Photoreaction of indazole metastable-state photoacid

Adnan Elgattar; Osamah Alghazwat; Alan B. Brown; Vyacheslav S. Bryantsev; Vera Bocharova; Yi Liao

doi:10.1016/j.jphotochem.2023.114599

Photoreaction of indazole metastable-state photoacid

Adnan Elgattar, Osamah Alghazwat, Alan B. Brown, Vyacheslav S. Bryantsev, Vera Bocharova, Yi Liao

Research output: Contribution to journal › Article › peer-review

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Abstract

Indazole metastable-state photoacids have been recently applied to modulating local pH of tumor and brain in animal studies. The mechanism of this type of photoacid was previously assumed to be the same as that of the extensively studied merocyanine photoacids. However, this work showed that the photo reaction of indazole photoacid is significantly different from merocyanine photoacid in water. An indazole photoacid with high water solubility up to 70 mM was designed and synthesized. Photoirradiation generates a quinoidal cis-conformer in water instead of the spiro conformer generally expected for a metastable-state photoacid. Although the twisted conformation reduced conjugation between the electron-withdrawing moiety and the acidic moiety, the cis-conformer possesses a higher acidity than that of the trans-conformer due to the unusual quinoidal structure. In organic solvents, the cis-isomer possesses a Kekule structure, which has lower acidity than that of the trans-conformer. In the presence of a weak base, photoirradiation reversibly converted the trans-conformer to the spiroconformer. Experiments showed that deprotonated cis-conformer is the intermediate for both the spiro formation and the reverse cis-to-trans reaction. Addition of an acid stops both reactions and locks the photoproduct to the protonated cis-conformer.

Original language	English
Article number	114599
Journal	Journal of Photochemistry and Photobiology A: Chemistry
Volume	439
DOIs	https://doi.org/10.1016/j.jphotochem.2023.114599
State	Published - May 1 2023

Funding

This research was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Separation Sciences. under Contract No. AC05-00OR22725. This work was produced by UT-Battelle LLC under Contract No. AC05-00OR22725 with the U. S. Department of Energy. The NMR spectrometer at Florida Institute of Technology was purchased with assistance from the U.S. National Science Foundation (CHE 03-42251). The publisher acknowledges the U.S. Government license to provide public access under the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan). This research was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Separation Sciences. under Contract No. AC05-00OR22725. This work was produced by UT-Battelle LLC under Contract No. AC05-00OR22725 with the U. S. Department of Energy. The NMR spectrometer at Florida Institute of Technology was purchased with assistance from the U.S. National Science Foundation (CHE 03-42251). The publisher acknowledges the U.S. Government license to provide public access under the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).

Keywords

Photoacid
Photoswitch
Quinoidal structure

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10.1016/j.jphotochem.2023.114599

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title = "Photoreaction of indazole metastable-state photoacid",

abstract = "Indazole metastable-state photoacids have been recently applied to modulating local pH of tumor and brain in animal studies. The mechanism of this type of photoacid was previously assumed to be the same as that of the extensively studied merocyanine photoacids. However, this work showed that the photo reaction of indazole photoacid is significantly different from merocyanine photoacid in water. An indazole photoacid with high water solubility up to 70 mM was designed and synthesized. Photoirradiation generates a quinoidal cis-conformer in water instead of the spiro conformer generally expected for a metastable-state photoacid. Although the twisted conformation reduced conjugation between the electron-withdrawing moiety and the acidic moiety, the cis-conformer possesses a higher acidity than that of the trans-conformer due to the unusual quinoidal structure. In organic solvents, the cis-isomer possesses a Kekule structure, which has lower acidity than that of the trans-conformer. In the presence of a weak base, photoirradiation reversibly converted the trans-conformer to the spiroconformer. Experiments showed that deprotonated cis-conformer is the intermediate for both the spiro formation and the reverse cis-to-trans reaction. Addition of an acid stops both reactions and locks the photoproduct to the protonated cis-conformer.",

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AU - Liao, Yi

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AB - Indazole metastable-state photoacids have been recently applied to modulating local pH of tumor and brain in animal studies. The mechanism of this type of photoacid was previously assumed to be the same as that of the extensively studied merocyanine photoacids. However, this work showed that the photo reaction of indazole photoacid is significantly different from merocyanine photoacid in water. An indazole photoacid with high water solubility up to 70 mM was designed and synthesized. Photoirradiation generates a quinoidal cis-conformer in water instead of the spiro conformer generally expected for a metastable-state photoacid. Although the twisted conformation reduced conjugation between the electron-withdrawing moiety and the acidic moiety, the cis-conformer possesses a higher acidity than that of the trans-conformer due to the unusual quinoidal structure. In organic solvents, the cis-isomer possesses a Kekule structure, which has lower acidity than that of the trans-conformer. In the presence of a weak base, photoirradiation reversibly converted the trans-conformer to the spiroconformer. Experiments showed that deprotonated cis-conformer is the intermediate for both the spiro formation and the reverse cis-to-trans reaction. Addition of an acid stops both reactions and locks the photoproduct to the protonated cis-conformer.

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Photoreaction of indazole metastable-state photoacid

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