Design, synthesis, and biological activities of arecoline derivatives containing 1,3,4-oxadiazole structure.

Pesticides play an important role in the development of agriculture, as they can prevent and control crop diseases and pests, improve crop yield and quality. However, the abuse and improper use of pesticides can lead to negative impacts such as environmental pollution and pest resistance issues. There is an urgent need to develop green, safe, and efficient pesticides. In this work, natural product arecoline was selected as parent structure, a series of arecoline derivatives were designed, synthesized, and systematically investigated antiviral activities against tobacco mosaic virus (TMV). These compounds were found to have good to excellent anti-TMV activities for the first time. The antiviral activities of 4a, 4 h, 4 l, 4p, 6a, 6c, and 6f are higher than that of ningnanmycin. Compounds 4 h (EC50 value 146 µg/mL) and 4p (EC50 value 161 µg/mL) with simple structures and excellent activities emerged as new antiviral candidates. We chose 4 h to further investigate the antiviral mechanism, which revealed that it can cause virus fragmentation by acting on the viral coat protein (CP). We further validated this result through molecular docking. These compounds also displayed broad-spectrum fungicidal activities against 8 plant pathogenic fungi. This work lays the theoretical foundation for the application of arecoline derivatives in the agricultural field.

Novel flavonol derivatives containing benzoxazole as potential antiviral agents: design, synthesis, and biological evaluation.

A series of flavonol derivatives containing benzoxazole were designed and synthesized, and the structures of all the target compounds were determined by nuclear magnetic resonance (NMR) and high-resolution mass spectrometry (HRMS). The structure of X2 was further confirmed by single crystal X-ray diffraction analysis. The results of the bioactivity tests showed that some of the target compounds possessed excellent antiviral activity against tobacco mosaic virus (TMV) in vivo. In particular, the median effective concentration (EC50) values for the curative and protective activities of X17 against TMV were 127.6 and 101.2 µg/mL, respectively, which were superior to those of ningnanmycin (320.0 and 234.6 µg/mL). The results of preliminary mechanism study indicated that X17 had a strong binding affinity for TMV coat protein (TMV-CP), which might hinder the self-assembly and replication of TMV particles. In addition, X17 was able to effectively inhibit tobacco leaf membrane lipid peroxidation and facilitate the removal of O2- from the body, thereby improving the disease resistance of tobacco plants. Therefore, the design and synthesis of flavonol derivatives containing benzoxazole provides value for the development of new antiviral drugs.

Design, synthesis, antiviral and fungicidal activities of novel polycarpine simplified analogues.

Fungal and viral diseases account for 70-80% of agricultural production losses caused by microbial diseases. Synthetic fungicides and antiviral agents have been used to treat plant diseases caused by plant pathogenic fungi and viruses, but their use has been criticized due to their adverse side effects. As alternative strategies, natural fungicides and antiviral agents have attracted many researchers' interest in recent years. Herein, we designed and synthesized a series of novel polycarpine simplified analogues. Antiviral activity research against tobacco mosaic virus (TMV) revealed that most of the designed compounds have good antiviral activities. The virucidal activities of 4, 6d, 6f, 6h, and 8c are higher than that of polycarpine and similar to that of ningnanmycin. The structure simplified compound 8c was selected for further antiviral mechanism research which showed that compound 8c could inhibit the formation of 20S protein discs by acting on TMV coat protein. These compounds also displayed broad-spectrum fungicidal activities against 7 kinds of plant fungi. This work lays the foundation for the application of polycarpine simplified analogues in crop protection.

Extraction and characterization of anti-virus anthraquinones from Nicotiana tabacum-derived Aspergillus oryzae YNCA1220.

