N-Acylated N-methylcarbamates have been prepared and tested for contact/stomach poison and systemic insecticidal activities, mammalian toxicity and in vitro anticholinesterase activity. The N-acyl derivatives in general have lower mammalian toxicities and somewhat lower insecticidal activities than the corresponding unacylated N-methylcarbamates and are relatively poor inhibitors of bee cholinesterase. Tentative reasons are given for these effects. IntroductionStedman,' following earlier work on the nature of the alkaloid physostigmine, synthesised a number of aryl N-methylcarbamates with anticholinesterase activity from phenols containing quaternary ammonium substituents. These derivatives were not insecticidal and Kolbezen et aL2 concluded that, because of their highly polar nature, such compounds are unable to penetrate the lipoid sheath of insect nerves. They synthesised a number of non-ionised N-substituted carbamates which were shown to have insecticidal properties. The present communication deals with the N-acylation of certain N-methylcarbamates and its effect on biological activity.

Many aryl N-methylcarbamates and their N-acyl derivatives have been prepared and tested against larvae of the sheep blowfly, Lucilia sericata. Mammalian toxicities and persistences on sheep fleece were also determined. The factors which led to the selection of Butacarb (3,5-di-t-butylphenyl N-methylcarbamate) as a new veterinary insecticide are discussed.

Dichlorvos resin pellets placed in bedding were found to be highly efficacious in eliminating Myobia musculi (Schrank) from a conventional mouse colony. The infested mice were exposed continuously to the insecticide for a 14-day period. At the end of this period no live mites or eggs were observed.

Methods of synthesis and insecticidal properties of a series of aryl N‐acyl‐N‐methylcarbamates are described. There is evidence to suggest that the usual mode of action involves de‐acylation within the insect, although the acyl group may initially aid penetration to the site of action. An unexpected finding was that the acyl derivatives were generally less toxic to mammals than the parent carbamates. The persistence of 3‐s‐butylphenyl N‐methylcarbamate on foliage was considerably improved by the introduction of a phenoxyacetyl group. However, acylation did not improve the outstanding activity and persistence on sheep fleece of the blowfly larvicide Butacarb (3,5‐di‐t‐butylphenyl N‐methylcarbamate).