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 production 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 ester, are described from the genus Vitis for the first time. The metabolites isolated as major constituents were investigated for their DPPH radical scavenging capacity.