Substituted Tetrahydropyrimidinones: A New Herbicidal Class of Compounds Inducing Chlorosis by Inhibition of Phytoene Desaturation: 1. Biological and Biochemical Results

Abstract

Substituted tetrahydropyrimidinones (1,3-diaryl-perhydropyrimidine-2-ones; "cyclic ureas") are new selective herbicides for preemergence use in cotton and rice. Using different experimental systems it was shown that these compounds are inhibitors of carotenoid biosynthesis at the phytoene desaturase (PD) step. Treated cress ( Lepidium sativum, L.) seedlings bleached out completely and accumulated large amounts of phytoene (analyzed by uv and mass spectrometry) which were below the detection limit in untreated plants. The same was shown to occur in green photomixotrophic cell cultures ( Catharanthus roseus) and also in unicellular cyanobacteria ( Anacystis). Chlorophyll bleaching was demonstrated to be a secondary photooxidative event caused by the loss of carotenoids as quenching substrates. Direct evidence for PD as the molecular target was obtained from in vitro experiments with thylakoid membranes from Anacystis. In this cell-free assay system an I 50 value for inhibition of phytoene desaturation of 9 × 10 −8 M for lead compound 1 could be determined. This value was the same as the constant measured in in vivo systems. Chemically, the new compounds combine several structural elements of well-known chlorotic substances, e.g., the meta-CF 3-phenyl substituent and a carbonyl-containing heterocyclic system. The PD inhibitors fluridone and fluometuron are parent molecules of the new structures.