Design, synthesis, and antiviral activities of myricetin derivatives containing pyridazinone

Abstract

26 derivatives of myricetin containing pyridazinone were designed and synthesized from the natural product myricitrin, which were structurally characterized by nuclear magnetic resonance (NMR) spectroscopy and high-resolution mass spectrometry (HRMS), and the structure of A14 was further determined using an X-ray single crystal diffractometer. The in vivo anti-tobacco mosaic virus (TMV) activity was tested by the half-leaf method, and the results showed that A4, A23 and A26 possessed better curative activity with effective concentration 50% (EC₅₀) of 131.6, 138.5 and 118.9 μg mL⁻¹, which were superior to that of ningnanmycin (NNM) (235.6 μg mL⁻¹), respectively. A24 and A26 possessed better protective activity with EC₅₀ values of 117.4 and 162.5 μg mL⁻¹, superior to that of NNM (263.2 μg mL⁻¹). Microcalorimetric thermophoresis (MST) and molecular docking assays showed that A23 and A26 had strong binding ability with TMV-CP. After treatment with A26, the chlorophyll content in tobacco was significantly higher than that in the control group, and the growth rate of malondialdehyde content was slowed down. This further confirmed that the drug molecules have good antiviral activity.

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1. Introduction

Plant virus diseases have always been a major threat to agriculture, where crop infection with viruses leads to shortened lifespan and reduced yields, causing huge yield losses worldwide. Among them, tobacco mosaic virus (TMV) has caused the most serious yield losses and economic losses.^1,2 TMV was the first virus to be discovered, and being the first among the top ten plant viruses,³ it is present stably in high concentrations in infected plants.^4,5 It mainly infects not only tobacco plants, but also a variety of lycopene plants such as tomato and pepper.⁶ Characterized by a wide host range, good persistent stability, high resistance, and natural plant inoculation, the virus infects plants and affects the photosynthetic system of the host plant, causes defects such as greenish discoloration.⁷ In addition, once the plant is infected, the virus destroys the cellular structure, deprives it of nutrients and affects its normal physiological conditions. It usually shows retarded development, leaf curling, necrosis, wilting and other developmental abnormalities, which can lead to plant death in severe cases.^8,9 The main defense at present is the use of plant virus suppression pesticides; however, drugs designed to suppress viruses may also cause damage to the host, which makes the control of plant virus diseases difficult.¹⁰ In addition, the long-term use of pesticides can lead to the development of plant resistance and residues of pesticides and their metabolites, which can also have adverse effects on human health and the ecological environment.^11–13 Therefore, it is important to explore the development of new, efficient and low-toxicity green antiviral agents for the control of TMV.

Plant-derived pesticides have great potential for development as antiviral drugs because they are environmentally friendly, efficient and safe, and not easy to develop drug resistance.¹⁴ As one of the plant-derived natural products, myricetin is a flavonoid compound from a wide range of sources and is found in plants such as onion, red wine,¹⁵ tea, vegetables,¹⁶ raspberry,¹⁷etc. It possesses a variety of biological activities such as antimicrobial, antioxidant, antimutagenic, anticarcinogenic, anti-inflammatory, antiallergic, analgesic activities and so on,^18,19 and thus has attracted a great deal of attention from researchers. In the previous studies of our group, the derivatives of myricetin were found to possess a variety of biological activities such as anticancer,²⁰ antiviral,^21–23 antibacterial,^24–26 and antifungal activities,^27,28 which provides a new idea for the discovery of new green pesticides.

Pyridazinones are an important class of nitrogen-containing small molecules that have been widely studied and applied in the fields of pesticides, pharmaceuticals, and chemical dyes due to the diversity of their biological activities. Pyridazinones exhibit biocidal, insecticidal, acaricidal, herbicidal, and plant growth regulating activities in the field of pesticides,^29–31 and anticancer,^32,33 antibacterial,³⁴ antiviral,³⁵ hypoglycemic,³⁶ anti-inflammatory,^37,38 and antipsychotic³⁹ activities in the field of pharmaceuticals. Therefore, research on pyridazinones has been of great interest. Some of the pesticides containing pyridazinone are listed in Fig. 1.

Fig. 1 Some commercial pesticides containing pyridazinone.

Based on this, a low-toxicity and highly efficient derivative of myricetin was expected to be obtained through the principle of active splicing, using myricetin as the lead compound and introducing pyridazinone active small molecules. To the best of our knowledge, this is the first report on the synthesis and evaluation of the antiviral activity of myricetin derivatives containing a fraction of pyridazinone.

2. Methods and materials

2.1 Chemicals and instruments

Melting points were determined using a binocular micro melting point tester, an X-4B instrument (Shanghai INESA Co., Ltd), which was not calibrated. The structural characterization of the target compounds was obtained using ASCEND400 (Bruker, Germany) and JEOL-ECX500 (Tokyo, Japan) proton NMR spectrometers using CDCl₃ as the solvent and TMS as the internal standard. High resolution spectra were obtained using the Thermo scientific Q Exactive mass spectrometer (Missour, USA). Crystal data were obtained using the Bruker D8-QUEST diffractometer (Bruker, Germany). Microscale thermophoresis was performed using a NanoTemp Monolith NT.115 microscale thermophoresis instrument (NanoTemper, Germany). The MDA content assay kit was purchased from Solarbio, and the OD values were determined using a Gen5 enzyme labeling instrument (Bio-Tek, Germany). The reagents used in the experiments were analytically pure and did not require further purification and drying.

2.2 Chemical compound synthesis

2.2.1 General synthesis of intermediates. Intermediate 1 was synthesized using the experimental method reported in the literature,^40,41 taking 6-hydroxy-2-phenylpyridazin-3(2H)-one as an example. 1.00 g (6.92 mmol) of phenyl hydrazine hydrochloride was dissolved in 25 mL of secondary water, and heated to 90 °C until completely dissolved, then 0.75 g (7.61 mmol) of maleic anhydride was added, and 8 mL of dilute hydrochloric acid was added dropwise to the mixture, and was refluxed for 3 h. At the end of the reaction, cooled to room temperature, the mixture was poured into ice water to precipitate, left to stand, filtrated under reduced pressure and washed. The resulting solid was dissolved in 10% aqueous sodium hydroxide solution, filtered to remove insoluble impurities, and dilute hydrochloric acid was added to adjust the pH to 2–3. The precipitate was formed, left to stand, and then filtrated under reduced pressure. Intermediates 2 and 3 were synthesized using the method reported in the literature, and the specific steps were described in the corresponding literature.^42,43

2.2.2 General synthesis of target compounds A1–A26. Taking A1 as an example, 0.38 g (2.00 mmol) of intermediate 1, 20 mL of DMF, and 1.00 g (7.24 mmol) of K₂CO₃ were added to a 100 mL round-bottomed flask sequentially, and after stirring for 10 min at room temperature, 0.85 g (1.67 mmol) of intermediate 3 was added, the reaction was heated, and the end point was monitored by thin-layer chromatography (TLC). At the end of the reaction, the reaction was cooled to room temperature, the precipitate was precipitated by pouring ice water, left to stand and then filtered under reduced pressure, washed with water, petroleum ether, dried using the filter cake, and then separated and purified by column chromatography (petroleum ether : ethyl acetate = 1 : 4, v/v) to obtain the target compounds. The specific synthetic route is detailed in Scheme 1.

