Two New 1,3,4-Oxadiazoles With Effective Antifungal Activity Against Candida albicans

Novel 1,3,4-oxadiazole derivatives of naproxen targeting EGFR: Synthesis, molecular docking studies, and cytotoxic evaluation

The close association between inflammation and cancer inspired the synthesis of a series of 1,3,4-oxadiazole derivatives (compounds H4-A-F) of 6-methoxynaphtalene. The chemical structures of the new compounds were validated utilizing Fourier-transform infrared, proton nuclear magnetic resonance, and carbon-13 nuclear magnetic resonance spectroscopic techniques and CHN analysis. Computer-aided drug design methods were used to predict the compounds biological target, ADMET properties, toxicity, and to evaluate the molecular similarities between the design compounds and erlotinib, a standard epidermal growth factor receptor (EGFR) inhibitor. The antiproliferative effects of the new compounds were evaluated by the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay, cell cycle analysis, apoptosis detection by microscopy, quantitative reverse transcription-polymerase chain reaction, and immunoblotting, and EGFR enzyme inhibition assay. In silico analysis of the new oxadiazole derivatives indicated that these compounds target EGFR, and that compounds H4-A, H4-B, H4-C, and H4-E show similar molecular properties to erlotinib. Additionally, the results indicated that none of the synthesized compounds are carcinogenic, and that compounds H4-A, H4-C, and H4-F are nontoxic. Compound H4-A showed the best-fit score against EGFR pharmacophore model, however, the in vitro studies indicated that compound H4-C was the most cytotoxic. Compound H4-C caused cytotoxicity in HCT-116 colorectal cancer cells by inducing both apoptosis and necrosis. Furthermore, compounds H4-D, H4-C, and H4-B had potent inhibitory effect on EGFR tyrosine kinase that was comparable to erlotinib. The findings of this inquiry offer a basis for further investigation into the differences between the synthesized compounds and erlotinib. However, additional testing will be needed to assess all of these differences and to identify the most promising compound for further research.

Chemical composition, antifungal, and anti-virulence action of the stem bark of Hancornia speciosa Gomes (Apocynaceae) against Candida spp

ETHNOPHARMACOLOGICAL RELEVANCE

Hancornia speciosa Gomes is a fruit and medicinal species used for treating infectious diseases of the genitourinary system. However, its mechanism of action against microbes is still not fully understood. Infections in the genitourinary system caused by Candida spp. are associated with its fungal resistance and pathogenicity. New plant-derived compounds are an alternative to fight these Candida infections.

AIM OF THE STUDY

The objective of this study was to evaluate the anti-Candida effects of extracts of the stem bark of H. speciosa. This research investigated the chemical composition of sulfuric ether (EEHS) and methanolic (MEHS) extracts, their drug-modifying action on fluconazole, and their anti-virulence action on the morphological transition of Candida species.

MATERIALS AND METHODS

The extracts (EEHS and MEHS) of the stem bark of H. speciosa were chemically characterized via qualitative phytochemical screening and by liquid chromatography coupled with mass spectrometry (UPLC-MS-ESI-QTOF). The extracts were evaluated regarding their antifungal effects and fluconazole-modifying activity against Candida albicans, Candida krusei, and Candida tropicalis using the broth microdilution method. Additionally, the study evaluated the inhibition of fungal virulence in Candida species through morphological transition assays.

RESULTS

The phytochemical screening revealed the presence of anthocyanidins, anthocyanins, aurones, catechins, chalcones, flavones, flavonols, flavanones, leucoanthocyanidins, tannins (condensed and pyrogallic), and xanthones in both extracts of the stem bark of H. speciosa. The UPLC-MS-ESI-QTOF analysis identified the same compounds in both extracts, predominating phenolic compounds. Some compounds were first time recorded in this species: gluconic acid, cinchonain IIb, cinchonain Ib isomer, and lariciresinol hexoside isomers. Most of the intrinsic antifungal activity was observed for the MEHS against C. krusei (IC50: 58.41 μg/mL). At subinhibitory concentrations (MC/8), the EEHS enhanced the action of fluconazole against all Candida strains. The MEHS exhibited greater efficacy than fluconazole inhibiting C. krusei growth. The EEHS completely inhibited hyphae appearance and reduced pseudohyphae formation in C. albicans.

