Discovery of Novel Benzo[4,5]thiazolo(oxazolo)[3,2-a]pyrimidinone Mesoionic Derivatives as Potential Antibacterial Agents and Mechanism Research

Development of dual-function disulfaneyl oxadiazole bactericides by structurally incorporating β-carboline moieties

Structural derivatization of known leads using the scaffold hopping strategy is a classic approach in pesticide discovery. However, the modificatory universality of lead skeletons profoundly influences the feasibility of this protocol. We herein report development of disulfaneyl oxadiazole bactericides involving β-carboline moieties. Derivative B18 is filtered out to exhibit excellent in vitro antibacterial properties with half-maximal effective concentrations of 0.47 mg/L, 1.72 mg/L, and 5.97 mg/L against Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzicola, and Xanthomonas citri pv. citri, respectively. The observed values fall short in comparison to the positive controls thiodiazole copper (TC) and allicin (AC). Moreover, in vivo pot studies reveal that B18 demonstrates enhanced curative (49.12 %) and protective (49.41 %) efficacy in comparison to the control groups TC and AC. Investigation regarding the mechanism of action indicates that B18 functions through a dual antibacterial approach. It not only interferes with the metabolic pathways of starch and sucrose in bacteria, and boosts the activity of rice defense enzymes while upregulating the expression of pyruvate kinase in the glycolytic pathway, thereby enhancing the plant resistance to bacterial pests.

Oxazole and isoxazole-containing pharmaceuticals: targets, pharmacological activities, and their SAR studies

Oxazole, a five-membered aromatic heterocycle featuring a nitrogen and an oxygen atom separated by a carbon atom, and its isomer isoxazole, with directly attached oxygen and nitrogen atoms, have been pivotal in medicinal chemistry. Over the past few decades, the U.S. Food and Drug Administration (FDA) has approved more than 20 drugs containing these nuclei for various clinical conditions, including Tafamidis and Oxaprozin. Due to their unique physicochemical properties, these drugs often exhibit superior pharmacokinetic profiles and pharmacological effects compared to those with similar heterocycles. This review provides a comprehensive overview of all FDA-approved drugs containing oxazole and isoxazole nuclei, focusing on their pharmacological activities and structure-activity relationships.

Discovery of Pyrido[1,2-α] Pyrimidinone Mesoionic Compounds as Potential Control Agents Against Potato Virus Y

Potato virus Y (PVY) relies on aphids and tubers to spread in the field and causes serious economic losses in the potato industry. Here, we found that pyrido[1,2-α] pyrimidinone mesoionic compounds with insecticidal activity against aphids possessed a good inhibitory effect on PVY. Among them, compound 35 had the best inhibitory activity against PVY (EC50 = 104 μg/mL), even superior to that of ningnanmycin (125 μg/mL). The fluorescence and qPCR results confirmed that compound 35 could inhibit the proliferation of PVY in Nicotiana benthamiana. Preliminary experiments on the mechanism of action indicated that compound 35 had good binding affinity with the coat protein (CP), which plays an essential role in aphid-PVY interactions. Molecular docking revealed that compound 35 could bind to the pocket of CP formed by Ser52, Glu204, and Arg208. Compound 35 had substantially lower binding affinity (Kd) values with CPS52A (219 μM), CPE204A (231 μM), and CPR208A (189 μM) than those with CPWT (5.80 μM). A luciferase assay confirmed that mutating Ser52, Glu204, and Arg208 significantly affected the expression level of CP and further reduced virus proliferation. Therefore, the broad-spectrum activity of compound 35 provides a unique strategy for the prevention and treatment of PVY.

Synthesis, Structural Characterization, and Biological Activities of 1,3,4- Thiadiazole Derivatives Containing Sulfonylpiperazine Structures

