1-(2,6-disubstituted benzoyl)-3-phenylurea insecticides: Inhibitors of chitin synthesis

The mode of action has been investigated of the 1-(2,6-dichlorobenzoyl)-3-phenyl ureas, a new type of insecticide. A microautoradiographical study was made of the incorporation of glucose, tyrosine, and proline in endocuticle of fifth-instar larvae of Pieris brassicae L., both normal and treated with 1-(2,6-dichlorobenzoyl)-3-(3,4-dichlorophenyl)-urea (DU 19111). The results of this work clearly indicate that DU 19111 blocks the synthesis of cuticular chitin. The nature of this inhibition was investigated by comparison of the rates of incorporation of [¹⁴C]glucose into the ultimate chitin precursor, uridine diphosphate N-acetyl glucosamine (UDPAG), in both normal and DU 19111-treated Pieris larvae. It was found that these levels did not differ significantly.The finding that only in DU 19111-treated Pieris larvae were substantial amounts of labeled N-acetyl glucosamine present 1 hr after the injection of [¹⁴C]glucose is considered as a clue to the mechanism by which this insecticide inhibits chitin synthesis. Apparently the coupling of UDPAG to the chitin synthetase still proceeds, but the function of connecting N-acetyl glucosamine moieties to the chitin chain is disrupted.Tentative results with a structural analog of DU 19111 suggest that this compound induces accumulation of UDPAG, but not of N-acetyl glucosamine. This would imply that in the latter case the polycondensing enzyme is completely blocked.