EVIDENCE OF STERIC FACTORS IN THE FUNGITOXIC MECHANISMS OF 8-QUINOLINOL AND ITS 2-, 3-, 4-, 5-, 6- AND 7-CHLORO AND BROMO ANALOGS

A study was made of the fungitoxicity of 2-, 3-, 4-, 5-, 6- and 7-chloro and bromo-8-quinolinols against Aspergillus niger, A, oryzae, Myrothecium verrucaria, Trichoderma viride and Trichophyton mentagrophytes in Sabouraud dextrose broth and in Yeast Nitrogen Base supplemented with 1% D-glucose and 0.088% L-asparagine. Based on the presence or absence of synergism between pairs of substituted 8-quinolinols and reversal or nonreversal of toxicity by L-cysteine or N-acetyl-L-cysteine, the following conclusions were reached: (1) substituents on the quinoline ring change the site(s) of action of the toxicant; (2) the sites of action of the 5-, 6-, and 7-chloro-8-quinolinols are different from each other and from 8-quinolinol and its 2-, 3-, and il-chloro analogues, and the same is true for the corresponding bromo compounds; (3) 8-quinolinol and its 3- and 4-chloro and bromo analogues appear to share common sites of action; (4) for good antifungal activity the 2 position of the ring must not be substituted by sterically bulky groups; (5) the geometry of the binding sites of action are not so constrained that they cannot accommodate the analogously substituted chloro- and bromo-8-quinolinols.