BackgroundMyricetin and 1,3,4-thiadiazole derivatives were reported to exhibit favorable antiviral and antibacterial activities. Aiming to discover novel myricetin analogues with potent activities, a series of novel myricetin derivatives containing 1,3,4-thiadiazole moiety were synthesized, and their antibacterial and antiviral activities were evaluated.ResultBioassay results indicated that some target compounds exhibited potential antibacterial and antiviral activities. Among them, compounds 2, 3a, 3b, 3d, 3f, 3i, 3m and 3p exhibited excellent antibacterial activities against Xanthomonas oryzae pv. Oryzae (Xoo), with EC50 values of 42.7, 38.6, 20.8, 12.9, 22.7, 27.3, 18.3 and 29.4 μg/mL, respectively, which were better than that of thiadiazole-copper (94.9 μg/mL). Compounds 3b, 3d, 3e, 3f, 3i and 3o showed good antibacterial activities against Ralstonia solanacearum (Rs), with EC50 values of 37.9, 72.6, 43.6, 59.6, 60.6 and 39.6 μg/mL, respectively, which were superior to that of thiadiazole-copper (131.7 μg/mL). In addition, compounds 3d, 3f, 3i and 3m showed better curative activities against tobacco mosaic virus (TMV), with EC50 values of 152.8, 99.7, 127.1, and 167.3 μg/mL, respectively, which were better than that of ningnanmycin (211.1 μg/mL).ConclusionsA series of myricetin derivatives containing 1,3,4-thiadiazole scaffold were synthesized, and their antibacterial activities against Xoo and Rs and their antiviral activity against TMV were evaluated. Bioassays indicated that some target compounds exhibited potential antibacterial and antiviral activities. These results indicated this kind of myricetin analogues could be further studied as potential alternative templates in the search for novel antibacterial and antiviral agents.Electronic supplementary materialThe online version of this article (doi:10.1186/s13065-017-0336-7) contains supplementary material, which is available to authorized users.

A series of myricetin derivatives containing amide, thioether, and 1,3,4-thiadiazole moieties were designed and synthesized, and their antiviral and antibacterial activities were assessed. The bioassays showed that all the title compounds exhibited potent in vitro antibacterial activities against Xanthomonas citri (Xac), Ralstonia solanacearum (Rs), and Xanthomonas oryzae pv. Oryzae (Xoo). In particular, the compounds 5a, 5f, 5g, 5h, 5i, and 5l, with EC50 values of 11.5–27.3 μg/mL, showed potent antibacterial activity against Xac that was better than the commercial bactericides Bismerthiazol (34.7 μg/mL) and Thiodiazole copper (41.1% μg/mL). Moreover, the in vivo antiviral activities against tobacco mosaic virus (TMV) of the target compounds were also tested. Among these compounds, the curative, protection, and inactivation activities of 5g were 49.9, 52.9, and 73.3%, respectively, which were better than that of the commercial antiviral Ribavirin (40.6, 51.1, and 71.1%, respectively). This study demonstrates that myricetin derivatives bearing amide, thioether, and 1,3,4-thiadiazole moieties can serve as potential alternative templates for the development of novel, highly efficient inhibitors against plant pathogenic bacteria and viruses.

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By introducing flavonoids group into H-phosphonate, fourteen novel phosphonate derivatives containing flavonoid unit were designed and synthesized. Their structures were characterized by 1 H NMR, 13 C NMR, 31 P NMR, MS, IR and HRMS, and their antibacterial activities were evaluated via turbidimeter test in vitro. The bioassays results reveal that part of the target compounds exhibit better activities against Xanthomonas oryzae pv. Oryzae (Xoo) and Xanthomonas axonopodis pv. Citri (Xac) than positive controls thiodiazole copper and bismerthiazol (≥ 57.4%). Among them, the inhibitory rates of (2-(2-methoxyphenyl)-7-methoxy-4-oxo-4H-chromen-3-yl)diethyl phosphonate (2b), (2-(2-methoxyphenyl)-7-ethoxy-4-oxo-4H-chromen-3-yl)diethyl phosphonate (2f) and (2-(3,4-dimethoxyphenyl)-7-ethoxy-4-oxo-4H-chromen-3-yl)diethyl phosphonate (2m) reached 92.8%, 87.7% and 88.3% against Xoo at a concentration of 100 µg/mL, respectively. In addition, the inhibitory rates of (2-(4-fluorophenyl)-7-ethoxy-4-oxo-4H-chromen-3-yl)diethyl phosphonate (2h) and (2-(p-tolyl)-7-ethoxy-4-oxo-4H-chromen-3-yl)diethyl phosphonate (2k) reached 85.1% and 71.7% against Xac at a concentration of 100 µg/mL, respectively.

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A series of novel mandelic acid pyrazole amide compounds were synthesized and characterized. Moreover, their antiviral activities against tobacco mosaic virus were evaluated. The bioassay results indicated that as‐prepared compounds showed antiviral activity against tobacco mosaic virus at a concentration of 500 g/mL. The curative activity of compound 4g is 59.5%, which was comparable with positive control (Ningnanmycin, 61.0%). The inactivation activity of the compound 4l exhibited 80.1%, which was higher than that of Ningnanmycin (75.0%), and its protective activity was 88.7%, which is comparable with that of Ningnanmycin (90.7%).