Reaction of 3-Dehydroshikimic Acid with Molecular Oxygen and Hydrogen Peroxide:  Products, Mechanism, and Associated Antioxidant Activity

Abstract

In the presence of molecular oxygen or hydrogen peroxide, inorganic phosphate catalyzes the conversion of 3-dehydroshikimic acid (DHS) into gallic acid. Other products formed in the reaction of DHS with oxygen include protocatechuic acid, tricarballylic acid, and pyrogallol. With hydrogen peroxide as oxidant, pyrogallol formation is not observed, and smaller amounts of tricarballylic acid are produced. Evidence favoring a mechanism involving phosphate-catalyzed tautomerization of DHS to a reactive enediol intermediate follows from the successful isolation of dihydrogallic acid when oxidant is excluded from phosphate-buffered solutions of DHS. The reductone-like solution chemistry of DHS and the radical quenching reactivity of the phenolics formed from DHS prompted an appraisal of DHS antioxidant activity. Based on two different analyses, DHS was discovered to possess significant antioxidant activity relative to α-tocopherol, gallic acid, propyl gallate, and tert-butylhydroquinone.

Bioactive Terpenoids and Guggulusteroids from Commiphora mukul Gum Resin of Potential Anti‐Inflammatory Interest

“…HR-FAB-MS of 5 displayed a molecular ion at m/z 305.2844 and indicated its molecular formula as C 21 C-NMR of the molecule showed the presence of 21 C-atoms in the molecule, and the DEPT spectrum helped to assign them to six CH, six CH 2 , and six Me groups, and three quaternary C-atoms. The DEPT spectrum also confirmed that one of the Me groups belonged to a MeO moiety.…”

Platinum tetrasulfophthalocyanine as selective catalyst for the aerobic oxidation of shikimic acid

“…3). An accurate analysis of 1 H NMR spectra showed weak signals in the aromatic region, attributable to the aromatic compounds previously found by Frost [9] (as seen by NMR, by adding small amounts of standard reference compounds), likely the by-products that are responsible for the reduced selectivity. An accurate analysis of the [a] D of the DHS produced always gave the expected value reported in the literature [15], thus ruling out the indirect involvement of racemization of the chiral centres of shikimic acid in the chemical transformation.…”

“…Among these, McKittrick and Ganem [8] reported 65% yields for DHS using THF as the solvent and an excess (3:1) of the exotic oxidant dichlorodicyanobenzoquinone. Another important aspect to be considered is the extreme lability of DHS under even mild oxidation conditions: water solutions of DHS in the presence of 1 M phosphate buffer at pH 6.7 and at 40°C under aerobic conditions result in its almost quantitative aromatisation to gallic and protocatechuic acid, and its decarboxylation to pyrogallol [9]. The large use of DHS makes it necessary to search for a low cost (and 'greener') chemical pathway for its synthesis.…”

Metabolic Engineering for Microbial Production of Aromatic Amino Acids and Derived Compounds

“…Production of DHS was associated with the formation of dehydroquinate and gallic acid, which could be products of abiotic conversion reactions (Richman et al, 1996). Gallic acid production could also be due to formation of protocatechuic acid by DHS dehydratase, followed by a hydroxylation step .…”