A series of novel myricetin derivatives containing a 1,2,4-triazole Schiff base were designed and synthesized. Their structures were systematically characterized using ¹H NMR, ¹³C NMR, and HRMS. During antibacterial bioassays, 6f, 6i, and 6q demonstrated a good inhibitory effect against Xanthomonas axonopodis pv. citri (Xac), with half-maximal effective concentration (EC₅₀) values of 10.0, 9.4, and 8.8 μg mL⁻¹, respectively, which were better than those of bismerthiazol (54.9 μg mL⁻¹) and thiodiazole copper (61.1 μg mL⁻¹). Note that 6w demonstrated a good inhibitory effect against Ralstonia solanacearum (Rs) with and EC₅₀ value of 15.5 μg mL⁻¹, which was better than those of bismerthiazol (55.2 μg mL⁻¹) and thiodiazole copper (127.9 μg mL⁻¹). Similarly, 6a, 6d, and 6e demonstrated a good inhibitory effect against Xanthomonas oryzae pv. oryzae (Xoo) with EC₅₀ values of 47.1, 61.2, and 61.0 μg mL⁻¹, respectively, which were better than those of bismerthiazol (148.2 μg mL⁻¹) and thiodiazole copper (175.5 μg mL⁻¹). Furthermore, we used scanning electron microscopy (SEM) to study the possible sterilization process of the target compound 6q against Xac. The results indicated the possibility of destroying the bacterial cell membrane structure, resulting in an incomplete bacterial structure, and thus achieving inhibition. Furthermore, antiviral bioassays revealed that most compounds exhibited excellent antiviral activity against tobacco mosaic virus (TMV) at a concentration of 500 μg mL⁻¹. The results of the molecular docking studies for 6g with TMV-CP (PDB code: 1EI7) showed that compound 6g had partially interacted with TMV-CP. Therefore, mechanistic studies of the action of compound 6g could be further studied based on that.

Plant bacteria such as Xanthomonas axonopodispv. citri (Xac), Pseudomonas syringaepv. actinidiae (Psa), Xanthomonas oryzaepv. oryzae (Xoo), and tobacco mosaic virus (TMV) have created huge obstacles to the global trade of food and economic crops. However, traditional chemical agents used to control these plant diseases have gradually become disadvantageous due to long-term irregular use. Therefore, finding new and efficient antibacterial and antiviral agents is becoming imperative. In this study, a series of myricetin derivatives containing a quinazolinone moiety were designed and synthesized, and the antibacterial and antiviral activities of these compounds were evaluated. The bioassay results showed that some target compounds exhibited good antibacterial activities in vitro and antiviral activities in vivo. Among them, the median effective concentration (EC₅₀) value of compound L18 against Xac was 16.9 μg/mL, which was better than those of the control drugs bismerthiazol (BT) (62.2 μg/mL) and thiodiazole copper (TC) (97.5 μg/mL). Scanning electron microscopy (SEM) results confirmed that compound L18 inhibited the growth of Xac by affecting the morphology of cells. Microscale thermophoresis (MST) test results indicated that the dissociation constant (K_d) value of compound L11 against TMV-CP was 0.012 μM, which was better than that of the control agent ningnanmycin (2.726 μM). This study reveals that myricetin derivatives containing a quinazolinone moiety are potential antibacterial and antiviral agents.