The metabolism of the phytoalexins camalexin (1), 1-methylcamalexin (10) and 6- methoxycamalexin (11) by Alternaria brassicicola and their antifungal activity is reported. This work establishes that camalexins are slowly biotransformed (ca. six days) to the corresponding indole-3-thiocarboxamides, which are further transformed to the indole-3- carboxylic acids. These metabolites are substantially less inhibitory to A. brassicicola than ...