Paroxan

Parathion when highly purified has low anti-cholinesterase activity in vitro compared to its activity in vivo. Diggle and Gage3 considered this to be due to isomerization to the -ethyl ester, but it may also be due to the formation4 of paroxan itself 0 II... 

EtO)2P—0—C6H4N02]. The pattern of inhibition produced by parathion resembles that produced by paroxan. 

In this connexion we will stress again that, although there is often a correspondence between toxic action of organo-phosphorus insecticides and anti-cholinesterase activity (p. 67), the relationship is not always simple. Thus parathion (p. 178), not itself an esterase inhibitor, is converted in vivo into an enzyme inhibitor.1 On the other hand, Aldridge2 has shown that the inhibitor paroxan can be hydrolysed enzymically to produce non-inhibitory substances. 

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