In this study, seven novel anthraquinones (1-7) and four described anthraquinones (8-11) were purified from Nicotiana tabacum-derived Aspergillus oryzae YNCA1220. It is worth noting that only analogs of 4 and 5 have been reported as natural products to date, while the nuclei of compounds 1-3, 6 and 7 were isolated for the first time in nature. Among them, compounds 1-3 bear an unusual anthra[2,3-b]furan-9,10-dione nucleus, 4 and 5 possess a rare 3-methyl-1H-pyrrol-2-yl substituent, and 6 and 7 are new framework anthraquinones bearing a 6-methyl-1,7-dihydro-2H-azepin-2-one ring. Interestingly, the in vivo assays indicated that 1, 4 and 5 had inactivation effects against tobacco mosaic virus (TMV) with inhibition rates of 41.6%, 55.4% and 38.6%, respectively, at a concentration of 50 µg/mL, which were better than that of the positive control agent, ningnanmycin (33.8%). Compounds 1, 4 and 5 also had protective effects with inhibition rates of 48.7%, 60.2% and 43.5% at the same concentration, while 4 had a better curative effect than ningnanmycin at a concentration of 100 µg/mL. In addition, mechanistic studies also revealed that a potent direct effect on TMV, the induction of SAR in tobacco plants, and the effective regulation of defense enzymes, defense genes, and defense hormones may be the reasons for the significant effects of 4 against TMV. At the same time, downregulation of the expression of total NtHsp70 protein by inhibiting the related Hsp70 genes may also be involved in tobacco resistance to TMV. To evaluate whether compounds have broader antiviral activities, the antirotavirus activities of new isolates were also evaluated and found to be highly effective with a therapeutic index (TI) value ranging from 11.6 to 17.7. This study suggests that the above anthraquinone compounds, particularly 4, have broad spectrum antiviral activities. The successful isolation and structure identification of the above anthraquinones provide new materials for the screening of anti-TMV agents and contribute to the improved utilization of N. tabacum-derived fungi.

Linalool Induces Resistance Against Tobacco Mosaic Virus in Tobacco Plants.

The essential oil of Cinnamomum camphora is the most widely consumed and used spice in the world today. It has therapeutic effects in medicine and has been shown to have good antibacterial and bacteriostatic effects in agriculture. This study found that C. camphora oil significantly induced plant disease resistance activity. Linalool, its main active component, significantly induced plant disease resistance activity (67.49% at a concentration of 800 µg/ml) over the same concentration of the chitosan oligosaccharide positive control but had no direct effect on tobacco mosaic virus (TMV). In this study of its antiviral mechanism, linalool induced hypersensitive reaction (HR); the overexpression of related defense enzymes SOD, CAT, POD, and PAL; and the accumulation of H2O2 and SA content in N. glutinosa. Besides, linalool induced crops resistance against Colletotrichum lagenarium, Botrytis cinerea, Sclerotinia sclerotiorum, and Phytophthora capsica. Taken together, the anti-TMV mechanism of linalool involved the induction of plant disease resistance through activation of a plant immune response mediated by salicylic acid. Linalool-induced plant disease resistance activity has a long duration, broad spectrum, and rich resources; linalool thus has the potential to be developed as a new plant-derived antiviral agent and plant immune activator.

Two new isoflavones from the roots of Sophora tonkinensis.

Two new isoflavones (1 and 2), as well as eight known ones were isolated from the roots of Sophora tonkinensis Gagnep. Compound 1 represents an unprecedented polymerization pattern constructed by isoflavone and cytisine. Their structures were elucidated by comprehensive spectroscopic data analysis, combined with ECD calculations. Compound 1 displayed significant anti-tobacco mosaic virus (TMV) activity compared with the positive control ningnanmycin. Moreover, compound 6 exhibited potent α-glucosidase inhibitory activity with IC50 value of 47.4 mg/L.

Discovery of Flavone Derivatives Containing Carboxamide Fragments as Novel Antiviral Agents.

Plant virus diseases seriously affect the yield and quality of agricultural products, and their prevention and control are difficult. It is urgent to develop new and efficient antiviral agents. In this work, a series of flavone derivatives containing carboxamide fragments were designed, synthesized, and systematically evaluated for their antiviral activities against tobacco mosaic virus (TMV) on the basis of a structural-diversity-derivation strategy. All the target compounds were characterized by 1H-NMR, 13C-NMR, and HRMS techniques. Most of these derivatives displayed excellent in vivo antiviral activities against TMV, especially 4m (inactivation inhibitory effect, 58%; curative inhibitory effect, 57%; and protection inhibitory effect, 59%), which displayed similar activity to ningnanmycin (inactivation inhibitory effect, 61%; curative inhibitory effect, 57%; and protection inhibitory effect, 58%) at 500 µg mL-1; thus, it emerged as a new lead compound for antiviral research against TMV. Antiviral mechanism research by molecular docking demonstrated that compounds 4m, 5a, and 6b could interact with TMV CP and disturb virus assembly.

