자료유형  

 학위논문

Control Number  

0017161437

International Standard Book Number  

9798382610696

Dewey Decimal Classification Number  

540

Main Entry-Personal Name  

Jiang, Yuhua.

Publication, Distribution, etc. (Imprint  

[S.l.] : Indiana University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

346 p.

General Note  

Source: Dissertations Abstracts International, Volume: 85-11, Section: B.

General Note  

Advisor: Lewis, Jared.

Dissertation Note  

Thesis (Ph.D.)--Indiana University, 2024.

Summary, Etc.  

요약This dissertation describes newly developed methodologies to expand the utility of biocatalytic halogenation, mainly by expanding the scope and reactivity of flavin-dependent halogenases (FDHs). This family of enzymes is capable of selectively halogenating a wide range of aromatic substrates using halide ions as halogen source under benign reaction conditions. Prior to this dissertation, our group had evolved variants of RebH, an FDH from the rebeccamycin biosynthetic pathway, with improved thermostability, expanded substrate scope and altered regioselectivity. These results demonstrated that FDHs possess unique activities and that they are amenable for further improvements via protein engineering.Chapter 1 provides an overview of biocatalytic halogenation with a focus on flavin-dependent halogenases (FDHs). Previous achievements on improving FDH limitations and exploring their utility are also discussed to highlight the potential of applying biocatalytic halogenation. Chapter 2 describes studies on FDH-catalyzed halocyclization reactions. I was involved in the halolactonization project, which constituted the first example of enzymatic enantioselective halocyclization on simple, achiral olefins. I then expanded the scope of this system to include the less nucleophilic alcohol substrates. A variety of chiral tetrahydrofuran moieties can be synthesized in high yields and enantioselectivity, and a one-pot enzymatic cascade reactions was also achieved by utilizing FDHs and ketoreductase. Chapter 3 summarizes the initial investigation of using carbon nucleophiles in FDH-catalyzed halocyclization reactions. An α-cyano ketone substrate was shown to have promising results in a selective bromocarbocyclization reaction. Through site-saturation mutagenesis of three active site residues, I identified several variants that provided improved yields and diverse selectivity.Chapter 4 highlights the biocatalytic potential of a unique single component flavin-dependent halogenase, AetF. This enzyme is a bifunctional flavin reductase/flavin halogenase discovered in 2019. We revealed that this enzyme can selectively halogenate a wide range of compounds, including relatively electron deficient arenes and heterocyclesthat were not accepted by previously investigated FDHs. AetF also catalyzes several enantioselective transformations that required extensive engineering in earlier FDHs. A novel biocatalytic iodination was also achieved using AetF. Chapter 5 describes the study of selective C-H halogenation of alkenes and alkynes enabled by single component flavin-dependent halogenases. We demonstrated that AetF could catalyze halogenation of a series of 1,1'-disubstituted alkenes with good-to-high stereoselectivity, and that AetF and selected homologues were capable of halogenating terminal alkynes, all of which expand the utility of biocatalytic halogenation reactions and provide insight into how halogenated natural products could be synthesized. Mutagenesis and deuterium kinetic isotope effects experiments were used to support a mechanistic proposal involving covalent catalysis for halogenation of unactivated alkynes. Chapter 6 discusses initial findings on FDH-catalyzed bromo-hydroxylation reactions. Initial screening and following validation revealed one variant of RebH that could catalyze the reaction with good yield and moderate enantioselectivity. Further protein engineering and reaction conditions optimizations are ongoing in our lab.

Subject Added Entry-Topical Term  

Chemistry.

Subject Added Entry-Topical Term  

Biochemistry.

Subject Added Entry-Topical Term  

Organic chemistry.

Index Term-Uncontrolled  

Flavin-dependent halogenases

Index Term-Uncontrolled  

Reactivity

Index Term-Uncontrolled  

Scope

Index Term-Uncontrolled  

Biocatalytic halogenation

Added Entry-Corporate Name  

Indiana University Chemistry

Host Item Entry  

Dissertations Abstracts International. 85-11B.

Electronic Location and Access  

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Control Number  

joongbu:658297