THE OXIDATION OF CAFFEIC ACID-DERIVATIVES AS MODEL REACTION FOR THE FORMATION OF POTENT GONADOTROPIN INHIBITORS IN PLANT-EXTRACTS

Synthetic caffeic acid derivatives, substoichiometrically oxidized wit h KMnO4, exhibit antigonadotropic activity against pregnant mare serum gonadotropin (PMSG) to a greater degree than caffeic acid itself. Inh ibitory compounds, formed after an oxidation of caffeic acid and its d erivatives are bound to PMSG dependent on their concentration to resul t in hormone-inhibitor complexes. These PMSG-inhibitor complexes exhib ited little or no biological activity, depending on the structure of t he inhibitor. The substoichiometric oxidation with KMnO4 led to the co rresponding unstable o-quinones as first products. The complete oxidat ion reaction could be divided into an initial KMnO4-dependent step fol lowed by a mangenese-catalyzed autoxidation, which was accompanied by a pronounced oxygen uptake from the solution. The HPLC analysis after an oxidation of caffeic acid derivatives led to product patterns with strong similarities to those of caffeic acid in the respective product UV spectra, suggesting the formation of compounds with similar struct ures.