Natural Product Cerbinal and Its Analogues Cyclopenta[c]pyridines: Synthesis and Discovery as Novel Pest Control Agents

Novel Cyclopenta[c]pyridine Derivatives Based on Natural Cerbinal as Potential Agrochemical Anti-TMV Agents and Insecticides

Based on natural cerbinal, a series of novel 4-bit modified cyclopenta[c]pyridine derivatives containing a substituted amide or ester moiety were designed and synthesized for the first time. Their structures were systematically characterized by NMR and high-resolution mass spectra (HRMS). The anti-TMV activities, such as protection, inactivation, and curative effects in vivo, were evaluated methodically. The lethal activities of the target compounds against the agriculturally common pests Plutella xylostella larvae and Aphis laburni kaltenbach were evaluated by the immersion method. The bioassay results indicated that most of the target compounds exhibited good to excellent anti-TMV activity levels, good lethal activity against P. xylostella larvae at 600 μg/mL, and greater insecticidal activities against A. laburni Kaltenbach compared to the plant-derived insecticide rotenone. The binding mode of cerbinal and cyclopenta[c]pyridine derivatives 4b, 4p, and 4v with the TMV protein was studied with a molecular docking method, which indicated that the functional group of the 2- and 4-positions is vital for anti-TMV activity. The systematic research provides strong evidence that these novel 4-bit modified cyclopenta[c]pyridine derivatives could become potential agrochemical insecticides and anti-TMV agents.

Recent Achievements in Antiviral Agent Development for Plant Protection

Plant virus disease is the second most prevalent plant diseases and can cause extensive loss in global agricultural economy. Extensive work has been carried out on the development of novel antiplant virus agents for preventing and treating plant virus diseases. In this review, we summarize the achievements of the research and development of new antiviral agents in the recent five years and provide our own perspective on the future development in this highly active research field.

Antifibrotic pyridine-containing monoterpene alkaloids from Caryopteris glutinosa

Three undescribed dimeric pyridine-containing alkaloids, caryopterisines C - E, and four unreported cyclopenta[c]pyridine-derived alkaloids, caryopterisines F - I, were identified from Caryopteris glutinosa Rehder (Lamiaceae), together with two known monoterpene alkaloids. Caryopterisine C, featuring with an unprecedented 6/5/6/6/5 pentacyclic rings scaffold, may biosynthetically stem from a Diels-Alder reaction of two cyclopenta[c]pyridine-containing monomers and a following aromatization rearrangement reaction. Caryopterisines D and E, possessing an unprecedented 6/6/6/6/5 fused rings framework, may originate from a same Diels-Alder reaction of two monomers and subsequent aromatization arrangement, Baeyer-Villiger oxidation, and a set of tailoring reactions. Caryopterisine C showed strong inhibition on collagen accumulation in NIH3T3 cells (IC₅₀ = 14.26 ± 1.46 μM). Caryopterisines G and I reduce collagen accumulation with IC₅₀ values 88.91 ± 0.95 μM and 33.09 ± 1.38 μM, respectively. The Western blotting of the transforming growth factor-β-activated signaling pathways revealed that caryopterisine C inhibits collagen expression and accumulation via suppression of the phosphorylation of ERK1/2, P38, and SMAD2/3. The present works indicate caryopterisine C is a potential lead compound for the development of antifibrotic drugs.

Sources, Transformations, Syntheses, and Bioactivities of Monoterpene Pyridine Alkaloids and Cyclopenta[c]pyridine Derivatives

Monoterpene pyridine alkaloids (MTPAs) are alkaloids derived from iridoid glycosides (IGs). The common molecular structure of MTPAs is the pyridine ring, while some of them have a cyclopenta[c]pyridine skeleton. Some compounds containing this structure are potentially bioactive medicinal agents. In this paper, seven drug candidates (A-G), ninety natural source products (1-90), thirty-seven synthesized compounds (91-127), as well as twenty-six key intermediates (S1-S26) were summarized. We categorized five types of MTPAs and one type of cyclopenta[c]pyridine alkaloids in all. Additionally, their possible genetic pathways were proposed. Then, the chemical transformation, biotransformation, chemical synthesis, as well as the bioactivity of MTPAs and cyclopenta[c]pyridine derivatives were analyzed and summarized. Cyclopenta[c]pyridine derivatives can be concisely and chirally synthesized, and they have shown potentials with antibacterial, insecticidal, antiviral, anti-inflammatory, and neuropharmacological activities.

