Inhibitory Effects of O,O-Dialkyl S-Substituted Phosphorothioates on Acetylcholinesterase from the Moroccan and Asian Migratory Locusts

The inhibitory effects of the phosphorus-containing compounds BD-16, BD-17, and BD-18 (O,O-dialkyl S-(2,3-epoxypropyl) phosphorothioates) and BD-54 (O,O-diethyl S-(4-piperidinobut-2-ynyl) phosphorothioate), synthesized at the National University of Uzbekistan, were investigated using acetylcholinesterase (AChE) isolated from the heads of Moroccan locusts (Dociostaurus maroccanus Thunb.) and Asian migratory locusts (Locusta migratoria L.) collected in the Syrdarya Region. Enzyme activity was determined spectrophotometrically by the Ellman method at 412 nm, using inhibitor concentrations of 10⁻³–10⁻⁶ M. Under control conditions, AChE activity in the Moroccan locust preparation (A₃₀ = 1.535) was 4.2-fold higher than that in the Asian migratory locust preparation (A₃₀ = 0.363). At 10⁻³ M, BD-16 inhibited Moroccan and Asian migratory locust AChE by 59.1% and 54.8%, respectively. At 10⁻⁶ M, its effect on the Moroccan locust enzyme was negligible (0.5%), whereas inhibition of the Asian migratory locust enzyme remained at 27.3%. BD-17 was the most active compound (69.8% inhibition at 10⁻³ M; I₅₀ ≈ 1.8 × 10⁻⁴ M), while BD-18 showed lower activity (47.5%). BD-54 inhibited AChE by 46.3% but had almost no effect on butyrylcholinesterase (≤5.8%). These findings suggest that alkyl-chain length and the nature of the S-substituent influence inhibitory activity and species-related selectivity.

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