Synthesis and antifungal activity of 3-(1,3,4-oxadiazol-5-yl)-indoles and 3-(1,3,4-oxadiazol-5-yl)methyl-indoles

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.

Regioselective C3Alkylation of Indoles for the Synthesis of Bis(indolyl)methanes and 3-Styryl Indoles

Herein, we describe an efficient transition-metal-free regioselective C3alkylation of indoles for the synthesis of bis(indolyl)methanes and 3-styryl indoles. Nitrobenzene is employed as the oxidant to oxidize the alcohols in the presence of a strong base and the reaction avoids the use of transition metals such as Ru and Mn. The protocol provides a favorable route to access biologically active compounds such as arundine, vibrindole A, and turbomycin B.

Indole-Containing Metal Complexes and Their Medicinal Applications

Indole is an important element of many natural and synthetic molecules with significant biological activity. Nonetheless, the co-presence of transitional metals in organic scaffold may represent an important factor in the development of effective medicinal agents. This review covers some of the latest and most relevant achievements in the biological and pharmacological activity of important indole-containing metal complexes in the area of drug discovery.

Recent advances in antifungal drug development targeting lanosterol 14α-demethylase (CYP51): A comprehensive review with structural and molecular insights

Fungal infections are posing serious threat to healthcare system due to emerging resistance among available antifungal agents. Among available antifungal agents in clinical practice, azoles (diazole, 1,2,4-triazole and tetrazole) remained most effective and widely prescribed antifungal agents. Now their associated side effects and emerging resistance pattern raised a need of new and potent antifungal agents. Lanosterol 14α-demethylase (CYP51) is responsible for the oxidative removal of 14α-methyl group of sterol precursors lanosterol and 24(28)-methylene-24,25-dihydrolanosterol in ergosterol biosynthesis hence an essential component of fungal life cycle and prominent target for antifungal drug development. This review will shed light on various azole- as well as non-azoles-based derivatives as potential antifungal agents that target fungal CYP51. Review will provide deep insight about structure activity relationship, pharmacological outcomes, and interactions of derivatives with CYP51 at molecular level. It will help medicinal chemists working on antifungal development in designing more rational, potent, and safer antifungal agents by targeting fungal CYP51 for tackling emerging antifungal drug resistance.

Investigation of Novel Benzoxazole-Oxadiazole Derivatives as Effective Anti-Alzheimer's Agents: In Vitro and In Silico Approaches

Alzheimer's disease (AD) is a progressive neurological illness that is distinguished clinically by cognitive and memory decline and adversely affects the people of old age. The treatments for this disease gained much attention and have prompted increased interest among researchers in this field. As a springboard to explore new anti-Alzheimer's chemical prototypes, the present study was carried out for the synthesis of benzoxazole-oxadiazole analogues as effective Alzheimer's inhibitors. In this research work, we have focused our efforts to synthesize a series of benzoxazole-oxadiazole (1-19) and evaluating their anti-Alzheimer properties. In addition, the precise structures of synthesized derivatives were confirmed with the help of various spectroscopic techniques including ¹H-NMR, ¹³C-NMR and HREI-MS. To find the anti-Alzheimer potentials of the synthesized compounds (1-19), in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), inhibitory activities were performed using Donepezil as the reference standard. From structure-activity (SAR) analysis, it was confirmed that any variation found in inhibitory activities of both acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) enzymes were due to different substitution patterns of substituent(s) at the variable position of both acetophenone aryl and oxadiazole aryl rings. The results of the anti-Alzheimer assay were very encouraging and showed moderate to good inhibitory potentials with IC₅₀ values ranging from 5.80 ± 2.18 to 40.80 ± 5.90 µM (against AChE) and 7.20 ± 2.30 to 42.60 ± 6.10 µM (against BuChE) as compared to standard Donepezil drug (IC₅₀ = 33.65 ± 3.50 µM (for AChE) and 35.80 ± 4.60 µM (for BuChE), respectively. Specifically, analogues 2, 15 and 16 were identified to be significantly active, even found to be more potent than standard inhibitors with IC₅₀ values of 6.40 ± 1.10, 5.80 ± 2.18 and 6.90 ± 1.20 (against AChE) and 7.50 ± 1.20, 7.20 ± 2.30 and 7.60 ± 2.10 (against BuChE). The results obtained were compared to standard drugs. These findings reveal that benzoxazole-oxadiazole analogues act as AChE and BuChE inhibitors to develop novel therapeutics for treating Alzheimer's disease and can act as lead molecules in drug discovery as potential anti-Alzheimer agents.

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.

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.

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.

