Our main goal is to develop new compounds to serve as more efficient antidotes and improve the treatment of highly toxic organophosphorus (OP) compound poisoning. OP compounds used as pesticides account for over 3,000,000 registered accidental or deliberate cases of poisoning per year worldwide. Furthermore, OPs known as nerve agents (soman, sarin, tabun, VX) present a threat in terrorist attacks and conflicts, as was the case recently in Syria. The main targets of OP compounds are cholinesterases: acetylcholinesterase (AChE), the essential enzyme in neurotransmission, and butyrylcholinesterase (BChE), its back-up enzyme. However, the antidotes currently in use, which act as reactivators of inhibited AChE, were empirically synthesized before the two enzyme’s crystal structures were resolved. Due to structural requirements, their binding affinity and reactivation rate have not been well-balanced. This project utilizes new compounds to gain a better understanding of the mechanistic basis of the limitations of reactivation and find new effective leads for further in vivo study. We will combine several approaches, including: a study of the finely tuned interplay between these two sister enzymes, computational and experimental studies of cholinesterase interactions with a wide range of ligands defining favourable characteristic for potential new antidotes, in silico design of novel compounds that will direct the subsequent synthesis of selected leads, and thorough in vitro and in vivo experimental evaluation guided by strict cost-benefit criteria. Such a comprehensive approach will enable us to test a wide selection of candidates in a more reliable manner and obtain unambiguous data for further enhancements of the antidotal treatment. This will also enable us to explore other possible OP treatments such as highly-effective bioscavengers. Many of the findings that would arise from this project should have an impact that reaches far beyond the level of cholinesterases.