INTRAMOLECULAR SYNERGISM, AN EXPLANATION FOR THE ENHANCED FUNGITOXICITY OF HALO-8-QUINOLINOLS

An antifungal study against Aspergillus niger, A. oryzae, Myrothecium verrucaria, and Trichoderma viride in Yeast Nitrogen Base supplemented with 1% D-glucose and 0.088% L-asparagine was carried out using 8-qui nolinol and 3-, 5-, 6-, 7-, 3,6-, and 5,7-chlorinated and brominated-8 -quinolinols. Binary mixtures of 3- and 6-halo- and 5- and 7-halo-8-qu inolinols were intermolecularly synergistic. MICs of the monohalo syne rgistic mixtures admired with a MIC of the corresponding dihalo-8-quin olinols were not synergistic. The dihalo-8-quinolinols with substituen ts in positions corresponding to those of the synergistic binary mixtu res appeared to attack the same sites of action as the binary pairs. T he enhanced activities of 3,6- and 5,7-dichloro-8-quinolinols and 3,6- and 5,7dibromo-8-quinolinols are believed to be due to intramolecular synergism. The greater fungitoxicity of 5-, 6-, and 7-monohalo-8-quin olinols over 8-quinolinol can also be explained as due to intramolecul ar synergism. 3,6-Dihaio- and 5,7-dihalo-8-quinolinols formed synergis tic pairs of compounds.