2,2-trichloroethyl (TCE), 2,2,2-tribromoethyl (TBE), 2-bromoethyl (2-BE) and 2-iodoethyl groups (2-IE). This invention also pertains to novel methods for the synthesis of Backbone Ester compounds and related Backbone Ester Acid Salts.