Development of Flavoproteins as Catalysts for Asymmetric Radical Reactions

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Project Summary The work described in this proposal aims to address the longstanding challenge of controlling the enantioselectivity and regioselectivity of synthetically valuable reactions mediated by radical intermediates. This work will develop novel mechanisms for generating free radical intermediates within protein active sites. Evolution of the protein will be conducted to enhance the chemo-, regio-, and enantioselectivity of the reactions performed within their protein active site. Building on findings in the previous funding period, we will develop couplings reactions between nitronates and alkyl halides. These reactions have two possible products: a redox- neutral reaction to afford chiral 𝛼-tertiary nitroalkanes and a reductive coupling to prepare cross-coupled products. We will design catalysts to favor each outcome. Secondly, we will develop a regioselective coupling of alkyl radicals with arenes. In this project, we will engineer the protein scaffold to favor functionalization at positions that are untouched using existing synthetic methods. Thirdly, we will explore alkene difunctionalization. In one manifold, we will oxidize radical intermediates to form carbocations which can be quenched with various nucleophiles. In a second approach, we will exploit Smiles rearrangements for radical termination. These approaches will enable the rapid synthesis of highly substituted products while also enabling the development of catalysts to precisely control the stereochemistry of stereocenters formed in C–C bond- forming events. In this application, we will also develop a new strategy for radical initiation using oxidative decarboxylation. This activation mode will be applied to the synthesis of secondary amines. Finally, we will create a biocatalytic cross-coupling reaction, where alkylated flavin adducts mimic the reactivity of organometallic intermediates. This method will enable the coupling of carboxylic acids and alkyl halides without using a metalloprotein. Together, these methods and the goals proposed in the Specific Aims have the potential to streamline the synthesis of biological probes and drug targets, creating a significant benefit to human health and associated biomedical sciences.