A solid-phase synthetic strategy for the preparation of peptide-based affinity labels: synthesis of dynorphin A analogs

: Solid‐phase synthetic methodology was developed for the preparation of peptide‐based affinity labels. The initial peptides synthesized were dynorphin A (Dyn A) analogs [Phe(p‐X)4,d‐Pro10]Dyn A(1–11)NH2 containing isothiocyanate (X = –N=C=S) and bromoacetamide (X = –NHCOCH2Br) groups. The peptides were assembled on solid supports using Fmoc‐protected amino acids, and the side chain amine to be functionalized, Phe(p‐NH2), was protected by the Alloc (allyloxycarbonyl) group. Following removal of the Alloc group by palladium(0), the reactive isothiocyanate and bromoacetamide functionalities were successfully introduced while the peptides were still attached to the resin. Synthesis of these peptides was carried out on polystyrene (PS) and polyethylene glycol–polystyrene (PEG–PS) resins containing the PAL [peptide amide linker, 5‐(4‐Fmoc‐aminomethyl‐3,5‐dimethoxyphenoxy)valeric acid] linker. Both the rate of Alloc deprotection and the purity of the crude affinity‐labeled peptides obtained were found to be dependent on the resin used for peptide assembly.