Efficient selective targeting of Candida CYP51 by oxadiazole derivatives designed from plant cuminaldehyde

Candida infection represents a global threat with associated high resistance and mortality rate. Azoles such as the triazole drug fluconazole are the frontline therapy against invasive fungal infections; however, the emerging multidrug-resistant strains limit their use. Therefore, a series of novel azole UOSO1-15 derivatives were developed based on a modified natural scaffold to combat the evolved resistance mechanism and to provide improved safety and target selectivity. The antifungal screening against C. albicans and C. auris showed that UOSO10 and 12-14 compounds were the most potent derivatives. Among them, UOSO13 exhibited superior potent activity with MIC50 values of 0.5 and 0.8 μg mL-1 against C. albicans and C. auris compared to 25 and 600 μg mL-1 for fluconazole, respectively. UOSO13 displayed significant CaCYP51 enzyme inhibition activity in a concentration-dependent manner with an IC50 10-fold that of fluconazole, while exhibiting no activity against human CYP50 enzyme or toxicity to human cells. Furthermore, UOSO13 caused a significant reduction of Candida ergosterol content by 70.3% compared to a 35.6% reduction by fluconazole. Homology modeling, molecular docking, and molecular dynamics simulations of C. auris CYP51 enzyme indicated the stability and superiority of UOSO13. ADME prediction indicated that UOSO13 fulfils the drug-likeness criteria with good physicochemical properties.

Discovery of novel indole and indoline derivatives against Candida albicans as potent antifungal agents

With the widespread use of azole antifungals in the clinic, the drug resistance has been emerging continuously. In this work, we have designed and prepared a series of novel indole and indoline derivatives, and in vitro antifungal activity against C. albicans were evaluated. The results showed that title compounds exhibited good antifungal effect on Azole-resistant C. albicans. Further mechanism study demonstrated that S18 could inhibit the biofilm formation and hyphae growth of C. albicans through the Ras-cAMP-PKA signaling pathway.

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.

Synthesis, crystal structure and Hirshfeld surface analysis of a zinc(II) coordination polymer of 5-phenyl-1,3,4-oxa-diazole-2-thiol-ate

A new zinc coordination polymer with 5-phenyl-1,3,4-oxa-diazole-2-thiol-ate, namely, catena-poly[zinc(II)-bis-(μ2-5-phenyl-1,3,4-oxa-diazole-2-thiol-ato)-κ2 N 3:S;κ2 S:N 3], [Zn(C8H5N2OS)2] n , was synthesized. The single-crystal X-ray diffraction analysis shows that the polymeric structure crystallizes in the centrosymmetric monoclinic C2/c space group. The ZnII atom is coordinated to two S and two N atoms from four crystallographically independent (L) ligands, forming zigzag chains along the [001] direction. This polymer complex forms an eight-membered [Zn-S-C-N-Zn-S-C-N] chair-like ring with two ZnII atoms and two ligand mol-ecules. On the Hirshfeld surface, the largest contributions come from the short contacts such as van der Waals forces, including H⋯H, C⋯H and S⋯H. Inter-actions including N⋯H, O⋯H and C⋯C contacts were also observed; however, their contribution to the overall stability of the crystal lattice is minor.

High Value-Added Application of Natural Plant Products in Crop Protection: Honokiol Monoester/Diester Derivatives Containing the Novel Core Scaffold of Benzodihydrofuran and Their Agricultural Bioactivities and Control Effects

To discover new potential botanical insecticides from plant secondary metabolites, a series of new honokiol-type monoester/diester derivatives containing the core scaffold of benzodihydrofuran were synthesized by structural modification of honokiol. Against Mythimna separata Walker, 2-hydroxymethy-5-(2'-(para-chlorobenzoyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (5) and 2-(2″-chloropyridin-5″-ylcarbonyloxy)methylene-5-(2'-(2″-chloropyridin-5″-ylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (37) displayed >2.1-fold promising insecticidal activity of the precursor honokiol. Against Aphis citricola Van der Goot, 2-hydroxymethy-5-(2'-(tridecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (21) (LD₅₀: 0.049 μg/nymph) and 2-(para-fluorobenzylcarbonyloxy)methylene-5-(2'-(para-fluorobenzylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (31) (LD₅₀: 0.040 μg/nymph) showed 3.5- and 4.3-folds potent aphicidal activity of honokiol (LD₅₀: 0.171 μg/nymph), respectively. Interestingly, 2-(tridecylcarbonyloxy)methylene-5-(2'-(tridecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (46) (LC₅₀: 0.186 mg/mL) and 2-(dodecylcarbonyloxy)methylene-5-(2'-(dodecylcarbonyloxy)-5'-(1″,2″-epoxypropanyl))phenyl-2,3-dihydrobenzofuran (53) (LC₅₀: 0.159 mg/mL: >6.4-fold of honokiol (LC₅₀: 1.024 mg/mL)) exhibited promising acaricidal activity and control efficiency against Tetranychus cinnabarinus Boisduval. Structure-activity relationships indicated that a specific length of the aliphatic chain is necessary for the agricultural activities of honokiol monoester/diester derivatives, especially for the acaricidal activity of diester derivatives.

