Carnosic acid, Carnosol and ferruginol - typed tricyclic diterpenes, are shown to be excellent natural antioxydants. The antioxidative quality of rosemary and sage, repeated-mentioned in literature, is caused by the occurrence of Carnosic acid in the leaves of these spices. Inhibition of O2-uptake of methyl+linolenate by the named compounds was measured in a Barcroft-Warburg-apparatus. Other diterpenes of similar structure are compared with Carnosic acid to determine the chemical arrangement responsible for the antioxidative efficiency. Inhibition is caused by cooperation of the two phenolic functions with the isopropyl-group in o-position. In comparison with synthetical antioxidants Carnosic acid and Carnosol demonstrate the same inhibition as butylated Hydroxytoluene. Both antioxidants protect methyllinolenate, too. Their effect depends on concentration. 5-Hydroxy-7,4′-dimethoxyflavone, a flavonoid compound of rosemary-leaves, shows weak synergistic properties in a methyllinolena/Carnosol/Cu2-Systeme. © 1969 Springer Verlag.
