Synthesis of novel quinolinomatrine derivatives and their insecticidal/acaricidal activities

Quinoline Derivatives in Discovery and Development of Pesticides

Finding highly active molecular scaffold structures is always the key research content of new pesticide discovery. In the research and development of new pesticides, the discovery of new agricultural molecular scaffold structures and new targets still faces great challenges. In recent years, quinoline derivatives have developed rapidly in the discovery of new agriculturally active molecules, especially in the discovery of fungicides. The unique quinoline scaffold has many advantages in the discovery of new pesticides and can provide innovative and feasible solutions for the discovery of new pesticides. Therefore, we reviewed the use of quinoline derivatives and their analogues as molecular scaffolds in the discovery of new pesticides since 2000. We systematically summarized the agricultural biological activity of quinoline compounds and discussed the structure-activity relationship (SAR), physiological and biochemical properties, and mechanism of action of the active compounds, hoping to provide ideas and inspiration for the discovery of new pesticides.

Application of Quinoline Ring in Structural Modification of Natural Products

Natural compounds are rich in pharmacological properties that are a hot topic in pharmaceutical research. The quinoline ring plays important roles in many biological processes in heterocycles. Many pharmacological compounds, including saquinavir and chloroquine, have been marketed as quinoline molecules with good anti-viral and anti-parasitic properties. Therefore, in this review, we summarize the medicinal chemistry of quinoline-modified natural product quinoline derivatives that were developed by several research teams in the past 10 years and find that these compounds have inhibitory effects on bacteria, viruses, parasites, inflammation, cancer, Alzheimer's disease, and others.

Benzamides Substituted with Quinoline-Linked 1,2,4-Oxadiazole: Synthesis, Biological Activity and Toxicity to Zebrafish Embryo

To develop new compounds with high activity, broad spectrum and low-toxicity, 17 benzamides substituted with quinoline-linked 1,2,4-oxadiazole were designed using the splicing principle of active substructures and were synthesized. The biological activities were evaluated against 10 fungi, indicating that some of the synthetic compounds showed excellent fungicidal activities. For example, at 50 mg/L, the inhibitory activity of 13p (3-Cl-4-Cl substituted, 86.1%) against Sclerotinia sclerotiorum was superior to that of quinoxyfen (77.8%), and the inhibitory activity of 13f (3-CF₃ substituted, 77.8%) was comparable to that of quinoxyfen. The fungicidal activities of 13f and 13p to Sclerotinia sclerotiorum were better than that of quinoxyfen (14.19 mg/L), with EC₅₀ of 6.67 mg/L and 5.17 mg/L, respectively. Furthermore, the acute toxicity of 13p was 19.42 mg/L, classifying it as a low-toxic compound.

The Advances on Bioactivities, Mechanisms of Action, and Structural Optimizations of Matrine and Its Derivatives

Matrine, a tetracyclo-quinolizidine alkaloid, is isolated from the industrial crop plant Sophora flavescens. Due to a wide range of pharmacological and agricultural properties, the research on the phytochemistry, pharmacology, toxicology and mechanisms of action of matrine and its derivatives has received much attention. On the other hand, to improve their biological activities, the study on structural optimizations and structure-activity relationships of matrine and its derivatives has also attached more and more importance. In this review article, the update advances on bioactivities, mechanisms of action, structural modifications and structure-activity relationships of matrine and its derivatives from 2017 to 2020 are presented. We hope that this review will provide a reference for the development and application of matrine and its derivatives as drugs or pesticides in the future.