Synthesis of indole-based oxadiazoles and their interaction with bacterial peptidoglycan and SARS-CoV-2 main protease: In vitro, molecular docking and in silico ADME/Tox study

In the present study, Indole-based-oxadiazole (1A-17A) compounds were successfully synthesized. The structures of all synthesized compounds were fully characterized by different sophisticated spectroscopic techniques such 1H NMR, 13C NMR, and HREI-MS. Further, the synthesized compounds were explored to investigate their broad-spectrum antibacterial and antibiofilm potential against multidrug resistant Pseudomonas aeruginosa (MDR-PA) and methicillin resistant Staphylococcus aureus (MRSA). The compounds possessed a broad spectrum of antibacterial activity having MIC values of values 1–8 mg/ml against the tested microorganisms. Compound A6 and A7 shows maximum antibacterial activity against MDR-PA, whereas A6, A7 and A11 shows highest activity against MRSA. Furthermore, antibiofilm assay shows that A6, A7 and A11 showed maximum inhibition of biofilm formation and it was found that at 4 mg/ml; A6, A7 and A11 inhibit MRSA biofilm formation by 81.1, 77.5 and 75.9%, respectively; whereas in case of P. aeruginosa; A6 and A7 showed maximum biofilm inhibition and inhibit biofilm formation by 81.5 and 73.7%, respectively. Molecular docking study showed that compounds A6, A7, A8, A10, and A11 had high binding affinity to bacterial peptidoglycan, indicating their potential inhibitory activity against tested bacteria, whereas A6 and A11 were found to be the most effective inhibitors of SARS CoV-2 main protease (3CLpro), with a binding affinity of − 7.78 kcal/mol. Furthermore, SwissADME and pkCSM-pharmacokinetics online tools was applied to calculate the ADME/Tox profile of the synthesized compounds and the toxicity of these chemicals was found to be low. The Lipinski, Veber, Ghose, and Consensus LogP criteria were also used to predict drug-likeness levels of the compounds. Our findings imply that the synthesized compounds could be a useful for the preventing and treating biofilm-related microbial infection as well as SARS-CoV2 infections.

1,3,4-Oxadiazole Contained Sesquiterpene Derivatives: Synthesis and Microbiocidal Activity for Plant Disease

A series of 1,3,4-oxadiazole contained sesquiterpene derivatives were synthesized, and the activity of the target compounds against Xanthomonas oryzae pv. oryzae (Xoo), Xanthomonas axonopodis pv. citri (Xac), and tobacco mosaic virus (TMV) were evaluated. The biological activity results showed that the EC₅₀ values of compounds H4, H8, H11, H12, H14, H16, and H19 for Xac inhibitory activity were 33.3, 42.7, 56.1, 74.5, 37.8, 43.8, and 38.4 μg/ml, respectively. Compounds H4, H8, H15, H19, H22, and H23 had inhibitory effects on Xoo, with EC₅₀ values of 51.0, 43.3, 43.4, 50.5, 74.6, and 51.4 μg/ml, respectively. In particular, the curative and protective activities of compound H8 against Xoo in vivo were 51.9 and 49.3%, respectively. In addition, the EC₅₀ values of the inactivation activity of compounds H4, H5, H9, H10, and H16 against TMV were 69.6, 58.9, 69.4, 43.9, and 60.5 μg/ml, respectively. The results of molecular docking indicated that compound H10 exhibited a strong affinity for TMV-coat protein, with a binding energy of −8.88 kcal/mol. It may inhibit the self-assembly and replication of TMV particles and have an anti-TMV effect, which supports its potential usefulness as an antiviral agent.

Diazotrifluoroethyl Radical: A CF3-Containing Building Block in [3 + 2] Cycloaddition

We present herein a visible-light-induced [3 + 2] cycloaddition of a hypervalent iodine(III) reagent with α-ketoacids for the construction of 5-CF₃-1,3,4-oxadiazoles that are of importance in medicinal chemistry. The reaction proceeds smoothly without a photocatalyst, metal, or additive under mild conditions. Different from the well-established trifluorodiazoethane (CF₃CHN₂), the diazotrifluoroethyl radical [CF₃C(·)N₂], a trifluoroethylcarbyne (CF₃CĊ:) equivalent and an unusual CF₃-containing building block, is involved in the present reaction system.

