Structural elucidation of tannins

Tannins and flavonoids are secondary metabolites of plants that display a wide array of biological activities. This peculiarity is related to the inhibition of extracellular enzymes that occurs through the complexation of peptides by tannins. Not only the nature of these interactions, but more fundamentally also the structure of these heterogeneous polyphenolic molecules are not completely clear. We developed a new analytical method for the structural characterization of tannins employing an in situ labeling of all labile H groups (aliphatic OH, phenolic OH, and carboxylic acids) with a phosphorus reagent. The 31P NMR analysis of 31P-labeled samples allowed the unprecedented quantitative and qualitative structural characterization of hydrolyzable tannins, proanthocyanidins, and catechin tannins.


F. Melone, R. Saladino, H. Lange, C. Crestini
Tannin Structural Elucidation and Quantitative 31P NMR Analysis. 1. Model Compounds.
J. Agric. Food Chem. 2013, 61, 9307-9315.

F. Melone, R. Saladino, H. Lange, C. Crestini
Tannin Structural Elucidation and Quantitative 31P NMR Analysis. 2. Hydrolyzable Tannins and Proanthocyanidins.
J. Agric. Food Chem. 2013, 61, 9316-9324.

C. Crestini, H. Lange, G. Bianchetti
Detailed Chemical Composition of Condensed Tannins via Quantitative 31P NMR and HSQC Analyses: Acacia catechu,
Schinopsis balansae, and Acacia mearnsii.
J. Nat. Prod. 2016, 79, 2287–2295.