Antioxidant Polyphenolic Constituents of Vitis × Labruscana cv. 'Isabella' Leaves

The polyphenolic composition and antioxidant properties of the methanol leaf extract of Vitis × labruscana cv. 'Isabella' has been performed by means of different spectrophotometric antioxidant methods. Intracellular ROS produc- tion was measured by cell fluorescence after loading with 2',7'-H2DCF-DA. The extract promising efficacy has laid the basis to its phytochemical characterization. Three hydroxycinnamoyl tartaric acids (1-3), isoquercitrin 4, and five flavonol glycuronides (5-9) were isolated from Vitis × labruscana cv. 'Isabella' leaves. Chemical structures were elucidated on the basis of their spectroscopic features. Metabolites 6, 7, and 9, characterized by glucuronic or galacturonic acid methyl es- ter, are described from the genus Vitis for the first time. The metabolites isolated as major constituents were investigated for their DPPH radical scavenging capacity.