4.3. Peptide Synthesis and Characterization

The peptide derivatives were prepared by solid phase peptide synthesis (SPPS) using 2-Chlorotrityl Chloride Resin, and the corresponding N-Fmoc protected amino acids with side chains properly protected by a tertbutyl group (tBu) or 2,2,5,7,8-pentamethyl-chroman-6-sulfonyl (Pmc). 20% piperidine DMF solution was used during deprotection of the Fmoc group. O-Benzotriazol-1-yl-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HBTU) was used as the coupling reagent. Finally, peptide derivative was cleaved using 95% of trifluoroacetic acid with 2.5% of PhSCH₃ and 2.5% of H₂O for 30 min. The crude products were purified by high performance liquid chromatography (HPLC) then frozen dried to obtain pure products.