Flavonol Derivatives Containing a Quinazolinone Moiety: Design, Synthesis, and Antiviral Activity.

A series of flavonol derivatives containing quinazolinone were designed and synthesized, and their antiviral activities against tobacco mosaic virus (TMV) were evaluated. The results of the half maximal effective concentration (EC50 ) test against TMV showed that the EC50 value of curative activity of K5 was 139.6 µg/mL, which was better than that of the commercial drug ningnanmycin (NNM) 296.0 µg/mL, and the EC50 value of protective activity of K5 was 120.6 µg/mL, which was superior to that of NNM 207.0 µg/mL. The interaction of K5 with TMV coat protein (TMV-CP) was investigated using microscale thermophoresis (MST) and molecular docking and the results showed that K5 can combine with TMV-CP more strongly to TMV-CP than that NNM can. Furthermore, the assay measuring malondialdehyde (MDA) content indicated that K5 had the ability to improve the disease resistance of tobacco. Hence, this study offers strong evidence that flavonol derivatives have potential as novel antiviral agents.

Design, Synthesis, Biological Activity Evaluation and Action Mechanism of Myricetin Derivatives Containing Thiazolebisamide.

The plant diseases caused by a variety of pathogens such as viruses, bacteria and fungi pose a great threat to global food production and food safety. Therefore, the search for green, efficient and pollution-free pesticides has become an important task. In this article, 23 myricetin derivatives containing thiazolebisamides active groups have been designed and synthesized. Their activities were evaluated by performing in vitro antibacterial and in vivo antiviral assays, microscale thermophoresis (MST) and molecular docking assays. The results of in vivo antiviral assays showed that compounds A4 and A23 exhibited good antiviral activity with EC50 values of 79.0 and 54.1 µg/mL for therapeutic activity and 103.3 and 91.2 µg/mL for protective activity, respectively. The dissociation constants (Kd) values of compounds A4 and A23 against TMV-CP were 0.021 and 0.018 µM, respectively, determined by microscale thermophoresis (MST), which were much smaller than those of the commercial drug ningnanmycin (NNM), which were 2.84 µM. The interaction of compounds A4, A23 with TMV-CP was further verified at the molecular level. In addition, in vitro antifungal assays of this series of compounds showed that they exhibited some inhibitory activity against a variety of fungi, especially against the phytophthora capsici. Among them, A13 and A20 showed similar inhibitory activity to the control drug azoxystrobin at 100 µg/mL against the phytophthora capsici.

Antiviral Activities of Novel Myricetin Derivatives Containing 1,3,4-Oxadiazole Bisthioether.

A class of novel myricetin derivatives containing 1,3,4-oxadiazole bisthioether were synthesized. The results of antiviral biological activity demonstrated that the partially compounds exhibited good antiviral effects against tobacco mosaic virus. The in vivo curative and protective activities of compound E12 against TMV was quite significant. The EC50 value of the curative activity of E12 was 128.8 µg/mL, while the value of ningnanmycin was 296.4 µg/mL. Similarly, the EC50 value of the protective activity of E12 was 99.1 µg/mL, while the value of ningnanmycin was 307.6 µg/mL. The microscale thermophoresis data indicated that the binding value of ningnanmycin and TMV-CP was 2.726±1.301 µM, which was not as good as the binding value of E12 and TMV-CP was 0.029±0.013 µM. This study showed that novel myricetin derivatives containing 1,3,4-oxadiazole bisthioether may be a kind of agricultural antiviral drugs with great potential.

Synthesis, antiviral activity, and molecular docking study of trans-ferulic acid derivatives containing acylhydrazone moiety.

In this study, we report the synthesis and antiviral activity of trans-ferulic acid derivatives containing acylhydrazone moiety. Biological tests demonstrated that most target compounds showed potent antiviral activity against tobacco mosaic virus (TMV). Compound D4 showed remarkable inactivating activity with EC50 value of 36.59µg/mL, which was obviously superior to ribavirin (126.05µg/mL). Molecular docking results revealed that compound D4 exhibited the optimal combining capacity with five hydrogen bonds to different amino-acid residues of TMV coat protein (TMV-CP). Docking results were consistent with the inactivating activity of target compounds against TMV.

