Synthesis of N-(2′S)-methylbutanoyl-2-methylbutylamide (Frianol), sex pheromone of sugarcane rhizome borer Migdolus fryanus, from renewable sources

Abstract

Rhizome borer Migdolus fryanus is the most prevalent and harmful beetle attacking sugarcane crops. The insect larvae feed on the plant roots and adults spend most of their lives also under the surface. Classical control methods are expensive and ineffective, pesticides, for instance, do not reach the beetles due to their underground habits. Using semiochemicals to control M. fryanus population is an outstanding alternative. The insect sex pheromone, N-(2′S)-methylbutanoyl-2-methylbutylamide, has already been successfully used in bated traps, but its synthesis is laborious and expensive. Therefore, we herein present a cost-effective and efficient method to prepare the pheromone, using renewable starting materials. The amide can be prepared in 3 steps, starting with the decarboxylation of isoleucine, leading to an imine intermediate. After an acidic hydrolysis, the ammonium salt formed reacts with 2-methylbutyric acid to give the pheromone as the only product in 87% overall yield.