Unveiling the chemistry behind bromination of quercetin: the ‘violet chromogen’ |
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Authors: | Mario C Foti Concetta Rocco |
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Institution: | Istituto di Chimica Biomolecolare del CNR, via P. Gaifami 18, I-95126 Catania, Italy |
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Abstract: | Bromination of quercetin with N-bromosuccinimide in neutral aqueous methanol occurs surprisingly in the electron-deficient A-ring only. Deprotonation of the acidic 7-OH is a major driver of this regioselective reaction. The increase of electron density makes in fact the quercetin anion suitable for an electrophilic attack by bromine at positions 8 and 6. Several pieces of evidence (NMR spectra and H/D exchange) are presented to substantiate the mechanism advanced. Bromoquinones/quinomethides produced in excess of N-bromosuccinimide are responsible for the formation of a stable ‘violet chromogen’. |
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Keywords: | Quercetin Bromination Deprotonation Violet chromogen Quinones |
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