Dissecting the Structural Prerequisites for the Antioxidative Capability of Phenolic Compounds and Their Related Derivatives as Predicted by Direct Acid Ferric Reduction Method

This study was conducted for the purpose of establishing rules-of-thumb of structural prerequisite which could account for distinct disparities in the antioxidative capabilities of various phenolic compounds. First, using a simple and rapid screening method based on the direct acid ferric reduction (DAFR) principle, we showed that the important structural feature of the compounds that could bestow a stronger reductive capability (RC) is the presence of either a catecholic or a quaiacolic nucleus. For example, the compounds that fulfill this criterion include 3, 4-dihydroxyphenylacetic acid (A), dihydroxylmandelic acid (B), dopamine (C) and epinephrine (D). Second, in examining the side chain attached para to phenolic hydroxyl group, “A” has a straight chain of acidic group; whereas, the β-carbon of the acidic group in “B” is hydroxylated. Conversely, “C” has a straight chain basic group; whereas both β-carbon and amine group are modified by hydroxylation and methylation in “D”. For these reasons, the relative strengths for RC in this group of compounds have an order of A＞B＞C＞D, respectively. This data suggests that the acid/base nature of the side chain attached para to the phenolic hydroxyl group also plays a pivotal role in determining the strength of the relative RC for either catechol-or guaiacol-containing compounds. Third, when one of the hydroxyl groups in catecholic moiety of A, B, C, D was modified by methylation forming homovanillic acid (E), vanilymandelic acid (F), 3-methody-tyramine (G) and metanephrine (H), we found a significant diminution of the relative RC. Finally, the length of side chain attached also has a bearing on the relative RC of a phenolic compound. For example, vanillic acid, having merely one ~CH2 less in its dise chain than homovanillic acid results in a 3-fold decrease in its relative RC. Taken together, our data conclude that amongst various compounds being compared, three structural criteria, namely: the numbers of hydroxyl groups present, acidic/basic characteristic and the length of side chain attached, can be used as a panel of predictors for their antioxidative capabilities.

並列關鍵字

phenolic compounds ； direct acid ferric reduction ； relative antioxidative capability ； catechol ； guaiacol

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