A series of new N-phenylacetamide derivatives containing 4-arylthiazole moieties was designed and synthesized by introducing the thiazole moiety into the amide scaffold. The structures of the target compounds were confirmed by ¹H-NMR, ¹³C-NMR and HRMS. Their in vitro antibacterial activities were evaluated against three kinds of bacteria—Xanthomonas oryzae pv. Oryzae (Xoo), Xanthomonas axonopodis pv. Citri (Xac) and X.oryzae pv. oryzicola (Xoc)—showing promising results. The minimum 50% effective concentration (EC₅₀) value of N-(4-((4-(4-fluoro-phenyl)thiazol-2-yl)amino)phenyl)acetamide (A₁) is 156.7 µM, which is superior to bismerthiazol (230.5 µM) and thiodiazole copper (545.2 µM). A scanning electron microscopy (SEM) investigation has confirmed that compound A₁ could cause cell membrane rupture of Xoo. In addition, the nematicidal activity of the compounds against Meloidogyne incognita (M. incognita) was also tested, and compound A₂₃ displayed excellent nematicidal activity, with mortality of 100% and 53.2% at 500 μg/mL and 100 μg/mL after 24 h of treatment, respectively. The preliminary structure-activity relationship (SAR) studies of these compounds are also briefly described. These results demonstrated that phenylacetamide derivatives may be considered as potential leads in the design of antibacterial agents.

In order to discover new lead compounds with high antibacterial activity, a series of new derivatives were designed and synthesized by introducing a sulfonate or carboxylate moiety into the 1,3,4-oxadiazole structure. Antibacterial activity against two phytopathogens, Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas axonopodis pv. citri (Xac), was assayed in vitro. The preliminary results indicated that ten compounds including 4a-1-4a-4 and 4a-11-4a-16 had good antibacterial activity against Xoo, with EC₅₀ values ranging from 50.1-112.5 µM, which was better than those of Bismerthiazol (253.5 µM) and Thiodiazole copper (467.4 µM). Meanwhile, 4a-1, 4a-2, 4a-3 and 4a-4 demonstrated good inhibitory effect against Xanthomonas axonopodis pv. citri with EC₅₀ values around 95.8-155.2 µM which were better than those of bismerthiazol (274.3 µM) and thiodiazole copper (406.3 µM). In addition, in vivo protection activity of compound 4a-2 and 4a-3 against rice bacterial leaf blight was 68.6% and 62.3%, respectively, which were better than bismerthiazol (49.6%) and thiodiazole copper (42.2%). Curative activity of compound 4a-2 and 4a-3 against rice bacterial leaf blight was 62.3% and 56.0%, which were better than bismerthiazol (42.9%) and thiodiazole copper (36.1%). Through scanning electron microscopy (SEM) analysis, it was observed that compound 4a-2 caused the cell membrane of Xanthomonas oryzae pv. oryzae ruptured or deformed. The present results indicated novel derivatives of 5-phenyl sulfonate methyl 1,3,4-oxadiazole might be potential antibacterial agents.