Scheme 1 Synthetic route of the target compounds A1–A26.

6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-phenylpyridazin-3(2H)-one (A1). White solid (56%), m.p.: 114.9–116.3 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.63 (d, J = 7.6 Hz, 2H, Ph–H), 7.44 (t, J = 7.9 Hz, 2H, Ph–H), 7.34 (t, J = 7.4 Hz, 1H, Ph–H), 7.31 (s, 2H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.92 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.36 (d, J = 2.3 Hz, 1H, Ph–H), 4.31 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.3 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 4.4 Hz, 6H, Ph–OCH₃), 3.86 (s, 6H, Ph–OCH₃), 2.18 (p, J = 6.3 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 173.98, 164.08, 161.04, 158.83, 152.99, 152.70, 141.58, 140.61, 139.92, 133.98, 128.69, 127.67, 126.86, 125.99, 125.06, 109.41, 105.84, 95.91, 92.46, 69.19, 64.24, 61.04, 56.49, 56.29, 55.90, 29.74. HRMS (ESI) calcd for C₃₃H₃₂N₂O₁₀ [M + H]⁺: 617.21297, found 617.21295.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(p-tolyl)pyridazin-3(2H)-one (A2). White solid (59%), m.p.: 148.6–150.5 °C. ¹H NMR (500 MHz, chloroform-d) δ 7.48 (d, J = 8.3 Hz, 2H, Ph–H), 7.31 (s, 2H, Ph–H), 7.23 (d, J = 8.2 Hz, 2H, Ph–H), 6.96 (d, J = 9.8 Hz, 1H, Ph–H), 6.90 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.1 Hz, 1H, Ph–H), 4.29 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.3 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 4.2 Hz, 6H, Ph–OCH₃), 3.86 (s, 6H, Ph–OCH₃), 2.37 (s, 3H, Ph–CH₃), 2.17 (p, J = 6.3 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (126 MHz, chloroform-d) δ 174.01, 164.12, 161.09, 158.89, 158.87, 153.04, 152.71, 152.65, 140.67, 139.98, 139.19, 137.66, 133.93, 129.34, 126.75, 126.04, 124.95, 109.45, 105.91, 95.94, 92.50, 69.24, 64.23, 61.07, 56.52, 56.33, 55.93, 29.78, 21.25. HRMS (ESI) calcd for C₃₄H₃₄N₂O₁₀ [M + H]⁺: 631.22862, found 631.22845.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(4-fluorophenyl)pyridazin-3(2H)-one (A3). White solid (54%), m.p.: 171.8–173.6 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.63 (d, J = 4.9 Hz, 2H, Ph–H), 7.30 (s, 2H, Ph–H), 7.12 (d, J = 8.3 Hz, 2H, Ph–H), 6.97 (d, J = 9.8 Hz, 1H, Ph–H), 6.92 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.1 Hz, 1H, Ph–H), 6.35 (d, J = 2.0 Hz, 1H, Ph–H), 4.30 (t, J = 6.4 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.2 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 3.1 Hz, 6H, Ph–OCH₃), 3.87 (s, 6H, Ph–OCH₃), 2.18 (p, J = 12.5, 6.2 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.01, 164.15, 161.10, 158.88, 158.80, 153.05, 152.79, 140.61, 140.02, 133.98, 127.03, 126.98, 126.95, 126.91, 126.88, 126.02, 115.63, 115.45, 109.45, 105.93, 95.96, 92.52, 69.15, 64.36, 61.07, 56.52, 56.38, 56.34, 55.93, 29.75. ¹⁹F NMR (376) MHz, chloroform-d) δ −113.84. HRMS (ESI) calcd for C₃₂H₃₁N₂O₁₀F [M + H]⁺: 635.20355, found 635.20355.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(4-chlorophenyl)-pyridazin-3(2H)-one (A4). White solid (63%), m.p.: 177.9–179.8 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.63 (d, J = 8.8 Hz, 2H, Ph–H), 7.40 (d, J = 8.8 Hz, 2H, Ph–H), 7.30 (s, 2H, Ph–H), 6.97 (d, J = 9.8 Hz, 1H, Ph–H), 6.92 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.36 (d, J = 2.2 Hz, 1H, Ph–H), 4.31 (t, J = 6.4 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.2 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 3.2 Hz, 6H, Ph–OCH₃), 3.87 (s, 6H, Ph–OCH₃), 2.18 (p, J = 6.3 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 173.94, 164.06, 161.01, 158.80, 158.66, 152.96, 152.77, 152.72, 140.52, 139.99, 139.90, 133.96, 133.03, 128.72, 127.01, 126.17, 125.94, 109.37, 105.82, 95.89, 92.43, 69.05, 64.31, 61.00, 56.47, 56.26, 55.86, 29.73. HRMS (ESI) calcd for C₃₃H₃₁N₂O₁₀Cl [M + H]⁺: 651.17400, found 651.17395.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy) 2-(3-bromophenyl)-pyridazin-3(2H)-one (A5). Yellow solid (43%), m.p.: 124.9–126.5 °C. ¹H NMR (500 MHz, chloroform-d) δ 7.83 (t, 1H, Ph–H), 7.62 (d, J = 8.0 Hz, 1H, Ph–H), 7.44 (d, J = 9.1 Hz, 1H, Ph–H), 7.31 (s, 1H, Ph–H, 7.29 (s, 2H, Ph–H), 6.95 (d, J = 9.9 Hz, 1H, Ph–H), 6.91 (d, J = 9.8 Hz, 1H, Ph–H), 6.48 (d, J = 2.1 Hz, 1H, Ph–H), 6.34 (d, J = 2.2 Hz, 1H, Ph–H), 4.30 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.15 (t, J = 6.2 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.89 (d, J = 5.4 Hz, 9H, Ph–OCH₃), 3.86 (s, 3H, Ph–OCH₃), 2.20 (p, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (126 MHz, chloroform-d) δ 173.99, 164.09, 161.05, 158.85, 158.67, 153.00, 152.83, 152.78, 142.58, 140.59, 139.93, 134.01, 130.62, 129.90, 128.06, 127.18, 125.99, 123.67, 122.01, 109.42, 105.87, 95.92, 92.47, 69.10, 64.32, 61.05, 56.50, 56.31, 55.90, 29.78. HRMS (ESI) calcd for C₃₃H₃₁N₂O₁₀Br [M + H]⁺: 695.12348, found 695.12341.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(3-methoxyphenyl)pyridazin-3(2H)-one (A6). White solid (41%), m.p.: 173.9–175.8 °C. ¹H NMR (500 MHz, chloroform-d) δ 7.34 (t, J = 8.0 Hz, 1H, Ph–H), 7.31 (s, 2H, Ph–H), 7.22 (s, 1H, Ph–H), 7.20 (d, 1H, Ph–H), 6.97 (d, J = 9.8 Hz, 1H, Ph–H), 6.92 (d, J = 9.8 Hz, 1H, Ph–H), 6.88 (d, J = 8.3 Hz, 1H, Ph–H), 6.49 (s, 1H, Ph–H), 6.35 (s, 1H, Ph–H), 4.31 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.15 (t, J = 6.2 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 4.7 Hz, 6H, Ph–OCH₃), 3.87 (s, 6H, Ph–OCH₃), 3.82 (s, 3H, Ph–OCH₃), 2.18 (p, J = 6.1 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (126 MHz, chloroform-d) δ 172.88, 162.99, 159.94, 158.61, 157.74, 157.73, 151.90, 151.63, 151.52, 141.52, 139.52, 138.82, 132.89, 128.32, 125.78, 124.90, 116.38, 112.55, 109.85, 108.31, 104.75, 94.81, 91.37, 68.08, 63.14, 59.95, 55.39, 55.20, 54.80, 54.41, 28.63. HRMS (ESI) calcd for C₃₄H₃₄N₂O₁₁ [M + H]⁺: 647.22354, found 647.22321.