CONCLUSION

The stem bark of H. speciosa is a rich source of bioactive compounds, especially phenolic. Phenolic compounds can have important roles in fighting infectious diseases of the genitourinary system, such as candidiasis. The extracts of H. speciosa improved the action of the drug fluconazole against Candida species, inhibited hyphae appearance, and reduced pseudohyphae formation. The results of this study can support the development of new therapeutics against resistant strains of Candida.

"Antibacterial effect and possible mechanism of action of 1,3,4-oxadiazole in Staphylococcus aureus"

Staphylococcus aureus is one of the main etiological agents causing foodborne diseases, and the development of new antibacterial agents is urgent. This study evaluated the antibacterial activity and the possible mechanism of action of the 1,3,4-oxadiazole LMM6 against S. aureus. The minimum inhibitory concentration (MIC) of LMM6 ranged from 1.95 to 7.81 µg ml-1. The time-kill assay showed that 48-h treatment at 1× to 8× MIC reduced S. aureus by 4 log colony forming unit (CFU), indicating a bacteriostatic effect. Regarding the possible mechanism of action of LMM6, there was accumulation of reactive oxygen species (ROS) and an increase in the absorption of crystal violet (∼50%) by the cells treated with LMM6 at 1× and 2× MIC for 6-12 h. In addition, there was increased propidium iodide uptake (∼84%) after exposure to LMM6 for 12 h at 2× MIC. After 48 h of treatment, 100% of bacteria had been injured. Scanning electron microscopy observations demonstrated that LMM6-treated cells were smaller compared with the untreated group. LMM6 exhibited bacteriostatic activity and its mechanism of action involves increase of intracellular ROS and disturbance of the cell membrane, which can be considered a key target for controlling the growth of S. aureus.

Anti-inflammatory and Antimicrobial Potential of 1, 3, 4-oxadiazoles and its Derivatives: A Review

1, 3, 4-oxadiazole and its derivatives have significant anti-inflammatory and antimicrobial property. Their precise mechanism of action is not known but it is postulated that they act by inhibiting the biosynthesis of certain prostaglandins. 1, 3, 4-oxadiazoles are a class of heterocyclic compounds with wide variety of biological and pharmacological activities. They have been reported to possess analgesic, antimicrobial, antipyretic and anti-inflammatory properties. These compounds are also active against a number of other inflammatory conditions such as arthritis, gout etc. A wide variety of these compounds have been synthesized and some of them are under clinical trials. In this review article, anti-inflammatory and antimicrobial activity of the 1, 3, 4- oxadiazole shall be discussed.

2-Substituted-3-(5-Substituted-1,3,4-oxadiazol/thiadiazol-2-yl) Thiazolidin-4-one Derivatives: Synthesis, Anticancer, Antimicrobial, and Antioxidant Potential

In this innovative research, a novel series of thiazolidin-4-one analogues having a 1,3,4-oxadiazole/thiadiazole moiety were derived and the structures of all the newly obtained molecules were established using different physicochemical and analytical means (¹H-NMR, FTIR, mass spectra, and elemental analyses). The synthesized molecules were then investigated for their antiproliferative, antimicrobial, and antioxidant potential. The cytotoxicity screening studies revealed that analogues D-1, D-6, D-15, and D-16 possessed comparable efficacy, within the IC₅₀ range (1 to 7 μM), when taking doxorubicin as a reference drug (IC₅₀ = 0.5 μM). The antimicrobial activity was assessed using different Gram-(+) and Gram-(-) bacterial and fungal strains and the results revealed that molecules D-2, D-4, D-6, D-19, and D-20 possessed potent activity against selective strains of microbes with MIC ranges of 3.58 to 8.74 µM. The antioxidant evaluation was performed using the DPPH assay and the screening results revealed that analogue D-16 was the most potent derivative (IC₅₀ = 22.3 µM) when compared with the positive control, ascorbic acid (IC₅₀ = 111.6 µM). Structure-activity relationship (SAR) studies of the synthesized novel derivatives revealed that para-substituted halogen and hydroxy derivatives have remarkable potential against the MCF-7 cancer cell line and antioxidant potential. Similarly, electron-withdrawing groups (Cl/NO₂) and -donating groups at the para position possess moderate to promising antimicrobial potential.

