Development of O-acyl isopeptide method

During over a decade of study on aspartic protease inhibitors and water insoluble prodrugs, in 2003, we discovered that the presence of an O-acyl instead of N-acyl residue within the peptide backbone significantly changed the secondary structure of the native peptide. In addition, the target peptide was subsequently generated by an O-N intramolecular acyl migration reaction. These findings led to the development of a novel method, called "O-acyl isopeptide method", for the synthesis of peptides containing difficult sequence. Further application of the method to Alzheimer's A beta 1-42 revealed that the O-acyl isopeptide of A beta 1-42 could be effectively synthesized and stored without spontaneous self-assembly. Intact monomer A beta 1-42 could then be obtained from the isopeptide under physiological experimental conditions. We named the O-acyl isopeptide "Click Peptide", because of its "quick and easy one-way conversion" to the parent A beta 1-42. Application of the click peptide has provided a new basis for the investigation of the biological functions of A beta 1-42 by inducible activation of its self-assembly. The O-acyl isopeptide method has further evolved as a general method for peptide synthesis with our recent developments of "O-acyl isodipeptide units" and "racemization-free segment condensation methodology". Isodipeptide units have enabled routine use of the O-acyl isopeptide method by avoiding the often difficult esterification reaction on resin. "Racemization-free segment condensation methodology" has been achieved by employing N-segments possessing a C-terminal urethane-protected O-acyl Ser/Thr residues. The synthesis of long peptides/proteins by racemization-free segment condensation has thus become possible at Ser/Thr residues instead of C-terminal Gly/Pro residues. As the O-acyl isopeptide method becomes more widely utilized, we have composed this review to facilitate its application for the production of peptides and proteins. (c) 2007 Wiley Periodicals, Inc.