Mechanism of Antifungal Action of 2,4,5,6‐Tetrachloroisophthalonitrile

Studies of the toxicity of 2,4,5,6‐tetrachloroisophthalonitrile (TCIN) to cells of Saccharomyces pastorianus and Neurospora crassa showed that 2 to 4 μg/ml of the toxicant were required to inhibit growth. Several thiol compounds reversed toxicity to growth. Glucose oxidation was severely impaired in treated cells of both test organisms. The toxicant at 2 or 4 μg/ml markedly reduced soluble thiol content of these cells. Bound thiol content was less affected in S. pastorianus cells than soluble thiol content. Uptake of toxicant by yeast cells was accompanied by formation of derivatives, some of which resembled those formed by reaction of glutathione with TCIN in vitro. Coenzyme A, glutathione, and 2‐mercaptoethanol readily formed derivatives with TCIN in vitro. The nature of these derivatives was studied using 2‐mercaptoethanol products as model substituents. Four derivatives were formed with 2‐mercaptoethanol each with similar functional groups but showing dissimilar degrees of mobility during silica gel chromatography. Evidence indicated that these are derivatives of TCIN in which 1 to 4 of the halogens has been substituted by 2‐mercaptoethanol. The mechanism of fungicidal action of TCIN is attributed to thiol inactivation.