Trifluoromethylpyridine 1,3,4-Oxadiazole Derivatives: Emerging Scaffolds as Bacterial Agents

A new class of trifluoromethylpyridine 1,3,4-oxadiazole derivatives (6a-6v) was obtained, and their antibacterial activities were evaluated. Some of them exhibited good activity, particularly 6a, which had the highest in vitro activity against Ralstonia solanacearum (R. solanacearum) and Xanthomonas axonopodis pv. citri (Xac). The half-maximal effective concentrations (EC50) were 26.2 and 10.11 μg/mL, respectively, which were lower than those of commercial thiodiazole copper (97.2 and 35.3 μg/mL, respectively). Furthermore, 6q showed much higher activity against Xanthomonas oryzae pv. oryzae (Xoo) with an EC50 value of 7.2 μg/mL; this was superior to bismerthiazol (57.2 μg/mL). Collectively, our findings provide a foundation for the development of trifluoromethylpyridine 1,3,4-oxadiazole derivatives.

Discovery of a Fungicide Candidate Targeting Succinate Dehydrogenase via Computational Substitution Optimization

Succinate dehydrogenase (SDH, EC 1.3.5.1) has proven to be an important fungicidal target, and the inhibition of SDH is useful in the treatment of plant pathogens. The discovery of a novel active SDH inhibitor is of high value. Herein, we disclose the discovery of a potent, highly active inhibitor as a fungicide candidate by using a computational substitution optimization method, a fast drug design method developed in our laboratory. The greenhouse experiments showed that compound 17c exhibited high protective activity against south corn rust, soybean rust (SBR), and rice sheath blight at a very low dosage of 0.781 mg/L. Moreover, the field trials indicated that compound 17c is comparable to and even better than commercial fungicides against SBR and cucumber powdery mildew at 50 mg/L concentration. Most surprisingly, compound 17c resulted to be strictly better in curative activity than the commercial fungicide benzovindiflupyr. The computation results indicated that 17c could form another hydrogen bond with C_S42 and then lead to strong van der Waals and electronic interactions with SDH. Our results suggested that 17c is a potential fungicide candidate for SDH.

Conventional and Microwave-Assisted Synthesis, Antitubercular Activity, and Molecular Docking Studies of Pyrazole and Oxadiazole Hybrids

Microwave-assisted organic reaction enhancement (MORE) has become more important in synthetic organic chemistry for efficient resource utilization. In this study, we synthesized bioactive compounds using both traditional and microwave methods. Microwave-assisted synthesis takes less time and produces higher yields and quality than conventional approaches. We reported the synthesis of N'-(1-(2-(3-(4-chlorophenyl)-1-phenyl-1H-pyrazol-4-yl)-5-phenyl-1,3,4-oxadiazol-3(2H)-yl)ethylidene) substituted hydrazides (4a-t). We also tested them against two strains: M. tuberculosis H₃₇Ra and M. bovis BCG. Against M. tuberculosis H₃₇Ra, the compounds 4e, 4h, 4k, 4p, and 4s were the most effective. Compounds 4f, 4g, and 4s showed significant activity against M. bovis BCG. The structures of newly synthesized molecules were determined using spectral methods. Furthermore, molecular docking investigations into the active site of mycobacterial InhA yielded well-clustered solutions for these compounds' binding modalities producing a binding affinity in the range of -10.366 to -8.037. Theoretical results were in good accord with the observed experimental values. The docking score of compound 4e was -10.366, and the Glide energy was -66.459 kcal/mol.

Synthesis of indole derivatives as prevalent moieties present in selected alkaloids

Indoles are a significant heterocyclic system in natural products and drugs. They are important types of molecules and natural products and play a main role in cell biology. The application of indole derivatives as biologically active compounds for the treatment of cancer cells, microbes, and different types of disorders in the human body has attracted increasing attention in recent years. Indoles, both natural and synthetic, show various biologically vital properties. Owing to the importance of this significant ring system, the investigation of novel methods of synthesis have attracted the attention of the chemical community. In this review, we aim to highlight the construction of indoles as a moiety in selected alkaloids.

