Reagents and materials

All 9-fluorenylmethoxycarbonyl (Fmoc)-PNA monomers were purchased from PolyOrg, Inc. (Leominster, MA, USA). Acetonitrile, Fmoc-Lys(Boc)-OH, acetic anhydride (Ac₂O), pyridine, dichloromethane (DCM), 1-[bis(dimethylamino)methylene]-1H-1,2,3-triazolo[4,5-b]pyridinium 3-oxid hexafluorophosphate (HATU), N,N-diisopropylethylamine (DIPEA), diethyl ether (Et₂O), N,N-dimethylformamide (DMF), Kaiser test reagents, m-cresol, N-methyl-2-pyrrolidinone (NMP), piperidine, and trifluoroacetic acid (TFA) were purchased from Sigma-Aldrich (St Louis, MO, USA). High purity water (18 MΩ) was generated from a Millipore (Billerica, MA, USA) Milli-Q water system. Rink Amide ProTide resin (LL, 100–200 mesh, 0.19 mmol/g) was purchased from CEM corporation (Matthews, NC, USA). NHS-Fluorescein (5/6-carboxyfluorescein succinimidyl ester, mixed isomer) was purchased from ThermoFisher Scientific (Waltham, MA, USA). Fmoc-8-amino-3,6-dioxaoctanoic acid was purchased from Peptides International, Inc. (Louisville, KY, USA). All Fmoc-protected thyclotide monomers were prepared using commercially available starting material from Entrechem (Spain) using protocols previously reported by our group (71).