| Cyclic peptides have gained steady interest in the past several decades as potential pharmaceutical drug leads. They exhibit unparallel diversity and complexity through variations in side chain residues, alpha-carbon stereochemistry, scaffold geometry, and cyclization linkages, to name a few. Cyclic peptides have been shown to be more cell permeable and proteolytically more stable than their linear counterparts. In this dissertation, we install an electrophilic chloroacetamide (CAM) functional group onto a diaminopropionic acid (Dap) residue of cyclic hexapeptides with a general scaffold of cyclo [Leu-Leu-Leu-Leu-Pro-Tyr]. We synthesize a library of 8 unique members where we vary the stereochemistry of the leucines and prolines and replace one leucine in each scaffold with a Dap residue. We conjugate the library to rhodamine and biotin reporter groups to make activity based probes to fish out protein targets in HeLa and mouse brain, heart, liver, kidney, spleen and lung tissue. We then investigate whether any observed selectivity is in an activity based manner and isolate the target via a pull down assay with immobilized avidin. We also synthesize a large combinatorial library of cyclo [LAla-X1-X 2-X3-X4-X5-Tyr] on large 2-chlorotrityl chloride (2-Cl-Trt-Cl) macrobeads utilizing 6 different amino acid building blocks, LGlycine, LAlanine, LLeucine, DPhenylalanine, DProline and DValine. We N-methylate half of the library with a novel method we developed that utilize a 50/50 mixture of 13CH3I/CH3I. Due to the perturbance to the natural abundance of 13C, we observe unique isotope distribution patterns on MS-LCMS that enable us, with the assistance of IDCalc RTM, to accurately predict how many amide nitrogens have been N-methylated. We then array the beads in 384 well plates and screen the library in bacillus subtilis and saccharomyces cerevisiae in a halo assay. |
