Reagents and conditions:
(a)
20% piperidine/DMF, 20 min; Fmoc-Lys(Alloc)–OH, HCTU, DIPEA/DMF,
1 h; (b) 20% piperidine/DMF, 20 min; Fmoc-Trp(Boc)–OH, HCTU,
DIPEA/DMF, 1 h; (c) 20% piperidine/DMF, 20 min; Fmoc-Arg(Pbf)–OH,
HCTU, DIPEA/DMF, 1 h; (d) 20% piperidine/DMF, 20 min; Fmoc-d-Phe-OH, HCTU, DIPEA/DMF, 1 h; (e) 20% piperidine/DMF, 20 min; Fmoc-His(Trt)–OH,
HCTU, DIPEA/DMF, 1 h; (f) 20% piperidine/DMF, 20 min; Fmoc-Asp(Allyl)–OH,
HCTU, DIPEA/DMF, 1 h; (g) 20% piperidine/DMF, 20 min; Fmoc-Nle–OH,
HCTU, DIPEA/DMF, 1 h; (h) 20% piperidine/DMF, 20 min; Fmoc-6-Ahx–OH,
HCTU, DIPEA/DMF, 1 h; (i) 20% piperidine/DMF, 20 min; Fmoc-Cys(Trt)–OH,
HCTU, DIPEA/DMF, 1 h; (j) PhSiH3, Pd(PPh3)4/DCM, 1 h; (k) HCTU, DIPEA/DMF,
2 h; (l) 20% piperidine/DMF, room temperature, 20 min; (m) TFA/TIS/H2O (95:2.5:2.5), 3 h.