Hydroxylated derivatives of dimethoxy-1,4-benzoquinone as redox switchable earth-alkaline metal ligands and radical scavengers

Abstract

Benzoquinones (BQ) have important functions in many biological processes. In alkaline environments, BQs can be hydroxylated at quinoid ring proton positions. Very little is known about the chemical reaction leading to these structural transformations as well as about the properties of the obtained hydroxyl benzoquinones. We analyzed the behavior of the naturally occurring 2,6-dimethoxy-1,4-benzoquinone under alkaline conditions and show that upon substitution of methoxy-groups, poly-hydroxyl-derivatives (OHBQ) are formed. The emerging compounds with one or several hydroxyl-substituents on single or fused quinone-rings exist in oxidized or reduced states and are very stable under physiological conditions. In comparison with the parent BQs, OHBQs are stronger radical scavengers and redox switchable earth-alkaline metal ligands. Considering that hydroxylated quinones appear as biosynthetic intermediates or as products of enzymatic reactions, and that BQs present in food or administered as drugs can be hydroxylated by enzymatic pathways, highlights their potential importance in biological systems.

New insights into the chemistry of Coenzyme Q-0: A voltammetric and spectroscopic study

“…Although the number of studies related to the chemical and redox features of CoQ family members has increased tremendously in the last three decades [8][9][10][11][12][13][14][15][16][17][18], many key features are still not well understood. In our last two publications we have shown that Coenzyme Q-1 (CoQ-1) and CoQ-10 undergo structural changes in strong alkaline environment or in the presence of Cytochrome P450 enzymes [19,20]. As main reaction products we identified several hydroxy derivatives of CoQ-1 and CoQ-10 [19,20].…”

“…The redox features of many hydrophilic and lipophilic Q and HQ have been intensively studied by various electrochemical methods [4,19,20,[24][25][26][27][28][29], but surprisingly, there are only few reports related to the electrochemical features of the simplest CoQ member, i.e. CoQ-0 [21][22][23].…”

“…Note that under such conditions, the CoQ-0 redox chemistry is sensitive to H + ions but not to other alkaline or earth-alkaline cations [20].…”

“…In our last two publications we have shown that Coenzyme Q-1 (CoQ-1) and CoQ-10 undergo structural changes in strong alkaline environment or in the presence of Cytochrome P450 enzymes [19,20]. As main reaction products we identified several hydroxy derivatives of CoQ-1 and CoQ-10 [19,20]. The "isoprenoid Q and HQ" mainly function as electron and proton carriers [4][5][6][7], but it was not until recently that new properties of the hydroxy derivatives of CoQ-1 and CoQ-10 were unraveled highlighting their potential for binding earth-alkaline cations and even facilitating their transfer across biomimetic membranes [19,20].…”

“…As main reaction products we identified several hydroxy derivatives of CoQ-1 and CoQ-10 [19,20]. The "isoprenoid Q and HQ" mainly function as electron and proton carriers [4][5][6][7], but it was not until recently that new properties of the hydroxy derivatives of CoQ-1 and CoQ-10 were unraveled highlighting their potential for binding earth-alkaline cations and even facilitating their transfer across biomimetic membranes [19,20]. Moreover, due to their higher electronic density profiles, the novel hydroxy derivatives of CoQ-1 and CoQ-10 show much higher antioxidative potential compared to the hydroquinone forms of native CoQ-1 and CoQ-10.…”