Streptochlorin analogues as potential antifungal agents: Design, synthesis, antifungal activity and molecular docking study

Natural and synthetic 5-(3'-indolyl)oxazoles: Biological activity, chemical synthesis and advanced molecules

5-(3'-Indolyl)oxazole moiety is a privileged heterocyclic scaffold, embedded in many biologically interesting natural products and potential therapeutic agents. Compounds containing this scaffold, whether from natural sources or synthesized, have demonstrated a wide array of biological activities. This has piqued the interest of synthetic chemists, leading to a large number of reported synthetic approaches to 5-(3'-indolyl)oxazole scaffold in recent years. In this review, we comprehensively overviewed the different biological activities and chemical synthetic methods for the 5-(3'-indolyl)oxazole scaffold reported in the literatures from 1963 to 2024. The focus of this study is to highlight the significance of 5-(3'-indolyl)oxazole derivatives as the lead compounds for the lead discovery of anticancer, pesticidal, antimicrobial, antiviral, antioxidant and anti-inflammatory agents, to summarize the synthetic methods for the 5-(3'-indolyl)oxazole scaffold. In addition, the reported mechanism of action of 5-(3'-indolyl)oxazoles and advanced molecules studied in animal models are also reviewed. Furthermore, this review offers perspectives on how 5-(3'-indolyl)oxazole scaffold as a privileged structure might be exploited in the future.

Novel pyrazole and imidazolone compounds: synthesis, X-ray crystal structure with theoretical investigation of new pyrazole and imidazolone compounds anticipated insecticide's activities against targeting Plodia interpunctella and nilaparvata lugens

In this study, we synthesized (2-propoxyphenyl)(3-(p-tolyl)oxiran-2-yl)methanone through oxidizing the double bond of the respective chalcone via the Weitz-Scheffer epoxidation reaction. Additionally, the chalcone with an oxirane ring served as a fundamental building block for the synthesis of various pyrazole and imidazole derivatives, employing diverse nitrogen nucleophiles. All synthesized compounds were confirmed via analytical and spectroscopic analysis, such as FT-IR, 1H NMR, 13C NMR, and mass spectroscopy. Furthermore, all these nitrogen heterocycles were optimized via the DFT/B3LYP/6-31G(d,p) basis set and their physical descriptors were identified. Compound 11 was further confirmed using single-crystal X-ray diffraction with Hirshfeld analysis, and the results were correlated with the optimized structure by comparing their bond length and bond angle, which provided excellent correlation. Additionally, the insecticidal activities of the newly synthesized compounds were tested against P. interpunctella and Nilaparvata lugens. The heterocyclic compounds exhibited remarkable activity compared to the standard reference thiamethoxam. These findings were further confirmed through docking simulation with different proteins, namely PDBID 3aqy and 3wyw. The compounds interacted effectively within the protein pockets, displaying a higher binding energy with amino acids.

Halogenated Antimicrobial Agents to Combat Drug-Resistant Pathogens

Antimicrobial resistance presents us with a potential global crisis as it undermines the abilities of conventional antibiotics to combat pathogenic microbes. The history of antimicrobial agents is replete with examples of scaffolds containing halogens. In this review, we discuss the impacts of halogen atoms in various antibiotic types and antimicrobial scaffolds and their modes of action, structure-activity relationships, and the contributions of halogen atoms in antimicrobial activity and drug resistance. Other halogenated molecules, including carbohydrates, peptides, lipids, and polymeric complexes, are also reviewed, and the effects of halogenated scaffolds on pharmacokinetics, pharmacodynamics, and factors affecting antimicrobial and antivirulence activities are presented. Furthermore, the potential of halogenation to circumvent antimicrobial resistance and rejuvenate impotent antibiotics is addressed. This review provides an overview of the significance of halogenation, the abilities of halogens to interact in biomolecular settings and enhance pharmacological properties, and their potential therapeutic usages in preventing a postantibiotic era. SIGNIFICANCE STATEMENT: Antimicrobial resistance and the increasing impotence of antibiotics are critical threats to global health. The roles and importance of halogen atoms in antimicrobial drug scaffolds have been established, but comparatively little is known of their pharmacological impacts on drug resistance and antivirulence activities. This review is the first to extensively evaluate the roles of halogen atoms in various antibiotic classes and pharmacological scaffolds and to provide an overview of their ability to overcome antimicrobial resistance.

