A structure–activity relationship study of flavonoids as inhibitors of E. coli by membrane interaction effect

Flavonoids exhibit a broad range of biological activities including antibacterial activity. However, the mechanism of their antibacterial activity has not been fully investigated. The antibacterial activity and membrane interaction of 11 flavonoids (including 2 polymethoxyflavones and 4 isoflavonoids) against Escherichia coli were examined in this study. The antibacterial capacity was determined as flavonoids > polymethoxyflavones > isoflavonoids. Using fluorescence, it was observed that the 5 flavonoids rigidified the liposomal membrane, while the polymethoxyflavones and isoflavonoids increased membrane fluidity. There was a significant positive correlation between antibacterial capacity and membrane rigidification effect of the flavonoids. A quantitative structure–activity relationship (QSAR) study demonstrated that the activity of the flavonoid compounds can be related to molecular hydrophobicity (CLogP) and charges on C atom at position3 (C3). The QSAR model could be used to predict the antibacterial activity of flavonoids which could lead to natural compounds having important use in food and medical industry.     

Reduction of leptin secretion by soy isoflavonoids in murine adipocytes in vitro

Daidzein and genistein are the main aglycones of soy isoflavonoid, and have many useful activities in vitro and in vivo. However, equol, a metabolite of daidzein in vivo, has attracted attention due to its stronger activity than that of the naturally occurring isoflavonoids. We subjected the soy isoflavonoids, including the naturally occurring (S)-equol, to mouse adipocytes, and compared the inhibitory activity on the leptin secretion. Equol, daidzein and genistein inhibited the leptin secretion, whereas O-desmethylangolensin had a lower activity. The inhibitory activity of the isoflavones was not affected by the addition of an iNOS inhibitor and an estrogen.     

Efficiency of newly prepared thiazole derivatives against some cutaneous fungi

A series of fourteen novel synthesized arylazothiazole and arylhydrazothiazole derivatives were tested for their antifungal activity and structure-activity relationship. The activity of the compounds depends mainly on the side chains of the nucleus compound. The antifungal activity was more significant when both side chains are aromatic?>?one aromatic and one aliphatic and substituted aromatic with CH₃ or OCH₃?>?non-substituted?>?substituted aromatic with chloro- or nitro-groups. Thiazole derivatives 7a, 7c, 7e, 7f, 7?g, 7i, 7?m, and 11a showed the most effective as antifungal compounds and were comparable with fluconazole as antifungal reference drug when investigated against Candida albicans, Microsporum gypseum and Trichophyton mentagrophytes. The minimum inhibitory concentration (MIC) reached 2?µg/mL in the case of C. albicans for compounds 7a, 7b, 7c and 11a and measured 4?µg/mL in the case of M. gypseum and T. mentagrophytes for the same compounds. The minimum fungicidal concentration (MFC) for the same compounds was 4?µg/mL for C. albicans and ranged from 8 to 32?µg/mL for the other two fungi. The results revealed that compounds 7c and 11a were the most antifungal compounds against the test fungi regarding keratinase activity and ergosterol biosynthesis. The in vivo efficacy of synthesized thiazoles 7c and 11a applied at their respective MFC was more effective in the treatment of skin infection of guinea pigs previously inoculated with the test fungi as compared with fluconazole. The Molecular Operating Environment (MOE) software was used to analyze the docking poses and binding energies of compound 11a and keratinase. The computational studies supported the biological activity results.     

Insect feeding deterrent activity of phytoalexin isoflavonoids

When incorporated into an agar-cellulose medium containing feeding stimulants, phytoalexin isoflavonoids from several legumes show feeding deterrent activity against larvae of the insect Costelytra zealandica and Heteronychus arator. The levels at which these compounds deter feeding are of the same order of magnitude as those at which they reduce fungal growth. The most active compound tested was phaseollin. These results suggest that phytoalexin isoflavonoids show a dual acitvity against insects and fungi.     

