Synthesis of NK1RL-Peptide Linker (6): Reagents and conditions:(a) (i) DCM, DMF wash, (ii) Fmoc-Asp(OtBu)-OH, PyBOP, DIPEA, DMF, 4 h; (b) (i) 20% piperidine in DMF, 3×10 min, (ii) Boc-DAP(Fmoc)-OH, PyBOP, DIPEA, DMF, 4 h; (c) (i) 20% piperidine in DMF, 3×10 min, (ii) Fmoc-Lys(Boc)-OH, PyBOP, DIPEA, DMF, 4 h; (d) (i) 20% piperidine in DMF, 3×10 min, (ii) Fmoc-Asp(OtBu)-OH, PyBOP, DIPEA, DMF, 4 h; (e) (i) 20% piperidine in DMF, 3×10 min, (ii) Fmoc-Arg(pbf)-OH, PyBOP, DIPEA, DMF, 4 h; (f) (i) 20% piperidine in DMF, 3×10 min, (ii) Fmoc-PEG2-OH, PyBOP, DIPEA, DMF, 4 h; (g) (i) 20% piperidine in DMF, 3×10 min, (ii) L-733060-AcOH, PyBOP, DIPEA, DMF, 12 h; (h) TFA:H2O:TIPS:EDT, 92.5:2.5:2.5:2.5, 3×5 mL × 15 min, 38 %.