Polydopamine: An Amine Oxidase Mimicking Sustainable Catalyst for the Synthesis of Nitrogen Heterocycles under Aqueous Conditions

• Published in: ACS sustainable chemistry & engineering 2019-05, Vol.7 (9), p.8274-8286
• Main Authors: Pawar, Shweta A, Chand, Ayushi N, Kumar, A. Vijay
• Format: Article
• Language: English
• ISSN: 2168-0485; 2168-0485
• DOI: 10.1021/acssuschemeng.8b06677

The catalytic activity of polydopamine (PDA) as an amine oxidase mimic is demonstrated under aqueous conditions for the synthesis of benzimidazoles, quinoxalines, quinazolinones and oxidation of secondary amines. The synthesis occurs through activation of the amines by the catechol-quinone moieties of PDA, followed by transamination and an oxidative cyclization of these benzylic (or) arylethyl imine adducts with o-phenylenediamines and 2-aminobenzamides akin to the amine oxidase enzymes in the presence of benign oxidant molecular oxygen. PDA demonstrated excellent efficiency on par with the existing regime of metal/nonmetal-based catalysts without any additives under aqueous conditions. The mechanistic studies showed evidence for an oxygen-mediated nonradical pathway via a quinone-imine step. Additionally, PDA was found to be easily recoverable and reusable for up to three cycles without any loss of catalytic activity. Moreover, the utility of nontoxic and cheap solvent such as water along with a biomimicking recyclable catalyst PDA makes it a benign protocol from the sustainability point of view.