Synthesis, thermal property and antifungal evaluation of pyrazine esters

Abstract

Synthesis, thermal properties, as well as antifungal assessment of pyrazine esters were handed in this work. The metal-free esterification of pyrazinyl methanol and acid chloride derivatives in a stoichiometric ratio yielded the following compounds: pyrazin-2-ylmethyl benzoate (3a), (5-methylpyrazin-2-yl) methyl benzoate (3b), 1-(pyrazin-2-yl) ethyl benzoate (3c), 2-(pyrazin-2-yl) ethyl benzoate (3d), pyrazin-2-ylmethyl pivalate (3e). The spectral results totally showed that the synthesis conditions used permitted the compounds to be produced with great yield. The characterization included 1H NMR, 13C NMR, IR, HRMS and organoleptic tests. Their thermal degradation process was examined by using the TG (thermogravimetry) and DSC (differential scanning calorimeter) methods. The pyrolysis products of the pyrazine esters in inert and oxidative atmospheres were analyzed by the Py-GC/MS (pyrolysis–gas chromatography/mass spectrometry) method. It revealed that 3a–3e were totally evaporated throughout the pyrolysis experiments at low temperatures. And they evaporated with high relative contents in pure nitrogen (86.12%–94.17%) and oxidative (75.01%–88.85%) atmospheres, with only a small amount decomposing into a series of substances. Additionally, the in vitro antifungal effects of compounds 3a–3e against R. solani, P. nicotianae, F. oxysporum, F. graminearum, and F. moniliforme were further investigated using the mycelial growth rate methodology. The findings shown that compound 3c has 94% and 80% inhibitor rates at 0.5 mg/ml against R. solani and P. nicotianae, respectively, with an EC50 value (half maximum effective concentration) of 0.0191 mg/ml and 0.1870 mg/ml, respectively. Similarly, that of compounds 3a and 3b exhibited 82% and 91% at 0.5 mg/ml against R. solani, with an EC50 value of 0.0209 mg/ml and 0.0218 mg/ml, respectively. The molecular docking of compound 3c with SDH (Succinate dehydrogenase) was preliminarily performed to reveal the binding modes in active pocket and analyze the interactions between the molecules and the protein.