Analogues of tentoxin: Tools for mechanistic investigations

Summary Tentoxin [cyclo-(MeAla¹-Leu²-MeΔPhe³-Gly⁴] is a metabolite isolated from a phytopathogenic fungusAlternaria alternata, which induces chlorosis of many plants. This potential natural herbicide binds specifically to the soluble part CF₁ of the chloroplastic coupling factor, which is a proton ATP-synthase. The effect of the toxin is concentration dependent: at low concentration it is a powerful inhibitor, while at higher concentration, it stimulates the enzyme. We synthesized tentoxin and we designed new analogues in order to vary the hydrophobicity on the side chain and to study the structure activity relationships. Comparative activities suggest that it is possible to separate inhibitory and activating effects using tentoxin analogues, showing some evidence for the existence of two binding sites with different affinity constant.