Structure-Activity Relationships of Flavonoids

Flavonoids are secondary metabolites produced in plants that have diverse biological activities. The present review summarizes information gathered mostly in the last six years on the flavonoids' structure-activity relationships, specifically with respect to: A) phytoestrogenic activity-flavonoids' potential to replace estrogen during the menopausal period and especially fascinating, the possibility of finding flavonoids selective for estrogen receptor β; B) as antioxidants-their potential to treat oxidative stress-associated diseases; C) as whitening agents-potentially active via their ability to inhibit the enzyme tyrosinase; D) flavonoids that are active due to their interaction with proteins (enzymes, receptors, transporters and transcription factors), an area which we believe will attract much more attention in the near future, in helping to understand the role of flavonoids and their mechanism of action in the treatment of human diseases. This review covers data collected from experiments performed using flavonoids with known structure rather than crude extracts, and in the first two sections (A and B), the focus is on results obtained from in-vivo experiments, where available.