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Flemer, Stevenson

Chemistry

2005

PhD

Protein-enzyme interplay is a crucial component in cellular signaling processes. It has been established, through the study of protein X-ray crystal structures, that a frequent secondary recognition motif in these interactions is the poly-L-proline type II (PPII) helix. Further, it has been shown that specific oligopeptide inhibitors for many protein kinases and SH2/SH3 domain interactions adopt a PPII conformation when bound to the active site. Since the sequence of specific amino acids within the peptide inhibitor is crucial to its efficacy, it became of interest to design the amino acid substructure such that PPII-forming potential of the peptide would be maximized while conserving the sidearm architecture of the individual residues. This duality of structure has been realized through the synthesis of proline-templated amino acids (PTAAs). Two PTAAs were synthesized in this effort, mimicking the sidearm structure of leucine (PTL) and arginine (PTR). Proline-templated arginine (PTR) emerged as the major object of scrutiny in this research, due in part to the requirement for arginine in many PPII binding sequences as well as to the overall importance of the basic arginine residue in many biological processes. Chemistry was developed and optimized toward the modification of the arginine guanidino headgroup, allowing for a wide spectrum of N-substitution patterns to be modeled for this important residue. Further, the utility of this synthetic protocol was tested through the successful construction of trimer and octamer model peptide systems incorporating these modified arginine systems. The success of the guanidinylation methodology initiated an investigation into its applicability as a general method, without constraint as simply an arginine modification protocol. The scope and limitations of a solution guanidine genesis were probed, allowing a more thorough understanding of the process and providing avenues into substitution patterns previously unobtainable using solid-supported methodologies. Polyguanidine libraries were constructed and utilized to show a general application pattern for this methodology.