Design, Synthesis and Various Bioactivity of Acylhydrazone-Containing Matrine Analogues.

Compounds with acylhydrazone fragments contain amide and imine groups that can act as electron donors and acceptors, so they are easier to bind to biological targets and thus generally exhibit significant biological activity. In this work, acylhydrazone fragments were introduced to the C-14 or C-11 position of matrine, a natural alkaloid, aiming to enhance their biological activities. The result of this bioassay showed that many synthesized compounds exhibited excellent anti-virus activity against the tobacco mosaic virus (TMV). Seventeen out of 25 14-acylhydrazone matrine derivatives and 17 out of 20 11-butanehydrazone matrine derivatives had a higher inhibitory activity against TMV than the commercial antiviral agent Ribavirin (the in vitro activity, in vivo inactivation, curative and protection activities at 500 µg/mL were 40.9, 36.5 ± 0.9, 38.0 ± 1.6 and 35.1 ± 2.2%, respectively), and four 11-butanehydrazone matrine derivatives even had similar to or higher activity than the most efficient antiviral agent Ningnanmycin (55.4, 57.8 ± 1.4, 55.3 ± 0.5 and 60.3 ± 1.2% at 500 µg/mL for the above four test modes). Among them, the N-benzyl-11-butanehydrazone of matrine formed with 4-bromoindole-3-carboxaldehyde exhibited the best anti-TMV activity (65.8, 71.8 ± 2.8, 66.8 ± 1.3 and 69.5 ± 3.1% at 500 µg/mL; 29, 33.5 ± 0.7, 24.1 ± 0.2 and 30.3 ± 0.6% at 100 µg/mL for the above four test modes), deserving further investigation as an antiviral agent. Other than these, the two series of acylhydrazone-containing matrine derivatives were evaluated for their insecticidal and fungicidal activities. Several compounds were found to have good insecticidal activities against diamondback moth (Plutella xylostella) and mosquito larvae (Culex pipiens pallens), showing broad biological activities.

Discovery of Barakacin and Its Derivatives as Novel Antiviral and Fungicidal Agents.

Pesticides are essential for the development of agriculture. It is urgent to develop green, safe and efficient pesticides. Bisindole alkaloids have unique and concise structures and broad biological activities, which make them an important leading skeleton in the creation of new pesticides. In this work, we synthesized bisindole alkaloid barakacin in a simple seven-step process, and simultaneously designed and synthesized a series of its derivatives. Biological activity research indicated that most of these compounds displayed good antiviral activities against tobacco mosaic virus (TMV). Among them, compound 14b exerted a superior inhibitory effect in comparison to commercially available antiviral agent ribavirin, and could be expected to become a novel antiviral candidate. Molecular biology experiments and molecular docking research found that the potential target of compound 14b was TMV coat protein (CP). These compounds also showed broad-spectrum anti-fungal activities against seven kinds of plant fungi.

Transcriptome analysis reveals the mechanism of zinc ion-mediated plant resistance to TMV in Nicotiana benthamiana.

Zinc ions (Zn2+) are used to promote plant growth and treat multiple diseases. However, it is still unclear which pathways in plants respond to Zn2+. In this study, we found that supplying (CH3COO)2Zn can effectively delay tobacco mosaic virus (TMV) replication and movement in Nicotiana benthamiana. To further understand the regulatory mechanism of antiviral activity mediated by Zn2+, we examined the transcriptomic changes of leaves treated with Zn2+. Three days after treatment, 7575 differential expression genes (DEGs) were enriched in the Zn2+ treatment group compared with the control group. Through GO and KEGG analysis, the pathway of phosphatidylinositol signaling system and inositol phosphate metabolism were significantly enriched after treated with Zn2+, and a large number of ethylene-responsive transcription factors (ERFs) involved in inositol phosphate metabolism were found to be enriched. We identified ERF5 performed a positive effect on plant immunity. Our findings demonstrated that Zn2+-mediated resistance in N. benthamiana activated signal transduction and regulated the expression of resistance-related genes. The results of the study uncover a global view of mRNA changes in Zn2+-mediated cellular processes involved in the competition between plants and viruses.