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(4-isopropylphenyl)pyridazin-3(2H)-one (A7). Yellow solid (56%), m.p.: 151.2–152.1 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.52 (d, J = 8.5 Hz, 2H, Ph–H), 7.31 (s, 2H, Ph–H), 7.29 (d, J = 8.5 Hz, 2H, Ph–H), 6.97 (d, J = 9.7 Hz, 1H, Ph–H), 6.91 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, 1H, Ph–H), 6.36 (d, 1H, Ph–H), 4.30 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.3 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 4.3 Hz, 6H, Ph–OCH₃), 3.86 (s, 6H, Ph–OCH₃), 2.93 (p, J = 13.8, 7.0 Hz, 1H, Ph-C̲H̲(CH₃)₂), 2.18 (p, J = 6.3 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–), 1.26 (d, J = 6.9 Hz, 6H, Ph–CH_2̲C̲H̲_2̲). ¹³C NMR (101 MHz, chloroform-d) δ 173.95, 164.04, 161.01, 158.82, 158.79, 152.96, 152.65, 152.60, 148.34, 140.59, 139.89, 139.28, 133.86, 126.70, 126.67, 125.96, 124.87, 109.37, 105.81, 95.87, 92.42, 69.18, 64.16, 61.00, 56.46, 56.26, 55.86, 33.88, 29.72, 23.97. HRMS (ESI) calcd for C₃₆H₃₈N₂O₁₀ [M + H]⁺: 659.25992, found 659.25970.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(4-(tert-butyl)phenyl)-pyridazin-3(2H)-one (A8). White solid (44%), m.p.: 148.2–149.7 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.54 (d, J = 8.8 Hz, 2H, Ph–H), 7.45 (d, J = 8.7 Hz, 2H, Ph–H), 7.31 (s, 2H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.91 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.36 (d, J = 2.2 Hz, 1H, Ph–H), 4.30 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.3 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 4.3 Hz, 6H, Ph–OCH₃), 3.86 (s, 6H, Ph–OCH₃), 2.18 (p, J = 6.3 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–), 1.33 (s, 9H, Ph–C(CH₃)₃). ¹³C NMR (101 MHz, chloroform-d) δ 173.95, 164.04, 161.01, 158.83, 158.79, 152.97, 152.64, 152.61, 150.53, 140.59, 139.89, 138.97, 133.87, 126.66, 125.97, 125.64, 124.48, 109.37, 105.81, 95.87, 92.42, 69.17, 64.17, 61.00, 56.46, 56.26, 55.86, 34.67, 31.33, 29.72. HRMS (ESI) calcd for C₃₇H₄₀N₂O₁₀ [M + H]⁺: 673.27557, found 673.27557.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(4-(trifluoromethyl)phenyl)pyridazin-3(2H)-one (A9). White solid (27%), m.p.: 119.7–120.8 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.86 (d, J = 8.0 Hz, 2H, Ph–H), 7.70 (d, J = 8.3 Hz, 2H, Ph–H), 7.30 (s, 2H, Ph–H), 6.99 (d, J = 9.7 Hz, 1H, Ph–H), 6.94 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.36 (d, J = 2.2 Hz, 1H, Ph–H), 4.33 (t, J = 6.4 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.17 (t, J = 6.2 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 4.8 Hz, 6H, Ph–OCH₃), 3.87 (s, 6H, Ph–OCH₃), 2.18 (p, J = 6.3 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 173.94, 164.08, 161.01, 158.81, 158.70, 152.97, 152.92, 152.76, 144.24, 140.48, 139.91, 134.08, 127.29, 125.92, 125.78, 125.75, 124.96, 109.36, 105.83, 95.89, 92.44, 68.99, 64.40, 60.98, 56.46, 56.25, 55.86, 29.64. ¹⁹F NMR (376 MHz, chloroform-d) δ -62.48. HRMS (ESI) calcd for C₃₄H₃₁N₂O₁₀F₃ [M + H]⁺: 685.20036, found 685.20032.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(3,4-dichlorophenyl)-pyridazin-3(2H)-one (A10). White solid (73%), m.p.: 149.2–151.1 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.87 (d, J = 2.4 Hz, 1H, Ph–H), 7.59 (d, J = 2.5 Hz, 1H, Ph–H), 7.50 (s, 1H, Ph–H), 7.30 (s, 2H, Ph–H), 6.96 (d, J = 9.8 Hz, 1H, Ph–H), 6.92 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.32 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.2 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 4.0 Hz, 6H, Ph–OCH₃), 3.87 (s, 6H, Ph–OCH₃), 2.18 (p, J = 6.2 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 173.93, 164.07, 161.00, 158.80, 158.55, 152.95, 152.86, 152.77, 140.63, 140.49, 139.89, 133.99, 132.35, 131.24, 130.14, 127.27, 126.66, 125.92, 124.11, 109.36, 105.83, 95.89, 92.44, 68.97, 64.35, 61.00, 56.46, 56.27, 55.86, 29.61. HRMS (ESI) calcd for C₃₃H₃₀N₂O₁₀Cl₂ [M + H]⁺: 685.13503, found 685.13489.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(3,4-difluorophenyl)-pyridazin-3(2H)-one (A11). White solid (57%), m.p.: 166.9–168.7 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.62 (s, 1H, Ph–H), 7.48 (d, J = 9.0 Hz, 1H, Ph–H), 7.30 (s, 2H, Ph–H), 7.20 (d, 1H, Ph–H), 6.97 (d, J = 9.8 Hz, 1H, Ph–H), 6.92 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.36 (d, J = 2.2 Hz, 1H, Ph–H), 4.32 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.2 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–), 3.96 (s, 3H, Ph–OCH₃), 3.90 (d, J = 3.7 Hz, 6H, Ph–OCH₃), 3.88 (s, 6H, Ph–OCH₃), 2.17 (p, J = 12.5, 6.3 Hz, 2H), –O–CH₂C̲H̲_2̲CH₂–O–. ¹³C NMR (101 MHz, chloroform-d) δ 173.99, 164.11, 161.04, 158.85, 158.63, 153.00, 152.83, 152.80, 140.53, 139.94, 134.06, 127.21, 125.97, 121.14, 121.08, 117.00, 116.82, 114.73, 114.52, 109.39, 105.86, 95.93, 92.47, 69.01, 64.38, 61.02, 56.49, 56.29, 55.89, 29.66. ¹⁹F NMR (376 MHz, chloroform-d) δ −135.96 (s), −138.42 (s). HRMS (ESI) calcd for C₃₃H₃₀N₂O₁₀F₂ [M + H]⁺: 653.19413, found 653.19391.