Date of Award

August 2018

Degree Type

Dissertation

Degree Name

Doctor of Philosophy

Department

Chemistry

First Advisor

Alan W Schwabacher

Committee Members

Alexander Arnold, Joseph Aldstadt, Nicholas Silvaggi, James Cook

Keywords

arginine, azo dyes, chemosensors, enduracididine, isoxazoline, polymers

Abstract

The field of molecular recognition focuses on the selective and reversible binding of small guest molecules to larger host molecules. This dissertation describes synthesis of small molecules as binding guests for enzymatic substrates as well as molecules as host chemosensors to detect and identify metal ions. Two approaches to new antibiotic drugs have been explored, and an array of sensors for the quantitation of aqueous metals is being commercialized.

As strains of deadly bacteria emerge with evolved resistance to known antibiotics, new drugs are needed with novel mechanisms of action. Natural product antibiotics containing enduracididine, a non-canonical amino acid derived from arginine, have been found effective against resistant organisms. Recently, the biosynthesis of enduracididine has been elucidated by the Silvaggi group. Various derivatives of arginine are of interest as guest molecules for the Mpp family of proteins. We have developed a particularly succinct route to γ-hydroxy-arginine, which has also been used as a precursor to other oxidized arginine derivatives. Our route provides quantities of arginine derivatives which have been synthesized via a four step route utilizing an isoxazoline intermediate. The synthetic methods for formation and subsequent reduction of the isoxazoline have been studied extensively; and this succinct and versatile synthesis yields either γ-hydroxy-arginine or the keto acid derived from it by changing the conditions of the reduction.

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In another approach to developing new antibiotic treatment, we have pursued the inhibition of the β-barrel assembly machine (BAM), through a small molecule scaffold that binds β-sheets. BAMa is the only known β-barrel protein that spontaneously folds, while all others require the help of BAMa. The β-barrel membrane proteins include efflux pumps, proteins for active transport that allow bacterial survival by ejection of antibiotic drugs. Inhibition of BAMa may itself prove bactericidal, or used in combination therapy increase efficacy of drugs rendered previously ineffective due to acquired resistance.

We have also developed metal ion chemosensors for simulataneous identification and quantitation of multiple metals. These are useful for monitoring metal ion concentrations in industrial wastewater. Current limitations in measuring metal concentration in wastewater can lead to increased costs and excess solid waste in order to meet compliance standards. Our goal is a simple system to allow continuous, real-time measurement of multiple metals on site to decrease over-treatment and detect spikes in pollutant metals. Utilizing UV/VIS absorption an array of semi-selective sensors each with its own spectral response to metal ions allows identification and concentration of pollutants to be determined. Toward this end, we have prepared chemosensors, demonstrated their sensing ability, and covalently attached them to transparent polymers and transparent supports in several ways that allow repeated use for metal-ion measurement. These dyes have been studied in solution and when covalently bound to polymers. Dyes with complementary metal-selectivity allow for high information from a few sensors; a model using three sensors has been demonstrated to simultaneously measure the concentration of seven metals in solution.

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