Synthesis and herbicidal potential of substituted aurones

Herbicidal efficacy and ecological safety of an allelochemical-based benzothiazine derivative

BACKGROUND

The development of allelochemical-based herbicides may be of particular value for weed management in cropping systems. However, the action of potential allelochemical-based herbicides on crop selectivity and ecotoxicology needs to be clarified before they can be introduced into cropping systems.

RESULTS

An allelochemical-based 3-(2-chloro-4-ethanesulfonyl)-benzoyl-hydroxy-2- methyl-2H-1,2-benzothiazine-1,1-dioxide, originating from the rice allelochemical tricin, was applied to a paddy system. The benzothiazine derivative could effectively control dominant weeds, while rice was not affected at rates of 75-100 g a.i. ha^-1 . Furthermore, this target compound significantly inhibited the growth of all weeds tested with excellent selectivity for maize; however, it was not safe for soybean. The benzothiazine derivative had no toxic effects on zebrafish and earthworms. The benzothiazine derivative was rapidly degraded in soil with half-lives of 17.51-20.47 days. MiSeq-pyrosequencing revealed relative safety to soil microorganisms at 5 mg kg^-1 of the benzothiazine derivative.

CONCLUSION

The allelochemical-based benzothiazine derivative at optimal application rates can be recommended to provide satisfactory control of paddy weeds. The benzothiazine derivative with excellent crop selectivity and ecological safety may be further developed for weed management in maize fields. © 2019 Society of Chemical Industry.

Design and Synthesis of Novel 4-Hydroxyl-3-(2-phenoxyacetyl)-pyran-2-one Derivatives for Use as Herbicides and Evaluation of Their Mode of Action

In order to develop a novel herbicide containing the β-triketone motif, a series of 4-hydroxyl-3-(2-phenoxyacetyl)-pyran-2-one derivatives were designed and synthesized. The bioassay results showed that compound II15 had good pre-emergent herbicidal activity even at a dosage of 187.5 g ha^-1. Moreover, compound II15 showed a broader spectrum of weed control when compared with a commercial herbicide 2,4-dichlorophenoxyacetic acid (2,4-D), and displayed good crop safety to Triticum aestivum L. and Zea mays Linn. when applied at 375 g ha^-1 under pre-emergence conditions, which indicated its great potential as a herbicide. More importantly, studying the molecular mode of action of compound II15 revealed that the novel triketone structure is a proherbicide of its corresponding phenoxyacetic acid auxin herbicide, which has a herbicidal mechanism similar to that of 2,4-D. The present work indicates that the 4-hydroxyl-3-(2-phenoxyacetyl)-pyran-2-one motif may be a potential lead structure for further development of novel auxin-type herbicides.

Allelochemicals and Signaling Chemicals in Plants

Plants abound with active ingredients. Among these natural constituents, allelochemicals and signaling chemicals that are released into the environments play important roles in regulating the interactions between plants and other organisms. Allelochemicals participate in the defense of plants against microbial attack, herbivore predation, and/or competition with other plants, most notably in allelopathy, which affects the establishment of competing plants. Allelochemicals could be leads for new pesticide discovery efforts. Signaling chemicals are involved in plant neighbor detection or pest identification, and they induce the production and release of plant defensive metabolites. Through the signaling chemicals, plants can either detect or identify competitors, herbivores, or pathogens, and respond by increasing defensive metabolites levels, providing an advantage for their own growth. The plant-organism interactions that are mediated by allelochemicals and signaling chemicals take place both aboveground and belowground. In the case of aboveground interactions, mediated air-borne chemicals are well established. Belowground interactions, particularly in the context of soil-borne chemicals driving signaling interactions, are largely unknown, due to the complexity of plant-soil interactions. The lack of effective and reliable methods of identification and clarification their mode of actions is one of the greatest challenges with soil-borne allelochemicals and signaling chemicals. Recent developments in methodological strategies aim at the quality, quantity, and spatiotemporal dynamics of soil-borne chemicals. This review outlines recent research regarding plant-derived allelochemicals and signaling chemicals, as well as their roles in agricultural pest management. The effort represents a mechanistically exhaustive view of plant-organism interactions that are mediated by allelochemicals and signaling chemicals and provides more realistic insights into potential implications and applications in sustainable agriculture.

Thiazole Amides, A Novel Class of Algaecides against Freshwater Harmful Algae

Currently, harmful algal blooms are being one of ever-increasing global environmental problems. Much attention has been paid to the use of natural products as the selective algaecides due to their low toxicity, high selectivity and eco-friendly properties. In the present study, the thiazole alkaloid (1), originally isolated from Thermoactino-myces strain TM-64, was shown to exhibit potent algicidal activity against three typically harmful cyanobacterial algae, S. obliqnus, M. aeruginosa, and C. pyrenoidosa. Based on our previous work, a practical, scalable synthesis of alkaloid (1) was developed and reaction could be readily scaled up to more than 100 g. In addition, twenty-six analogues of alkaloid (1) by replacement of tryptamine moiety with different aromatic and aliphatic amines were also prepared. The bioassay results showed that most of these derivatives displayed potent algicidal activity against three harmful algae S. obliqnus, M. aeruginosa, and C. pyrenoidosa with IC50 values in the range of 1.5-5.0 μg/mL. Amongst them, compounds (10) and its hydrochloric salt (10S) were found to reveal powerful growth inhibitory activity against harmful cyanobacterial algae with IC50 values as low as 0.08 μg/mL, comparable to those of commercial algicide CuSO4 and herbicide Diuron.

