Mass Spectrometry and 1H-NMR Study of Schinopsis lorentzii (Quebracho) Tannins as a Source of Hypoglycemic and Antioxidant Principles

The ethyl acetate extract of the commercial tannin Tan'Activ QS-SOL (fromSchinopsis lorentziiwood), employed for the production of red wine, was subjected to chromatography on Sephadex LH-20, providing nine fractions (A-1-A-9), which were estimated for total phenols content (GAE), antioxidant activity (DPPH, ORAC), and hypoglycemic activity (alpha-glucosidase and alpha-amylase inhibition). All the fractions were analyzed by means of HPLC/ESI-MS/MS and(1)H-NMR to identify the principal active constituents. Fractions A-1 and A-3 showed the highest antioxidant activity and gallic acid (1), pyrogallol (3), eriodictyol (6), catechin (12), and taxifolin (30) were identified as the major constituents. The highest alpha-glucosidase and alpha-amylase inhibitory activity was observed in fractions A-7-A-9 containing condensed (9 ',15,18,19,23, and27) hydrolysable tannins (13and32) as well as esters of quinic acid with different units of gallic acid (5,11,11 ',14, and22). This last class of gallic acid esters are here reported for the first time as alpha-glucosidase and alpha-amylase inhibitors.