Chapter 7 - The Structure–Activity Relationships of Plant Secondary Metabolites with Antimicrobial, Free Radical Scavenging and Inhibitory Activity toward Selected Enzymes

Abstract

Abstract People have been using plants for thousands of years due to therapeutic effects exerted by many secondary metabolites. Polyphenols, alkaloids, or terpenoids are components commonly encountered in many herbal formulas. In many cases their pharmacological activity is directly linked with their structures. The structure–activity relationships (SARs) depend both on the structure of a given compound and on the target particle. Plant compounds with OH or ketone groups usually create hydrogen bonds or interact via van der Waals forces with different target molecules. The OH groups may chelate metal ions, in the reaction mixture or in a cell, what have an impact on compounds' antioxidant, antimicrobial, and inhibitory activity toward enzymes. Plant secondary metabolites possessing both phenolic ring and conjugated double bonds are the most potent direct antioxidants, for example, eugenol, cinammic acid derivatives, or flavonols. The antimicrobial activity of some compounds may be due to their interaction with structural or enzymatic proteins of bacteria. Moreover, they may lead to the oxidized condensation, inhibiting the bacterial growth. This review highlights the recent advances in investigating SARs of secondary plant metabolites with antimicrobial, free radical scavenging activities, and inhibitory properties against selected enzymes.