A Magnetic Heterogeneous Biocatalyst Composed of Immobilized Laccase and 2,2,6,6-Tetramethylpiperidine-1-Oxyl (Tempo) for Green One-Pot Cascade Synthesis of 2-Substituted Benzimidazole and Benzoxazole Derivatives Under Mild Reaction Conditions Publisher



Mogharabimanzari M^{1, 2} ; Kiani M¹ ; Aryanejad S¹ ; Imanparast S¹ ; Amini M² ; Faramarzi MA¹ Show Affiliations
Source: Advanced Synthesis and Catalysis Published:2018

Abstract

The design of reusable high-performance heterogeneous catalysts via the immobilization of chemical and biochemical species on magnetic nanoparticles increases the efficiency of catalytic systems by facilitating easy, fast, and clean separation processes. Laccase and 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl were separately immobilized on amine functionalized iron (II, III) oxide nanoparticles with covalent bonding using glutaraldehyde as a coupling reagent. The prepared catalyst was used to synthesize 12 benzoxazole and benzimidazole derivatives. The one-pot, two-step enzymatic aerobic oxidation reaction included the condensation of in situ-produced salicylaldehyde derivatives with aromatic amines, followed by an enzymatic dehydrogenation process. Optimal reaction conditions consisted of a citrate buffer (10 mM, pH 4.5) at 40 °C for an incubation time of 10 h and a heterogeneous catalyst containing immobilized laccase (80 mg, 100 U) and immobilized 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) (40 mg, 2 mol%). The catalyst retained more than 85% of its initial activity after 10 runs. In addition to the potential for reuse without significant losses in performance, eco-friendly attributes of this catalytic system include its high catalytic activity and the ease with which it can be recovered from the reaction mixture using an external magnet. (Figure presented.). © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim