Mass Spectrometry and ¹ H-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 (from Schinopsis lorentzii wood), 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 (α-glucosidase and α-amylase inhibition). All the fractions were analyzed by means of HPLC/ESI-MS/MS and ¹H-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 α-glucosidase and α-amylase inhibitory activity was observed in fractions A-7-A-9 containing condensed (9', 15, 18, 19, 23, and 27) hydrolysable tannins (13 and 32) as well as esters of quinic acid with different units of gallic acid (5, 11, 11', 14, and 22). This last class of gallic acid esters are here reported for the first time as α-glucosidase and α-amylase inhibitors.

Keywords: 1H-NMR; DPPH; ORAC; mass spectrometry; tannins; α-amylase; α-glucosidase.