Phytotoxicity of Triterpenes and Limonoids from the Rutaceae and Meliaceae. 5α,6β,8α,12α-Tetrahydro-28-norisotoonafolin - a Potent Phytotoxin from Toona ciliata

Limonoids and triterpenes are the largest groups of secondary metabolites and have notable biological activities. Meliaceae and Rutaceae are known for their high diversity of metabolites, including limonoids, and are distinguished from other families due to the frequent occurrence of such compounds. The increased interest in crop protection associated with the diverse bioactivity of these compounds has made these families attractive in the search for new allelopathic compounds. In the study reported here we evaluated the bioactivity profiles of four triterpenes (1-4) and six limonoids (5-10) from Meliaceae and Rutaceae. The compounds were assessed in a wheat coleoptile bioassay and those that had the highest activities were tested on the standard target species Lepidium sativum (cress), Lactuca sativa (lettuce), Lycopersicon esculentum (tomato) and Allium cepa (onion). Limonoids showed phytotoxic activity and 5 alpha,6 beta,8 alpha,12 alpha-tetrahydro-28-norisotoonafolin (10) and gedunin (5) were the most active, with bioactivity levels similar to, and in some cases better than, those of the commercial herbicide Logran. The results indicate that these products could also be allelochemicals involved in the ecological interactions of these plant species.