Diisopropyl carbodiimide

Dichloromethane (DCM), dimethylformamide (DMF), and methanol (MeOH) were purchased from Fisher (Hampton, NH, USA). 1-Hydroxybenzotriazole hydrate (HOBt), diisopropylcarbodiimide (DIC), diisopropylethylamine (DIEA), amino acids (unless otherwise noted), and resin were purchased from Chem-Impex (Wood Dale, IL, USA). Boc-Pro-OH was purchased from EMD (La Grange, IL, USA). Boc-DTrp-OH was purchased from Advanced ChemTech (Louisville, KY, USA). 4-Tert-butyl-cyclohexanecarboxylic acid was purchased from TCI (Portland, OR, USA). Trifluoroacetic acid (TFA) was purchased from Alfa Aesar (Haverhill, MA, USA). Borane-tetrahydrofuran was purchased from Acros Organics (Branchburg, NJ, USA). Piperidine and acetic anhydride were purchased from Sigma-Aldrich. Cyanogen bromide was purchased from ThermoScientific (Waltham, MA, USA).

All solvents required for synthesis, including ethanol, methanol, acetone, acetonitrile (ACN), tetrahydrofuran (THF), petroleum spirit, chloroform, dichloromethane (DCM), N-methyl-2-pyrrolidone (NMP) and dimethylformamide (DMF), were purchased from Merck and ChemSupply Pty (Aust.). Special reagents for the solid phase peptide synthesis (SPPS), i.e., piperidine, diisopropyl carbodiimide (DIC), diisopropylethylamine (DIPEA), acetic anhydride, Oxyma Pure (ethyl cyanohydroxyiminoacetate), trifluoroacetic acid (TFA) and triisopropyl silane (TIPS), were purchased from various suppliers - Chem-Impex Inc., Novabiochem^®, Sigma-Aldrich Pty Ltd. and Thermo Fisher Scientific. Solid bed support (Rink amide AM and Wang resin) having 0.3–0.6 mmol/g loading, and Fmoc-protected amino acids were purchased from Chem-Impex Inc. and P3Biosystems.

Fmoc‐protected amino acids for peptide synthesis were purchased from EMD Millipore. Fmoc‐azidolysine was purchased from Combi‐Blocks Inc. Dichloromethane (DCM) was purchased from Millipore Sigma. Dimethylformamide (DMF) and diethyl ether were purchased from Oakwood Chemical Inc. Piperidine was purchased from Alfa Aesar. Oxyma and diisopropyl carbodiimide (DIC) were purchased from ChemImpex. TFA was purchased from Oakwood, and Rink Amide resin was purchased from Novabiochem. Dibenzocyclooctyne‐Sulfo‐N‐hydroxysuccinimide (DBCO‐sulfo‐NHS) linker was purchased from Click Chemistry Tools. All oligonucleotides were purchased from Integrated DNA Technologies.