| Summary: | In this study, using the botanical active component thiochromanone as the lead compound, a total of 32 new thiochromanone derivatives containing a carboxamide moiety were designed and synthesized and their in vitro antibacterial activities against <i>Xanthomonas oryzae</i> pv. <i>oryzae</i> (<i>Xoo</i>), <i>Xanthomonas oryzae</i> pv. <i>oryzicolaby</i> (<i>Xoc</i>), and <i>Xanthomonas axonopodis</i> pv. <i>citri</i> (<i>Xac</i>) were determined, as well as their in vitro antifungal activities against <i>Botryosphaeria dothidea</i> (<i>B. dothidea</i>), <i>Phomopsis</i> sp., and <i>Botrytis cinerea</i> (<i>B. cinerea</i>). Bioassay results demonstrated that some of the target compounds exhibited moderate to good in vitro antibacterial and antifungal activities. In particular, compound <b>4e</b> revealed excellent in vitro antibacterial activity against <i>Xoo</i>, <i>Xoc</i>, and <i>Xac</i>, and its EC<sub>50</sub> values of 15, 19, and 23 μg/mL, respectively, were superior to those of Bismerthiazol and Thiodiazole copper. Meanwhile, compound <b>3b</b> revealed moderate in vitro antifungal activity against <i>B. dothidea</i> at 50 μg/mL, and the inhibition rate reached 88%, which was even better than that of Pyrimethanil, however, lower than that of Carbendazim. To the best of our knowledge, this is the first report on the antibacterial and antifungal activities of this series of novel thiochromanone derivatives containing a carboxamide moiety.
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