Ortho-methoxy group as a mild inhibitor of the reactions between carboxylic acid and phenols

Abstract

According to the current database of natural products, over 25,000 compounds contain a vanillyl ring in their structure. The reasoning behind the high occurrence of the vanillyl ring structure seemed to be poorly understood, specifically the preference for a methoxy-substituted phenol structure as opposed to its dihydroxy analogue. To better understand this, we investigated the reaction mechanisms of two methoxy-phenol structures, in syn and anti conformations, two hydroxyphenol structures, also in syn and anti conformations, and phenol as a reference structure, with acetic acid. Of the starting structures, the syn hydroxyphenol was found to be kinetically the most reactive, and formed the most stable product, while both hydroxyl-substituted phenols reacted more favorably with acetic acid than the methoxyphenols. A preference for the methoxyphenol molecule may exist as a way to hinder the formation of stable covalent bonds between natural products and cellular components.