Anti-TMV activity and effects of three prieurianin-type limonoids from Munronia henryi.

Three prieurianin-type limonoids (1-3), including two new compounds (1 and 2) and one known compound (3) were isolated from Munronia henryi. These compounds were tested for their activities against tobacco mosaic virus (TMV) by the conventional half-leaf method and the outcomes were analyzed by western blotting and RT-PCR assays. The three tested compounds, at 100 µg/mL, showed strong antiviral activities in the pretreated tobacco plants with inhibition rates ranging from 70.5% to 81.3%, which were significantly higher than that of the positive control, ningnanmycin (55.6%). Their potential of inducing systemic acquired resistance (SAR) was also evaluated, in which compound 1 showed excellent induction activities. Furthermore, it was found that potentiation of defense-related enzyme activity and the contents of SA was increased. Compound 1 could also inhibit the expression of TMV CP and up-regulate the expression of defense-related genes. This work revealed that these limonoids, especially compound 1 could induce resistance in tobacco plants against the viral pathogen TMV. Meanwhile, compounds 1-3 could down-regulate the expression of NtHsp70-1 and Nthsp70-261 genes, indicating that these limonoids possibly inhibit TMV infection by suppressing NtHsp70-1 and Nthsp70-261 expression. This study is the first to report antiviral compounds with two different mechanisms of action.

Two new cytisine-type alkaloids from the seeds of Thermopsis lanceolata.

Two new (1 and 2) cytisine-type alkaloids that were chemically inseparable isomers (present in a 1:1 ratio) were identified from the seeds of Thermopsis lanceolata R. Br. Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, NMR, HRESIMS) and ECD calculation. Compound 1 displayed significant anti-tobacco mosaic virus (TMV) activity, while compounds 1 and 2 displayed moderate insecticidal activities against Aphis fabae with LC50 value of 43.15 and 46.47 mg/L, respectively.

Synthesis and Evaluation of 11-Butyl Matrine Derivatives as Potential Anti-Virus Agents.

Matrine derivatives were reported to have various biological activities, especially the ester, amide or sulfonamide derivatives of matrine deriving from the hydroxyl or carboxyl group at the end of the branch chain after the D ring of matrine is opened. In this work, to investigate whether moving away all functional groups from the C-11 branch chain could have an impact on the bioactivities, such as anti-tobacco mosaic virus (TMV), insecticidal and fungicidal activities, a variety of N-substituted-11-butyl matrine derivatives were synthesized. The obtained bioassay result showed that most N-substituted-11-butyl matrine derivatives had obviously enhanced anti-TMV activity compared with matrine, especially many compounds had good inhibitory activity close to that of commercialized virucide Ningnanmycin (inhibition rate 55.4, 57.8 ± 1.4, 55.3 ± 0.5 and 60.3 ± 1.2% at 500 µg/mL; 26.1, 29.7 ± 0.2, 24.2 ± 1.0 and 27.0 ± 0.3% at 100 µg/mL, for the in vitro activity, in vivo inactivation, curative and protection activities, respectively). Notably, N-benzoyl (7), N-benzyl (16), and N-cyclohexylmethyl-11-butyl (19) matrine derivatives had higher anti-TMV activity than Ningnanmycin at both 500 and 100 µg/mL for the four test modes, showing high potential as anti-TMV agent. Furthermore, some compounds also showed good fungicidal activity or insecticidal activity.

Design, Synthesis, and Bioactivities of Novel Tryptophan Derivatives Containing 2,5-Diketopiperazine and Acyl Hydrazine Moieties.