Design, Synthesis, and Study of the Insecticidal Activity of Novel Steroidal 1,3,4-Oxadiazoles

A series of novel steroidal derivatives with a substituted 1,3,4-oxadiazole structure was designed and synthesized, and the target compounds were evaluated for their insecticidal activity against five aphid species. Most of the tested compounds exhibited potent insecticidal activity against Eriosoma lanigerum (Hausmann), Myzus persicae, and Aphis citricola. Compounds 20g and 24g displayed the highest activity against E. lanigerum, showing LC₅₀ values of 27.6 and 30.4 μg/mL, respectively. Ultrastructural changes in the midgut cells of E. lanigerum were detected by transmission electron microscopy, indicating that these steroidal oxazole derivatives might exert their insecticidal activity by destroying the mitochondria and nuclear membranes in insect midgut cells. Furthermore, a field trial showed that compound 20g exhibited effects similar to those of the positive controls chlorpyrifos and thiamethoxam against E. lanigerum, reaching a control rate of 89.5% at a dose of 200 μg/mL after 21 days. We also investigated the hydrolysis and metabolism of the target compounds in E. lanigerum by assaying the activities of three insecticide-detoxifying enzymes. Compound 20g at 50 μg/mL exhibited inhibitory action on carboxylesterase similar to the known inhibitor triphenyl phosphate. The above results demonstrate the potential of these steroidal oxazole derivatives to be developed as novel pesticides.

Synthesis and Characterization of Novel Thiazolidinones and Thioxothiazolidinones Derived from Substituted Indole

Based on recent discoveries concerning the numerous biological properties of thiazolidinones and thiosemicarbazones, new N-substituted heterocyclic derivatives have been designed by combining the indole ring with thioxothiazolidinone, thiazolidinone or thiosemicarbazone. Thus, a series of new thioxothiazolidinone, thiazolidinone, or thiosemicarbazone derivatives bearing indole-based moiety have been designed, synthesized, and developed in good yields.

In vitro Evaluation of Isatin derivatives as Potent Anti-Breast Cancer Agents against MCF-7, MDA MB 231, MDA-MB 435 and MDA-MB 468 Breast Cancers cell lines: A Review

INTRODUCTION

Breast cancer (BC) is one of the most frequent malignancy and most common reasons of impermanence in women. The backbone of therapy for BC is principally chemotherapy, but due to its non-specific nature between normal cells and cancer cells and severe side effects are the main barriers in its therapy. So, there is an intense requirement for the enlargement of more efficacious, more specific and safer anti-BC agents.

OBJECTIVE

Isatin (IST) is an endogenous molecule which is a principal class of heterocyclic compounds and exhibits a wide range of therapeutic activities which can be used as a starting material for the synthesis of several drug molecules. Many literatures were reported previously on different pharmacological activities of IST derivatives and particularly on anticancer activity but this review mainly focus on anti-BC activities of IST derivatives through MCF-7, MDA MB 231, MDA-MB 435 and MDA-MB 468 cell lines. Here in we mentioned, a total 33 IST derivatives (compound 24- 56) which shown good anti-BC activity. IST derived compounds are also available in market and are used for various cancer types like sunitinib for renal cell carcinoma (RCC) and Nintedanib used for the cryptogenic fibrosing alveolitis treatment but when evaluated for BC did not get much success.

CONCLUSION

This review mainly highlights anti-BC activities of various IST analogues using MCF-7, MDA MB 231, MDA-MB 435 and MDA-MB 468 cell lines, display the potent compound of the series and structure-activity relationships of compounds with molecular docking also. So, this study mainly shows the importance of IST as major sources for drug design and development of newer anti-BC drugs.

Optimization of Osthole in the Lactone Ring: Structural Elucidation, Pesticidal Activities, and Control Efficiency of Osthole Ester Derivatives

Here, we prepared a series of novel osthole-type ester derivatives modified in the lactone ring of osthole, which is isolated from Cnidium monnieri. The positions of H-3 and H-4 of the representative compound 4z were determined by a ¹H-¹H COSY spectrum. By opening the lactone ring of osthole, the double bonds at the C-3 and C-4 positions of diol 3 and esters 4a-4z, 4a', and 4b' were still retained as a Z configuration. That is, H-3 and H-4 of compounds 3 and 4a-4z, 4a', and 4b' were all in the cis relationship. The steric configurations of 4k, 4v, and 4z were further undoubtedly determined by single-crystal X-ray diffraction. Against Tetranychus cinnabarinus Boisduval, four aliphatic esters 4c (R = n-C₃H₇; LC₅₀: 0.31 mg/mL), 4d (R = CH₃(CH₂)₁₀; LC₅₀: 0.24 mg/mL), 4a' (R = CH₃(CH₂)₉; LC₅₀: 0.28 mg/mL), and 4b' (R = CH₃(CH₂)₁₂; LC₅₀: 0.32 mg/mL) showed the most promising acaricidal activity, and compounds 4c, 4d, and 4a' also exhibited a potent control efficiency. Especially, compound 4d exhibited greater than fivefold acaricidal activity of the precursor osthole (LC₅₀: 1.22 mg/mL). Against Mythimna separata Walker, compounds 4g, 4l, and 4m displayed 1.6-1.8-fold potent insecticidal activity of osthole. It demonstrated that the lactone ring of osthole is not necessary for the agricultural activities, thiocarbonylation of osthole was not beneficial for the agricultural activities, introduction of R as an aliphatic chain is vital for the acaricidal activity, notably, the length of the aliphatic chain is related to the acaricidal activity, 4d could be further studied as a lead acaricidal agent, and to the aromatic series, R containing the fluorine atom(s) is important for the insecticidal activity.