Design, synthesis, antifungal activity and molecular docking of ring-opened pimprinine derivative containing (thio)amide structure

BACKGROUND

To obtain new environmentally friendly fungicides, we used the natural product pimprinine as the lead compound, and designed and synthesized two series of ring-opening derivatives of pimprinine containing amide/thioamide. We then studied their antifungal activity against six common plant pathogenic fungi in vitro.

RESULTS

Most of the target compounds have good antifungal activity against six important plant pathogenic fungi in vitro. At a concentration of 50 μg ml-1 , compound 3o showed prominent antifungal effects on Alternaria solani and Rhioctornia solani, with inhibition rates of 91.8% and 97.4%, and a 50% effective concentration (EC50 ) of 6.2255 and 0.6969 μg ml-1 respectively. The EC50 of compound 3o against Alternaria solani was significantly lower than that of boscalid (13.0380 μg ml-1 ) and flutriafol (11.9057 μg ml-1 ). In addition, compound 3o had good antifungal activity against Sclerotinia sclerotiorum, cucumber powdery mildew, cucumber Botrytis cinerea and Phytophthora capsici in vivo; the antifungal activity of compound 3o against cucumber Botrytis cinerea is 91.7%. At the same time, docking results for highly active compound 3o with the presumed target succinate dehydrogenase and the molecular docking prediction scores of all compounds further indicate its possible antifungal activity mechanism.

CONCLUSION

The designed and optimized derivative 3o of ring-opening pimprinine has good antifungal activity and can be used as a new antifungal drug for further research. © 2023 Society of Chemical Industry.

Discovery of Novel Benzoxaborole-Containing Streptochlorin Derivatives as Potential Antifungal Agents

Streptochlorin is a kind of indole alkaloid derived from marine microorganisms. It is a promising lead compound due to its potent bioactivity in preventing many phytopathogens, as shown in our previous study. To explore the potential applications of this natural product, a series of novel benzoxaborole-containing streptochlorin derivatives were designed and synthesized through a one-step and catalyst-free reaction in water at room temperature. All target compounds were first screened for their antifungal profiles in vitro against six common phytopathogenic fungi. The results of bioassay revealed that most of the designed compounds exhibited more significant antifungal activities against Botrytis cinrea, Gibberella zeae, Rhizoctorzia solani, Colletotrichum lagenarium, and alternaria leaf spot under the concentration of 50 μg/mL, and this is highlighted by compounds 4i and 5f, which demonstrated impressive antifungal effects against G. zeae and R. solani, with their corresponding EC₅₀ values 0.2983 and 0.2657 μg/mL, which are obviously better than positive control flutriafol and boscalid (5.2606 and 1.2048 μg/mL, respectively). Scanning electron microscopy on the hyphae morphology showed that compound 5b might cause mycelial abnormalities of G. zeae. 3D-QSAR studies of CoMFA and CoMSIA were carried out on 29 target compounds with antifungal activity against B. cinrea. The analysis results indicated that introducing appropriate electronegative groups at the 5-position of benzoxaborole and the 4,5-positions of the indole ring could effectively improve the anti-B. cinrea activity. Moreover, compound 5b showed good antifungal activities in vivo against Phytophthora capsici. Molecular docking was further explored to ascertain the practical value of the active compound as a potential inhibitor of LeuRS. The abovementioned results indicate that the designed benzoxaborole-containing streptochlorin derivatives could be further studied as template molecules of novel antifungal agents.

Design, Synthesis, Antifungal Activity, and Molecular Docking of Streptochlorin Derivatives Containing the Nitrile Group

Based on the structures of natural products streptochlorin and pimprinine derived from marine or soil microorganisms, a series of streptochlorin derivatives containing the nitrile group were designed and synthesized through acylation and oxidative annulation. Evaluation for antifungal activity showed that compound 3a could be regarded as the most promising candidate-it demonstrated over 85% growth inhibition against Botrytis cinerea, Gibberella zeae, and Colletotrichum lagenarium, as well as a broad antifungal spectrum in primary screening at the concentration of 50 μg/mL. The SAR study revealed that non-substituent or alkyl substituent at the 2-position of oxazole ring were favorable for antifungal activity, while aryl and monosubstituted aryl were detrimental to activity. Molecular docking models indicated that 3a formed hydrogen bonds and hydrophobic interactions with Leucyl-tRNA Synthetase, offering a perspective for the possible mechanism of action for antifungal activity of the target compounds.

