Short-RInChIKey=SA-FUHFF-UHFFFADPSC-OSJUMAZEBB-UHFFFADPSC-NUHFF-NVDVK-NUHFF-ZZZ

For the cyclization of the linear precursor N,N,N',N'-tetramethyl-O-(7-azabenzotriazol-1-yl)uroniumhexafluorophosphate (HATU, 38.78 mg, 102 μmol, 0.750 equiv.) was dissolved in 30.0 mL of DMF. The linear precursor (147.8 mg, 136 μmol, 1.00 equiv.) was dissolved in 20.0 mL of DMF and mixed with DIPEA (189 μL, 8.00 equiv.). 10 mL of this solution was added to the HATU solution in DMF at 21 °C over 6 hours (1.60 mL/h). Subsequently, another portion of HATU (0.750 equiv.) was added to the reaction mixture. The remaining 10 mL of the linear precursor solution was added dropwise (1.60 mL/h), and the mixture was stirred at 21 °C for 12 hours. The solvent was removed under reduced pressure. To remove the Boc-protecting group, the residue from the cyclization reaction was treated with 5.00 mL of a 95% solution of trifluoroacetic acid (TFA) in DCM and stirred for at least 1 hour at 21 °C. The solvent was removed by a counter-flow of air.After purification by preparative HPLC (5-95% acetonitrile in water, with 0.1% TFA over 45 minutes), the product was isolated as a colorless powder (23.3 mg, 25.0 μmol, 15% yield over 15 reaction steps).