To develop novel bacterial biofilm inhibiting agents, a series of 1,3,4-thiadiazole derivatives containing sulfonylpiperazine structures were designed, synthesized, and characterized using 1H nuclear magnetic resonance (1H NMR), 13C nuclear magnetic resonance (13C NMR), and high-resolution mass spectrometry. Meanwhile, their biological activities were evaluated, and the ensuing structure-activity relationships were discussed. The bioassay results showed the substantial antimicrobial efficacy exhibited by most of the compounds. Among them, compound A24 demonstrated a strong efficacy with an EC50 value of 7.8 μg/mL in vitro against the Xanthomonas oryzae pv. oryzicola (Xoc) pathogen, surpassing commercial agents thiodiazole copper (31.8 μg/mL) and bismerthiazol (43.3 μg/mL). Mechanistic investigations into its anti-Xoc properties revealed that compound A24 operates by increasing the permeability of bacterial cell membranes, inhibiting biofilm formation and cell motility, and inducing morphological changes in bacterial cells. Importantly, in vivo tests showed its excellent protective and curative effects on rice bacterial leaf streak. Besides, molecular docking showed that the hydrophobic effect and hydrogen-bond interactions are key factors between the binding of A24 and AvrRxo1-ORF1. Therefore, these results suggest the utilization of 1,3,4-thiadiazole derivatives containing sulfonylpiperazine structures as a bacterial biofilm inhibiting agent, warranting further exploration in the realm of agrochemical development.

Repurposing Salicylamides to Combat Phytopathogenic Bacteria and Induce Plant Defense Responses

Based on the research strategy of "drug repurposing", a series of derivatives and marketed drugs that containing salicylic acid skeleton were tested for their antibacterial activities against phytopathogens. Salicylic acid can not only regulate some important growth metabolism of plants, but also induce plant disease resistance. The bioassay results showed that the salicylamides exhibited excellent antibacterial activity. Especially, oxyclozanide showed the best antibacterial effect against Xanthomonas oryzae, Xanthomonas axonopodis pv. citri and Pectobacterium atroseptica with MICs of 0.78, 3.12 and 12.5 μg.mL-1, respectively. In vivo experiments with rice bacterial leaf blight had further demonstrated that oxyclozanide exhibited stronger antibacterial activity than the commercial bactericide, thiodiazole copper. Oxyclozanide could induce plant defense responses through the determination of salicylic acid content and the activities of defense-related enzymes including CAT, POD, and SOD in rice. The preliminarily antibacterial mechanism study indicated that oxyclozanide exhibited the antibacterial activity by disrupting cell integrity and reducing bacterial pathogenicity. Additionally, oxyclozanide could induce plant defense responses through the determination of salicylic acid content.

Design, synthesis, and antimicrobial evaluation of 2-aminothiazole derivatives bearing the 4-aminoquinazoline moiety against plant pathogenic bacteria and fungi

BACKGROUND

To find more effective agricultural antibiotics, a class of new 2-aminothiazole derivatives containing the 4-aminoquinazoline moiety were synthesized and evaluated for their antimicrobial properties against phytopathogenic bacteria and fungi of agricultural importance.

RESULTS

All the target compounds were fully characterized by 1 H NMR, 13 C NMR, and high-resolution mass spectrometry. The bioassay results showed that compound F29 with a 2-pyridinyl substituent exhibited an outstanding antibacterial effect against Xanthomonas oryzae pv. oryzicola (Xoc) in vitro, having an half-maximal effective concentration (EC50 ) value as low as 2.0 μg/mL (over 30-fold more effective than the commercialized agrobactericide bismerthiazol, with an EC50 value of 64.3 μg/mL). In addition, compound F8 with a 2-fluorophenyl group demonstrated a good inhibitory activity toward the bacterium Xanthomonas axonopodis pv. citri (Xac), around twofold more active than bismerthiazol in terms of their EC50 values (22.8 versus 71.5 μg/mL). Interestingly, this compound also demonstrated a notable fungicidal effect against Phytophthora parasitica var. nicotianae, with an EC50 value largely comparable with that of the commercialized fungicide carbendazim. Finally, mechanistic studies revealed that compound F29 exerted its antibacterial effects by increasing the permeability of bacterial membranes, reducing the release of extracellular polysaccharides, and triggering morphological changes of bacterial cells.

CONCLUSION

Compound F29 has promising potential as a lead compound for developing more efficient bactericides to fight against Xoc. © 2023 Society of Chemical Industry.

