DPPH (2,2-diphenyl-1-picrylhydrazyl) radical scavenging reactions of protocatechuic and gallic acids, and their methyl esters, have been investigated by NMR. In acetone, methyl protocatechuate was gradually converted to a Diels-Alder adduct of two molecules of the intermediate quinone in the reaction with DPPH radical, whereas methyl gallate rapidly gave a symmetrical dimer via a putative quinone precursor. Both dimers are rather unstable and their structures have been deduced by in situ NMR measurements of the reaction mixtures. Gallic acid also gave a corresponding symmetrical dimer in the same reaction as methyl gallate, although protocatechuquinone produced from protocatechuic acid did not yield a Diels-Alder adduct, unlike its methyl ester. Interestingly, these dimer formations were not observed in methanol solution.

The DPPH radical-scavenging abilities of the naturally occurring phenolic acid, 2,3,4-trihydroxybenzoic acid, and its methyl ester were evaluated. Both compounds in acetonitrile scavenged as many as four radicals compared to three or fewer radical consumption in acetone or ethanol. Only the ester showed relatively high ability in methanol. Oxidation with o-chloranil in acetonitrile resulted in methyl 2,3,4-trihydroxybenzoate giving a novel benzocoumarin-type dimer, its chemical structure being confirmed by spectroscopic evidence. The formation of this dimer might partly account for the higher radical-scavenging efficiency of the ester in acetonitrile or methanol.Key words: 2,3,4-trihydroxybenzoic acid; phenolic acid; oxidative coupling; DPPH radical; o-chloranil Hydroxybenzoic acids and esters are widely distributed in plants and have attracted considerable attention for their antioxidative activities. [1][2][3][4] The radical-scavenging reaction of catechol-and pyrogallol-type hydroxybenzoic acids typically comprises two distinctive phases, initially fast and subsequently slow. 5,6) The former phase is recognized as the conversion of an o-diphenol to the corresponding o-quinone, whereas complex reactions including oligomerization of the resulting quinone would occur in the latter slow phase. The difference in total radical-scavenging efficiency of each hydroxybenzoic acid inherently depends on this latter phase, although little has been found for this complex stage. So far, a protocatechuic (3,4-dihydroxybenzoic) ester (1) gave its quinone dimer, 6) quinone acetal 7) and adducts, [8][9][10][11] and a gallic (3,4,5-trihydroxybenzoic) ester (2) and its analogs also produced quinone dimers 6,12,13) and adducts.12) In contrast to protocatechuic and gallic acids, there has been no report on the oxidation reaction of another naturally occurring phenolic acid, 2,3,4-trihydroxybenzoic acid (3).14-16) We have investigated the DPPH (2,2-diphenyl-1-picrylhydrazyl) radicalscavenging abilities and the oxidant-mediated reaction of 2,3,4-trihydroxybenzoic acid (3) and its ester (4) (Fig. 1), and identified a novel oxidative dimer in the reaction mixture with o-chloranil (3,4,5,6-tetrachloro-obenzoquinone) in acetonitrile. Materials and MethodsReagents. 2,3,4-Trihydroxybenzoic acid (3) (Tokyo Kasei Kogyo Co.), 2,2-diphenyl-1-picrylhydrazyl (DP-PH) radical (Wako Pure Chem. Ind.) and o-chloranil (Aldrich Chem. Co.) were purchased from each supplier. Methyl 2,3,4-trihydroxybenzoate (4) was prepared from 3 by heating with methanol containing 10% hydrogen chloride. All solvents used were of technical grade.Colorimetric radical-scavenging tests. DPPH radical scavenging tests were conducted as described in the previous paper. y To whom correspondence should be addressed. Fax: +81-11-706-2496; E-mail: junk@chem.agr.hokudai.ac.jpBiosci. Biotechnol. Biochem., 71 (7), [1731][1732][1733][1734] 2007 tion, UV 260 or 400 nm. Under these conditions, 3 and 4 were eluted at t R ¼ 23:4 and 37.5 min, respectively.Isolation of benzocoumarin dim...

There are few reports on the relationship between the items examined for deterioration of oral function and the oral health related quality of life (OHRQoL), while it is considered that four phases of early frailty signs in the food environment and oral function are related to OHRQoL. In this study, the morbidity of deterioration of oral function and its effect on OHRQoL in community residents in Sapporo were evaluated. Methods: The subjects of this study were those aged over 65 who agreed to the research. Examinations on oral function were carried out and OHRQoL was evaluated by OHIP-14. For statistical analysis, the Wilcoxon test or Kruskal-Wallis was used for comparison of OHIP-14 and each variable. The Steel-Dwass test was used for multiple comparison. Spearman's rank correlation coefficient was calculated from the number of items with oral hypofunction and the OHIP-14 score. The odds ratio for OHIP-14 for each test was determined by logistic regression analysis. Results: The OHIP-14 score was significantly higher for the subjects with less than 20 teeth. Eighteen percent of the subjects corresponded to three items or more and were judged as oral hypofunction. There was a significant correlation between the number of items with oral hypofunction and the OHIP-14 score, and the number of remaining teeth and swallowing were factors significantly related to the OHIP-14 score. Conclusion: Eighteen percent of the subjects were diagnosed as oral hypofunction among community residents interested in oral health. The number of remaining teeth and swallowing were related to the OHIP-14 score. As the number of items of oral hypofunction increased, OHRQoL decreased.