Nuclear chemistry

Polyphenol

Catalysis

Tannic acid

Food science

Proanthocyanidin

Medicinal chemistry

Organic chemistry

Catechol

Gallic acid

Amination

Pyrogallol

Antioxidant

Tannin

Chemistry

Holzforschung

The reaction behavior of condensed tannins and related polyphenols with ammonia (NH 3 ) water was examined. NH 3 water treatment of pyrogallol, gallic acid, and epigallocatechin, which have a pyrogallol nucleus, caused regioselective amination in the presence of molecular oxygen (O 2 ) to form 2-aminoresorcinol, 4-amino-3,5-dihydroxybenzoic acid and 4′- C -amino-epigallocatechin, respectively. In contrast, other polyphenols, such as catechol, protocatechuic acid, and epicatechin, which have a catechol nucleus, did not undergo amination even in the presence of O 2 . Under nitrogen atmosphere (in the absence of O 2 ), epimerization at the C-2 position took place during NH 3 treatment of epigallocatechin, in addition to amination. The same epimerization took place during NH 3 treatment of epicatechin regardless of the presence or absence of O 2 . By NH 3 treatment, pyrogallol-type B-rings of condensed tannin from Acacia mearnsii underwent regioselective amination to yield 4′-amino-3′,5′-dihydroxybenzene-type B-rings in the presence of O 2 , whereas catechol-type B-rings of condensed tannin from quebracho showed little amination regardless of the presence or absence of O 2 . From these results, it was concluded that amination of pyrogallol nucleus by NH 3 treatment should proceed via oxidation and reduction, and therefore this reaction would be attributed to the oxidation property of condensed tannins and related polyphenols.

Amination of pyrogallol nucleus of condensed tannins and related polyphenols by ammonia water treatment