Research Progress of Benzothiazole and Benzoxazole Derivatives in the Discovery of Agricultural Chemicals

Benzoxazole and benzothiazole have a broad spectrum of agricultural biological activities, such as antibacterial, antiviral, and herbicidal activities, which are important fused heterocyclic scaffold structures in agrochemical discovery. In recent years, great progress has been made in the research of benzoxazoles and benzothiazoles, especially in the development of herbicides and insecticides. With the widespread use of benzoxazoles and benzothiazoles, there may be more new products containing benzoxazoles and benzothiazoles in the future. We systematically reviewed the application of benzoxazoles and benzothiazoles in discovering new agrochemicals in the past two decades and summarized the antibacterial, fungicidal, antiviral, herbicidal, and insecticidal activities of the active compounds. We also discussed the structural-activity relationship and mechanism of the active compounds. This work aims to provide inspiration and ideas for the discovery of new agrochemicals based on benzoxazole and benzothiazole.

Design, synthesis, crystal structure, and antimicrobial activities of new quinazoline derivatives containing both the sulfonate ester and piperidinylamide moieties

BACKGROUND

To discover more efficient antimicrobial agents in agriculture, a series of new quinazoline derivatives bearing both sulfonate ester and piperidine-4-carboxamide moieties were synthesized and assessed for their antimicrobial effects.

RESULTS

All of the target compounds were fully characterized by proton (¹ H) nuclear magnetic resonance (NMR), carbon-13 (¹³ C) NMR, and high-resolution mass spectroscopy (HRMS), and compound III-6 containing a 3-bromophenyl substituent was clearly confirmed via single-crystal X-ray diffraction analysis. The bioassay results indicated that some compounds displayed noticeable inhibitory effects in vitro against Xanthomonas oryzae pv. oryzicola (Xoc). Further measurements of median effective concentration (EC₅₀ ) values showed that compound III-17 bearing a 4-methoxyphenyl group had the best anti-Xoc efficacy (EC₅₀  = 12.4 μg mL^-1 ), far better than the commercialized bismerthiazol (77.5 μg mL^-1 ). Moreover, this compound also demonstrated good protection and curative activities in vivo against rice bacterial leaf streak caused by Xoc.

CONCLUSION

Compound III-17 had a good potential for further development as a new bactericide for controlling Xoc. © 2023 Society of Chemical Industry.

Hydrazone modification of non-food natural product sclareolide as potential agents for plant disease

Plant diseases and their drug resistance pose a serious threat to agricultural production. One way to solve this problem is to discover new and efficient botanical pesticides. Herein, a series of novel hydrazide-hydrazone-containing sesquiterpenoid derivatives were synthesized by simply modifying the structure of the non-food natural product sclareolide. The biological activity results illustrated that compared to ningnanmycin (39.2 μg/mL), compound Z28 had the highest antiviral activity against tobacco mosaic virus (TMV), and the concentration for 50% of maximal effect (EC₅₀) of its inactivation activity was 38.7 μg/mL, followed by compound Z14 (40.6 μg/mL). Transmission electron microscopy (TEM) demonstrated that TMVs treated with compounds Z14 and Z28 were broken into rods of different lengths, and their external morphology was fragmented or even severely fragmented. Autodocking and molecular dynamics (MD) simulations indicated that compound Z28 had a strong affinity for tobacco mosaic virus coat protein (TMV-CP), with a higher binding energy of -8.25 kcal/mol compared to ningnanmycin (-6.79 kcal/mol). The preliminary mechanism revealed that compound Z28 can achieve an antiviral effect by targeting TMV-CP, rendering TMV unable to self-assemble and replicate, and might be a candidate for a novel plant antiviral agent. Furthermore, the curative and protective activities of compound Z22 (EC₅₀ = 16.1 μg/mL) against rice bacterial blight were 51.3% and 50.8%, respectively. Its control effect was better than that of bismerthiazol (BT) and thiadiazole copper (TC), compound Z22 that can be optimized as an active molecule.

Pyrido [1,2-a] Pyrimidinone Mesoionic Compounds Containing Vanillin Moiety: Design, Synthesis, Antibacterial Activity, and Mechanism

Xanthomonas oryzae pv. oryzicola (Xoo) is a plant pathogen responsible for rice bacterial blight disease that remains challenging for prevention and cure. To discover innovative and extremely potent antibacterial agents, vanillin moiety was introduced to develop a series of novel mesoionic derivatives. Compound 15 demonstrated excellent in vitro antibacterial activity against Xoo, with a 50% effective concentration value (EC₅₀) of 27.5 μg/mL, which was superior to that of the positive control agent thiodiazole copper (97.1 μg/mL) and comparable to that of compound "A11" (17.4 μg/mL). The greenhouse pot experiment also revealed that compound 15 had 38.5% curative and 36.8% protective efficacy against rice bacterial leaf blight in vivo at 100 μg/mL, which was higher than those of thiodiazole copper (31.2 and 32.6%, respectively) and compound "A11" (29.6 and 33.2%, respectively). Compound 15 enhanced the activities of related defense enzymes, increased chlorophyll content, and promoted the resistance of rice to bacterial infection by modulating the photosynthetic pathway. This study provides a basis for the subsequent structural modification and mechanism research of mesoionic derivatives.