Novel 1,3,4-oxadiazole sulfonate/carboxylate flavonoid derivatives: synthesis and biological activity.

BACKGROUND: With the long-term use of traditional bactericides and antiviral agents, drug resistance has become increasingly prominent, resulting in impaired crop growth and yields. Based on this, the introduction of small molecular active groups into natural products has become the direction of research for green pesticides. RESULTS: In this study, novel 1,3,4-oxadiazole sulfonate/carboxylate flavonoid derivatives were explored. Among them, D4 exhibited good inhibitory effects on plant bacteria. It is worth mentioning that D4 (15 µg ml-1 ) exhibited an excellent median effective concentration (EC50 ) value against Xanthomonas oryzae pv. oryzae (Xoo), which was better than bismerthiazol (73 µg ml-1 ) and thiodiazole copper (100 µg ml-1 ). The EC50 for D4 was much lower than the two positive controls (bismerthiazol, thiodiazole copper), making D4 more potent in this assay of bacterial growth inhibition. In addition, mechanism research using scanning electron microscopy revealed that D4 could cause deformation or rupture of the cell membranes of Xoo and Pseudomonas syringae pv. actinidiae. Moreover, D4 exhibited the best EC50 for in vivo curative (132 µg ml-1 ) and protective (101 µg ml-1 ) activities against tobacco mosaic virus, which were more effective than ningnanmycin. Microscale thermophoresis data suggested that D4 [dissociation constant (Kd ) = 0.038 ± 0.011 µmol L-1 ] exhibited a stronger binding capacity than the control agent ningnanmycin (Kd = 4.707 ± 2.176 µmol L-1 ). CONCLUSION: The biological activity data and mode of action demonstrated that D4 had the best antibacterial and antiviral effects. Compound D4 discovered in the current work may be a very promising agricultural drug. © 2022 Society of Chemical Industry.

Anti-TMV effects of seco-pregnane C21 steroidal glycosides isolated from the roots of Cynanchum paniculatum.

Tobacco mosaic virus (TMV) is known to infect a wide range of plants, resulting in reduced yield and productivity. Novel, effective, and plant-based pesticides are required to protect plants against TMV infection. To identify novel anti-TMV agents from natural sources, we systematically studied the roots of Cynanchum paniculatum and isolated six new seco-pregnane C21 steroidal glycosides, along with 14 known compounds. Their structures were elucidated by comprehensive spectroscopic data analysis. The anti-TMV activity of compounds were screened using the half-leaf method. Biological tests revealed that compounds 1, 2, 5, 9, 10, 15, and 16 displayed significant anti-TMV activities compared with the positive control ningnanmycin. In addition, reverse transcription-polymerase chain reaction (RT-PCR) and western blot analysis confirmed the antiviral activity of these compounds, as evident from reduced TMV coat protein (TMV-CP) gene replication and TMV-CP protein expression. These compounds downregulated the expression of NtHsp70-1 and NtHsp70-261, indicating that these steroidal glycosides possibly inhibit the TMV infection by suppressing the expression of NtHsp70-1 and NtHsp70-061 expression.

Identification of anti-TMV active flavonoid glycosides and their mode of action on virus particles from Clematis lasiandra Maxim.

