Antibacterial activity of resveratrol structural analogues: A mechanistic evaluation of the structure-activity relationship.

Structure-activity relationship (SAR) studies have led to significant improvement in desirable biological activity in different classes of molecules. A general consensus about the substitutions that improve the activity remains elusive in stilbene class of molecules especially in regard to antibacterial activity. Lack of this knowledge remains a major hurdle in developing stilbene based antibacterial molecules. A panel of gram positive and gram negative bacteria were employed for screening the comparative efficacy of the stilbenes. In addition, the mechanisms that contribute to the antibacterial activity were investigated and correlated to structural changes. Employing the notorious nosocomial agent S. aureus we show how changes in structure alters not only the antibacterial activity but also the underlying mechanisms. Antibacterial activity by CLSI (Clinical & Laboratory Standards Institute) guidelines, oxidative stress and membrane damage by fluorescence based methods, DNA binding by spectroscopy, DNA cleavage by gel electrophoresis, substrate efflux by efflux mutant and cell wall damage by scanning electron microscopy were investigated. Antibacterial activity varied drastically among stilbenes bearing different functional groups. The best stilbenes in terms of activity also scored higher in one or more molecular events that contribute to cell death. Stilbenes superior to resveratrol in antibacterial acitvity were identified and probable causes for better activity were also identified. Our study revealed dimerization, halogenation and hydroxy group in conjunction with methoxy group resulted in the best antibacterial molecules. Design of stilbene based drugs would be benefitted with the outcome and rationale presented in the current investigation.