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Abstract
8-Quinolinol-5-sulfonic acid was nearly devoid of antimicrobial activity, due to what was believed to be an unfavorable partition coefficient. Since twenty six 8-quinolinol-5- and 7-sulfonic acids were available from our previous work, they were tested against six fungi. The 7-chloro and 7-bromo-5-sulfonic acids and the 5-chloro and 5-bromo-7-sulfonic acids showed fungal inhibition within one order of magnitude of that of 8-quinolinol. It is suggested that a nonchelating mechanism is in part responsible for this fungi toxicity. Five additional 5-sulfonic acids with chlorine in positions 3-, 6-, 3,6-, 3,7-, and 6,7- that were suitable for studies in synergism became available more recently. The enhanced activities of the dichlorosulfonic acids over the correspondingly substituted monochlorosulfonic acids is attributed to intramolecular synergism.