The multiproduct sesquiterpene synthase MtTPS5 from Medicago truncatula catalyzes the conversion of farnesyldiphosphate (FDP) into a complex mixture of 27 terpenoids. 3-Bromo substrate analogues of geranyl diphosphate (3-BrGDP) and farnesyldiphosphate (3-BrFDP) were evaluated as substrates of MTPS5 enzyme. Kinetic studies demonstrated that these compounds were highly potent competitive inhibitors