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy) 2-(3-chloro-4-fluorophenyl)-pyridazin-3(2H)-one (A12). White solid (77%), m.p.: 178.0–179.4 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.79 (s, 1H, Ph–H), 7.59 (d, J = 4.7 Hz, 1H, Ph–H), 7.30 (s, 2H, Ph–H), 7.21 (d, J = 8.8 Hz, 1H, Ph–H), 6.96 (d, J = 9.8 Hz, 1H, Ph–H), 6.92 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.31 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.16 (t, J = 6.2 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.90 (d, J = 3.3 Hz, 6H, Ph–OCH₃), 3.88 (s, 6H, Ph–OCH₃), 2.18 (p, J = 6.2 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 173.95, 164.08, 161.01, 158.82, 158.60, 152.97, 152.84, 152.76, 140.51, 139.91, 133.95, 127.32, 127.25, 125.95, 124.94, 124.87, 116.43, 116.21, 109.37, 105.83, 105.74, 95.89, 92.44, 68.99, 64.34, 61.00, 56.47, 56.27, 55.87, 29.63. ¹⁹F NMR (376 MHz, chloroform-d) δ −116.18. HRMS (ESI) calcd for C₃₃H₃₀N₂O₁₀ClF [M + H]⁺: 669.16479, found 669.16458.
6-(3-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)propoxy)-2-(naphthalen-2-yl)pyridazin-3(2H)-one (A13). White solid (27%), m.p.: 145.2–146.7 °C. ¹H NMR (400 MHz, chloroform-d) δ 8.16 (d, J = 1.9 Hz, 1H, Ph–H), 7.90 (d, J = 9.0 Hz, 2H, Ph–H), 7.87 (s, 1H, Ph–H), 7.75 (d, J = 2.1 Hz, 1H, Ph–H), 7.49 (d, J = 9.5 Hz, 2H, Ph–H), 7.30 (s, 2H, Ph–H), 7.02 (d, J = 9.8 Hz, 1H, Ph–H), 6.96 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.3 Hz, 1H, Ph–H), 6.36 (d, J = 2.3 Hz, 1H, Ph–H), 4.35 (t, J = 6.3 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂–O–), 4.18 (t, J = 6.3 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.89 (d, J = 12.3 Hz, 6H, Ph–OCH₃), 3.84 (s, 6H, Ph–OCH₃), 2.20 (p, J = 6.3 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 173.95, 164.05, 161.01, 158.98, 158.80, 152.95, 152.78, 152.69, 140.58, 139.88, 138.99, 133.98, 133.07, 132.39, 128.42, 127.62, 126.86, 126.50, 126.42, 125.95, 123.62, 123.16, 109.38, 105.81, 95.87, 92.42, 69.15, 64.24, 60.99, 56.46, 56.25, 55.86, 29.71. HRMS (ESI) calcd for C₃₇H₃₄N₂O₁₀ [M + H]⁺: 667.22864, found 667.22862.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-phenylpyridazin-3(2H)-one (A14). White solid (66%), m.p.: 121.8–123.6 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.64 (d, J = 7.4 Hz, 2H, Ph–H), 7.44 (t, J = 7.8 Hz, 2H, Ph–H), 7.34 (s, 2H, Ph–H), 7.32 (d, J = 7.4 Hz, 1H, Ph–H), 6.99 (d, J = 9.7 Hz, 1H, Ph–H), 6.95 (d, J = 9.8 Hz, 1H, Ph–H), 6.50 (d, J = 2.3 Hz, 1H, Ph–H), 6.35 (d, J = 2.3 Hz, 1H, Ph–H), 4.16 (t, J = 6.0 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 5.9 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.91 (d, J = 1.6 Hz, 9H, Ph–OCH₃), 3.91 (s, 3H, Ph–OCH₃), 1.90 (p, J = 5.2, 1.7 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.89 (p, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, CDCl₃) δ 174.03, 164.01, 161.02, 158.80, 152.95, 152.84, 152.66, 141.58, 140.59, 139.85, 133.91, 128.65, 127.63, 126.96, 126.08, 125.06, 109.40, 105.84, 95.84, 92.41, 71.83, 66.94, 61.03, 56.45, 56.30, 55.85, 26.94, 25.35. HRMS (ESI) calcd for C₃₄H₃₄N₂O₁₀ [M + H]⁺: 631.22862, found 631.22821.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(p-tolyl)pyridazin-3(2H)-one (A15). White solid (26%), m.p.: 141.6–143.4 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.50 (d, J = 8.3 Hz, 2H, Ph–H), 7.34 (s, 2H, Ph–H), 7.23 (d, J = 8.3 Hz, 2H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.93 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.1 Hz, 1H, Ph–H), 6.35 (d, J = 2.1 Hz, 1H, Ph–H), 4.14 (t, J = 6.1 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–CH₃), 3.91 (d, J = 2.2 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 2.37 (s, 3H, Ph–CH₃), 1.96 (p, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.88 (p, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.02, 164.00, 161.02, 158.85, 158.80, 152.95, 152.77, 152.65, 140.60, 139.84, 139.14, 137.62, 133.81, 129.28, 126.82, 126.08, 124.92, 109.41, 105.84, 95.83, 92.41, 71.85, 66.91, 61.03, 56.45, 56.30, 55.85, 26.95, 25.34, 21.19. HRMS (ESI) calcd for C₃₅H₃₆N₂O₁₀ [M + H]⁺: 645.24427, found 645.24359.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(4-fluorophenyl)pyridazin-3(2H)-one (A16). White solid (46%), m.p.: 175.6–177.6 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.62 (d, J = 4.9 Hz, 2H, Ph–H), 7.34 (s, 2H, Ph–H), 7.12 (d, J = 8.7 Hz, 2H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.95 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.0 Hz, 1H, Ph–H), 6.35 (d, J = 1.9 Hz, 1H, Ph–H), 4.16 (t, J = 6.2 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.05 (t, J = 6.1 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–CH₃), 3.91 (d, J = 2.2 Hz, 9H, Ph–CH₃), 3.90 (s, 3H, Ph–CH₃), 1.94 (p, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.88 (p, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.09, 164.11, 161.10, 158.88, 158.82, 153.04, 152.97, 152.74, 140.66, 139.97, 133.95, 127.18, 126.98, 126.91, 126.15, 115.63, 115.44, 109.47, 105.94, 95.92, 92.51, 71.83, 67.04, 61.09, 56.52, 56.38, 55.92, 26.96, 25.39. ¹⁹F NMR (471 MHz, chloroform-d) δ −113.87. HRMS (ESI) calcd for C₃₄H₃₃N₂O₁₀F [M + H]⁺: 649.21920, found 649.21906.