Discovery of Novel Pimprinine and Streptochlorin Derivatives as Potential Antifungal Agents

Pimprinine and streptochlorin are indole alkaloids derived from marine or soil microorganisms. In our previous study, they were promising lead compounds due to their potent bioactivity in preventing many phytopathogens, but further structural modifications are required to improve their antifungal activity. In this study, pimprinine and streptochlorin were used as parent structures with the combination strategy of their structural features. Three series of target compounds were designed and synthesized. Subsequent evaluation for antifungal activity against six common phytopathogenic fungi showed that some of thee compounds possessed excellent effects, and this is highlighted by compounds 4a and 5a, displaying 99.9% growth inhibition against Gibberella zeae and Alternaria Leaf Spot under 50 μg/mL, respectively. EC₅₀ values indicated that compounds 4a, 5a, 8c, and 8d were even more active than Azoxystrobin and Boscalid. SAR analysis revealed the relationship between 5-(3'-indolyl)oxazole scaffold and antifungal activity, which provides useful insight into the development of new target molecules. Molecular docking models indicate that compound 4a binds with leucyl-tRNA synthetase in a similar mode as AN2690, offering a perspective on the mode of action for the study of its antifungal activity. These results suggest that compounds 4a and 5a could be regarded as novel and promising antifungal agents against phytopathogens due to their valuable potency.

Discovery and Preliminary Structure-Activity Investigation of 3-Substituted-1H-imidazol-5-yl-1H-indoles with In Vitro Activity towards Methicillin-Resistant Staphylococcus aureus

Antibiotics have been the cornerstone of modern medicine saving lives by virtue of being able to cure infectious diseases and to prevent infections in those who are immune compromised. Their intense use has led to a surging increase in the incidence of antibiotic-resistant bacteria resulting in a desperate need for antibiotics with new mechanisms of action. As part of our search for new antimicrobials we have screened an in-house library of compounds and identified two 3-substituted-1H-imidazol-5-yl-1H-indoles as weak growth inhibitors (MIC 16 µg/mL) against methicillin-resistant Staphylococcus aureus (MRSA). An extensive library of analogues was prepared using the Van Leusen three-component reaction, biological evaluation of which led to the identification of two analogues (26 and 32) with favorable anti-MRSA activity (MIC ≤ 0.25 µg/mL) which also lacked cytotoxic or hemolytic properties. The screening campaign also identified two derivatives, a phenethyl-indole-imidazole 57 and a 5-phenyl-1H-imidazole 111 that were non-toxic selective antifungals towards Cryptococcus neoformans. These results have identified 3-substituted-1H-imidazol-5-yl-1H-indoles and 5-phenyl-1H-imidazoles as new structural scaffolds for further investigation as anti-MRSA and anti-C. neoformans agents, respectively.

Synthesis of Novel Indole Schiff Base Compounds and Their Antifungal Activities

A series of novel indole Schiff base derivatives (2a–2t) containing a 1,3,4-thiadiazole scaffold modified with a thioether group were synthesized, and their structures were confirmed using FT-IR, ¹H NMR, ¹³C NMR, and HR-MS. In addition, the antifungal activity of synthesized indole derivatives was investigated against Fusarium graminearum (F. graminearum), Fusarium oxysporum (F. oxysporum), Fusariummoniliforme (F.moniliforme), Curvularia lunata (C. lunata), and Phytophthora parasitica var. nicotiana (P. p. var. nicotianae) using the mycelium growth rate method. Among the synthesized indole derivatives, compound 2j showed the highest inhibition rates of 100%, 95.7%, 89%, and 76.5% at a concentration of 500 μg/mL against F. graminearum, F. oxysporum, F.moniliforme, and P. p. var. nicotianae, respectively. Similarly, compounds 2j and 2q exhibited higher inhibition rates of 81.9% and 83.7% at a concentration of 500 μg/mL against C. lunata. In addition, compound 2j has been recognized as a potential compound for further investigation in the field of fungicides.

