Imparting unique function in peptides and peptide-based materials using non-natural amino acids

The chemical modification of proteins and peptides is one of the most prominent techniques used to study complex biological processes. Among the plethora of methods available to tailor the biomolecule in question, most rely on the alteration of a specific functional group. In some proteins, a natural post-translational modification process provides a chemical handle that can be utilized to study molecular function. More commonly, a specific amino acid is targeted for modification using a molecule that reacts selectively with the functional group in question on the natural form of the protein. Alternatively, the mutation of an amino acid to a non-natural residue through specialized expression systems allows the same type of modification to occur in a more selective fashion through a bioorthogonal reaction. Regardless of the method used, the chemical alteration has a designed function and can provide useful information about the origin, behavior, or fate of the protein. The first portion of this study is aimed at imparting function in peptides through the synthesis of non-natural amino acids for their incorporation into peptide materials. Our initial efforts toward the construction of a suitably protected gamma-carboxyglutamic acid directed the development of novel chiral auxiliary that allowed completion of a highly stereoselective synthesis of Fmoc-Gla(OtBu)2-OH to be used in the solid phase synthesis of calcium-binding peptides. This work is followed by investigations into a new method for bioconjugation to create functional proteins, where the reactivity of 3-(2H)-furanones toward biologically relevant amines is evaluated. Finally, we turned our attention to the development of a photocaged beta-hairpin peptide capable of undergoing two independently triggered phase transitions. This peptide, while fully soluble in a low ionic strength solution, undergoes a triggered folding and self-assembly event upon addition of buffer containing a high concentration of salt. The resulting hydrogel then subsequently proceeds through a triggered gel-sol transition upon irradiation with UV light.