Antifungal and insecticidal activities of rhein derivatives: synthesis, characterization and preliminary structure-activity relationship studies

There is an urgent need to replace highly polluting pesticides with environmentally friendly green pesticides of high efficiency and low toxicity, because of the growing concern for quality and safety of agricultural products. To discover new pesticides with diverse chemical structures from natural products, a series of rhein derivatives 3a-9b were designed, synthesized, and evaluated for their antifungal activity and insecticidal activity. The bioassay showed that some compounds exhibited moderate antifungal activity against Rhizoctonia solani, but lower activity against the other five pathogens. Surprisingly, most compounds displayed potent insecticidal activity against Spodoptera litura and Tetranychus cinnabarinus at a concentration of 2 μmol/mL. In particular, compounds 3a, 5a and 3 b exhibited potent insecticidal activities against S. litura at 72 h, with mortality rates of 100%, 100% and 92.1%, respectively, which were equivalent to that of the insecticide fipronil (100%). Their structure-activity relationships were also discussed. The findings of this experiment provide helpful research ideas for the development of these rhein derivatives as novel natural product-based pesticides in crop protection.

Matrine-Family Alkaloids: Versatile Precursors for Bioactive Modifications

Matrine-family alkaloids as tetracycloquinolizindine analogues from Traditional Chinese Medicine Sophora flavescens Ait, Sophora subprostrata and Sophora alopecuroides L possess various pharmacological activities and have aroused great interests over the past decades. Especially, a lot of matrine derivatives have been designed and synthesized and their biological activities investigated, and encouraging results have continuously been achieved in recent several years. These studies are helpful to develop more potent candidates or therapeutic agents and disclose their molecular targets and mechanisms. This paper reviews recent advances in the bioactive modifications of matrine-family alkaloids from derivatization of the C-13, C-14 or C-15 position, opening D ring, fusing D ring and structural simplification.

Synthesis, characterization of two matrine derivatives and their cytotoxic effect on Sf9 cell of Spodoptera frugiperda

The invasion of Spodoptera frugiperda has imposed a serious impact on global food security. Matrine is a botanical pesticide with a broad spectrum of insecticidal activity which was recommended for controlling Spodoptera frugiperda. In order to discover effective insecticide for Spodoptera frugiperda, two matrine derivatives modified with carbon disulfide and nitrogen-containing groups were systhesized. And their inhibition activities on Sf9 cell were evaluated. The structural configuration of compounds were characterized by IR, HPLC, MS, NMR and XRD, with yields of 52% and 65%, respectively. The IC₅₀ of the two newly synthesized compounds on Sf9 cell reduced to 0.648 mmol/L and 1.13 mmol/L, respectively, compared with that of matrine (5.330 mmol/L). In addition, microscopic observation of Sf9 cell treated with the compounds showed that the number of adherent cells decreased, the cells shrunk, vacuolated and apoptotic bodies appeared. The two newly synthesized compounds exhibited better inhibitory effect on Sf9 cell than that of the parent matrine, suggesting that the positive effect of the introduction of 1-pyrrolidinecarbodithioate and diethylcarbamodithioate groups to matrine. The morphological observation of Sf9 cell induced by derivatives indicated that apoptosis induction may be a mechanism that inhibits insect cell proliferation and exerts insecticidal effect.

Semi-synthesis and characterization of some new matrine derivatives as insecticidal agents

BACKGROUND

Matrine is an important traditional plant-derived insecticide with broad-spectrum activity. However, due to its moderate activity, matrine is mainly applied in combination with other pesticides. In order to discover new potential natural-product-based crop protection agents, a series of matrine derivatives characterized by cyclohexylamine group were synthesized to screen their insecticidal activity against seven typically agricultural pests.

RESULTS

The structural configurations of compounds were characterized by IR, ¹ H NMR, ¹³ C NMR, MS and XRD, with the pure yields of 42%, 65% and 71%, respectively. Although all compounds showed poor insecticidal activity against five lepidoptera pests, the compounds 2 and 4 displayed remarkable insecticidal activities against Lipaphis erysimi and Mulberry Root-Knot Nematode with a concentration-dependent manner within 0.5~1.5 mg/ mL. Compared with matrine (60%), compounds 2 and 4 exhibited potent insecticidal activities against L. erysimi, with a corrected mortality of 83.3% and 89.7%, respectively. They also showed excellent control effects on Mulberry Root-Knot Nematode, with corrected mortality as high as 88% and 80%, respectively.