Synthesis, crystal structure and Hirshfeld surface analysis of a zinc(II) coordination polymer of 5-phenyl-1,3,4-oxadiazole-2-thiolate

The mol­ecular and crystal structure of a zinc coordination polymer with 5-phenyl-1,3,4-oxa­diazole-2-thiol­ate were studied and Hirshfeld surfaces and fingerprint plots were generated to investigate various inter­molecular inter­actions.

A new zinc coordination polymer with 5-phenyl-1,3,4-oxa­diazole-2-thiol­ate, namely, catena-poly[zinc(II)-bis­(μ₂-5-phenyl-1,3,4-oxa­diazole-2-thiol­ato)-κ²N³:S;κ²S:N³], [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 Zn^II 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 Zn^II atoms and two ligand mol­ecules. 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. Inter­actions 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.

New 1,3,4-oxadiazole compound with effective antibacterial and antibiofilm activity against Staphylococcus aureus

Staphylococcus aureus is one of the main aetiological agents causing food-borne diseases. Some strains produce enterotoxins responsible for food poisoning. In addition, they can form biofilms on several surfaces such as plastics, glass and stainless steel making it difficult to eliminate them. The present study evaluated, for the first time, the antibacterial and antibiofilm activities of the synthetic compound LMM6 against S. aureus. The minimum inhibitory concentration was 0·97, 1·95 and 1·95 μg ml^-1 against S. aureus ATCC 25923, S. aureus 629/94 and S. aureus FRI S-6, respectively. The time-kill curves showed that 96 h treatment with LMM6 reduced approximately 4 log CFU per ml at all tested concentrations. Furthermore, LMM6 reduced S. aureus preformed biofilm by approximately 1 log CFU per cm² . During biofilm formation, a reduction of approximately 4 log CFU per cm² was observed. LMM6 also reduced biofilm biomass during (~60%) and after biofilm formation (~25 to 45%), as shown by the crystal violet assay. Based on these results, we conclude that LMM6 exhibits antibacterial and antibiofilm activity and may be an innovative synthetic molecule for controlling S. aureus.

Potential Synthetic Routes and Metal-Ion Sensing Applications of 1,3,4-Oxadiazoles: An Integrative Review

Oxadiazoles, especially 1,3,4-oxadiazole scaffolds, stand among the foremost heterocyclic fragments with a broad spectrum of applications in diverse fields, including pharmacology, polymers, material science, and organic electronics, among others. In this comprehensive review, we summarize the pivotal synthetic strategies for 1,3,4-oxadiazole derivatives including dehydrogenative cyclization of 1,2-diacylhydrazines, oxidative cyclization of acylhydrazones, condensation cyclization, C-H activation of oxadiazole ring, decarboxylative cyclization and oxidative annulation along with plausible mechanisms. The set of 1,3,4-oxadiazoles selected from the literature and discussed herein epitomize the ease of synthesis as well as the possibility of linking π-conjugated groups; thereby encouraging the use of these molecules as important starting building blocks for a wide variety of fluorescent frameworks, particularly in the development of potential chemosensors. High photoluminescent quantum yield, excellent thermal and chemical stability, and the presence of potential coordination (N and O donor atoms) sites make these molecules a prominent choice for metal-ions sensors. An overview of selective metal-ion sensing, the detection limit along with the sensing mechanisms (photo-induced electron transfer, excited-state intramolecular proton transfer, and complex formation) is also included.

