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

Abstract

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.

Air oxidized activated carbon catalyst for aerobic oxidative aromatizations of N-heterocycles

“…27 Several metal-free approaches with graphene oxide (GO), 28 reduced graphene oxide (rGO), 29 mesoporous graphitic carbon nitride (mpg-C 3 N 4 ), 30 polymaleimide, 31 and polydopamine have been published as well. 32 Interestingly, Hayashi and co-workers published several convincing reports where they used untreated ACs to synthesize anthracenes, pyridines, pyrazoles and indoles under mild oxidative conditions. 11,[33][34][35][36] Furthermore, they demonstrated that untreated AC delivers higher yields of quinolines and isoquinolines than Pd/C in MeCN.…”

Ionic‐Liquid‐Catalyzed Synthesis of Imines, Benzimidazoles, Benzothiazoles, Quinoxalines and Quinolines through C−N, C−S, and C−C Bond Formation

“…2‐(3,4,5‐Trimethoxyphenyl)‐1H‐benzoimidazole (7 j) [29] Yield (219 mg, 77 % yield, white solid), m.p. 257 – 259 °C.…”

Polydopamine-based nanoreactors: synthesis and applications in bioscience and energy materials

“…110 Recently, the catalytic activity of PDA as an amine oxidase mimic has been reported for the synthesis of benzimidazoles, quinoxalines, quinazolinones and oxidation of secondary amines. 111 Different from supporting material for metallic catalyst, PDA cannot be considered as an inert component or coating as it can generate reactivity. Generally, PDA itself as catalyst has been less explored compared to PDA supported metallic catalyst especially in the form of nanoreactors.…”