Synthesis of peptide amides using Fmoc-based solid-phase procedures on 4-methylbenzhydrylamine resins

A two-step low-high protocol for the efficient synthesis of peptide amides is described. The protocol exploits the efficiency of Reagent K for side-chain deprotection with the capability of the hard acid trifluoromethane-sulfonic acid (TFSMA) for cleavage of the peptide from the benzhydrylamine resin. This procedure has proven to be an effective method for the synthesis of peptide amides. The formation of α-aminosuccinimide (Asu) derivatives were observed with aspartyl-containing peptides as a minor side reaction product of this procedure, but this Asp→Asu rearrangement could be successfully suppressed by employing low temperature conditions. The N- to O-acyl rearrangement of threonine and/or serine residues also only occurred to a minor extent under these synthetic conditions. © Munksgaard 1995.