Synthesis of 5-[(1H-indol-3-yl)methyl]-1,3,4-oxadiazole-2(3H)-thiones and their protective activity against oxidative stress

A small library of 2-[(1H-indol-3-yl)methyl]-5-(alkylthio)-1,3,4-oxadiazoles was prepared, starting from indole-3-acetic acid methyl ester and its 5-methyl-substituted derivative. The synthetic route involved the formation of intermediate hydrazides, their condensation with carbon disulfide, and intramolecular cyclization to corresponding 5-[(1H-indol-3-yl)methyl]-1,3,4-oxadiazole-2(3H)-thiones. The latter were then S-alkylated, and in case of ester derivatives, they were further hydrolyzed into corresponding carboxylic acids. All 5-[(1H-indol-3-yl)methyl]-1,3,4-oxadiazole-2(3H)-thiones and their S-alkylated derivatives were then screened for their protective effects in vitro and in vivo. Methyl substitution on the indole ring and propyl, butyl, or benzyl substitution on sulfhydryl group-possessing compounds were revealed to protect Friedreich's ataxia fibroblasts against the effects of glutathione depletion induced by the γ-glutamylcysteine synthetase inhibitor, buthionine sulfoximine. Two of the active compounds also reproducibly increased the survival of Caenorhabditis elegans exposed to juglone-induced oxidative stress.

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

Streptochlorin is a small molecule of indole alkaloid isolated from marine Streptomyces sp., it is a promising lead compound due to its potent bioactivity in preventing many phytopathogens in our previous study, but further structural modifications are required to improve its antifungal activity. Our work in this paper focused on the replacement of oxazole ring in streptochlorin with the imidazole ring, to discover novel analogues. Based on this design strategy, three series of streptochlorin analogues were efficiently synthesized through sequential Vilsmeier-Haack reaction, Van Leusen imidazole synthesis and halogenation reaction. Some of the analogues displayed excellent activity in the primary assays, and this is highlighted by compounds 4g and 4i, the growth inhibition against Alternaria Leaf Spot and Rhizoctorzia solani under 50 μg/mL are 97.5% and 90.3%, respectively, even more active than those of streptochlorin, pimprinine and Osthole. Molecular docking models indicated that streptochlorin binds with Thermus thermophiles Leucyl-tRNA Synthetase in a similar mode to AN2690, offering a perspective on the mode of action study for antifungal activities of streptochlorin derivatives. Further study is still ongoing with the aim of discovering synthetic analogues, with improved antifungal activity and clear mode of action.

Design, synthesis, and biological activity of novel 1,2,4-oxadiazole derivatives

Background

Plant diseases seriously threaten food security, it is urgent to discover efficient and low-risk chemical pesticides. 1,2,4-Oxadiazole derivatives exhibit broad spectrum of agricultural biological activities. For discovering novel molecules with excellent agricultural activities, novel 1,2,4-oxadiazole derivatives were synthesized and evaluated for their agricultural activities.

Result

Bioassays results showed that the title compounds exhibited moderate nematocidal activity against Meloidogyne incognita and anti-fungal activity to Rhizoctonia solani. It’s worth noting that compounds 5m, 5r, 5u, 5v, 5x and 5y showed strong antibacterial effects on Xanthomonas oryzae pv. oryzae (Xoo), with EC₅₀ values of 36.25, 24.14, 28.82, 19.44, 25.37 and 28.52 μg/mL, respectively, superior to bismerthiazol (BMT, EC₅₀ = 77.46 μg/mL) and thiodiazole copper (TDC, EC₅₀ = 99.31 μg/mL). Compounds 5p, 5u and 5v exhibited excellent antibacterial ability against Xanthomonas oryzae pv. oryzicola (Xoc), with EC₅₀ values of 31.40, 19.04 and 21.78 μg/mL, respectively, better than that of BMT (EC₅₀ = 68.50 μg/mL) and TDC (EC₅₀ = 91.05 μg/mL). In addition, compound 5v exerted moderate antibacterial effects on rice bacterial leaf blight.

Conclusions

Twenty-six novel 1,2,4-oxadiazole derivatives were obtained and their biological activities were evaluated. Compound 5u and 5v exhibited excellent antibacterial activity Xoo and Xoc. These results indicated that 1,2,4-oxadiazole derivatives containing a trifluoromethyl pyridine moiety could be as potential alternative templates for discovering novel antibacterial agents.

