Insecticidal potential of some Acephate derivatives and their quantitative structure-activity relationship (QSAR)

Organophosphates (OPs), one of the most important pesticide groups, are used worldwide to control pests. Acetylcholinesterase (EC 1.14.18.1) (AChE), an enzyme from insects’ nervous systems, is the leading target site of this group of pesticides, such as Acephate. Inhibition of enzyme activity through Acephate-derived compounds can control both resistant and non-resistant pests to OPs. In this research, the toxicity of these compounds was assayed regarding the control of Xanthogaleruca luteola (Muller). Results of the in vivo screening test revealed that two derived compounds of phosphorhydrazides (PHA) (i.e., NH2-C(O) NH-NH P(O)(OC6H5) and OC4H3-C(O)NH-NHP(S)(OCH3)2) showed the most significant insecticidal potential. AChE was purified and isolated from the third instar larvae of elm leaf beetle, X. luteola, using affinity chromatography. IC50 values, inhibition mechanisms, and inhibitory constant (Ki) of NH2-C(O) NH-NH P(O)(OC6H5) and OC4H3-C(O)NH-NHP(S)(OCH3)2 as inhibitors were calculated for the purified AChE. These compounds inhibited acetylcholinesterase (AChE) and general esterases of third instar larvae of elm leaf beetle. These compounds, by mix inhibition mechanism, inhibited AChE enzyme, and Ki obtained was 1.16 and 0.88 µM-1 min-1 for NH2-C(O) NH-NH P(O)(OC6H5) and OC4H3-C(O)NH-NHP(S)(OCH3)2, respectively. QSAR study based on multiple linear regressions (MLR) and principal component analysis (PCA) showed that the non-descriptor net charge of the nitrogen atom influenced by the polarization of N-H group had the most significant effect on the insecticidal potential. Therefore, designing new compounds that control the N-H polarization of the nitrogen atom could be an excellent option to study insecticidal properties of Acephate-derived compounds.