Synthesis of Indolyl Isothiocyanate and Its Inhibitory Activity against Fungi

Based on previous research, this study synthesized 24 compounds by splicing the substructures of the indolyl group and the isothiocyanate group. <i>Alternaria alternata</i>, <i>Phytophthora capsici</i>, <i>Botrytis cinerea,</i> and <i>Valsa mali</i> were used to test the activity of the target compounds. At 100 μg/mL, compounds <b>8</b>, <b>13</b>, <b>14</b>, and <b>17</b> exhibited excellent inhibitory effects of more than 80% on <i>P. capsici</i>, <i>B. cinerea,</i> and <i>V. mail</i>. The EC₅₀ values of compounds <b>13</b> and <b>14</b> were 0.64 and 2.08 μg/mL, respectively. Potted antifungal activity demonstrated that compounds <b>13</b> and <b>14</b> had a protective effect of around 80% against <i>B. cinerea</i> at 200 μg/mL. Further physiological and biochemical studies on <i>B. cinerea</i> revealed that compound 13 thickened cell walls and caused mitochondrial vacuolization. Moreover, theoretical calculations indicated that the charge distribution of indolyl isothiocyanate compounds played a crucial role in the observed fungicidal activity. In summary, this study provided fundamental reference data for the derivative synthesis of these indolyl isothiocyanate compounds.