Fungicidal Activity of a Safe 1,3,4-Oxadiazole Derivative Against Candida albicans

Candida albicans is the most common species isolated from nosocomial bloodstream infections. Due to limited therapeutic arsenal and increase of drug resistance, there is an urgent need for new antifungals. Therefore, the antifungal activity against C. albicans and in vivo toxicity of a 1,3,4-oxadiazole compound (LMM6) was evaluated. This compound was selected by in silico approach based on chemical similarity. LMM6 was highly effective against several clinical C. albicans isolates, with minimum inhibitory concentration values ranging from 8 to 32 µg/mL. This compound also showed synergic effect with amphotericin B and caspofungin. In addition, quantitative assay showed that LMM6 exhibited a fungicidal profile and a promising anti-biofilm activity, pointing to its therapeutic potential. The evaluation of acute toxicity indicated that LMM6 is safe for preclinical trials. No mortality and no alterations in the investigated parameters were observed. In addition, no substantial alteration was found in Hippocratic screening, biochemical or hematological analyzes. LMM6 (5 mg/kg twice a day) was able to reduce both spleen and kidneys fungal burden and further, promoted the suppresses of inflammatory cytokines, resulting in infection control. These preclinical findings support future application of LMM6 as potential antifungal in the treatment of invasive candidiasis.

One Century of Study: What We Learned about Paracoccidioides and How This Pathogen Contributed to Advances in Antifungal Therapy

Paracoccidioidomycosis (PCM) is a notable fungal infection restricted to Latin America. Since the first description of the disease by Lutz up to the present day, Brazilian researchers have contributed to the understanding of the life cycle of this pathogen and provided the possibility of new targets for antifungal therapy based on the structural and functional genomics of Paracoccidioides. In this context, in silico approaches have selected molecules that act on specific targets, such as the thioredoxin system, with promising antifungal activity against Paracoccidioides. Some of these are already in advanced development stages. In addition, the application of nanostructured systems has addressed issues related to the high toxicity of conventional PCM therapy. Thus, the contribution of molecular biology and biotechnology to the advances achieved is unquestionable. However, it is still necessary to transcend the boundaries of synthetic chemistry, pharmaco-technics, and pharmacodynamics, aiming to turn promising molecules into newly available drugs for the treatment of fungal diseases.

Overview of Antifungal Drugs against Paracoccidioidomycosis: How Do We Start, Where Are We, and Where Are We Going?

Paracoccidioidomycosis is a neglected disease that causes economic and social impacts, mainly affecting people of certain social segments, such as rural workers. The limitations of antifungals, such as toxicity, drug interactions, restricted routes of administration, and the reduced bioavailability in target tissues, have become evident in clinical settings. These factors, added to the fact that Paracoccidioidomycosis (PCM) therapy is a long process, lasting from months to years, emphasize the need for the research and development of new molecules. Researchers have concentrated efforts on the identification of new compounds using numerous tools and targeting important proteins from Paracoccidioides, with the emphasis on enzymatic pathways absent in humans. This review aims to discuss the aspects related to the identification of compounds, methodologies, and perspectives when proposing new antifungal agents against PCM.

Impact of serial systemic infection on Candida albicans virulence factors

Aim: To evaluate changes in virulence and pathogenicity approaches from Candida albicans after successive passages in a murine model of systemic candidiasis. Materials & methods: Phenotypic assays were performed using colonies recovered from animals infected serially, totalizing five passages. Results: A progressive infection was observed along the passages, with increased fungal burden and the presence of greater inflammatory areas in the histopathological findings. Recovered strains exhibited increased filamentation and biofilm abilities, along with modulation of phospholipase and proteinase activities. Conclusion: Repeated contact between yeast and host increased the expression of virulence factors. Furthermore, a correspondence between phenotypic profile and proteomic data obtained previously was observed.

