Synthesis and Antibacterial and Antifungal Activities of Novel Thiochroman-4-one Derivatives Incorporating Oxime Ether and 1,3,4-Oxadiazole Thioether Moieties

In this study, 18 novel thiochroman-4-one derivatives incorporating oxime ether and 1,3,4-oxadiazole thioether moieties were synthesized and their structures analyzed by H-1 NMR, C-13 NMR, and HRMS. Their in vitro antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac) as well as antifungal activities against Botrytis cinerea (B. cinerea), Verticillium dahliae (V. dahliae), and Fusarium oxysporum (F. oxysporum) were determined. Bioassay results showed that compound 6-chloro-2-(5-(methylthio)-1,3,4-oxadiazol-2-yl)thiochroman-4-one O-methyl oxime (7a) was found to be the most active against Xoo and Xac, with the median effective concentration values (EC50) of 17 and 28 mu g/mL, respectively, which were even better than those of Bismerthiazol and Thiodiazole copper. Meanwhile, compound 2-(5-(ethylthio)-1,3,4-oxadiazol-2-yl)-6-methylthiochroman-4-one O-methyl oxime (7j) showed better in vitro antifungal activity against B. cinerea, with the inhibition rate of 79%, than that of Carbendazim. As far as we know, this paper is the first report on the synthesis and antibacterial and antifungal activities of this series of novel thiochroman-4-one derivatives incorporating oxime ether and 1,3,4-oxadiazole thioether moieties.