Although peptides play an essential role in wide-ranging biological processes, they have had relatively limited utility as therapeutic agents due either to poor receptor sub-type selectivity, poor biostability or unfavorable absorption properties. For this reason, the design of high affinity and specific peptidomimetic ligands continues to be an extremely important endeavor in the fields of medicinal chemistry and molecular recognition. In a successfully designed peptidomimetic, the essential amino acid side-chains of the corresponding peptide are displayed on a non- peptide scaffold such that the spatial orientation of the side-chains correspond to the bioactive conformation of the peptide. In order to expedite the synthesis and evaluation of peptidomimetics, many researchers have focused on the design and synthesis of general peptidomimetic scaffolds that are based upon secondary structural motifs which are often present in the present in the bioactive conformations of peptides. In these efforts, the design and synthesis of peptidomimetic scaffolds based on the beta-turn structure has received the most attention due to the importance of this structure in peptide and protein recognition. Unfortunately, the identification of high affinity beta-turn peptidomimetic generally requires the synthesis and evaluation of many derivatives incorporating different side-chains or side-chain orientations, since the determination of the bioactive conformation of most peptides has remained elusive. The identification of high affinity peptidomimetics would be greatly expedited by constructing a library of peptidomimetics based on the beta- turn structural motif where the individual peptidomimetics incorporate different combinations of the amino acid side-chains as well as multiple relative orientations of those side-chains. screening this biased library against receptor targets where the turn structure has been implicated in the bioactive conformation of the corresponding peptide ligand should result in the rapid identification of high-affinity peptidomimetic ligands. In order to accomplish this long term goal, the following specific aims must be realized. (1) A general and high yielding solid-phase synthesis sequence must be developed to prepare mimetics based on the beta-turn structure. The synthesis sequence should be compatible with the side-chain functionality that is present in the naturally occurring amino acids. The synthesis sequence should also provide access to multiple relative orientations of the side-chains that are incorporated into the peptidomimetic. (2) The efficient simulataneous synthesis of a library of the peptidomimetics must be accomplished. (3) Evaluation of the peptidomimetic library against receptor targets to provide high affinity peptidomimetic ligands should be demonstrated.
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