Streptomyces distallicus, a Potential Microbial Biolarvicide

Infected mosquitos from the genus Aedes have become one of the world's most influential contributors to human morbidity and death. To explore new biopesticides with activity against Aedes aegypti, Streptomyces distallicus, a species related to the subspecies group of Streptomyces netropsis, was investigated. Six metabolites, aureothin, allo-aureothin, deoxyaureothin, 4',7-dihydroxy isoflavone, 2-methyl-5-(3-indolyl)oxazole, and 2-ethyl-5-(3-indolyl)oxazole were isolated, and chemical structures, were elucidated based on one- and two-dimensional NMR spectroscopy analyses and HRMS. The A. aegypti larvicidal activity of these compounds was evaluated. Only two isomeric compounds, aureothin and allo-aureothin, showed larvicidal activity against A. aegypti with LC₅₀ values of 1.5 and 3.1 ppm for 24 h post-treatment, respectively, and 3.8 and 7.4 ppm for 48 h post-treatment, respectively. The crude extract of S. distallicus also demonstrated potent larvicidal activity with LC₅₀ values of 1.46 and 1.2 ppm for 24 and 48 h post-treatment, respectively. Deoxyaureothin, a furan ring reduced form of aureothin, showed no activity against A. aegypti. The hybrid imported fire ants activity of aureothin was also evaluated, but it did not show any activity at the highest dose of 62.5 μg/g. Described here is the first report on a bioassay-directed investigation of the secondary metabolites of S. distallicus and biological evaluation of isolated compounds aureothin and its isomer and intermediates as potential microbial larvicides. S. distallicus and crude extracts thereof are a promising source of potential microbial biolarvicides.

An insight into the recent developments in anti-infective potential of indole and associated hybrids

Prevention, accurate diagnosis, and effective treatment of infections are the main challenges in the overall management of infectious diseases. The best example is the ongoing SARs-COV-2(COVID-19) pandemic; the entire world is extremely worried about at present. Interestingly, heterocyclic moieties provide an ideal scaffold on which suitable pharmacophores can be designed to construct novel drugs. Indoles are amongst the most essential class of heteroaromatics in medicinal chemistry, which are ubiquitous across natural sources. The aforesaid derivatives have become invaluable scaffolds because of their wide spectrum therapeutic applications. Therefore, many researchers are focused on the design and synthesis of indole and associated hybrids of biological relevance. Hence, in the present review, we concisely discuss the indole containing natural sources, marketed drugs, clinical candidates, and their biological activities like antibacterial, antifungal, anti-TB, antiviral, antimalarial, and anti-leishmanial activities. The structure-activity relationships study of indole derivatives is also presented for a better understanding of the identified structures. The literature data presented for the anti-infective agents herein covers largely for the last twelve years.

Role of Indole Derivatives in Agrochemistry: Synthesis and Future Insights

Abstract:

Heterocycles constitute a wider class of organic compounds which contribute significantly in every facet of pure and applied chemistry. Indole, one of the bicyclic heterocyclic compounds containing nitrogen atom, witnessed unparalleled biological activity such as antiviral, antibacterial, anticancer, anti-depressant and antifungal activities. Different biological activities exhibited by indole derivatives provide the impulsion to explore its activity against anti-phytopathogenic microbes to save the plants from pests and disease, as food security will once again become a rigid demand. This review mainly focuses on various methods related to the synthesis of indole derivatives and its role in agriculture.

Influence of Steric Effect on the Pseudo-Multicomponent Synthesis of N-Aroylmethyl-4-Arylimidazoles

A pseudo-three-component synthesis of N-aroylmethylimidazoles 3 with three new C-N bonds formed regioselectively under microwave conditions was developed. Products were obtained by reacting two equivalents of aroylmethyl bromide (ArCOCH2Br, 1) with the appropriate amidine salt (RCN2H3.HX, 2) and with K2CO3 as a base in acetonitrile. The bicomponent reaction also occurred, giving the expected 4(5)-aryl-1H-imidazoles 4. Notably, the ratio of products 3 and 4 is governed by steric factors of the amidine 2 (i.e., R = H, CH3, Ph). Therefore, a computational study was carried out to understand the reaction course regarding product ratio (3/4), regioselectivity, and the steric effects of the amidine substituent group.