Antibacterial activity of Barbatimão (Stryphnodendron adstringens) against Staphylococcus aureus: in vitro and in silico studies

We evaluated the activity of the aqueous fraction and the ethyl acetate fraction of Stryphnodendron adstringens against Staphylococcus aureus and proposed their mechanism of action. The antibacterial activity of S. adstringens fractions was evaluated against S. aureus and the cell targets were rated by docking. The fractions showed moderate antibacterial activity against S. aureus without toxicity on two mammalian cell lines. They also showed synergistic antibacterial activity with tannic acid (TA). In silico assays indicated FabG, FabZ and FabI as probable targets. The metabolic pathway for fatty acid biosynthesis in S. aureus was affected by components of S. adstringens. The synergistic effect when combining TA with S. adstringens fractions suggests a natural alternative to S. aureus control. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first study describing the possible targets of action of Stryphnodendron adstringens on Staphylococcus aureus. Molecular dynamics simulations showed that the components of S. adstringens affected the metabolic pathway for fatty acid biosynthesis (FAS II) in S. aureus, inhibiting the FabI, FabG and FabZ enzymes. As tannic acid (TA) is a known inhibitor of some targets identified, we showed synergistic antibacterial activity of S. adstringens in combination with TA. This combination did not show toxicity against HaCaT and Vero cells and based on all these results we suggest that S. adstringens can be a natural and sustainable alternative to S. aureus control.

In vitro and in vivo activity of a possible novel antifungal small molecule against Candida albicans

Nosocomial infections by fungi are important causes of morbidity and mortality, and the adhesion capacity of yeast on abiotic and biotic surfaces has been considered an important step in this process. Als3 proteins are widely studied for their ability to allow Candida albicans to bind to various surfaces. The objective of the present study was to verify, with more details, the action of F2768-0318 in relation to its antifungal activity as well as its ability to act on C. albicans virulence factors related to adhesion and biofilm formation in vitro and in vivo by inhibiting the Als3 protein. F2768-0318 was assessed in tests of biofilm formation and adhesion on abiotic surfaces (polystyrene plates) and adherence on biotic surfaces, including human endocervical (HeLa) cells, human umbilical vein endothelial cells (HUVECs), and fresh buccal epithelial cells (BEC). Our results showed F2768-0318 was useful in reducing the adhesion and biofilm formation of C. albicans on abiotic surfaces, indicating the possibility of treating hospital materials and preventing biofilm formation on these types of equipment. Further studies are still needed, including optimization of the molecule to allow this molecule to be effective on other types of surfaces, such as human cells.

Promising antifungal activity of new oxadiazole against Candida krusei

Candida krusei is one of the most common agents of invasive candidiasis and candidemia worldwide, leading to high morbidity and mortality rates. This species has become a problem due to its intrinsic resistance and reduced susceptibility to azoles and polyenes. Moreover, the number of antifungal drugs available for candidiasis treatment is limited, demonstrating the urgent need for the discovery of novel alternative therapies. In this work, the in vivo and in vitro activities of a new oxadiazole (LMM11) were evaluated against C. krusei. The minimum inhibitory concentration ranged from 32 to 64 μg/mL with a significant reduction in the colony forming unit (CFU) count (~3 log₁₀). LMM11 showed fungicidal effect, similar to amphotericin, reducing the viable cell number (>99.9%) in the time-kill curve. Yeast cells presented morphological alterations and inactive metabolism when treated with LMM11. This compound was also effective in decreasing C. krusei replication inside and outside macrophages. A synergistic effect between fluconazole and LMM11 was observed. In vivo treatment with the new oxadiazole led to a significant reduction in CFU (0.85 log₁₀). Furthermore, histopathological analysis of the treated group exhibited a reduction in the inflammatory area. Taken together, these results indicate that LMM11 is a promising candidate for the development of a new antifungal agent for the treatment of infections caused by resistant Candida species such as C. krusei.