Discovery of Novel α-Aminophosphonates with Hydrazone as Potential Antiviral Agents Combined With Active Fragment and Molecular Docking

A series of novel α-aminophosphonate derivatives containing hydrazone were designed and synthesized based on active fragments. Bioassay results demonstrated that title compounds possessed good activities against tobacco mosaic virus. Among them, compounds 6a, 6g, 6i, and 6j were equivalent to the commercial antiviral agents like dufulin. On structure optimization-based molecular docking, compound 6k was synthesized and displayed excellent activity with values of 65.1% curative activity, 74.3% protective activity, and 94.3% inactivation activity, which were significantly superior to the commercial antiviral agents dufulin and ningnanmycin. Therefore, this study indicated that new lead compounds could be developed by adopting a joint strategy with active fragments and molecular docking.

Design, Synthesis, and Bioactivities of Phthalide and Coumarin Derivatives Based on the Biosynthesis and Structure Simplification of Gossypol

Because gossypol and hemigossypol show antiviral activity but are structurally complex, we designed and synthesized a series of structurally simpler phthalide and coumarin derivatives. The phthalide derivatives were synthesized by opening the naphthalene ring of hemigossypol, and the coumarin derivatives were synthesized by ring-opening reactions of the phthalide derivatives with the goal of investigating the effect of the lactone ring size on bioactivity. The bioassay results showed that the two series of target compounds possessed moderate to good activities against tobacco mosaic virus, One of the compounds showed in vivo inactivation, curative, and protection activities of 50 ± 1, 53 ± 3, and 48 ± 2% at 500 mg/L, values which are higher than those of gossypol (32 ± 1, 35 ± 1, 29 ± 1%, respectively) and comparable to those of hemigossypol (55 ± 1, 49 ± 1, and 48 ± 1%, respectively) and the commercial antiviral agent ningnanmycin (56 ± 2, 54 ± 1, 58 ± 1%) at the same dose. Thus, this compound is a promising candidate for the development of new anti-plant-virus agents. In addition, most of the synthesized compounds showed broad-spectrum activity when tested against 14 kinds of phytopathogenic fungi and showed selectivity against Sclerotinia sclerotiorum, Physalospora piricola, and Rhizoctonia cerealis. Moreover, some of the compounds exhibited activity against Plutella xylostella larvae; the two most active compounds exhibited larvicidal activities (LC₅₀) of 4.10 and 5.47 mg/L, respectively. Further studies showed that these compounds also exhibited insecticidal activities against Mythimna separata, Helicoverpa armigera, and Pyrausta nubilalis larvae.

Preparation and Anti-Tobacco Mosaic Virus Activities of Crocetin Diesters

The development of antiviral agents with an original structure and noticeable effect is always in great need. Natural products are important lead compounds in the development of new pesticides. Crocin-1 and crocin-2 were effectively isolated from Gardeniae fructus and found to have higher anti-tobacco mosaic virus (TMV) activity levels than ribavirin. A series of the crocetin diester derivatives were synthesized with separated crocetin-1 as material and evaluated for their anti-TMV activities. They could be dissolved in common organic solvents as dichloromethane, ethyl acetate, tetrahydrofuran, and methanol. Compounds 5, 9, 13, 14, and 15 displayed higher activities in vivo than ribavirin. Compound 14 with significantly higher antiviral activities than lead compounds (crocin-1 and crocin-2) emerged as a new antiviral candidate.

Synthesis of Four Optical Isomers of Antiviral Agent NK0209 and Determination of Their Configurations and Activities against a Plant Virus

Previously, we reported for the first time that harmala alkaloids harmine and tetrahydroharmine exhibit activity against plant viruses, and we developed an analogue, designated NK0209, that efficiently prevents and controls plant virus diseases. Here, to investigate the influence of the spatial configuration of NK0209 on its antiviral activities, we synthesized its four optical isomers, determined their configurations, and evaluated their activities against tobacco mosaic virus. All four isomers were significantly more active than ningnanmycin, which is one of the most successful commercial antiviral agents, with in vivo inactivation, cure, and protection rates of 57.3 ± 1.9, 54.2 ± 3.3, and 55.0 ± 4.1% at 500 μg/mL. Furthermore, analysis of structure-activity relationships demonstrated for the first time that the spatial conformation of NK0209 is an important determinant of its antiviral activity, and our results provide information about the possible optimum configuration for interaction of this molecule with its target protein.