REACTION OF 3-DEHYDROSHIKIMIC ACID WITH MOLECULAR-OXYGEN AND HYDROGEN-PEROXIDE - PRODUCTS, MECHANISM, AND ASSOCIATED ANTIOXIDANT ACTIVITY

In the presence of molecular oxygen or hydrogen peroxide, inorganic ph osphate 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, a nd smaller amounts of tricarballylic acid are produced. Evidence favor ing a mechanism involving phosphate-catalyzed tautomerization of DHS t o a reactive enediol intermediate follows from the successful isolatio n of dihydrogallic acid when oxidant is excluded from phosphate-buffer ed solutions of DHS. The reductone-like solution chemistry of DHS and the radical quenching reactivity of the phenolics formed from DHS prom pted an appraisal of DHS antioxidant activity. Based on two different analyses, DHS was discovered to possess significant antioxidant activi ty relative to cl-tocopherol, gallic acid, propyl gallate, and tert-bu tylhydroquinone.