Enabling in vivo catalytic activation of bioorthogonal chemistry with light using Si-rhodamine and the universal and modular synthesis of monoaryltetrazines from functionalized arylboronic acids
Date
2022
Authors
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Publisher
University of Delaware
Abstract
Tetrazine (Tz) ligation is a useful tool to probe the biochemistry in living organisms, due to its rapid catalyst-free kinetics, innocuous byproducts, and orthogonality toward native cellular processes. In the first chapter, I will give a brief introduction to the development of tetrazine ligation as a bioorthogonal chemical reaction, and the application of tetrazine ligation to different fields like cell imaging, and medicinal chemistry, protein synthesis, and materials science. ☐ My graduate research had been focusing on developing new catalysts and reagents to empower this chemical tool. In chapter 2, I will talk about the first cytocompatible photocatalyst that will activate tetrazine ligation in vivo, which was repurposed from a widely used chromophore. Chromophores that absorb in the tissue-penetrant far-red/near-infrared window have long served as photocatalysts to generate singlet oxygen for photodynamic therapy. However, the cytotoxicity and side reactions associated with singlet oxygen sensitization have posed a problem for using long-wavelength photocatalysis to initiate other types of chemical reactions in biological environments. Herein, silicon-Rhodamine compounds (SiRs) are described as photocatalysts for inducing rapid bioorthogonal chemistry using 660 nm light through the oxidation of a dihydrotetrazine to a tetrazine in the presence of trans-cyclooctene dienophiles. SiRs have been commonly used as fluorophores for bioimaging but have not been applied to catalyze chemical reactions. A series of SiR derivatives were evaluated, and the Janelia Fluor-SiR dyes were found to be especially effective in catalyzing photooxidation (typically 3%). A dihydrotetrazine (DHT)/tetrazine pair is described that displays high stability in both oxidation states. A protein that was site-selectively modified by trans-cyclooctene (TCO) was quantitatively conjugated upon exposure to 660 nm light and a dihydrotetrazine. By contrast, a previously described methylene blue catalyst was found to rapidly degrade the protein. SiR-red light photocatalysis was used to cross-link hyaluronic acid (HA) derivatives functionalized by dihydrotetrazine and trans-cyclooctenes, enabling 3D culture of human prostate cancer cells. Photoinducible hydrogel formation could also be carried out in live mice through subcutaneous injection of a Cy7-labeled hydrogel precursor solution, followed by brief irradiation to produce a stable hydrogel. This cytocompatible method for using red light photocatalysis to activate bioorthogonal chemistry is anticipated to find broad applications where spatiotemporal control is needed in biological environments. ☐ In chapter 3, while reviewing known methodology to synthesize and modify tetrazines, I will also describe the development of a new reagent ‘h-Tz’, which could be safely prepared and could be used for the universal and modular synthesis of mono-aryltetrazines from functionalized arylboronic acids using and Ag-mediated Liebeskind-Srogl cross-coupling.
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Keywords
Catalytic activation, Bioorthogonal chemistry, Silicon rhodamine, Modular synthesis, Monoaryltetrazine, Arylboronic acid