Efficient Synthesis of Novel 1,3,4-Oxadiazoles Bearing a 4-N,N-Dimethylaminoquinazoline Scaffold via Palladium-Catalyzed Suzuki Cross-Coupling Reactions

Two series of novel (symmetrical and unsymmetrical) quinazolinylphenyl-1,3,4-oxadiazole derivatives were synthesized using palladium-catalyzed Suzuki cross-coupling reactions. The presented synthetic methodology is based on the use of bromine-substituted 2-phenyl-4-N,N-dimethylaminoquinazolines and either a boronic acid pinacol ester or a diboronic acid bis(pinacol) ester of 2,5-diphenyl-1,3,4-oxadiazole. The reactions are conducted in a two-phase solvent system in the presence of catalytic amounts of [1,1′-bis(diphenylphosphino)ferrocene]-dichloropalladium(II), sodium carbonate, and tetrabutylammonium bromide, which plays the role of a phase-transfer catalyst. The luminescence properties of the obtained compounds are discussed in the context of applying these compounds in optoelectronics. Specifically, two highly-conjugated final products: N,N-dimethyl-2-phenyl-6-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)quinazolin-4-amine (8f) and 6,6′-(4,4′-(1,3,4-oxadiazole-2,5-diyl)bis(4,1-phenylene))bis(N,N-dimethylquinazolin-4-amine (9f), which contain a 1,3,4-oxadiazole moiety connected to a quinazoline ring by a 1,4-phenylene linker at the 6 position, exhibit strong fluorescence emission and high quantum yields.

Design and synthesis of novel 1,3,4-oxadiazole sulfone compounds containing 3,4-dichloroisothiazolylamide moiety and evaluation of rice bacterial activity

In this study, thirty 1,3,4-oxadiazole sulfone derivatives containing 3,4-dichloroisothiazolamide moiety were designed and synthesized, and their antibacterial activities were evaluated. Bioassay results showed that some compounds exhibited excellent antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xoc) in vitro and in vivo. Notably, the EC₅₀ values of compounds 2 and 3 against Xoo were 0.79 and 0.85 μg/mL, respectively, which were superior to those of the control agents isotianil, bismerthiazol, and thiodiazole copper. In addition, in vivo antibacterial activities revealed that the compound 2 at 50 μg/mL possessed protective and curative activities of 43.99% and 41.06% against Xoo, respectively, which were better than positive controls. Furthermore, the preliminary mechanism study disclosed that compound 2 exhibited effective antibacterial activity against Xoo by inhibiting the formation of extracellular polysaccharides from Xoo, increasing cell permeability, and changing the shape of cells. This study suggested that 1,3,4-oxadiazole sulfone derivatives containing 3,4-dichloroisothiazolamide moiety displayed excellent antibacterial activity and could be further explored and developed as commercial pesticides.

Synthesis and biological activities of novel trifluoromethylpyridine amide derivatives containing sulfur moieties

A series of trifluoromethylpyridine amide derivatives containing sulfur moieties (thioether, sulfone and sulfoxide) was designed and synthesized. Their antibacterial activities against Xanthomonas oryzae pv. oryzae (Xoo), Ralstonia solanacearum (R. solanacearum) and insecticidal activities against P. xylostella were evaluated. Notably, the half-maximal effective concentration (EC50) value of sulfone-containing compound F10 is 83 mg L-1 against Xoo, which is better than that of commercial thiodiazole copper (97 mg L-1) and bismerthiazol (112 mg L-1). Thioether-containing compounds E1, E3, E5, E6, E10, E11 and E13 showed much higher activities against R. solanacearum with the EC50 value from 40 to 78 mg L-1, which are much lower than that of thiodiazole copper (87 mg L-1) and bismerthiazol (124 mg L-1). Generally, most of the sulfone-containing compounds and sulfoxide-containing compounds showed higher activities against Xoo than that of the corresponding thioether-containing compound, but most of the thioether-containing compounds contributed higher antibacterial activities against R. solanacearum. Furthermore, title compounds E3, E11, E24 and G2 showed good insecticidal activities of 75%, 70%, 70% and 75%, respectively.

Blue LED Mediated Intramolecular C-H Functionalization and Cyclopropanation of Tryptamines: Synthesis of Azepino[4, 5-b]indoles and Natural Product Inspired Polycyclic Indoles

We report a novel blue LED mediated intramolecular C-H functionalization of tryptamine derivatives to generate azepino[4, 5-b]indoles (4) in moderate to good yields. By altering the substitution at the tryptamine nitrogen, intramolecular cyclopropanation is achieved in high yields under the same reactions condition to provide natural product inspired polycyclic indoles (6), which are further transformed to spiropiperidino (5 and 8) indoles in decent yields. The mechanism of formation of the compounds was investigated through DFT studies.