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(4-chlorophenyl)-pyridazin-3(2H)-one (A17). White solid (26%), m.p.: 132.3–134.2 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.64 (d, J = 8.9 Hz, 2H, Ph–H), 7.39 (d, J = 8.9 Hz, 2H, Ph–H), 7.34 (s, 2H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.94 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.17 (t, J = 6.1 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.05 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.96 (s, 3H, Ph–OCH₃), 3.91 (d, J = 2.0 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 1.92 (p, J = 7.9, 5.5 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.89 (p, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.07, 164.07, 161.05, 158.83, 158.72, 152.99, 152.72, 140.61, 140.05, 139.89, 133.95, 133.08, 128.76, 127.22, 126.25, 126.10, 109.41, 105.86, 95.89, 92.46, 71.76, 67.02, 61.06, 56.48, 56.33, 55.89, 26.90, 25.32. HRMS (ESI) calcd for C₃₄H₃₃N₂O₁₀Cl [M + H]⁺: 665.18976, found 665.18965.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(3-bromophenyl)-pyridazin-3(2H)-one (A18). Yellow solid (52%), m.p.: 115.9–117.8 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.83 (s, 1H, Ph–H), 7.64 (d, J = 8.1 Hz, 1H, Ph–H), 7.44 (d, J = 8.9 Hz, 1H, Ph–H), 7.34 (s, 2H, Ph–H), 7.29 (t, J = 8.1 Hz, 1H, Ph–H), 6.98 (d, J = 9.8 Hz, 1H, Ph–H), 6.94 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.17 (t, J = 6.1 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.91 (d, J = 2.9 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 1.92 (p, J = 7.8, 5.7 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.86 (p, J = 8.0, 5.9 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.03, 164.02, 161.02, 158.80, 158.64, 152.99, 152.96, 152.66, 142.58, 140.59, 139.85, 133.94, 130.57, 129.85, 128.04, 127.31, 126.09, 123.66, 121.99, 109.41, 105.83, 95.85, 92.42, 71.77, 67.10, 61.04, 56.46, 56.31, 55.86, 26.92, 25.33. HRMS (ESI) calcd for C₃₄H₃₃N₂O₁₀Br [M + H]⁺: 709.13913, found 709.13867.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(3-methoxyphenyl)pyridazin-3(2H)-one (A19). White solid (61%), m.p.: 124.8–126.5 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.34 (s, 2H), 7.31 (s, 1H, Ph–H), 7.24 (t, 1H, Ph–H), 7.20 (d, J = 2.2 Hz, 1H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.94 (d, J = 9.7 Hz, 1H, Ph–H), 6.88 (d, J = 8.3 Hz, 1H, Ph–H), 6.49 (d, J = 2.0 Hz, 1H, Ph–H), 6.35 (d, J = 2.0 Hz, 1H, Ph–H), 4.15 (t, J = 5.9 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 5.9 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.91 (d, J = 1.7 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 3.81 (s, 3H, Ph–OCH₃), 1.94 (m, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.88 (m, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.02, 164.02, 161.04, 159.70, 158.81, 158.79, 152.98, 152.77, 152.65, 142.65, 140.61, 139.87, 133.95, 129.39, 126.98, 126.10, 117.48, 113.59, 110.96, 109.42, 105.85, 95.85, 92.43, 71.84, 66.99, 61.04, 56.46, 56.31, 55.87, 55.47, 26.98, 25.37. HRMS (ESI) calcd for C₃₅H₃₆N₂O₁₁ [M + H]⁺: 661.23919, found 661.23914.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(4-isopropylphenyl)pyridazin-3(2H)-one (A20). Yellow solid (28%), m.p.: 123.1–123.8 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.53 (d, J = 8.5 Hz, 2H, Ph–H), 7.34 (s, 2H, Ph–H), 7.28 (d, J = 8.4 Hz, 2H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.93 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.15 (t, J = 6.0 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.91 (d, J = 1.7 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 2.94 (p, J = 13.8, 6.9 Hz, 1H, Ph-C̲H̲(CH₃)₂), 1.95 (p, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.87 (p, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–), 1.25 (d, J = 6.9 Hz, 6H, Ph–CH_2̲C̲H̲_2̲). ¹³C NMR (101 MHz, chloroform-d) δ 174.03, 164.02, 161.05, 158.84, 158.82, 152.97, 152.80, 152.64, 148.33, 140.62, 139.86, 139.35, 133.86, 126.80, 126.72, 126.11, 124.91, 109.43, 105.85, 95.85, 92.43, 71.85, 66.92, 61.04, 56.47, 56.31, 55.87, 33.89, 26.97, 25.38, 23.98. HRMS (ESI) calcd for C₃₇H₄₀N₂O₁₀ [M + H]⁺: 673.27557, found 673.27557.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(4-(tert-butyl)phenyl)-pyridazin-3(2H)-one (A21). White solid (46%), m.p.: 104.3–105.6 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.55 (d, J = 8.7 Hz, 2H, Ph–H), 7.44 (d, J = 8.7 Hz, 2H, Ph–H), 7.34 (s, 2H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.93 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.15 (t, J = 6.0 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.91 (d, J = 1.6 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 1.93 (m, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.87 (m, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–), 1.32 (s, 9H, Ph–C(CH₃)₃). ¹³C NMR (101 MHz, chloroform-d) δ 174.03, 164.01, 161.03, 158.85, 158.81, 152.96, 152.81, 152.64, 150.52, 140.61, 139.86, 139.02, 133.85, 126.79, 126.09, 125.64, 124.51, 109.41, 105.85, 95.84, 92.42, 71.84, 66.91, 61.02, 56.45, 56.30, 55.85, 34.67, 31.33, 26.95, 25.37. HRMS (ESI) calcd for C₃₈H₄₂N₂O₁₀ [M + H]⁺: 687.29122, found 687.29010.