Use of a bioresource nanocomposite as a heterogeneous base catalyst for the green synthesis of novel bioactive pyrazoles: antibacterial evaluation using molecular docking

Abstract

Chitosan modified with diallylamine (CS-DAA) was synthesized and mixed with nano magnesium oxide (in various percentages) to prepare CS-DAA–MgO nanocomposites for use as a heterogeneous base catalyst for the synthesis of novel pyrazole derivatives. ¹³C NMR spectroscopic analysis confirmed the synthesis of the new functionalized chitosan CS-DAA. The nanocomposite containing 5% MgO exhibited the highest thermal stability as shown in the thermogravimetry curves. The X-ray diffraction pattern and scanning electron microscopy confirmed the formation of the nanocomposite CS-DAA–MgO. The ecofriendly, biodegradable nanocomposite was used as a heterogeneous base catalyst for the synthesis of four novel pyrazole derivatives. Pyrazolone was condensed with thiocarbohydrazide in two different ratios to afford the corresponding hydrazones (1 and 2). These hydrazones were treated with α-haloesters or hydrazonoyl halides in the presence of the heterogeneous nanocomposite catalyst, resulting in the formation of thiadiazines (3) and thiazolidin-4-one (4). The catalytic effect of the nanocomposite showed higher catalytic efficiency compared to the traditional homogeneous base catalysts Et₃N and NaOH. The four pyrazole structures were confirmed using elemental analysis, ¹H NMR and ¹³C NMR. A molecular docking study was used to predict the inhibition potential for the four pyrazole derivatives as anti-bacterial drugs for Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis. The results showed that all the compounds exhibit good inhibition potential as anti-bacterial drugs, especially compound (3) and compound (4).