Phiphob Naweephattana, Nalinee Kongkaew, Panida Surawatanawong, Nawee Kungwan, Yin Fang,
Peter Wolschann, Phornphimon Maitarad, Kowit Hengphasatporn, Yasuteru Shigeta,
Thanyada Rungrotmongkol,* and Alisa S. Vangnai*

Organophosphate (OP) compounds, such as paraoxon (POX), inhibit enzymes critical for neurotransmission, causing severe neurotoxic effects. Pralidoxime (2-pyridine aldoxime methyl chloride) or 2-PAM is commonly employed to reverse this inhibition, but its reactivation efficiency is limited. This study computationally explores the reactivation mechanisms of 2-PAM and its methyl-substituted analogs, 4-methyl-2-PAM (4-Met-2-PAM), and 4,6-dimethyl-2-PAM (4,6-Dimet-2-PAM). The reactivation process involves several key steps, such as hydrogen transfer and nucleophilic substitution (SN2). Introducing methyl groups at positions 4 and 6 increases the negative charge on the oxime oxygen, improving nucleophilicity and reactivity. Both 4-Met-2-PAM and 4,6-Dimet-2-PAM show better reactivity than 2-PAM, with 4,6-Dimet-2-PAM demonstrating the greatest improvement. This enhanced reactivity shifts the rate-determining step from nucleophilic substitution to the initial hydrogen transfer. These findings offer valuable insights for designing more effective oxime based antidotes for organophosphate poisoning.

Reference: Naweephattana, P.; Kongkaew, N.; Surawatanawong, P.; Kungwan, N.; Fang, Y.; Wolschann, P.; Maitarad, P.; Hengphasatporn, K.; Shigeta, Y.; Rungrotmongkol, T.; Vangnai, A. S., Mechanistic Insights into Enhanced Reactivation of Organophosphate-Inhibited Enzymes by Methyl-Substituted 2-Pralidoxime Analogs. The Journal of Physical Chemistry B 2025, 129 (23), 5698-5706. https://doi.org/10.1021/acs.jpcb.5c01375

Authors
Phiphob Naweephattana − Center of Excellence in Biocatalyst and Sustainable Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.
Nalinee Kongkaew − Program in Bioinformatics and Computational Biology, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand.
Panida Surawatanawong − Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Mahidol University, Bangkok 10400, Thailand.
Nawee Kungwan − Department of Chemistry, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand.
Yin Fang − Research Center for Translational Medicine Shanghai East Hospital Affiliated to, Tongji University, Shanghai 200120, China.
Peter Wolschann − Institute of Theoretical Chemistry, University of Vienna, Vienna 1010, Austria.
Phornphimon Maitarad − Research Center of Nano Science and Technology, Department of chemistry, College of Science, Shanghai University, Shanghai 200444, China.
Kowit Hengphasatporn − Center for Computational Sciences, University of Tsukuba, Ibaraki, Tsukuba 305-8577, Japan.
Yasuteru Shigeta − Center for Computational Sciences, University of Tsukuba, Ibaraki, Tsukuba 305-8577, Japan. 
Thanyada Rungrotmongkol − Center of Excellence in Biocatalyst and Sustainable Biotechnology, Department of Biochemistry, Faculty of Science and Program in Bioinformatics and Computational Biology, Graduate School, Chulalongkorn University, Bangkok 10330, Thailand.
Alisa S. Vangnai − Center of Excellence in Biocatalyst and Sustainable Biotechnology, Department of Biochemistry, Faculty of Science, Chulalongkorn University, Bangkok 10330, Thailand.