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(4-(trifluoromethyl)phenyl)pyridazin-3(2H)-one (A22). White solid (51%), m.p.: 110.8–111.7 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.86 (d, J = 8.4 Hz, 2H, Ph–H), 7.68 (d, J = 8.6 Hz, 2H, Ph–H), 7.33 (s, 2H, Ph–H), 6.99 (d, J = 9.8 Hz, 1H, Ph–H), 6.96 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.19 (t, J = 6.2 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 6.1 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.94 (s, 3H, Ph–OCH₃), 3.91 (d, J = 2.3 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 1.98 (p, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.86 (p, J = 8.1, 5.8 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.04, 164.06, 161.02, 158.81, 158.73, 153.12, 152.98, 152.69, 144.31, 140.58, 139.88, 134.05, 127.47, 126.08, 125.78, 125.74, 125.01, 109.39, 105.84, 95.87, 92.45, 71.67, 67.08, 61.02, 56.45, 56.30, 55.86, 26.86, 25.30. ¹⁹F NMR (376 MHz, chloroform-d) δ −62.49. HRMS (ESI) calcd for C₃₅H₃₃N₂O₁₀F₃ [M + H]⁺: 699.21601, found 699.21497.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy) 2-(3,4-dichlorophenyl)-pyridazin-3(2H)-one (A23). White solid (83%), m.p.: 146.2–147.8 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.86 (d, J = 2.4 Hz, 1H, Ph–H), 7.60 (d, J = 2.5 Hz, 1H, Ph–H), 7.49 (s, 1H, Ph–H), 7.34 (s, 2H, Ph–H), 6.97 (d, J = 9.3 Hz, 1H, Ph–H), 6.96 (s, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.18 (t, J = 6.2 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 6.1 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.92 (d, J = 3.3 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 1.93 (p, J = 7.8, 5.8 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.89 (p, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.03, 164.04, 161.02, 158.80, 158.58, 153.07, 152.97, 152.68, 140.66, 140.58, 139.87, 133.97, 132.38, 131.25, 130.14, 127.47, 126.69, 126.07, 124.15, 109.39, 105.84, 95.86, 92.44, 71.70, 67.14, 61.03, 56.45, 56.31, 55.86, 26.86, 25.30. HRMS (ESI) calcd for C₃₄H₃₂N₂O₁₀Cl₂ [M + H]⁺: 699.15068, found 699.15021.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy) 2-(3,4-difluorophenyl)-pyridazin-3(2H)-one (A24). White solid (67%), m.p.: 119.2–120.8 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.61 (d, J = 1.6 Hz, 1H, Ph–H), 7.48 (s, 1H, Ph–H), 7.33 (s, 2H, Ph–H), 7.20 (d, J = 9.7 Hz, 1H, Ph–H), 6.97 (d, J = 9.8 Hz, 1H, Ph–H), 6.94 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.18 (t, J = 6.2 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.05 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.91 (d, J = 3.4 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 1.93 (dd, J = 8.0, 5.8 Hz, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.87 (dd, J = 8.5, 4.0 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.03, 164.04, 161.02, 158.80, 158.61, 152.97, 152.68, 140.57, 139.87, 133.99, 127.35, 126.07, 121.13, 121.10, 121.07, 116.95, 116.77, 114.71, 114.51, 109.38, 105.83, 95.85, 92.43, 71.68, 67.08, 61.02, 56.44, 56.29, 55.86, 26.85, 25.29. ¹⁹F NMR (376 MHz, chloroform-d) δ −136.01, −138.47. HRMS (ESI) calcd for C₃₄H₃₂N₂O₁₀F₂ [M + H]⁺: 667.20978, found 667.20874.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy) 2-(3-chloro-4-fluorophenyl)-pyridazin-3(2H)-one (A25). White solid (82%), m.p.: 165.9–168.1 °C. ¹H NMR (400 MHz, chloroform-d) δ 7.77 (s, 1H, Ph–H), 7.60 (d, J = 4.8 Hz, 1H, Ph–H), 7.33 (s, 2H, Ph–H), 7.19 (d, J = 8.7 Hz, 1H, Ph–H), 6.96 (s, 1H, Ph–H), 6.95 (d, J = 9.8 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.17 (t, J = 6.1 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.05 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.91 (d, J = 3.3 Hz, 9H, Ph–OCH₃), 3.90 (s, 3H, Ph–OCH₃), 1.94 (p, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.88 (p, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.04, 164.05, 161.03, 158.81, 158.63, 153.04, 152.98, 152.68, 140.59, 139.88, 137.91, 133.92, 127.43, 127.34, 126.08, 124.96, 124.89, 116.41, 116.19, 109.40, 105.84, 95.86, 92.45, 71.71, 67.12, 61.03, 56.46, 56.31, 55.87, 26.88, 25.31. ¹⁹F NMR (376 MHz, chloroform-d) δ −116.34. HRMS (ESI) calcd for C₃₄H₃₂N₂O₁₀ClF [M + H]⁺: 683.18023, found 683.17963.
6-(4-((5,7-Dimethoxy-4-oxo-2-(3,4,5-trimethoxyphenyl)-4H-chromen-3-yl)oxy)butoxy)-2-(naphthalen-2-yl)pyridazin-3(2H)-one (A26). White solid (65.4%), m.p.: 129.4–130.7 °C. ¹H NMR (400 MHz, chloroform-d) δ 8.16 (d, J = 1.9 Hz, 1H, Ph–H), 7.89 (d, J = 8.6 Hz, 1H, Ph–H), 7.86 (d, J = 3.8 Hz, 1H, Ph–H), 7.85 (t, 1H, Ph–H), 7.77 (t, 1H, Ph–H), 7.49 (d, J = 3.9 Hz, 1H, Ph–H), 7.47 (s, 1H, Ph–H), 7.33 (s, 2H, Ph–H), 7.04 (d, J = 9.7 Hz, 1H, Ph–H), 6.98 (d, J = 9.7 Hz, 1H, Ph–H), 6.49 (d, J = 2.2 Hz, 1H, Ph–H), 6.35 (d, J = 2.2 Hz, 1H, Ph–H), 4.20 (t, J = 6.1 Hz, 2H, –O–C̲H̲_2̲CH₂CH₂CH₂–O–), 4.06 (t, J = 6.0 Hz, 2H, –O–CH₂CH₂CH₂C̲H̲_2̲–O–), 3.95 (s, 3H, Ph–OCH₃), 3.90 (s, 6H, Ph–OCH₃), 3.90 (d, J = 1.2 Hz, 6H, Ph–OCH₃), 2.00 (p, 2H, –O–CH₂C̲H̲_2̲CH₂CH₂–O–), 1.88 (p, J = 8.0, 3.4 Hz, 2H, –O–CH₂CH₂C̲H̲_2̲CH₂–O–). ¹³C NMR (101 MHz, chloroform-d) δ 174.07, 164.04, 161.03, 159.04, 158.82, 153.01, 152.97, 152.71, 140.61, 139.87, 139.05, 133.95, 133.10, 132.42, 128.45, 128.42, 127.64, 127.04, 126.53, 126.44, 126.09, 123.69, 123.22, 109.41, 105.86, 95.86, 92.44, 71.86, 67.02, 61.04, 56.45, 56.31, 55.87, 26.94, 25.37. HRMS (ESI) calcd for C₃₈H₃₆N₂O₁₀ [M + H]⁺: 681.24427, found 681.24341.