Discovery of Pyrido[1,2-a]pyrimidine Mesoionic Compounds Containing Benzo[b]thiophene Moiety as Potential Pesticide Candidates

The increasing evolution of insect resistance has made it challenging for traditional insecticides to control the bean aphid (Aphis craccivora Koch). To address this pending issue, a range of pyrido[1,2-a]pyrimidine mesoionic compounds containing benzo[b]thiophene were designed and synthesized. The biological activity test results of the target compounds indicated that they had moderate to outstanding insecticidal activity against the bean aphid (Aphis craccivora) and moderate insecticidal activity against the white-backed planthopper (Sogatella furcifera). Compound L14 exhibited significant insecticidal activity against A. craccivora, with an LC₅₀ value of 1.82 μg/mL, which was superior to triflumezopyrim (LC₅₀ = 4.76 μg/mL). The results of enzyme activity assay showed that compound L14 had a definite inhibitory effect on ATPase. Moreover, the proteomics and docking findings of compound L14 suggested that it may act on the central nervous system of aphids and interact with nicotinic acetylcholine receptors. Therefore, compound L14 is a potentially novel insecticide candidate for further utilization.

First Discovery of Imidazo[1,2-a]pyridine Mesoionic Compounds Incorporating a Sulfonamide Moiety as Antiviral Agents

The applications of mesoionic compounds and their analogues as agents against plant viruses remain unexplored. This was the first evaluation of the antiviral activities of mesoionic compounds on this issue. Our study involved the design and synthesis of a series of novel imidazo[1,2-a]pyridine mesoionic compounds containing a sulfonamide moiety and the assessment of their antiviral activities against potato virus Y (PVY). Compound A33 was assessed on the basis of three-dimensional quantitative structure-activity relationship (3D-QSAR) model analysis and displayed good curative, protective, and inactivating activity effects against PVY at 500 mg/L, up to 51.0, 62.0, and 82.1%, respectively, which were higher than those of commercial ningnanmycin (NNM, at 47.2, 50.1, and 81.4%). Significantly, defensive enzyme activities and proteomics results showed that compound A33 could enhance the defense response by activating the activity of defense enzymes, inducing the glycolysis/gluconeogenesis pathway of tobacco to resist PVY infection. Therefore, our study indicates that compound A33 could be applied as a potential viral inhibitor.

Discovery of Mesoionic Derivatives Containing a Dithioacetal Skeleton as Novel Potential Antibacterial Agents and Mechanism Research

In this study, the design and synthesis of novel pyrido[1,2-a]pyrimidinone mesoionic derivatives incorporating dithioacetal structures were carried out. The three-dimensional quantitative structure-activity relationship (3D-QSAR) model was built according to the EC₅₀ values and directed the synthesis of compound A32. The biological activity test against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc) indicated that compound A32 showed good antibacterial activity with EC₅₀ values of 10.9 and 17.5 mg/L, which were lower than the EC₅₀ values of bismerthiazol (29.3 and 39.8 mg/L) and thiodiazole copper (64.8 and 78.1 mg/L). Furthermore, the in vivo antibacterial activity against bacterial leaf blight (BLB) and bacterial leaf streak (BLS) revealed that the protective activity of compound A32 was 43.9 and 41.7%, respectively, which was better than the protective activity of thiodiazole copper (40.6 and 35.0%). In addition, the protective activity against bacterial leaf blight of compound A32 was associated with the increasing rice defensive enzyme activity and the upregulation of proteins involved in oxidative phosphorylation. Moreover, compound A32 could upregulate the expression of complex I (nicotinamide adenine dinucleotide hydrogen (NADH) dehydrogenase) in the oxidative phosphorylation pathway, which was verified by complex I activity evaluation.