Date on Master's Thesis/Doctoral Dissertation

5-2013

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Chemistry

Committee Chair

Nantz, Michael H.

Subject

Chemical tests and reagents

Abstract

The reaction between an aminooxy moiety (RONH2) and a carbonyl group of either an aldehyde or a ketone — known as an oximation reaction — is a versatile click chemistry coupling that generates a robust oxime ether linkage. The oximation reaction is chemoselective and can be performed under mild conditions in a large variety of solvents, including water. The attractive properties of the aminooxy group and derived oximation reactions, reviewed in Chapter 1, inspired us to use this chemistry as a key feature of our research. Specifically, we prepare functionalized aminooxy compounds so that the oximation chemistry can then serve as a prelude to new synthetic or analytical methods. For example, Chapter 2 presents an improved preparation of O- (diphenylphosphinyl)hydroxylamine (DPPH), an aminooxy-containing reagent, using the classic Schotten-Baumann conditions. We show how DPPH can then be used as a chemoselective nitrogen transfer reagent for a one-pot aldehyde-to-nitrile functional group transformation. Sixteen aldehydes were smoothly transformed to their in another application, we use functionalized aminooxy reagents to achieve quantitative multiplexed gas chromatography-mass spectrometry (GC-MS) analysis. Specifically, we chemoselectively derivatize carbonyl (aldehyde and ketone) metabolites using the aminooxy-containing reagents. Chapter 3 presents a focused fundamental study of the propensity of oxime ethers to undergo MS-induced fragmentations, such as the McLafferty rearrangement. In particular, we studied structural factors that promoted a,ß-fragmentation in oximes of both ketones and aldehydes, as well as the derived silyl ethers of these adducts. We determined that 1) the propensity of the McLafferty rearrangement was greatly enhanced by oxygen at the b-position of silyl oxime ethers, 2) the McLafferty rearrangement is more prominent for E-isomers of oxime and silyl oxime ethers than for the corresponding Z-isomers, and 3) Z-isomers of silyl oxime ethers with CH2 at the b-position generate nitrilium ions to a greater extent than their corresponding E-isomers. Chapter 4 describes the 3-step synthesis of a new class of stable isotope-labeled derivatizing reagents –– aminooxyethyl propionate reagents (AEP) –– that enable multiplexed GC-MS analysis of small molecule carbonyl compounds. The AEP reagents contain 1) an aminooxy moiety, and 2) a propionate ester moiety that generates a reporter isotope-labeled mass spectral tag (MST) in the form of an ethyl carbenium ion via an ester a-cleavage. The AEP MSTs appear in an m/z zone of minimal interference (ZMI) in the range m/z 32-34. This is a key feature in that unobstructed observation of reporter MSTs in this zone significantly improves simultaneous quantitation of carbonyl analytes from multiple samples without recourse to MS peak deconvolution strategies. Also, and in contrast to known isotope coding reagents for GC-MS, AEP reagents are not affected by the chromatographic isotope effect. The versatility of the technology for carbonyl metabolite profiling and absolute quantification is demonstrated by an analysis of turmeric extract, serving as a representative complex biological sample. A series of analogous methyl ketones were profiled from characteristic MS fragmentations of the AEP-derived oxime ether adducts, and two members, 2-nonanone and 2-undecanone, were quantified using AEP-labeled external standards. Finally, Chapter 5 concludes with additional demonstrations of click chemistry. We used oximation to ligate linker molecules to fluorophores and gold nanoparticles (AuNPs) to generate a fluorescent nano-entity for breast cancer location and diagnosis. Five homologous linkers, each consisting of a thiol-terminated hydrophobic domain coupled to an aminooxy-terminated PEG-based domain, were prepared using a 6-step synthesis in 7-25% overall yield. The aminooxy end subsequently was reacted with an aldehyde-functionalized cypate fluorophore, and the thiol end was used for attachment to gold nanoparticles. Linker attachment to cypate in this manner was superior to previously investigated amide coupling involving linker amines and cypate carboxylic acid. Collectively, the results from these investigations demonstrates a novel strategy that employs functionalized aminooxy substrates and reagents to first exploit the high yielding and selective click coupling with carbonyl substrates to set the stage for secondary synthetic or analytical operations. Approaches developed in this multifaceted study appear to be applicable to a variety of synthetic problems ranging from those of a purely chemical nature to other impacting biological systems.

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