Curcumin: Structure-Activity Relationship Towards its Role as a Versatile Multi-Targeted Therapeutics

Curcumin, a polyphenolic pigment of turmeric, is one of the very promising natural products that have been extensively investigated from both the biological and structural point of view. It has been shown to possess activity towards variety of targets at cellular and molecular levels that provide a basis for its use against multiple human diseases. In recent decades, it has been subjected to various pharmacological, biochemical and clinical investigations which proposed its multifaceted therapeutic potential being attributed mainly to its unique chemical structure and physicochemical properties. Thus, this review discusses the structure-activity relationship of curcumin in relation to its biological activities to gain more understanding on the mechanistic basis of its therapeutic action. Curcumin is a diferuloylmethane molecule with two ferulic acid residues joined by a seven carbon methylene bridge. The three important structural features of curcumin include two aromatic o-methoxy phenolic groups, β-dicarbonyl moiety and a seven carbon linker containing two enone moeities. Extensive research in the last two decades has provided evidence for the role of these different functional groups in its crucial biological activities. In addition to this, the polypharmacology of curcumin may also be attributed to the unexpected chemical diversity exhibited by its metabolites. Structural modifications in these specific functional moeities of curcumin have led to the development of new analogues with improved physicochemical properties and biological activity either by affecting its solubility, specificity or potency. Thus, the understanding of such structure-activity relationship may impose the exploration of the range of its biological activity.