Electron deficient dihydrotetrazines: synthesis, redox properties and applications in biochemical systems
Date
2019
Authors
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Publisher
University of Delaware
Abstract
Oxidatively stable, electron deficient dihydro-s-tetrazines (DHTzs) can be readily synthesized using a variety of methods. These DHTzs can quickly be converted via oxidation into their corresponding tetrazine (Tzs). Tz are highly reactive towards appropriate dienophiles for use in tetrazine ligation while the DHTz is complete inactive. Control of the DHTz/Tz redox state allows for an “on-off” switch-like control of tetrazine ligation which has important implications for bioorthogonal chemistry. ☐ Chapter 2 discusses the characteristics of several classes of electron deficient DHTz/Tz redox pairs such as dipyridyl systems and mixed ester/pyridyl DHTz systems. Factors influencing the oxidation such as electronics, solvent effects, illumination, trace metals and others are detailed and solutions to their control and utilization are outlined. The basic mechanism and properties of the enzymatic oxidation of dipyridyl DHTz by horseradish peroxidase is also explored in chapter 2. ☐ Perhaps the most powerful method of DHTz oxidation and activation of tetrazine ligation is photooxidation. Chapter 3 describes the used of photosensitizers such as methylene blue and xanthene based dyes as photosensitizers of DHTz oxidation. Photosensitized oxidation of DHTz is extremely fast and efficient with clean, generally quantitative chemistry. A variety of photocatalysts can be used including some common cell permeant dyes. ☐ Chapter 4 explores an application of great interest to DHTz oxidation: the use of DHTz as a near-IR/red light photo activated caging molecule. Several chemotherapeutic agents were synthesized as conjugates to a DHTz molecule with a link cable of cleaving only upon oxidation of to the Tz. The relative toxicity of the prodrug and activated prodrug towards several cell lines is examined in viability and microscopy experiments.