SUBSTITUTED TETRAHYDROPYRIMIDINONES - A NEW HERBICIDAL CLASS OF COMPOUNDS INDUCING CHLOROSIS BY INHIBITION OF PHYTOENE DESATURATION .1. BIOLOGICAL AND BIOCHEMICAL RESULTS

Substituted tetrahydropyrimidinones (1,3-diaryl-perhydropyrimidine-2-o nes; ''cyclic ureas'') are new selective herbicides for preemergence u se in cotton and rice. Using different experimental systems it was sho wn that these compounds are inhibitors of carotenoid biosynthesis at t he phytoene desaturase (PD) step. Treated cress (Lepidium sativum, L.) seedlings bleached out completely and accumulated large amounts of ph ytoene (analyzed by uv and mass spectrometry) which were below the det ection limit in untreated plants. The same was shown to occur in green photomixotrophic cell cultures (Catharanthus roseus) and also in unic ellular cyanobacteria (Anacystis). Chlorophyll bleaching was demonstra ted to be a secondary photooxidative event caused by the loss of carot enoids as quenching substrates. Direct evidence for PD as the molecula r target was obtained from in vitro experiments with thylakoid membran es from Anacystis. In this cell-free assay system an I-50 value for in hibition of phytoene desaturation of 9 x 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 stru ctural elements of well-known chlorotic substances, e.g., the meta-CF3 -phenyl substituent and a carbonyl-containing heterocyclic system. The PD inhibitors fluridone and fluometuron are parent molecules of the n ew structures. (C) 1995 Academic Press, Inc.