Quinolizidine Alkaloids with Antitomato Spotted Wilt Virus and Insecticidal Activities from the Seeds of Thermopsis lanceolata R. Br

Chemical constituents of the herb of Thermopsis lanceolata R. Br. and their stimulation of seed germination of Triticum aestivum L

To discover novel plant growth regulators (PGRs) from natural products, the chemical constituents of the herb Thermopsis lanceolata were systematically investigated, leading to the isolation of 17 quinolizidine alkaloids (QAs) (1-17), 9 sesquiterpenes (18-26), 20 lignans (27-46), 13 isoflavones (47-59), and 2 pterocarpans (60 and 61), including 4 previously undescribed compounds (1, 2, 18, 27) and one product previously derived as synthetic (3). Their structures were elucidated through comprehensive spectroscopic analysis (IR, UV, NMR, and HRESIMS) and ECD calculations. The seed germination and seedling growth regulatory activities of the isolated compounds on Triticum aestivum were evaluated using the petri dish method. Among the components, 25 and 39 significantly promoted the seedling growth of T. aestivum compared to the negative control, with seed germination rate, root length, coleoptile length, root fresh weight, and coleoptile fresh weight increasing by more than 31.1 % at a concentration of 25 μg/mL. Integrative physiological assays revealed that 25 and 39 enhance T. aestivum growth by increasing the levels of ethylene, auxins, gibberellins, and brassinosteroids; enhancing the activities of α-amylase and antioxidant enzymes (peroxidase, superoxide dismutase, and catalase); and increasing the contents of soluble sugar, soluble protein, and chlorophyll. This research holds promise for the development of novel, efficient, and ecologically compatible PGRs derived from natural products.

Isoflavones and Stilbenes With Antifungal Activities From the Seeds of Thermopsis lanceolata R. Br

In order to discover novel fungicides from natural products, the phytochemical investigation of Thermopsis lanceolata seeds was thoroughly conducted. Eight new isoflavone derivatives (1-5 and 8-10), two new stilbenes (6 and 7), as well as 21 known isoflavones (11-31) were obtained from the crude extract of T. lanceolata seeds following a bioassay-guided method. The structures of 1-31 were confirmed via HRESIMS, NMR, IR, UV, and quantum chemistry calculations. The antifungal activities of 1-31 against Phytophthora nicotiana, Colletotrichum orbiculare, Rhizoctonia solani, and Botrytis cinerea were screened according to the mycelial inhibition test. Compound 6 displayed significant antifungal activity against B. cinerea in vitro (EC50: 9.68 μg/mL) and had an 8 5.7% prevention and control effect in vivo (100 μg/mL). Moreover, antifungal mechanism studies revealed that 6 causes the accumulation of reactive oxygen species, increases the level of lipid peroxidation, decreases the activity of MDH, and finally triggers molecular damage and cell death in vitro. Therefore, 6 can be utilized as a lead compound for novel fungicides.

Sophflarines B-E, four distinctive matrine alkaloids from Sophora flavescens with potential neuroprotective activities

The four matrine-derived alkaloids, namely sophflarines B-E (1-4), with distinct skeleton types, were isolated from Sophora flavescens. Compounds 1 and 2 possess rare 1-aza-11-oxatricyclo[5.3.1.02,6] undecane cores, featuring unprecedented N,O-heterocyclic systems of 5/5/6/6/6 and 6/5/5/6/6, respectively. Compounds 3 and 4 exhibit two novel C15 units with tetracyclic skeletons of 5/6/6/6 and 6/5/6/6, respectively. The structures were elucidated through spectroscopic analyses, quantum chemical calculations, and X-ray diffraction data. A plausible biosynthetic pathway for these newly discovered compounds was proposed. Furthermore, compounds 1 and 2 showed anti-neuroinflammatory activity against the cytokines NO, TNF-α, and IL-6. Compound 2 exhibited a neuroprotective effect potentially mediated by activating the Keap1-Nrf2/HO-1 pathway to reduce inflammation and oxidative stress.

Fungicidal Activity of Novel 6-Isothiazol-5-ylpyrimidin-4-amine-Containing Compounds Targeting Complex I Reduced Nicotinamide Adenine Dinucleotide Oxidoreductase

To discover novel inhibitors of the complex I reduced nicotinamide adenine dinucleotide (NADH) oxidoreductase as fungicides, a series of 6-isothiazol-5-ylpyrimidin-4-amine-containing compounds were designed using a computer-aided pesticide design method and splicing of substructures from diflumetorim and isotianil. In vitro fungicidal bioassays indicated that compounds T17-T24 showed high inhibitory activity against Rhizoctonia solani with an effective concentration (EC50) value falling between 2.20 and 23.85 μg/mL, which were more active than or equivalent to the lead diflumetorim with its EC50 of 19.80 μg/mL. In vivo antifungal bioassays demonstrated that, at a concentration of 200 μg/mL, T7 and T21 showed higher inhibition against Pseudoperonospora cubensis than all other compounds, while T23 exhibited the highest inhibition against Sphaerotheca fuliginea. T23 showed an approximately twofold lower inhibition potency against R. solani complex I NADH oxidoreductase than diflumetorim. Molecular docking and transcriptomic analyses indicated that T23 and diflumetorim both might share the same mode of action, targeting NADH oxidoreductase. T23 as a good fungicidal candidate against R. solani is worthy of further investigation.

