Design, synthesis, and antimicrobial evaluation of 2-aminothiazole derivatives bearing the 4-aminoquinazoline moiety against plant pathogenic bacteria and fungi.

Background: To find more effective agricultural antibiotics, a class of new 2-aminothiazole derivatives containing the 4-aminoquinazoline moiety were synthesized and evaluated for their antimicrobial properties against phytopathogenic bacteria and fungi of agricultural importance.

Results: All the target compounds were fully characterized by H NMR, C NMR, and high-resolution mass spectrometry. The bioassay results showed that compound F29 with a 2-pyridinyl substituent exhibited an outstanding antibacterial effect against Xanthomonas oryzae pv. oryzicola (Xoc) in vitro, having an half-maximal effective concentration (EC ) value as low as 2.0 μg/mL (over 30-fold more effective than the commercialized agrobactericide bismerthiazol, with an EC value of 64.3 μg/mL). In addition, compound F8 with a 2-fluorophenyl group demonstrated a good inhibitory activity toward the bacterium Xanthomonas axonopodis pv. citri (Xac), around twofold more active than bismerthiazol in terms of their EC values (22.8 versus 71.5 μg/mL). Interestingly, this compound also demonstrated a notable fungicidal effect against Phytophthora parasitica var. nicotianae, with an EC value largely comparable with that of the commercialized fungicide carbendazim. Finally, mechanistic studies revealed that compound F29 exerted its antibacterial effects by increasing the permeability of bacterial membranes, reducing the release of extracellular polysaccharides, and triggering morphological changes of bacterial cells.

Conclusion: Compound F29 has promising potential as a lead compound for developing more efficient bactericides to fight against Xoc. © 2023 Society of Chemical Industry.