Curcumin Bioconjugates: Studies on Structure-Activity Relationship and Antibacterial Properties against Clinically Isolated Strains

Curcumin bioconjugates, with folic acid, fatty acids and dipeptide, have shown much lower MIC than curcumin against clinically isolated Gram-positive, S.viridians, and Gram-negative bacterial strains, E. coli, P. mirabilis and K. pneumoniae. Polynomial regression analysis was performed to establish a correlation between lipophilicity (logP) and antibacterial activity (pMIC), which showed the efficacy of these molecules against the bacterial strains in the following order: E. coli > S viridans = K. pneumoniae > P. mirabilis. The regression coefficients (R2 = 0.62 to 0.91) derived for each strain were correlated significantly and led to a conclusion that it was the amphiphilic nature that governed the antibacterial activity. Thus, the bioconjugate 2, having folic acid attached at active methylene site of curcumin with free phenolic hydroxyls, showed the best result.