Biological activities of flavonoids from Nitraria retusa (Forssk.) Asch. and their acylated derivatives

The antioxidant activity and antiproliferative property towards Caco2 cells of water and methanol extracts/fractions of Nitraria retusa were investigated. The total phenolic and flavonoid contents of the extracts/fractions were determined, and the four major flavonoids were identified as isorhamnetin, isorhamnetin-3-O-glucoside, isorhamnetin-3-O-rutinoside and isorhamnetin-3-O-robinobioside. The results showed a relationship between the extracts/fractions activities and their flavonoid contents. Moreover, the chloroform extract which was enriched with the aglycone flavonoid isorhamnetin exhibited the highest activities. The activities of N. retusa flavonoids were compared to those of model flavonoids, quercetin, isoquercitrin and rutin. In all cases, the aglycone compounds were more active than their glycosylated derivatives. Isorhamnetin-based flavonoids presented higher antiproliferative activities than quercetin-based ones, while similar antioxidant properties were observed. The enzymatic acylation of isorhamnetin-3-O-glucoside with ethyl laurate and ethyl butyrate enhanced its capacity to inhibit xanthine oxidase and its antiproliferative activity but decreased its radical scavenging activity.