Abstract:
Investigations of arylcarbamates as potential insecticides began in 1949 with a study of physostigmine sulphate and other quaternary ammonium derivatives of aryl N-methylcarbamates (99) Their parasympathomimetic action is said to arise from inhibition of cholinesterase (ChE), this generally being of short duration indicating biological instability of the compounds. Observed disruptions of normal synaptic activity are dependent on the stereochemical relationship to Acetylcholine (98). Many carbamates which are ionized at physiological pH are inactive, or less active, insecticides than anticipated from their in vitro ChE activity or toxicity to mammals (70). This appears to result from the relative impermeability of the insect cuticle and nerve sheath to ionized materials and the lack of a cholinergic neuro-muscular junction in insects (19, 70, 109). The introduction of ionic centres into a molecule by a detoxication mechanism may prevent penetration through membranes inside the body, thus giving a non-toxic product (122).
