Synthesis and Chirality of Novel Heterocyclic Compounds Designed for Crop Protection

Abstract

More than 60% of the novel development products in agrochemistry, synthetic or of natural origin, contain heterocyclic ring systems. It will be shown that many modern formulations based on these new core structures can be used at very low application rates per hectare. In many cases these new structures are chiral. Synthetic investigations to produce enantiomerically pure products by stereoselective processes are discussed with examples A, B and C: 1 1-Substituted-imidazole-5-carboxylic acid derivatives were discovered as a new herbicidal class by the screening of pharmaceutical products. The R-enantiomer A proved to be a highly active inhibitor of the obtusifoliol-14-α-methyl-demethylase in the plant sterol metabolism. A pharmacophore substructure was proposed based on conformational analysis and was used to predict activities of stereoisomeric analogs. 2 A stereoselective synthesis of (2R,4S)-4-(2-ethyl-1,3-dioxolan-4-yl-methoxy)-phenyl-(3-fluoro-phenyl)-ether B, a 1,3-dioxolane type juvenile hormone mimic with two chiral centers, is described. A (-)-Camphor-10-sulfonamide served as a chiral auxiliary. 3 Synthetic methods to produce the post-emergence herbicide (+)-hydantocidin (ribantoin) C, a metabolite isolated from Streptomyces hygroscopicus, strain Tü 2474, with four contiguous stereogenic centers, are discussed. One reaction sequence features the Bucherer reaction and another highly stereoselective method, an intramolecular oxygen-bridged Vorbrüggen coupling, as key steps.