2.3 Biological activity testing

2.3.1 In vivo antiviral bioactivity test. The in vivo antiviral activity of A1–A26 against TMV was carried out using the half-leaf blight method,⁴⁴ in which heartleaf tobacco of the same length and size was selected for in vivo curative, protection and inactivation resistance tests, and three parallel trials were conducted using the commercially available antiviral agent NNM as a positive control. Specific experimental methods were described in the ESI.†

2.3.2 Microscale thermophoresis experiment. The modes of binding of the target compounds to tobacco mosaic virus capsid proteins (TMV-CP) and the affinities of intermolecular interactions were investigated using MST assays. The binding affinities of A15, A23 and A26 to TMV-CP were tested with reference to the methodology reported in the literature,⁴⁵ and the commercial drug NNM was used as a positive control. The details of the experimental methods were described in the ESI.†

2.3.3 Molecular docking experiment. The binding sites of ligand compounds and receptor proteins were simulated by molecular docking to further verify the binding ability between the two. Referring to the method reported in the literature,⁴⁶A23 and A26 were selected for molecular docking with TMV-CP, and NNM was used as a positive control. TMV-CP (PDB code: 1EI7) was obtained from the Protein Data Bank (PDB https://www.rcsb.org). Docking, visualization and analysis were achieved by using Dock Ligands in Discovery Studio. The specific experimental methods were described in the ESI.†

2.3.4 In vivo chlorophyll content test. Chlorophyll content in leaves is closely related to crop photosynthesis and nutrient absorption, and crop growth was characterized by measuring chlorophyll content. When tobacco is infected by viruses, chloroplasts were damaged and as a result, chlorophyll content was affected. In order to investigate the mechanism of action of the compounds, chlorophyll a, chlorophyll b, and total chlorophyll contents of A26-treated and unsprayed tobacco leaves were determined after virus infection by referring to the method reported in the literature.⁴⁷ The experimental methodology was described in the ESI.†

2.3.5 Malondialdehyde content test. Malondialdehyde content is a reflection of the degree of cytoplasmic peroxidation in plants. When plants are subjected to adversity stresses such as senescence, disease, cold or other injuries, the body's oxidative stress response is intensified and membrane peroxidation is severe. When tobacco is infected with virus, the cell membrane is seriously injured and malondialdehyde content will increase. Referring to the method reported in the literature,^48,49 the mechanism of drug action was investigated by determining the content of malondialdehyde in A26-treated and non-drug-treated leaves when tobacco was infested with the virus.

3. Results and discussion

3.1 Chemistry

Twenty-six target compounds, numbered A1–A26, were synthesized according to the above experimental route. All compounds were structurally characterized by NMR spectroscopy and HRMS, and the detailed data are listed in the ESI.† To further clarify the structures of the target compounds, the crystal structure of A14 was cultured and analyzed by X-ray single crystal diffraction. The crystal structure and cell stacking of A14 (CCDC: 2247966) are shown in Fig. 2, and the detailed data are listed in the ESI.†

Fig. 2 Crystal structure (A) and crystal packing diagram (B) of A14.

3.2 In vivo antiviral activity

The antiviral activity of A1–A26 against TMV was determined using the half-leaf blotch method with NNM as the positive control. The detailed data are shown in Table 1. The curative activities of A4, A8, A23 and A26 against TMV were 74.8, 71.7, 73.5 and 76.8%, respectively, which were superior to that of NNM (68.0%), while the protective activities of A24 and A26 were 78.1 and 69.5%, respectively, which were superior to that of NNM (62.2%). The results of A26 and NNM against TMV were characterized on the leaf as shown in Fig. 3. The EC₅₀ values of the compounds against TMV were tested and are shown in Table 2. The antiviral curative EC₅₀ values of A4, A23 and A26 were 131.6, 138.5 and 118.9 μg mL⁻¹, respectively, which were superior to that of the control drug NNM (235.6 μg mL⁻¹). The antiviral protective EC₅₀ values of A24 and A26 were 117.4 and 162.5 μg mL⁻¹, respectively, which were superior to that of the control drug NNM (263.2 μg mL⁻¹).

Table 1 Antiviral activities of the target compounds against TMV^ain vivo at 500 μg mL⁻¹

Compd.	n	R	Curative (%)	Protection (%)	Inactivation (%)
a Average of the three replicates. b Commercial antiviral agent NNM.
A1	3	H	59.9 ± 6.1	36.6 ± 4.4	50.1 ± 5.8
A2	3	4-CH3	51.6 ± 1.6	59.4 ± 7.1	61.3 ± 4.0
A3	3	4-F	39.8 ± 2.8	58.8 ± 9.8	37.3 ± 4.0
A4	3	4-Cl	74.8 ± 6.0	64.1 ± 4.1	50.1 ± 4.4
A5	3	3-Br	64.2 ± 3.8	67.9 ± 6.7	43.7 ± 8.7
A6	3	3-OCH3	65.2 ± 4.2	68.0 ± 3.0	62.6 ± 1.5
A7	3	4-i-Pr	62.3 ± 2.3	56.0 ± 2.4	31.0 ± 0.9
A8	3	4-t-Bu	71.7 ± 0.6	47.2 ± 8.1	40.6 ± 5.2
A9	3	4-CF3	55.2 ± 8.9	56.2 ± 2.2	49.6 ± 4.7
A10	3	3,4-di-Cl	57.0 ± 4.3	55.7 ± 5.9	54.3 ± 2.5
A11	3	3,4-di-F	47.5 ± 6.4	62.8 ± 4.2	47.8 ± 3.7
A12	3	3-Cl-4-F	49.7 ± 7.2	59.9 ± 4.0	50.6 ± 8.1
A13	3	Ph	55.4 ± 3.5	67.4 ± 4.8	51.9 ± 2.7
A14	4	H	67.0 ± 3.0	60.5 ± 7.2	47.9 ± 3.7
A15	4	4-CH3	65.5 ± 1.3	62.0 ± 2.0	63.2 ± 7.0
A16	4	4-F	44.7 ± 4.7	67.1 ± 1.0	57.7 ± 6.9
A17	4	4-Cl	57.4 ± 4.0	57.2 ± 5.9	64.9 ± 8.6
A18	4	3-Br	66.7 ± 6.1	64.4 ± 3.0	49.4 ± 0.2
A19	4	3-OCH3	58.6 ± 1.9	52.2 ± 6.9	52.3 ± 5.1
A20	4	4-i-Pr	61.2 ± 6.5	44.0 ± 6.1	54.3 ± 2.5
A21	4	4-t-Bu	54.5 ± 2.0	56.3 ± 4.2	30.2 ± 5.1
A22	4	4-CF3	47.8 ± 2.4	60.8 ± 4.3	61.3 ± 8.2
A23	4	3,4-di-Cl	73.5 ± 5.6	62.9 ± 5.6	63.0 ± 2.9
A24	4	3,4-di-F	52.5 ± 3.4	78.1 ± 5.3	37.2 ± 5.6
A25	4	3-Cl-4-F	62.0 ± 3.3	54.5 ± 7.6	60.9 ± 1.2
A26	4	Ph	76.8 ± 3.3	69.5 ± 9.6	67.9 ± 3.4
NNM	—		68.0 ± 6.0	62.2 ± 6.4	86.3 ± 4.0

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Fig. 3 Tobacco leaf morphology effects of A26 and NNM against tobacco mosaic virus in vivo (left leaf: not treated with the compound; right leaf: smeared with the compound).