Based on the scaffolds widely used in drug design, a series of novel tryptophan derivatives containing 2,5-diketopiperazine and acyl hydrazine moieties have been designed, synthesized, characterized, and evaluated for their biological activities. The bioassay results showed that the target compounds possessed moderate to good antiviral activities against tobacco mosaic virus (TMV), among which compounds 4, 9, 14, 19, and 24 showed higher inactivation, curative, and protection activities in vivo than that of ribavirin (39 ± 1, 37 ± 1, 39 ± 1 at 500 mg/L) and comparable to that of ningnanmycin (58 ± 1, 55 ± 1, 57 ± 1% at 500 mg/L). Thus, these compounds are a promising candidate for anti-TMV development. Most of these compounds showed broad-spectrum fungicidal activities against 13 kinds of phytopathogenic fungi and selective fungicidal activities against Alternaria solani, Phytophthora capsica, and Sclerotinia sclerotiorum. Additionally, some of these compounds exhibited larvicidal activities against Tetranychus cinnabarinus, Plutella xylostella, Culex pipiens pallens, Mythimna separata, Helicoverpa armigera, and Pyrausta nubilalis.

Indole Alkaloids and Chromones from the Stem Bark of Cassia alata and Their Antiviral Activities.

The Cassia (Leguminosae) genus has attracted a lot of attention as a prolific source of alkaloids and chromones with diverse structures and biological properties. The aim of this study is to screen the antiviral compounds from Cassia alata. The extract of the stem bark of this plant was separated using silica gel, MCI, ODS C18, and Sephadex LH-20 column chromatography, as well as semi-preparative HPLC. As a result, three new indole alkaloids, alataindoleins A-C (1-3); one new chromone, alatachromone A (4); and a new dimeric chromone-indole alkaloid, alataindolein D (5) were isolated. Their structures were determined by means of HRESIMS and extensive 1D and 2D NMR spectroscopic studies. Interestingly, alataindolein D (5) represents a new type of dimeric alkaloid with an unusual N-2-C-16' linkage, which is biogenetically derived from a chromone and an indole alkaloid via an intermolecular nucleophilic substitution reaction. Compounds 1-5 were tested for their anti-tobacco mosaic virus (TMV) and anti-rotavirus activities, and the results showed that compounds 2-4 showed high anti-TMV activities with inhibition rates of 44.4%, 66.5%, and 52.3%, respectively. These rates were higher than those of the positive control (with inhibition rate of 32.8%). Compounds 1 and 5 also showed potential anti-TMV activities with inhibition rates of 26.5% and 31.8%, respectively. In addition, compounds 1-5 exhibited potential anti-rotavirus activities with therapeutic index (TI) values in the range of 9.75~15.3. The successful isolation and structure identification of the above new compounds provided materials for the screening of antivirus drugs, and contributed to the development and utilization of C. alata.

Synthesis and Biological Activity of Novel Oxazinyl Flavonoids as Antiviral and Anti-Phytopathogenic Fungus Agents.

A series of oxazinyl flavonoids were synthesized on the basis of flavone. The structures of all target compounds were characterized by 1H NMR, 13C NMR, and HRMS. The effect of the different substituent on the N-position of oxazinyl flavonoids against tobacco mosaic virus (TMV) activities and plant pathogen activities was systematically investigated. In vivo anti-TMV activity showed that most of the compounds showed moderate-to-excellent antiviral activities against TMV at 500 µg/mL. Compounds 6b, 6d, 6j-6k, and 6n-6q showed better antiviral activities than ribavirin (a commercially available antiviral agent) and apigenin. In particular, compounds 6n and 6p even displayed slightly higher activities than ningnanmycin, which were expected to become new antiviral candidates. Antiviral mechanism research by molecular docking exhibited that compounds 6n and 6p could interact with TMV CP and inhibit virus assembly. Then, the antifungal activities of these compounds against six kinds of plant pathogenic fungi were tested, and the results showed that these oxazinyl flavonoids had broad-spectrum fungicidal activities. Compounds 6h exhibited antifungal activity of up to 91% against Physalospora piricola and might become a candidate drug for new fungicides.

Design, synthesis and anti-TMV activity of novel α-aminophosphonate derivatives containing a chalcone moiety that induce resistance against plant disease and target the TMV coat protein.