Synthesis and Evaluation of Antimicrobial Activities of Novel N-Substituted Indole Derivatives

Indole motifs are one of the most significant scaffolds in the discovery of new drugs. We have described a synthesis of new N-substituted indole derivatives (1-3), and their in vitro antimicrobial activities were investigated. The synthesis of titled compounds has been demonstrated by utilizing commercially available starting materials. The antibacterial and antifungal activities were performed using new strains of bacteria Staphylococcus aureus, Escherichia coli, and Candida albicans using the disc diffusion method. Notably, the compound 4-(1-(2-(1H-indol-1-yl) ethoxy) pentyl)-N,N-dimethyl aniline (1) was found to be most potent than the other analogues (2 and 3), which has shown higher inhibition than the standard drug chloramphenicol.

Diversity-oriented synthesis and antifungal activities of novel pimprinine derivative bearing a 1,3,4-oxadiazole-5-thioether moiety

Based on the strategy of diversity-oriented synthesis and the structures of natural product pimprinine and streptochlorin, two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized under the optimized reaction conditions. Biological assays conducted at Syngenta showed the designed derivatives displayed an altered pattern of biological activity, of which 5h was identified as the most promising compound with strong activity against Pythium dissimile and also a broad antifungal spectrum in primary screening. Further structural optimization of pimprinine and streptochlorin derivatives is well under way, aiming to discover synthetic analogues with improved antifungal activity. Two series of novel pimprinine derivatives containing 1,3,4-oxadiazole-5-thioether moieties were efficiently synthesized through diversity-oriented synthesis strategy under the optimized conditions. Biological assays showed the designed derivatives exhibited potential activity.

Indole-core-based novel antibacterial agent targeting FtsZ

Background

The prevalence of drug-resistant bacterial infections urges the development of new antibacterial agents that possess a mechanism of action different from traditional antibiotics. FtsZ has been recognized as a key functional protein in bacterial cell division and it is currently believed to be a potential target for the development of novel antibacterial agents.

Purpose

The primary aim of the study is to screen out an inhibitor targeting at FtsZ and followed to investigate its antibacterial activity and mode of action.

Methods

Cell-based cell division inhibitory screening assay, antimicrobial susceptibility test, minimum bactericidal concentration assay, time-killing curve determination, FtsZ polymerization assay, GTPase activity assay, and molecular modeling were performed in the present study.

Results

The screening study from a small library consisting of benzimidazole and indole derivatives discovered a compound (CZ74) with an indole-core structure. The compound exhibited strong cell division inhibitory effect. In addition, CZ74 shows high antibacterial potency against a number of tested Gram-positive bacteria, such as methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus. The minimum inhibitory concentration values obtained were within the range of 2–4 µg/mL. The results of biological study revealed that CZ74 at 2 µg/mL is able to disrupt FtsZ polymerization and inhibit GTPase activity and cell division. From molecular modeling study, CZ74 is found possibly binding into the interdomain cleft of FtsZ protein and then leads to inhibitory effects.

Conclusion

This indole-cored molecule CZ74 could be a potential lead compound and could be further developed as a new generation of antibacterial agents targeting FtsZ to combat against multidrug-resistant bacteria.

Synthesis and In Vitro and In Vivo Biological Activity Evaluation and Quantitative Proteome Profiling of Oxadiazoles Bearing Flexible Heterocyclic Patterns

A novel series of simple 1,3,4-oxadiazoles that bear flexible heterocyclic patterns was prepared, and their biological activities in plant pathogenic bacteria, fungi, oomycetes, and Meloidogyne incognita in vitro and in vivo were screened to explore low-cost and versatile antimicrobial agents. Screening results showed that compounds, such as A₀, B₀, and C₄, were bioactive against Xanthomonas oryzae pv oryzae in vitro and in vivo, and such bioactivities were superior to those of commercial agents bismerthiazol and thiodiazole copper. Their antibacterial mechanisms were further investigated by quantitative proteomics and concentration-dependent scanning electron microscopy images. Antifungal results indicated that compound A₀ displayed a selective and better antifungal effect on Botrytis cinerea with inhibition rate of 96.8% at 50 μg/mL. Nematocidal bioassays suggested that compound D₁ had good in vitro nematocidal activity toward M. incognita at 24, 48, and 72 h, with the corresponding insecticidal efficiency of 48.7%, 64.1%, and 87.2% at 40 μg/mL. In vivo study further confirmed that compounds D₁ and F₂ showed nematocidal actions at 80 μg/mL with a disease index of 1.5. Given these advantages, this kind of molecular frameworks could be a suitable platform for exploring highly efficient agrochemicals.