Synthesis of Gallic Acid Analogs as Histamine and Pro-Inflammatory Cytokine Inhibitors for Treatment of Mast Cell-Mediated Allergic Inflammation.

Gallic acid (3,4,5-trihydroxybenzoic acid), is a natural product found in various foods and herbs that are well known as powerful antioxidants. Our previous report demonstrated that it inhibits mast cell-derived inflammatory allergic reactions by blocking histamine release and pro-inflammatory cytokine expression. In this report, various amide analogs of gallic acid have been synthesized by introducing different amines through carbodiimide-mediated amide coupling and Pd/C-catalyzed hydrogenation. These compounds showed a modest to high inhibitory effect on histamine release and pro-inflammatory cytokine expression. Among them, the amide bearing (S)-phenylglycine methyl ester 3d was found to be more active than natural gallic acid. Further optimization yielded several (S)- and (R)-phenylglycine analogs that inhibited histamine release in vitro. Our findings suggest that some gallamides could be used as a treatment for allergic inflammatory diseases.