Plant viral diseases, known as "plant cancer", with high contagiosity can substantially reduce crop quality and yield. To identify potential anti-tobacco mosaic virus (TMV) agents with different mechanisms, a series of novel α-aminophosphonate derivatives containing a chalcone moiety were designed and synthesized. Bioassay results revealed that some target compounds exhibited improved curative activity against TMV in vivo, and the EC50 value of compound B3 was 356.7 mg L-1. The activities of the defensive enzymes POD and CAT from tobacco leaves treated with B3 and B17 showed that these target compounds could improve the photosynthetic ability of the leaves and activate plant host resistance against TMV infection. The binding constant between B3 and TMV Coat Protein (CP) (2.51 × 108 M-1), calculated by the fluorescence titration experiment and docking results, revealed that B3 has a strong interaction with TMV CP. Further docking analysis revealed that B3 was embedded between two layers of the TMV CP, which was consistent with the 2:1 binding mode of TMV CP and B3 determined by the binding affinity experiment. The TEM morphological study of TMV treated with B3 and B17 indicated that this series of target compounds may trigger the disassembly of TMV by interacting directly with TMV CP. This study provides new insight for the discovery of antiviral compounds with two different mechanisms of action.

Anti-tobacco mosaic virus (TMV) activity of chemical constituents from the seeds of Sophora tonkinensis.

Two new compounds, including one new arylbenzofuran (1) and one new pterocarpanoid (2), along with nine known ones, were isolated from the seeds of Sophora tonkinensis. The structures of the new compounds were elucidated based on a comprehensive spectroscopic data analysis. Compounds 2 and 3 exhibited good anti-tobacco mosaic virus (TMV) activities with the protective inhibition rate of 69.62% and 68.72% respectively, at concentration of 100 µg/ml.

Discovery of Cysteine and Its Derivatives as Novel Antiviral and Antifungal Agents.

Based on the structure of the natural product cysteine, a series of thiazolidine-4-carboxylic acids were designed and synthesized. All target compounds bearing thiazolidine-4-carboxylic acid were characterized by 1H-NMR, 13C-NMR, and HRMS techniques. The antiviral and antifungal activities of cysteine and its derivatives were evaluated in vitro and in vivo. The results of anti-TMV activity revealed that all compounds exhibited moderate to excellent activities against tobacco mosaic virus (TMV) at the concentration of 500 µg/mL. The compounds cysteine (1), 3-4, 7, 10, 13, 20, 23, and 24 displayed higher anti-TMV activities than the commercial plant virucide ribavirin (inhibitory rate: 40, 40, and 38% at 500 µg/mL for inactivation, curative, and protection activity in vivo, respectively), especially compound 3 (inhibitory rate: 51%, 47%, and 49% at 500 µg/mL for inactivation, curative, and protection activity in vivo, respectively) with excellent antiviral activity emerged as a new antiviral candidate. Antiviral mechanism research by TEM exhibited that compound 3 could inhibit virus assembly by aggregated the 20S protein disk. Molecular docking results revealed that compound 3 with higher antiviral activities than that of compound 24 did show stronger interaction with TMV CP. Further fungicidal activity tests against 14 kinds of phytopathogenic fungi revealed that these cysteine derivatives displayed broad-spectrum fungicidal activities. Compound 16 exhibited higher antifungal activities against Cercospora arachidicola Hori and Alternaria solani than commercial fungicides carbendazim and chlorothalonil, which emerged as a new candidate for fungicidal research.

Design, synthesis and anti-TMV activities of novel chromone derivatives containing dithioacetal moiety.

Thirty-five novel chromone derivatives containing dithioacetal moiety were designed, synthesized, and their anti-TMV activities were evaluated through half-leaf method. The results showed compound c23 illustrates highly curative, protective and inactivating activities against TMV at 500 mg/L, with the values of 68.8%, 58.8%, 86.0% respectively, which were superior to that of Ribavirin (42.3%, 49.8%, 68.4%, respectively) and similar to that of Ningnanmycin (59.4%, 52.4%, 88.4%, respectively). The EC50 value of inactivating activities of compound c23 is 9.3 mg/L, which was better than that of Ribavirin (135.2 mg/L), and equivalent to that of Ningnanmycin (8.8 mg/L). Furthermore, compound c23 can destroy the integrity of TMV-CP, resulting in reduced infectivity of TMV. Meanwhile, compound c23 can combine with TMV protein coat and hydrolyze TMV protein coat to impact the process of self-assembling of TMV, with the association constant (Kd) 4.5 mg/L. This finding suggests that chromone derivatives containing dithioacetal moiety can be used as new antiviral agent.