The title compound was obtained by solid-phase peptide synthesis starting from N-Boc-S-(4-methylbenzyl)cysteine linked to PAM resin (I). The protected peptide template (XVII) was synthesized by sequential coupling-deprotection cycles using the appropriate combination of either Boc- or Fmoc- N-alpha-protected amino acids. The following side-chain-protected amino acid residues were assembled: Gly (III), Lys(Boc) (V), Glu(cyclohexyl ester) (VII), Lys(Boc) (V), Pro (X), Gly (III), Lys(Boc) (V), Lys(chlorobenzyloxycarbonyl) (XIV) and Lys(Boc) (XVI) to produce the peptide resins (IV), (VI), (VIII), (IX), (XI), (XII), (XIII), (XV) and (XVII), respectively. Subsequent removal of the N-terminal and the four side-chain Boc protecting groups by means of trifluoroacetic acid yielded the peptide resin (XVIII).

Simultaneous coupling of five N-Boc-arginin (XIX) residues to the free amino groups of the peptide template (XVIII), followed by acid deprotection of the Boc groups, furnished (XX). To this were assembled five N-Boc-proline residues (XXI) to provide, after acid deprotection, resin (XXII). Then, reductive condensation with Boc-protected lysinal (XXIII) furnished the protected pseudopeptide adduct (XXIV). Finally, simultaneous cleavage from the resin and removal of protecting groups was effected by treatment with anhydrous hydrogen fluoride.