Solid-Phase synthesis of peptide nucleic acids

Peptide nucleic acids (PNA) were synthesized by a modified Merrifield method using several improvements. Activation by O-(benzotriazol-1-yl)-1,1,3,3-tetramethyluronium hexafluorophosphate in combination with in situ neutralization of the resin allowed efficient coupling of all four Boc-protected PNA monomers within 30 min. HPLC analysis of the crude product obtained from a fully automated synthesis of the model PNA oligomer H-CGGACTAAGTCCATTGC-Gly-NH₂, indicated an average yield per synthetic cycle of 97.1%. N¹-benzyloxycarbonyl-N6³-methylimidazole triflate substantially outperformed acetic anhydride as a capping reagent. The resin-bound PNAs were successfully cleaved by the ‘low–high’ trifluoromethanesulphonic acid procedure.