Antifungal Activity of Isothiocyanates and Related Compounds: I. Naturally Occurring Isothiocyanates and Their Analogues

Data are presented concerning the antifungal activity of 11 natural isothiocyanates and 27 synthetized analogues in Aspergillus niger, Penicillium cyclopium, and Rhizopus oryzae, as well as in 13 additional saprophytic and parasitic fungi. A remarkable antifungal activity was observed in some analogues of benzylisothiocyanate and β-phenylethylisothiocyanate. The latter-mentioned compounds have not been described previously. In the group of benzylisothiocyanates, a correlation, which was inversely proportional, was detected between ed₁₀₀ values for A. niger and R. oryzae and the corresponding molar solubilities of compounds in water. In contradistinction, no relationship was observed between antifungal activity and chemical reactivity of investigated derivatives.     

Chemotaxis and nod Gene Activity of Bradyrhizobium japonicum in Response to Hydroxycinnamic Acids and Isoflavonoids

For Bradyrhizobium japonicum, the chemotactic and the nod gene-inducing effects of hydroxycinnamic acids and two of their derivatives were compared with those of isoflavonoids. Only the hydroxycinnamic acids were strong chemoattractants, while the other substances tested were chemotactically inactive. Besides the known nod gene induction by isoflavonoids, a weak nod gene induction by coniferyl alcohol, chlorogenic acid, and ferulic acid was found.     

Dolichins A and B,two pterocarpans from bacteria-treated leaves of Dolichos biflorus

Two minor isoflavonoids isolated from bacteria-inoculated leaves of Dolichos biflorus have been identified as the 6aR; 11aR; 2′S and 6aR; 11aR; 2′S isomers of 3,9-dihydroxy-10-2′-hydroxy-3′-methyl-3′-butenyl pterocarpan.     

Synthesis and evaluation of novel azoles as potent antifungal agents

Using a rational approach to the design of antifungal agents, a series of azole agents with 1,3,4-oxadiazole side chains were designed and synthesized. The results of preliminary in vitro antifungal tests with eight human pathogenic compounds showed that all of the title compounds exhibited excellent activities against all of the tested fungi except Aspergillus fumigatus. Compounds 11e and 11f were found to be the most effective, with a minimum inhibitory concentration of 0.0039 μg/mL, followed by voriconazole, which has a MIC of 0.0625 μg/mL. The 1,3,4-oxadiazole side chain is not the major contributor but plays a role in eliciting the observed antifungal activity.     

Repurposing approach identifies new treatment options for invasive fungal disease

Drug repositioning is the process of discovery, validation and marketing of previously approved drugs for new indications. Our aim was drug repositioning, using ligand-based and structure-based computational methods, of compounds that are similar to two hit compounds previously selected by our group that show promising antifungal activity. Through the ligand-based method, 100 compounds from each of three databases (MDDR, DrugBank and TargetMol) were selected by the Tanimoto coefficient, as similar to LMM5 or LMM11. These compounds were analyzed by the scaffold trees, and up to 10 compounds from each database were selected. The structure-based method (molecular docking) using thioredoxin reductase as the target drug was performed as a complementary approach, resulting in six compounds that were tested in an in vitro assay. All compounds, particularly raltegravir, showed antifungal activity against the genus Paracoccidioides. Raltegravir, an antiviral drug, showed promising antifungal activity against the experimental murine paracoccidioidomycosis, with significant reduction of the fungal burden and decreased alterations in the lung structure of mice treated with 1 mg/kg of raltegravir. In conclusion, the combination of two in silico methods for drug repositioning was able to select an antiviral drug with promising antifungal activity for treatment of paracoccidioidomycosis.     

Scaffold hopping of sampangine: Discovery of potent antifungal lead compound against Aspergillus fumigatus and Cryptococcus neoformans

Discovery of novel antifungal agents against Aspergillus fumigatus and Cryptococcus neoformans remains a significant challenge in current antifungal therapy. Herein the antifungal natural product sampangine was used as the lead compound for novel antifungal drug discovery. A series of D-ring scaffold hopping derivatives were designed and synthesized to improve antifungal activity and water solubility. Among them, the thiophene derivative S2 showed broad-spectrum antifungal activity, particularly for Aspergillus fumigatus and Cryptococcus neoformans. Moreover, compound S2 also revealed better water solubility than sampangine, which represents a promising antifungal lead compound for further structural optimization.     

