Dissertation Defense: Fathima Thanzeel
Candidate Name: Fathima Thanzeel
Advisor: Christian Wolf, Ph.D.
Title: Accelerated Asymmetric Reaction Screening and Sensing of Biomolecules Using Small Molecular Probes
Chiroptical sensing has recently gained interest as a rapid technique for screening asymmetric reactions and quantification of important biomolecules. In this thesis an array of probes and chiroptical sensing strategies that accomplish these tasks were developed and
Both L- and D-amino acids can co-exist as nonracemic mixtures in the human and mammalian central nervous system and endocrine organs, and have clinical relevance. A selective, molecular probe that allows accurate quantification of the enantiomeric excess (ee) and concentration of cysteine was introduced. The sensing is based on ipso-substitution at an electrondeficientaryl sulfonate probe. The colorimetric UV change provides information of the concentration and the distinct circular dichroism (CD) signal gives the absolute configuration of the major enantiomer and the ee of D/L cysteine. This method is fast and compatible with aqueous solutions including simulated body fluids. The probe is highly specific for cysteine and other amino acids and biothiols, such as homocysteine and glutathione, do not interfere with the chiroptical analysis.
Asymmetric reaction optimization has become a critical part across the chemical and pharmaceutical sciences. Yet, the determination of optimal reaction conditions is often time consuming and labor intensive. A sensing strategy was developed for the rapid analysis of the conversion and asymmetric induction of 54 asymmetric allylation reactions of nine different isatins in various solvents. The inherent CD/UV change during product formation was used to determine the optimal reaction conditions by a single operator in less than 20 work hours without the need for calibration curves. The efficiency of this strategy was shown by successful upscaling of two optimized isatin allylations with 98–99% yield and 91–94% ee.
The inherent practicality and ruggedness of click reactions was exploited for operationally simple sensing of amines, amino alcohols, alcohols, amino acids with 4-halocoumarins. The click sensing is high yielding, shows fast substrate consumption at room temperature with no by-product formation, it is wide in scope, insensitive to air and water, has excellent solvent compatibility and proceeds under mild reaction conditions at room temperature. The irreversible bond formation results in characteristic CD/UV spectra, which allow determination of the absolute configuration, ee, and concentration of a large variety of chiral compounds. The potential of this approach was
demonstrated by the determination of ee and the conversion of crude reaction mixtures of iridium catalyzed asymmetric imine hydrogenations.
A method that can be used in a high throughput setting for the rapid analysis of amino acids has potential as a diagnostic tool. With this important purpose in mind, a small molecular probe that undergoes smooth binding with each of the 19 standard amino acids in aqueous solutions was introduced. The probe is inexpensive, readily available and reports concentration, ee and absolute configuration within a short period of time. The assay was used for the accurate analysis of aspartic acid samples of various ee’s and concentrations. This was further extended to the analysis of the enantiomeric composition of binary mixtures of amino acids, amines and biothiols. The sensing of alcohols is often challenging due to their low nucleophilicity. Chromophoric chlorophosphite probes that can undergo irreversible bond formation with an alcohol group or other nucleophiles were used for the CD/UV sensing of almost 30 compounds including alcohols, diols, hydroxy acids, hydroxy amides, amines and amino alcohols. The applicability of this assay was demonstrated by accurate determination of concentration, ee and absolute configuration of scalemic samples containing 1-phenylethyl alcohol using a relay assay sensing strategy.