Development of O ‐acyl isopeptide method

During over a decade of study on aspartic protease inhibitors and water‐soluble 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 Aβ1‐42 revealed that the O ‐acyl isopeptide of Aβ1‐42 could be effectively synthesized and stored without spontaneous self‐assembly. Intact monomer Aβ1‐42 could then be obtained from the isopeptide under physiological experimental conditions. We named the O ‐acyl isopeptide as “Click Peptide,” because of its “quick and easy one‐way conversion” to the parent Aβ1‐ 42. Application of the click peptide has provided a new basis for the investigation of the biological functions of Aβ1‐42 by inducible activation of its self‐assembly. The O ‐acyl isopeptide method has further evolved as a general method for peptides 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. “Racemizationfree segment condensation methodology” has been achieved by employing N ‐segments possessing a C‐terminal urethaneprotected 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 Cterminal 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. © 2007 Wiley Periodicals, Inc. Biopolymers (Pept Sci) 88: 253–262, 2007. This article was originally published online as an accepted preprint. The ‘Published Online’ date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com