Table 2 The EC₅₀ values of several target compounds against TMV^a

	Compd	n	R	Regression equation	r	EC50 (μg mL^−1)
a Average of the three replicates. b Commercial antiviral agent NNM.
Curative activity	A4	3	4-Cl	y = 1.0702x + 2.7319	0.9888	131.6
	A8	3	4-t-Bu	y = 1.0736x + 2.6653	0.9961	149.5
	A23	4	3,4-di-Cl	y = 1.0882x + 2.6698	0.9649	138.5
	A26	4	Ph	y = 1.1059x + 2.6962	0.9903	118.9
	NNM^b	—	—	y = 0.9651x + 2.7107	0.9629	235.6
Protection activity	A24	4	3,4-di-F	y = 1.1000x + 2.7234	0.9772	117.4
	A26	4	Ph	y = 0.8650x + 3.0875	0.9755	162.5
	NNM^b	—	—	y = 0.9057x + 2.8079	0.9748	263.2

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3.3 Microscale thermophoresis analysis

The affinity of the target compounds with TMV-CP was illustrated by the MST test, and the binding affinity was evaluated using the K_d value to accurately reflect the intermolecular interactions. The results of the MST test are shown in Fig. 4, and the K_d values of the binding affinities of A15, A23, A26 and NNM with TMV-CP were 0.176, 0.133, 0.047 and 1.028 μM, respectively, and the detailed data are listed in Table 3. It can be seen that the K_d values of A15, A23, and A26 with TMV-CP were significantly better than that of the control agent NNM, which indicated that the compounds had a stronger binding ability to TMV-CP than that of the control agent.

Fig. 4 Microscale thermophoresis (MST) of A15, A23, A26 and NNM.

Table 3 The dissociation constant of A15, A23, A26 and NNM with TMV-CP

Compd.	K d (μM)
a Commercial antiviral agent NNM.
A15	0.1761 ± 0.0805
A23	0.1331 ± 0.0254
A26	0.0468 ± 0.0191
NNM^a	1.0279 ± 0.4888

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3.4 Molecular docking analysis

The binding mode of the drug molecules was explored through molecular docking experiments to simulate the interaction of drugs A23 and A26 with TMV-CP, using NNM as a positive control. As shown in Fig. 5, both A23 and A26 exhibited hydrogen bonding interactions with key amino acid residues, GLN257 and ARG134 of TMV-CP. NNM exhibits hydrogen bonding interactions with several amino acid residues including GLN257 and ARG134. It could be seen that the bond lengths of the hydrogen bonds produced by the binding of A23 to GLN257 and ARG134 were 1.60 and 1.57 Å, respectively, and that of the hydrogen bond produced by the binding of A26 to GLN257 was 1.57 Å, whereas those of the hydrogen bonds produced by the binding of NNM to GLN257 and ARG134 were 2.74 and 1.85 Å, respectively. Although the docking of NNM to TMV-CP formed more hydrogen bonds, in terms of bond length, the drug molecules exhibited shorter hydrogen bond lengths and would bind more tightly to TMV-CP.

Fig. 5 The binding mode of A23 (A, a), A26 (B, b), and NNM (C, c) docked with TMV-CP.

3.5 Analysis of chlorophyll content in tobacco

The chlorophyll content in plants is closely related to the health status of plants, and chlorophyll not only plays a decisive role in photosynthesis but also improves the disease resistance of plants. As can be seen from Fig. 6, in the healthy group, the chlorophyll content in the CK control plants changed slightly over time, but the overall chlorophyll content in the tobacco leaves treated with A26 was higher than that in the CK group and peaked on the fifth day. The chlorophyll content in plants treated with A26 in the susceptible group was significantly higher than that in the TMV control group. The results showed that A26 could be involved in regulating the chlorophyll content in plants, promoting plant photosynthesis, mobilizing the plant's defense ability, and then improving the plant's disease resistance.

Fig. 6 Changes in chlorophyll content in tobacco upon A26 curative treatment.

3.6 Analysis of malondialdehyde content

The presence of unfavorable environments during plant growth triggers the action of oxygen radicals on lipids in the plant, resulting in membrane lipid peroxidation and the production of a complex series of compounds, including malondialdehyde. The degree of plant membrane damage and plant disease resistance was studied by testing the malondialdehyde content. As shown in Fig. 7, the overall malondialdehyde content in the leaves of the CK group showed an increasing trend with time and reached the peak on the 3rd day, which indicated that the plants contained antioxidant enzymes in the plant body during the senescence process, which had a certain regulatory effect. The malondialdehyde content in the A26-treated plants was significantly lower than that in the CK group, indicating that the drug molecules could inhibit tobacco from being subjected to adversity stress. The malondialdehyde content in plants of the TMV-sensitive group was significantly increased and was the highest among the groups, which fully responded to the serious damage caused by TMV to tobacco. The malondialdehyde content in plants of the A26 + TMV-sensitive group was significantly lower than that in the TMV-sensitive group, which showed that TMV was the most effective drug in the TMV-sensitive group, and that it could be used in the TMV-sensitive group. The drug molecules could inhibit the injury of TMV on leaves and reduce the destruction speed. In summary, the drug molecule A26 could inhibit TMV from infecting plants, participate in the regulation of membrane lipid peroxidation, inhibit the production of malondialdehyde in tobacco, and enhance the antioxidant capacity and disease resistance of plants.

Fig. 7 Changes in MDA activity in tobacco following A26 curative treatment.

4. Conclusion

In summary, a series of myricetin derivatives containing pyridazinone were designed and synthesized. The results of antiviral activity tests showed that some of the target compounds exhibited good antiviral activity. Among them, A4, A23 and A26 exhibited good curative activity with EC₅₀ values of 131.6, 138.5 and 118.9 μg mL⁻¹, respectively, which were better than that of the control drug NNM (235.6 μg mL⁻¹). A24 and A26 exhibited good protective activity with EC₅₀ values of 117.4 and 162.5 μg mL⁻¹, respectively, which were better than that of the control drug NNM (263.2 μg mL⁻¹). The biological activities of A23 and A26 were further confirmed by microcalorimetric thermophoretic assays and molecular docking to investigate the mechanism of action of the drug molecules, which were tightly bound to TMV-CP with higher binding affinity and shorter hydrogen bonds to exert antiviral effects. In addition, the chlorophyll and malondialdehyde contents of tobacco plants were tested, and it was found that the drug molecules could be involved in regulating the chlorophyll content of plants, promoting plant photosynthesis, participating in the regulation of membrane lipid peroxidation, inhibiting the TMV-infected plants, mobilizing the plant's defense ability, and thus enhancing the antioxidant ability and disease resistance of plants. Therefore, myricetin derivatives containing pyridazinone offer a reference point for the development of novel antiviral pesticides with great potential for development.

Author contributions

Wei Xue: conceived and designed the experiments. Provide experiment drawing software and method. Li Xing: performed the experiments, analyzed the data and writing-original draft preparation. Da Liu, Youshan An, Yishan Qin: evaluated the antiviral activities of the target compounds. Hui Xin, Tianyu Deng, Kaini Meng: provided the material for evaluating the antiviral activities. All authors have given approval to the final version of the manuscript.

Conflicts of interest

The authors declare no competing financial interest. All authors have contributed to the work, read the manuscript, and agreed to be listed as authors.

Acknowledgements

The authors gratefully acknowledge the Science Foundation of Guizhou Province (No. 20192452) and the Key Laboratory of Institute of Environment and Plant Protection (No. HZSKFKT202208).

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Footnote

† Electronic supplementary information (ESI) available: The NMR and HRMS data for A1–A26. CCDC 2247966. For ESI and crystallographic data in CIF or other electronic format see DOI: https://doi.org/10.1039/d3nj04902g

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