Discovery of a novel series of phenylthiazole thioether (sulfone) compounds based on natural thiasporine A as potential candidates for controlling rice fungal and bacterial diseases

Half of the world's population depends on rice for their calories. Protecting rice in the growth period from damage caused by phytopathogens is faced with a great challenge under the frequent extreme climate. To find novel fungicides to control rice diseases, 35 novel phenylthiazole-1,3,4-oxadiazole-thioether (sulfone) derivatives were synthesized and evaluated for their efficacy against destructive fungal and bacterial diseases of rice. Bioassay results demonstrated that most of G-series compounds possessed excellent antifungal and antibacterial activities. In particular, compounds G1 (EC₅₀ = 2.22 μg/mL, R.s) and G7 (EC₅₀ = 2.76 μg/mL, R.s) showed the most promising antifungal activities in vitro and exhibited superior protective and curative activities against rice sheath blight in vivo compared with commercial carbendazim. Surprisingly, compound G2 exhibited the remarkable antibacterial activity against Xanthomonas oryzae pv. oryzae (Xoo) with an EC₅₀ value of 1.98 μg/mL, and demonstrated superior protective activity (88.08%) than thiodiazole copper (79.39%) against rice bacterial leaf blight at 200 μg/mL. The abovementioned results fully manifested that the phenylthiazole-1,3,4-oxadiazole-sulfone structure, especially compounds G1 and G2, had the potential to develop as commercial agents for controlling rice fungal and bacterial diseases.