Quinolizidine Alkaloids and Isoflavones from the Herb of Thermopsis lupinoides and Their Antiviral, Antifungal, and Insecticidal Activities

As part of our ongoing investigation of natural bioactive substances from the genus Thermopsis of the tribe Fabaceae for agricultural protection, the chemical constituents of the herb Thermopsis lupinoides were systematically investigated, which led to the isolation of 39 quinolizidine alkaloids (QAs) (1-39), including 14 new QAs (1-14) and 14 isoflavones (40-53). Their structures were elucidated through comprehensive spectroscopic data analysis (IR, UV, NMR, HRESIMS), ECD calculations, and X-ray crystallography. The antitomato spotted wilt virus (TSWV) and antifungal (against Botrytis cinerea, Gibberella zeae, Phytophythora capsica, and Alternaria alternata) and insecticidal (against Aphis fabae and Tetranychus urticae) activities of the isolated compounds were screened using the lesion counting method, mycelial inhibition assay, and spray method, respectively. The bioassay results showed that 34 exhibited excellent protective activity against TSWV, with an EC50 value of 36.04 μg/mL, which was better than that of the positive control, ningnanmycin (86.03 μg/mL). The preliminary mechanistic exploration illustrated that 34 induced systemic acquired resistance in the host plant by acting on the salicylic acid signaling pathway. Moreover, 1 showed significant antifungal activity against B. cinerea (EC50 value of 20.83 μg/mL), while 2 exhibited good insecticidal activity against A. fabae (LC50 value of 24.97 μg/mL). This research is promising for the invention of novel pesticides from QAs with high efficiency and satisfactory ecological compatibility.

Three new quinolizidine alkaloids from the roots of Sophora tonkinensis

Three new quinolizidine alkaloids (1 - 3), including one new naturally isoflavone and cytisine polymer (3), along with 6 known ones were isolated from the ethanol extract of Sophora tonkinensis Gagnep. Their structures were elucidated by comprehensive spectroscopic data analysis (IR, UV, HRESIMS, 1D and 2D NMR), combined with ECD calculations. The antifungal activity against Phytophythora capsica, Botrytis cinerea, Gibberella zeae, and Alternaria alternata of the compounds was evaluated in a mycelial inhibition assay. Biological tests indicated that compound 3 exhibited strong antifungal activity against P. capsica with EC50 values of 17.7 μg/ml.

The Chemical Ecology of Plant Natural Products

Plants are excellent chemists with an impressive capability of biosynthesizing a large variety of natural products (also known as secondary or specialized metabolites) to resist various biotic and abiotic stresses. In this chapter, 989 plant natural products and their ecological functions in plant-herbivore, plant-microorganism, and plant-plant interactions are reviewed. These compounds include terpenoids, phenols, alkaloids, and other structural types. Terpenoids usually provide direct or indirect defense functions for plants, while phenolic compounds play important roles in regulating the interactions between plants and other organisms. Alkaloids are frequently toxic to herbivores and microorganisms, and can therefore also provide defense functions. The information presented should provide the basis for in-depth research of these plant natural products and their natural functions, and also for their further development and utilization.

Quinolizidine-Type Alkaloids: Chemodiversity, Occurrence, and Bioactivity

Quinolizidine alkaloids (QAs) are nitrogen-containing compounds produced naturally as specialized metabolites distributed in plants and animals (e.g., frogs, sponges). The present review compiles the available information on the chemical diversity and biological activity of QAs reported during the last three decades. So far, 397 QAs have been isolated, gathering 20 different representative classes, including the most common such as matrine (13.6%), lupanine (9.8%), anagyrine (4.0%), sparteine (5.3%), cytisine (6.5%), tetrahydrocytisine (4.3%), lupinine (12.1%), macrocyclic bisquinolizidine (9.3%), biphenylquinolizidine lactone (7.1%), dimeric (7.1%), and other less known QAs (20.9%), which include several structural patterns of QAs. A detailed survey of the reported information about the bioactivities of these compounds indicated their potential as cytotoxic, antiviral, antimicrobial, insecticidal, anti-inflammatory, antimalarial, and antiacetylcholinesterase compounds, involving favorable putative drug-likeness scores. In this regard, research progress on the structural and biological/pharmacological diversity of QAs requires further studies oriented on expanding the chemical space to find bioactive scaffolds based on QAs for pharmacological and agrochemical applications.

Matrine-Type Alkaloids with Anti-Tomato Spotted Wilt Virus Activity from the Root of Sophora tonkinensis Gagnep

As a continuation of our research on the development of pesticide active quinolizidine alkaloids (QAs) from the family Fabaceae, the chemical constituents of the root of Sophora tonkinensis Gagnep. were systematically investigated. Seventeen new matrine-type alkaloids (1-17), including one new naturally occurring compound (17), along with 20 known ones were isolated from the EtOH extract of S. tonkinensis. Notably, compound 5 possessed an unprecedented 6/6/5/4/6/6 hexacyclic system. Their structures were confirmed via comprehensive spectroscopic data analysis (IR, UV, NMR, HRESIMS), ECD calculation, and X-ray crystallography. Biological tests indicated that compounds 1, 4, 10, 12, 13, and 30 displayed significant anti-tomato spotted wilt virus (TSWV) activities compared with the positive control ningnanmycin. Moreover, compound 12 strongly inhibited the expression of the TSWV N, NSs, and NSm genes and TSWV NSs protein in plant host. Furthermore, compounds 4, 10, 12, 20, and 22 exhibited moderate insecticidal activities against TSWV thrip vector (Frankliniella occidentalis).