engleski

Photochemical dehydration and deamination of phenols to quinone methides

Quinone methides (QMs) are important intermediates in the reactions of phenols[1] that attracted scientific interest owing to their biological activity.[2] Some anticancer antibiotics exert they antiproliferative action based on intracellular formation of QMs. However, QMs are usually reactive species characterized by short lifetimes. Therefore, they have to be prepared in situ. Photochemical methods to generate QMs represent mild approach, particularly appealing in biological system. The most common photochemical reactions to generate QMs rely on dehydration[3] or deamination of suitably substituted phenols.[4] For the application of QMs in biology it is pivotal to fully unravel reaction mechanism of their formation. We have recently undertaken experimental and computational study to elucidate photodehydration mechanism of o-hydroxymethylphenol (1) that delivers QM.[5] Upon excitation, antiaromatic character of 1 (S1) provides a driving force on the S1 potential energy surface towards QM that is non-aromatic. Therefore, QM is formed in an ultrafast adiabatic photochemical reaction. A similar mechanistic scenario takes place for the deamination of 2, where the corresponding QM is formed in an ultrafast adiabatic photochemical reaction taking place very efficiently.[6] Furthermore, for applications in biology, it is important to extend the chromophoric system and excite molecule with visible light. Therefore, we incorporated QM precursors into structure of BODIPY chromophores, such as 3.[7] Upon excitation of these BODIPY-QM precursor molecules to S1, photodeamination does not take place due to an energy barrier on the S1 potential energy surface. However, excitation to higher excited singlet states provides QMs with BODIPY chromophore.

antiaromatic excited state ; photodehydration ; photodeamination ; quinone methide

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