Résumé
Tentoxin 1 (TTX)1 is a natural cyclic tetrapeptide (cyclo(L-NMeAla-L-LeuNMeiΔ(Z)Phe-Gly)) produced by the phytopathogenic fungus Alternaria alternata. This cyclopeptide is a selective weedkiller which causes the chlorosis of some higher plants2. A possible mechanism involves the inhibition of photophosphorylation in the chloroplasts. In vitro and at low concentrations (10-8-10-7), TTX inhibits the F1 moiety of H+ATPsynthase, but at higher concentrations it stimulates the ATPase activity3. 4. TTX is the only natural effector known to inhibit the catalytic part of chloroplast ATP-synthase, and is noncompetitive for nucleotide binding. In order to understand this mechanism we developed a large number of TTX analogues, either by total synthesis and chemical modification, or by biotransformation. This report describes the study of two close analogues: dihydro-tentoxin (DH-TTX)2 a metabolite also isolated from Alternaria alternata and presumably precursor of TTX during its biosynthesis, and iso-tentoxin (Iso-TTX)3 a photochemical derivative of TTX.