Synthesis and Antimicrobial Activities of Some Polyphenol Compounds by Nano ZnO-TBAB as a Heterogeneous Catalytic Media

Abstract

Introduction: Mannich reaction is a typical example of a three-component condensation reaction and the chemistry of Mannich bases has been the matter of search by researchers. Here, an efficient procedure for the synthesis of some new Mannich derivatives of simple phenols is described. Methods: In this procedure, a microwave-assisted and solventless condensation was done between different phenols, secondary amines and paraformaldehyde. The reactions proceeded in the presence of the catalytic amount of nano ZnO and tetrabutylammonium bromide (TBAB) in excellent yields. Ten new compounds were synthesized (A<sub>1</sub>-A<sub>10</sub>). Chemical structures of all new compounds were confirmed by different spectroscopic methods. We optimized the chemical reactions in different conditions. Optimization reactions were done in the presence of different mineral oxides, different amounts of TBAB and also different solvents. Nano ZnO and TBAB in catalytic amounts and solvent-free conditions were the best conditions. All the synthesized compounds were screened for their antimicrobial activities. Antifungal and antibacterial activities of the synthesized compounds were evaluated against some Candida species, filaments fungi, gram-positive and gram-negative bacteria by the broth microdilution method as recommended by CLSI. Results: The result showed that compounds A<sub>2</sub>, A<sub>3</sub> and A<sub>4</sub> against most of the tested Candida species and compounds A<sub>5</sub> and A<sub>7</sub> against C. parapsilosis and C. tropicalis exhibited considerable antifungal activities. Moreover, compounds A<sub>8</sub> and A<sub>10</sub> showed desirable antifungal activities against C. neoformance and C. parapsilosis, respectively. The antibacterial activities of the synthesized compounds were also evaluated. Compounds A<sub>6</sub> - A<sub>10</sub> against E. fecalis and compounds A<sub>5</sub>, A<sub>7</sub>, A<sub>9</sub> and A<sub>10</sub> against P. aeruginosa showed desirable antibacterial activities. Discussion: We have synthesized some new Mannich adducts of poly-hydroxyl phenols in the presence of nano- ZnO as a reusable catalyst, with the hope of discovering new lead compounds serving as potent antimicrobial agents. The advantages of this method are generality, high yields with short reaction times, simplicity, low cost and matching with green chemistry protocols. The antimicrobial studies of Mannich derivatives of phenols showed desirable results in vitro.