Date on Master's Thesis/Doctoral Dissertation
unsaturated aldehyde; exhaled VOC; breath analysis
The peroxidation of unsaturated fatty acids is a widely recognized metabolic process that creates a complex mixture of volatile organic compounds including aldehydes. Elevated levels of reactive oxygen species in cancer cells promote random lipid peroxidation, which leads to an increase in a variety of aldehydes. Many of these volatile aldehydes are exhaled and are of interest as potential markers of disease. Chapter 1 presents a review of reported aldehydes in the exhaled breath of lung cancer patients. alpha,beta-Unsaturated aldehydes, detected primarily when derivatized during exhaled breath preconcentration, are underreported in the reviewed articles. Chapter 1 concludes with our hypothesis that better methods for detection of exhaled alpha,beta-unsaturated aldehydes are needed and will translate into more accurate diagnoses of disease. Chapter 2 details a new approach to selectively derivatize, concentrate and analyze the underrepresented subset of carbonyl-containing VOC metabolites produced by cells under oxidative stress, namely alpha,beta-unsaturated aldehydes. We examined, using a peristaltic pump and gas dispersion tube, passing gaseous breath samples through solutions containing thiol derivatization reagents. Thiol reagents were prepared and investigated for their ability to chemoselectively react with alpha,beta-unsaturated carbonyls. The goal of targeting alpha,beta-unsaturated aldehydes via thiol-Michael addition was not achieved, likely due lack of phase transfer of VOCs and slow reaction rate of the 1,4 addition. Chapter 3 describes a novel breath analysis approach that couples established carbonyl preconcentration technology with UV-Vis spectroscopy to constitute a fast, inexpensive, and noninvasive test for disease. The underlying principle of this work exploits the characteristic absorbance of conjugated alpha,beta-unsaturated aldehydes in the UV spectrum. An increase in cellular oxidative stress, as happens in diseased cells, will result in even higher levels of aldehydes, including unsaturated compounds, in exhaled breath. Thus, we explored UV spectral detection of the unsaturated metabolite fraction within the complex breath carbonyl mixture. A pilot study comparing 10 healthy and 10 symptomatic COVID-19 positive patient breath samples was performed to test the hypothesis that the distinct absorbances of unsaturated carbonyls could be used as a diagnostic indicator. Breath samples were preconcentrated using silicon microreactor technology known to isolate carbonyl compounds as oxime ether adducts. Solvent elution from the microreactor provided sample solutions that then were directly analyzed by UV-Vis spectroscopy. The data indicate that even trace amounts of alpha,beta-unsaturated aldehyde adducts increase UV absorptions in the presence of higher concentration saturated analogs. A significant elevation in UV absorptions from COVID-19 positive samples was observed, a result that may be due to increases in concentrations of alpha,beta-unsaturated aldehyde metabolites from lipid peroxidation in the positive cohort. On comparing the averaged absorbance from the healthy group to averaged absorbance from the COVID-19 positive group, with plus or minus one standard deviation, at wavelengths from 235 to 305 nm, we noted a clear distinction between the error ranges for the two groups. The data suggests that a UV absorbance threshold could be established, an absorbance above which is indicative of SARS-CoV-2 infection. Application to other diseases may be possible, especially if related to cellular oxidative stress conditions. As alpha,beta-unsaturated aldehydes are known to elicit harmful effects through alkylation of DNA, proteins, and other biomacromolecules, we explored the toxic effects of a well-known metabolite of benzene, muconaldehyde. For this work we developed a new synthesis. Chapter 4 describes a new synthesis of (E, E)-muconaldehyde, an open-ring metabolite of benzene, from muconic acid. Several syntheses of muconaldehyde have been reported, each requiring multiple steps with the best synthesis having an overall yield of 32%. By our method, muconaldehyde was prepared in 71% yield using a one-pot procedure by selective DIBAL-H-mediated mono-reduction of muconic acid activated as a bis(N-acyl-N,N'-diisopropylurea). The method was demonstrated on gram scale (1.14 g muconaldehyde was prepared in 65% yield). Finally, Chapter 5 provides the experimental details and spectral characterizations of compounds synthesized during the course of my PhD research.
Sutaria, Saurin R., "Alpha, beta-unsaturated aldehydes: the underrepresented markers of disease." (2022). Electronic Theses and Dissertations. Paper 4035.
Retrieved from https://ir.library.louisville.edu/etd/4035
Available for download on Friday, June 16, 2023