Applying a Bioisosteric Replacement Strategy in the Discovery and Optimization of Mesoionic Pyrido[1,2-a]pyrimidinone Insecticides: A Review

Mesoionic pyrido[1,2-a]pyrimidinones are a unique class of heterocyclic compounds. Compounds from this class with a n-propyl group substituted at the 1 position of the mesoionic core were discovered with interesting insecticidal activity in our screen. In this overview, we showcase how a bioisosteric replacement strategy was applied during the discovery and optimization of this class of compounds. Through exploring various substituents at the 1 position, evaluating a variety of mesoionic bicyclic ring scaffolds, and examining substituents on the phenyl group at the 3 position of the mesoionic core as well as substituents on the mesoionic ring skeleton, many compounds were discovered with excellent hopper activity or potent activity against a wide range of Lepidoptera. Ultimately, dicloromezotiaz was identified for commercial development to control a broad spectrum of lepidopteran pests.