Enzymatic transformation of caffeic acid with enhanced cyclooxygenase-2 inhibitory activity

Convenient enzymatic transformation of the phenylpropanoid caffeic acid (1) with polyphenol oxidase originating from pear afforded three new oxidized metabolites, caffeoxynic acid (2), caffeicinic acid (3), and isocaffeicinic acid (4), along with, 7,8-erythro-caffeicin (5) and phellinsin A (6). The structures of the three new caffeic acid oxidation products were elucidated on the basis of spectroscopic methods. The new products 2 and 3 exhibited significantly enhanced inhibitory activity against cyclooxygenase-2 (COX-2) when compared to parent caffeic acid.