| Macrocyclization endows peptidic compounds with distinct advantages over their linear counterparts, such as increased proteolytic resistance, cell permeability, and binding affinity toward their biomolecular targets. As cyclic peptides comprise a number of viable drug candidates, their further design and diversification is of utmost interest for the modulation of challenging targets, such as protein-protein interactions (PPIs). PPIs generally have been considered intractable due to their large, shallow binding clefts, but recent successes exemplify macrocyclic peptides as ideal scaffolds for targeting such surfaces. In nature, macrocyclic peptides are accessible only through complex microbial non-ribosomal cyclization pathways or through extensive post-translational modifications of ribosomal polypeptide precursor sequences. Thus, methods which can generate cyclic peptides in a facile manner while also providing a route for compound diversification and screening against drug targets is of critical importance.;This thesis investigates a modular synthesis and application of macrocyclic organo-peptide hybrids (MOrPHs): cyclic peptides which harbor diversifiable non-proteinogenic scaffolds. In this approach, ribosomally-produced peptides were generated which contained an unnatural amino acid (UAA) moiety and a C-terminal intein protein. Exploiting these two functionalities, a diverse set of bifunctional synthetic scaffolds were shown to undergo dual-ligation with the peptide sequences via UAA ligation (triazole formation or oxime formation) and intein excision to afford side-chain to C-terminus macrocyclic products. Organo-peptide compounds could thus be furnished comprising 4-12 residues in length and harboring a diverse set of synthetic, organic linker scaffolds. In addition to macrocyclization, further ring constrain was imposed through installation of disulfide bridges, affording a wide array of bicyclic ring topologies. As cyclic peptides could be generated in conjunction with N-terminal protein fusion, the ability to explore MOrPH libraries via a plasmid display system was examined in effort to isolate MOrPH ligands which exhibit potent affinity for the oncoprotein HDM2.;Lastly, MOrPH compounds were designed via a rational approach to inhibit the interaction between the tumor suppressor p53 and the oncoproteins HDM2 and HDMX. These macrocycles contained a functional alpha-helix motif and were shown to bind HDM2/X and inhibit its association with p53 with nanomolar potency. This work demonstrated that MOrPH compounds can harbor a helical structure and can be implemented for the inhibition of therapeutically relevant PPIs. |