BACKGROUND: Tobacco mosaic virus (TMV) is a disreputable plant pathogen that causes a decline in the quality and yield of various economic crops. Natural products are important potential sources of biopesticides to control TMV. This study focuses on the discovery of anti-TMV active flavonoid glycosides and their mode of action on TMV particles from Clematis lasiandra Maxim. RESULTS: A new benzoyl acylated flavonoid glycoside, kaempferol 3-O-(2''-benzoyl)-ß-d-glucopyranosyl-7-O-α-l-rhamnopyranoside (1), and nine known flavonoids (2-10) were identified first from C. lasiandra. The hydroxyl group at C-7, E-p-coumarate at C-6'' in the Glc of C-6, and the glucuronic acid at C-3 were functional groups for the antiviral flavonoid glycosides. Flavonoids 2, 5, and 6 showed higher inactivation efficacies of 64.62% to 82.54% compared with ningnanmycin at 500 µg ml-1 . The protective and curative efficacies for 2 and 5 were 57.44-59.00% and 41.17-43.92% at 500 µg ml-1 , respectively. Compound 5 showed higher TMV systemic resistance with control efficacies of 41.64%, 36.56% and 27.62% at concentrations of 500, 250 and 125 µg ml-1 compared with ningnanmycin in K326 tobaccos, respectively. Compound 5 can directly fracture TMV particles into small fragments combining with the fusion phenomena, and TMV-CP was an important target for 5 to break TMV particles. CONCLUSION: Flavonoid glycosides from C. lasiandra showed potent antiviral activities against TMV with multiple modes of action including inactivation, protective and curative effects, and inducing systemic resistance. TMV-CP was an important target for active flavonoid glycosides to fracture TMV particles. The results provided evidence that flavonoid glycosides from C. lasiandra have the potential to control TMV.

Antibacterial and Antiviral Activities of 1,3,4-Oxadiazole Thioether 4H-Chromen-4-one Derivatives.

Various 1,3,4-oxadiazole thioether 4H-chromen-4-one derivatives were conceived. The title compounds demonstrated striking inhibitory effects against Xac, Psa, and Xoo. EC50 data exhibited that A8 (19.7 µg/mL) had better antibacterial activity against Xoo than myricetin, BT, and TC. Simultaneously, the mechanism of action of A8 had been verified by SEM. The results of anti-tobacco mosaic virus indicated that A9 had the best in vivo antiviral effect compared with ningnanmycin. From the data of MST, it could be seen that A9 (0.003 ± 0.001 µmol/L) exhibited a strong binding capacity, which was far superior to ningnanmycin (2.726 ± 1.301 µmol/L). This study shows that the 1,3,4-oxadiazole thioether 4H-chromen-4-one derivatives may become agricultural drugs with great potential.

Ningnanmycin inhibits tobacco mosaic virus virulence by binding directly to its coat protein discs.

Tobacco mosaic virus (TMV) causes severe plant diseases worldwide; however, effective antiviral agents for controlling TMV infections are not available. This lack of effective antiviral agents is mainly due to the poor understanding of potential targets associated with TMV infections. During infection, the coat protein (CP), which is delivered by viral particles into susceptible host cells, provides protection for viral RNA. Here, we found that Ningnanmycin (NNM), a commercially used plant antibacterial agent, inhibits the assembly of the CP by directly binding several residues. These interactions cause the disassembly of the CP from discs into monomers, leading to an almost complete loss of pathogenicity. Substitutions in the involved binding residues resulted in mutants that were significantly less sensitive to NNM. Thus, targeting the binding of viral CPs through small molecular agents offers an effective strategy to study the mechanism of NNM.

Binding interactions between enantiomeric α-aminophosphonate derivatives and tobacco mosaic virus coat protein.

Tobacco mosaic virus (TMV) is an important plant virus that can cause considerable crop loss. Our group synthesized a series of enantiomeric α-aminophosphonate derivatives with high anti-TMV activities. The activity of (R)-diphenyl-1-(4-methylbenzothiazole-2-amino)-1-(thiphene-2-yl)-methylphosphonate (Q-R) was found to be superior to that of (S)-diphenyl-1-(4-methyl benzothiazole-2-amino)-1-(thiphene-2-yl)-methylphosphonate (Q-S). However, the mechanism for inhibition of the R-isomer (Q-R) of infection activity is not clear. Thus, we studied the interactions between Q-R and Q-S and TMV by using TMV coat proteins (CP) as a potential target for fluorescence spectroscopy, isothermal titration calorimetry, microscale thermophoresis, and molecular docking. Arg90 was found to play a major role in the interaction of Q-R with TMV CP, as demonstrated by the interaction experiments and the results of molecular modeling. The substitution of arginine with glycine resulted in a mutant that was significantly less sensitive to Q-R. These results indicate that Q-R undermines the structural stability of the TMV R90G virus particle by binding with Arg90, eventually leading to the loss of the virus' ability for infection.