The peptide was synthesized by a solid-phase method using a p-methylbenzhydrylamine resin to which N1-Boc-N6-Fmoc-L-lysine (I) was coupled giving (II). To this solid phase the following protected amino acids Nalpha-Boc-N1-formyl-L-tryptophan (III), Nalpha-Boc-Nomega-Tos-L-arginine (V), Nalpha-Boc-D-(2-naphthyl)alanine (VII), Nalpha-Boc-Npi-L-histidine (IX) and Nalpha-Boc-Ogamma-Fm-L-aspartic acid (XI) were sequentially coupled yielding resins (IV), (VI), (VIII), (X) and (XII).
The coupling sequences were continued with Nalpha-Boc-L-norleucine (XIII) to afford resin (XIV). Elimination of the Fmoc and OFm protecting groups of (XIV) was performed with piperidine in NMP allowing the formation of the lactam ring by cyclization with BOP and DIEA in NMP providing the macrocyclic lactam (XV).
Elimination of the Boc protecting group of (XV) with trifluoroacetic acid followed by acetylation of the free amino group with acetic anhydride yielded resin (XVI) with a terminal acetyl group. Finally, this resin was treated with FH, anisole and dithioethane to complete the deprotection process and elimnate the solid phase resin affornig the target macrocyclic peptide.