CONCLUSION

All four synthesized matrine derivatives showed poor insecticidal activity against five lepidoptera pests, but the compounds 2 and 4 exhibited much stronger insecticidal activities against L. erysimi and Mulberry Root-Knot Nematode than matrine. Combined with the structural characteristics of compounds 1~4, we conclude that 4-methylcyclohexylamine, not the carbon disulfide group or cyclohexylamine group alone, mainly contributed to the improvement of insecticidal activities of matrine derivatives against these two agricultural pests. This work provides a direction and foundation for structural optimization of the matrine pesticides in the future. © 2020 Society of Chemical Industry.

The crystal structure of a matrine derivative, 13-(methylamine-1-yl) carbodithioate matrine, C17H27N3OS2

C17H27N3OS2, monoclinic, P21 (no. 4), a = 8.8052(10) Å, b = 10.8860(10) Å, c = 18.6705(2) Å, β = 99.2730(10)°, V = 1766.24(3) Å3, Z = 4, Rgt (F) = 0.0298, wR ref(F 2) = 0.0802, T = 100.00(10) K.

Semisynthesis of Matrinic Acid/Alcohol/Ester Derivatives, Their Pesticidal Activities, and Investigation of Mechanisms of Action against Tetranychus cinnabarinus

To discover new natural-product-based potential pesticides, 85 matrinic acid/alcohol/ester derivatives were synthesized by structural modifications of a quinolizidine alkaloid matrine. N-(4-Methyl)benzylmatrinyl n-decylate (76) and N-(2-chloro)benzylmatrinyl n-undecylate (86) exhibited greater than seven-fold more pronounced acaricidal activity than matrine against Tetranychus cinnabarinus; N-(2-chloro)benzylmatrinyl benzoate (80) showed the most promising insecticidal activity against Mythimna separata. The carboxyl group of matrinic acids and introduction of n-decyl/ n-undecylcarbonyl into matrinic alcohols were important for the acaricidal activity; introduction of alkyloxy into the carboxyl of matrinic acids and introduction of the electron-withdrawing groups on the N-benzyl of matrinic esters were necessary for the insecticidal activity. Through RT-PCR and qRT-PCR analysis, it was shown that the lactam ring of matrine was vital for action on VGSC; opening the lactam ring of matrine and the alkylcarbonyl of side-chain were two important factors for acting with α1, α2, and α4 nAChR subunits; α1, α2, α4, and β3 subunits may be the target of action of compound 86 against T. cinnabarinus.

Synthesis of Piperine Analogs Containing Isoxazoline/Pyrazoline Scaffold and Their Pesticidal Bioactivities

In continuation of our program to discover new potential pesticidal agents, thirty-one piperine analogs containing isoxazoline/pyrazoline scaffold were prepared, and confirmed by infrared spectra, proton/carbon-13 nuclear magnetic resonance spectra, and high-resolution mass spectra. The structures of compounds VIIb and VIIIc were further determined by ¹H-¹H COSY spectra. Especially the configuration of compound VIIIc was unambiguously confirmed by single-crystal X-ray diffraction. Their pesticidal activities were evaluated against three serious and typically crop-threatening agricultural pests, Tetranychus cinnabarinus Boisduval (spider mite), Mythimna separata Walker (Oriental armyworm), and Plutella xylostella Linnaeus (diamondback moth). Compounds VIIIb and VIIIc exhibited greater than 40-fold more potent acaricidal activity than the lead compound piperine against T. cinnabarinus. Notably, compounds VIa-c exhibited more pronounced oral toxicity against P. xylostella than toosendanin; compounds VIb and VIc displayed more promising growth inhibitory activity against M. separata than toosendanin. It demonstrated that the methylenedioxy and isoxazoline scaffolds were important for the oral toxicity and growth inhibitory activity against P. xylostella and M. separata, respectively; the ethylenedioxy and isoxazoline scaffolds were vital for the acaricidal activity against T. cinnabarinus. Moreover, compounds VIb, VIIf, and VIIIc showed very low toxicity against NRK-52E cells.