Enzymatic and toxicological evaluation of new aromatic phosphorus selenides: In silico and in vitro studies

Organophosphate pesticides, such as chlorpyrifos (CPF), remain widely used in agriculture despite major toxicological concerns, particularly those associated with acetylcholinesterase (AChE) inhibition. In this study, we investigated the toxicological profile of six phosphorus selenide (R-PSe) compounds using an integrated in silico and in vitro approach, with CPF as a reference compound. In silico analyses using OSIRIS and pkCSM predicted a low toxicological risk for all R-PSe compounds. Molecular docking suggested that compounds 1-4 interact with the AChE active site, whereas compounds 5 and 6 showed weak binding affinity. Consistently, compounds 1-4 inhibited rat cerebral AChE activity in vitro, with IC₅₀ values ranging from 0.06 to 1.60 μM, while compounds 5 and 6 were inactive under the tested conditions. The SAR analyses indicate that a SeP linkage, aromatic moieties, hydrogen-bond-accepting substituents, and a less bulky, more rigid carbon chain, are associated with AChE inhibitory activity. Increasing substrate concentration did not modify the inhibitory effect of compounds 1-4, indicating that their inhibition was not overcome by excess substrate. None of the compounds had pro-oxidant activity, a recognized critical secondary action mechanism of organophosphates. Overall, these findings identify phosphorus selenides 1-4 as potent mammalian AChE inhibitors and highlight that their potential biological application requires careful toxicological assessment.