Reaction of condensed tannins with ammonia
Résumé
Reaction of condensed (flavonoid) mimosa tannin extracts with concentrated aqueous ammonia has been investigated. For that purpose, catechin was also used as a flavonoid model compound and treated in similar conditions. Solid state CP-MAS C-13 NMR and MALDI-ToF spectroscopy studies revealed that, unlike what was recently theorised, amination is not always regioselective and leading to the conversion of one single-OH group in C4' into-NH2. In the present study, new reactions have been evidenced, clearly leading to multiamination of several phenolic hydroxyl groups, heterocycle opening, and oligomerisation and cross-linking through the formation of-N= bridges between flavonoid units.