4-(Indol-3-yl)thiazole-2-amines and 4-ιndol-3-yl)thiazole Acylamines as Νovel Antimicrobial Agents: Synthesis, In Silico and In Vitro Evaluation

This manuscript deals with the synthesis and computational and experimental evaluation of the antimicrobial activity of twenty-nine 4-(indol-3-yl)thiazole-2-amines and 4-ιndol-3-yl)thiazole acylamines. An evaluation of antibacterial activity against Gram (+) and Gram (-) bacteria revealed that the MIC of indole derivatives is in the range of 0.06-1.88 mg/mL, while among fourteen methylindole derivatives, only six were active, with an MIC in the range of of 0.47-1.88 mg/mL. S. aureus appeared to be the most resistant strain, while S. Typhimurium was the most sensitive. Compound 5x was the most promising, with an MIC in the range of 0.06-0.12 mg/mL, followed by 5d and 5m. An evaluation of these three compounds against resistant strains, namely MRSA P. aeruginosa and E. coli, revealed that they were more potent against MRSA than ampicillin. Furthermore, compounds 5m and 5x were superior inhibitors of biofilm formation, compared to ampicillin and streptomycin, in terms Compounds 5d, 5m, and 5x interact with streptomycin in additive manner. The antifungal activity of some compounds exceeded or was equipotent to those of the reference antifungal agents bifonazole and ketoconazole. The most potent antifungal agent was found to be compound 5g. Drug likeness scores of compounds was in a range of -0.63 to 0.29, which is moderate to good. According to docking studies, E. coli MurB inhibition is probably responsible for the antibacterial activity of compounds, whereas CYP51 inhibition was implicated in antifungal activity. Compounds appeared to be non-toxic, according to the cytotoxicity assessment in MRC-5 cells.

Expedient discovery for novel antifungal leads: 1,3,4-Oxadiazole derivatives bearing a quinazolin-4(3H)-one fragment

Developing novel fungicide candidates are intensively promoted by the rapid emergences of resistant fungi that outbreak on agricultural production. Aiming to discovery novel antifungal leads, a series of 1,3,4-oxadiazole derivatives bearing a quinazolin-4(3H)-one fragment were constructed for evaluating their inhibition effects against phytopathogenic fungi in vitro and in vivo. Systematically structural optimizations generated the bioactive molecule I₃₂ that was identified as a promising inhibitor against Rhizoctonia solani with the in vivo preventative effect of 58.63% at 200 μg/mL. The observations that were captured by scanning electron microscopy and transmission electron microscopy demonstrated that the bioactive molecule I₃₂ could induce the sprawling growth of hyphae, the local shrinkage and rupture on hyphal surfaces, the extreme swelling of vacuoles, the striking distortions on cell walls, and the reduction of mitochondria numbers. The above results provided an indispensable complement for the discovery of antifungal lead bearing a quinazolin-4(3H)-one and 1,3,4-oxadiazole fragment.

Design, synthesis, and molecular simulation studies of N-phenyltetrahydroquinazolinones as protoporphyrinogen IX oxidase inhibitors

Discovering new protoporphyrinogen oxidase (PPO, EC 1.3.3.4) inhibitors is a promising direction for agrochemical research. Herein, we reported the discovery and in silico structure-guided optimization of N-phenyltetrahydroquinazolinones 1 and 2 as new PPO inhibitors. Most of the obtained compounds 1 and 2 exhibited significantly enhanced Nicotiana tabacum PPO (NtPPO) inhibitory potency than that of flumioxazin. Promisingly, 1-(tert-butoxy)-1-oxopropan-2-yl 2-chloro-4-fluoro-5-(4-oxo-5,6,7,8-tetrahydroquinazolin-3(4H)-yl)benzoate, 2o, with a K_i value of 4 nM, showed ten folds more enhanced NtPPO-inhibiting potency than flumioxazin. Additionally, compounds 2b and 2i showed a broad spectrum of broadleaf weeds control at 37.5-150 g ai/ha, and selective for wheat at 150 g ai/ha in the post-emergent application. The molecular simulation studies revealed the vital basis between N-phenyltetrahydroquinazolinones and NtPPO. The present work indicated that the N-phenyltetrahydroquinazolinone motif might be a potential scaffold for herbicide discovery.