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

Abstract

The reaction behavior of condensed tannins and related polyphenols with ammonia (NH3) water was examined. NH3 water treatment of pyrogallol, gallic acid, and epigallocatechin, which have a pyrogallol nucleus, caused regioselective amination in the presence of molecular oxygen (O2) 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 O2. Under nitrogen atmosphere (in the absence of O2), epimerization at the C-2 position took place during NH3 treatment of epigallocatechin, in addition to amination. The same epimerization took place during NH3 treatment of epicatechin regardless of the presence or absence of O2. By NH3 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 O2, whereas catechol-type B-rings of condensed tannin from quebracho showed little amination regardless of the presence or absence of O2. From these results, it was concluded that amination of pyrogallol nucleus by NH3 treatment should proceed via oxidation and reduction, and therefore this reaction would be attributed to the oxidation property of condensed tannins and related polyphenols.

High surface – Highly N-doped carbons from hydrothermally treated tannin

“…1) was aminated, which situation happens at room conditions according to Hashida et al (2009) and Morisada et al (2011). This statement is consistent with the results for H-EAT.…”

“…Until recently, amination of Mimosa tannin was thought to be regioselective, only affecting the position 4 at which the hydroxyl group can be converted into amine (see asterisk in Fig. 1) (Hashida et al, 2009). However, we have recently demonstrated that reactions of flavonoid tannins in concentrated ammonia solution at room temperature are more complex, leading to multiamination of a higher proportion of phenolic hydroxyl groups in both A and B rings, as suggested in Fig.…”

Biotransformation of Myricetin: A Novel Metabolic Pathway to Produce Aminated Products in Mice

“…In the small intestine, phosphate‐activated glutaminase (PAG) catalyzes the hydrolysis of glutamine to yield glutamate as well as ammonia, and in the colon, the major source of ammonia was from the breakdown of urea by intestinal bacteria, which contain urease . Previous studies have been demonstrated that several polyphenols with a vic ‐trihydroxyl group such as epigallocatechin (EGC) and pyrogallol have the capacity to chemically react with ammonia and generate aminated products in in vitro systems . Recently, we demonstrated for the first time that tea polyphenol epigallocatechin‐3‐gallate (EGCG) could react with ammonia in vivo to generate the aminated metabolites .…”

Modified tannins for alkyd based anticorrosive coatings

“…The amination reaction takes place in a onestep procedure (Figure 3). The previous studies show that this reaction under mild conditions and without a catalyst is a regio-selective reaction [33,34]. The aminated hydroxyl groups lead to oligomerization and cross-linking via connections between N and OH within the tannin molecules.…”