Supramolecular interactions of methylated amino acids: investigations using small molecule aromatic cage mimics




Whiting, Amanda Lee

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The recognition of modified amino acids by reader proteins is governed by the competing interplay of weak, attractive, intermolecular forces and solvation effects. For the recognition of hydrophobic cations like methyl-lysines and methyl-arginines, native reader proteins utilize structural cages always containing multiple aromatic amino acids and sometimes an occasional acidic residue. Through the highly ordered arrangement of multiple aromatic surfaces, reader proteins can invoke the attractive forces of electrostatic, cation-pi, and in the case of arginine, pi-pi interactions. The hydrophobic effect can also significantly affect these binding events in aqueous environments. In this thesis, a number of small molecule, synthetic cages containing significant aromatic surface area have been synthesized. Variation in both total host hydrophobicity and degree of flexibility were explored to determine what effect they have on the overall binding of methylated amino acids in water. Significant flexibility in the first generation of highly aromatic hosts was shown to be detrimental to binding. However, strong binding was observed for guests with significant hydrophobic character despite this flexibility. The cause of the strong affinities in this family of synthetic cages was shown to be due to the hydrophobic effect, rather than any attraction due to cation-pi interactions. Synthetic efforts towards hosts with more rigid structures led to the use of Tröger’s base as a structural building block. Hosts incorporating Tröger’s bases into well-defined aromatic cavities were found to exhibit strong binding to both methyl-lysine and methyl-arginine derivatives in pure water. Differences in guest selectivity were due to the rigid altered host geometry introduced by the Tröger’s base cleft.



organic chemistry, supramolecular chemistry, post-translational modifications, amino acid recognition, hydrophobic effect