Importantes agentes para defesa contra armas de guerra química são reativadores da acetilcolinesterase humana (huAChE) inibida por compostos organofosforados neurotóxicos (OP), e precisam de uma permeabilidade razoável pela barreira hematoencefálica (HB). Neste trabalho, oximas neutras, que penetram HB melhor do que as oximas catiônicas atualmente utilizadas como agentes de defesa, foram testadas como reativadores da huAChE inibida com paraoxon usando o método de Ellman modificado e pralidoxima (2-PAM) como padrão positivo. A oxima neutra mais ativa foi a 2-tiofenoaldoxima, que reativou 93% da huAChE inibida, sendo 12% mais eficiente do que a 2-PAM. Os resultados mostraram que oximas neutras simples possuem potencial para atuarem como antídotos para intoxicação com OPs neurotóxicos, sugerindo maior investigação no desenvolvimento de agentes de defesa neutros.Important defense agents against chemical warfare weapons, which are reactivators of human acetylcholinesterase (huAChE) inhibited by neurotoxic organophosphorus compounds (OP), need a reasonable permeation of the hematoencephalic barrier (HB). In this work, neutral oximes, which permeate HB better than the cationic oximes currently used as defense agents, were tested as reactivators of huAChE inhibited with paraoxon using the modified Ellman test with pralidoxime (2-PAM) as positive standard. The most active neutral oxime was (thiophen-2-yl)aldoxime, which reactivated 93% of the inhibited huAChE and was 12% more effective than 2-PAM. The results showed that simple neutral oximes have potential to function as antidotes for intoxication with neurotoxic OPs, suggesting further research on the development of neutral defense agents.Keywords: neutral oximes, huAChE reactivation, paraoxon, chemical warfare, (thiophen-2-yl)aldoxime IntroductionIntoxication with neurotoxic organophosphorus compounds is a serious problem caused by some pesticides used in agriculture, such as paraoxon (1) and malathion (2) ( Figure 1) and chemical warfare agents. [1][2][3][4][5][6][7][8][9][10][11] According to the World Health Organization, there are about 220,000 intoxications with organophosphorus pesticides throughout the world every year, leading to approximately 20,000 deaths. 1,[12][13][14] The most dangerous neurotoxic compounds are the chemical warfare agents soman (3), sarin (4), tabun (5) and VX (6) ( Figure 1). Though their use is prohibited by the United Nations, these agents have been employed as weapons by terrorist groups and by countries that did not sign the Chemical Weapon Convention administered by the Organization for the Prohibition of Chemical Weapons (OPCW).The principal target for the action of neurotoxic organophosphorus compounds is the enzyme acetylcholinesterase (AChE), a serine hydrolase that controls the nerve impulses at the cholinergic receptors in the central and peripheral nervous systems. 1,15-20 As shown in Ribeiro et al. 1217 Vol. 23, No. 7, 2012 Figure 2, the function of AChE (7) is the hydrolysis of the nerve impulse transmitter acetylcholine...