Effect of allelochemical tricin and its related benzothiazine derivative on photosynthetic performance of herbicide-resistant barnyardgrass

Despite increasing knowledge of allelochemicals as leads for new herbicides, relatively little is known about the mode of action of allelochemical-based herbicides on herbicide-resistant weeds. In this study, herbicidal activities of a series of allelochemical tricin-derived compounds were evaluated. Subsequently, a benzothiazine derivative 3-(2-chloro-4-methanesulfonyl)-benzoyl-hydroxy-2-methyl-2H-1,2-benzothiazine-1,1-dioxide with 4-hydroxyphenyl-pyruvate dioxygenase (HPPD) inhibiting activity was identified as a target compound on photosynthetic performance of penoxsulam-resistant versus -susceptible barnyardgrass (Echinochloa crus-galli). Regardless of barnyardgrass biotype, the benzothiazine derivative greatly affected chlorophyll fluorescence parameters (Fv/Fm, ETR_1min and NPQ_1min), reduced the chloroplast fluorescence levels and expression of HPPD gene. In particular, the benzothiazine derivative interfered with photosynthetic performance of resistant barnyardgrass more effectively than the allelochemical tricin itself. These results showed that the benzothiazine derivative effectively inhibited the growth of resistant barnyardgrass and its mode of action on photosynthesis system was similar to HPPD-inhibiting sulcotrione, making it an ideal lead compound for further development of allelochemical-based herbicide discovery.

Aurone Mannich base derivatives as promising multifunctional agents with acetylcholinesterase inhibition, anti-β-amyloid aggragation and neuroprotective properties for the treatment of Alzheimer's disease

A series of aurone Mannich base derivatives were designed, synthesized and evaluated as multifunctional agents for the treatment of Alzheimer's disease. In vitro assays demonstrated that most of the derivatives were selective AChE inhibitors with good multifunctional properties. Among them, compound 7d exhibited outstanding inhibitory activity for RatAChE, EeAChE and HuAChE (IC₅₀ = 0.00878 ± 0.0002 μM, 0.0212 ± 0.006 μM and 0.0371 ± 0.004 μM, respectively). Moreover, 7d displayed high antioxidant activity and could confer significant neuroprotective effect against H₂O₂-induced PC-12 cell injury. In addition, 7d also showed biometal chelating abilities, good self- and Cu²⁺-induced Aβ_1-42 aggregation inhibitory potency and high BBB permeability. These multifunctional properties highlight 7d as promising candidate for further studies directed to the development of novel drugs against AD.

Green synthesis of aurones and related compounds under solvent-free conditions

3-Coumaranones were condensed with aldehydes on alumina or alumina–potassium fluoride without solvent under microwave irradiation or classical heating. Novel aurones and analogues bearing ferrocenyl, benzodioxole or benzodioxane groups were obtained in good yields without use of heavy metal reagents.

Synthesis and anti-cancer activity evaluation of new aurone derivatives

In this study, we have synthesized 2-[3- or 4-(2-aryl-2-oxoethoxy)arylidene]benzofuran-3-one derivatives (D1-D38) and evaluated their anti-cancer activities. The final compounds were obtained in multistep synthesis reactions using benzofuranon-3-one derivatives (A1-A4, B) as starting materials which were gained in various synthetic ways. Aurone derivatives (C1-C10) were acquired with the condensation reaction of these starting materials and 3-/4-hydroxybenzaldehyde which were then reacted with α-bromoacetophenones to get final compounds. The anti-cancer activity of the selected compounds was performed by National Cancer Institute (NCI), USA against 60 human tumor cell lines derived from nine neoplastic diseases. Compounds exhibited anti-cancer activity in varying ratios.

Synthesis and evaluation of 4-hydroxyl aurone derivatives as multifunctional agents for the treatment of Alzheimer's disease

A series of 4-hydroxyl aurone derivatives were designed synthesized and evaluated as potential multifunctional agents for the treatment of Alzheimer's disease. The results demonstrated that most of the derivatives exhibited good multifunctional properties. Among them, compound 14e displayed good inhibitory activities of self- and Cu(2+)-induced Aβ1-42 aggregation with 99.2% and 84.0% at 25μM, respectively, and high antioxidant activity with a value 1.90-fold of Trolox. In addition, 14e also showed remarkable inhibitory activities of both monoamine oxidase A and B with IC50 values of 0.271μM and 0.393μM, respectively. However the 6-methoxyl aurones 15a-c revealed excellent selectivity toward MAO-B. Furthermore, the representative compounds 14e and 15b displayed good metal-chelating abilities and blood-brain barrier (BBB) permeabilities in vitro.

Aurones: a promising heterocyclic scaffold for the development of potent antileishmanial agents

A series of (Z)-2-benzylidenebenzofuran-3-(2H)-ones (aurones) bearing a variety of substituents on rings A and B were synthesized and evaluated for their antiparasitic activity against the intracellular amastigote form of Leishmania infantum and their cytotoxicity against human THP1-differentiated macrophages. In general, aurones bearing no substituents on ring A (compounds 4a–4f) exhibit higher toxicity than aurones with 4,6-dimethoxy substitution (compounds 4g–4l). Among the latter, two aurones possessing a 2′-methoxy or a 2′-methyl group (compounds 4i and 4j) exhibit potent antileishmanial activity (IC₅₀ = 1.3 ± 0.1 μM and IC₅₀ = 1.6 ± 0.2 μM, resp.), comparable to the activity of the reference drug Amphotericin B, whereas they present significantly lower cytotoxicity than Amphotericin B as deduced by the higher selectivity index.