Characterization of Genes Involved in Biosynthesis of a Novel Antibiotic from Burkholderia cepacia BC11 and Their Role in Biological Control of Rhizoctonia solani

Genetic manipulation of fluorescent pseudomonads has provided major insight into their production of antifungal molecules and their role in biological control of plant disease. Burkholderia cepacia also produces antifungal activities, but its biological control activity is much less well characterized, in part due to difficulties in applying genetic tools. Here we report genetic and biochemical characterization of a soil isolate of B. cepacia relating to its production of an unusual antibiotic that is very active against a variety of soil fungi. Purification and preliminary structural analyses suggest that this antibiotic (called AFC-BC11) is a novel lipopeptide associated largely with the cell membrane. Analysis of conditions for optimal production of AFC-BC11 indicated stringent environmental regulation of its synthesis. Furthermore, we show that production of AFC-BC11 is largely responsible for the ability of B. cepacia BC11 to effectively control the damping-off of cotton caused by the fungal pathogen Rhizoctonia solani in a gnotobiotic system. Using Tn5 mutagenesis, we identified, cloned, and characterized a region of the genome of strain BC11 that is required for production of this antifungal metabolite. DNA sequence analysis suggested that this region encodes proteins directly involved in the production of a nonribosomally synthesized lipopeptide.     

Diversities in Virulence,Antifungal Activity,Pigmentation and DNA Fingerprint among Strains of Burkholderia glumae

Burkholderia glumae is the primary causal agent of bacterial panicle blight of rice. In this study, 11 naturally avirulent and nine virulent strains of B. glumae native to the southern United States were characterized in terms of virulence in rice and onion, toxofalvin production, antifungal activity, pigmentation and genomic structure. Virulence of B. glumae strains on rice panicles was highly correlated to virulence on onion bulb scales, suggesting that onion bulb can be a convenient alternative host system to efficiently determine the virulence of B. glumae strains. Production of toxoflavin, the phytotoxin that functions as a major virulence factor, was closely associated with the virulence phenotypes of B. glumae strains in rice. Some strains of B. glumae showed various levels of antifungal activity against Rhizoctonia solani, the causal agent of sheath blight, and pigmentation phenotypes on casamino acid-peptone-glucose (CPG) agar plates regardless of their virulence traits. Purple and yellow-green pigments were partially purified from a pigmenting strain of B. glumae, 411gr-6, and the purple pigment fraction showed a strong antifungal activity against Collectotrichum orbiculare. Genetic variations were detected among the B. glumae strains from DNA fingerprinting analyses by repetitive element sequence-based PCR (rep-PCR) for BOX-A1R-based repetitive extragenic palindromic (BOX) or enterobacterial repetitive intergenic consensus (ERIC) sequences of bacteria; and close genetic relatedness among virulent but pigment-deficient strains were revealed by clustering analyses of DNA fingerprints from BOX-and ERIC-PCR.     

Desert legume Prosopis cineraria as a novel source of antioxidant flavonoids / isoflavonoids: Biochemical characterization of edible pods for potential functional food development

Flavonoids and isoflavonoids in foods are attracting attention as they are significant antioxidant and phytoestrogenic compounds that are beneficial for human health. In this study, the edible pods of the underutilized desert legume Prosopis cineraria from Rajasthan, India were used to extract flavonoids. The pods from semi-arid zone showed the highest flavonoid content (432 mg Rutin hydrate/gm). UV spectrophotometric analysis was also done to characterize flavonoids. The flavonoids and isoflavonoids were further purified from semi-arid zone plants using column chromatography with Amberlite XAD7HP and Sephadex LH-20. LC-MS analysis revealed the presence of medicinally valuable antioxidant flavonoids and isoflavonoids in the pods, viz. vitexin, puerarin, phloridzin, and daidzein. It was seen that the flavonoids/isoflavonoids are present in the selected legume in different forms i.e. pure aglycone, C-glycoside as well as O-glycoside. This finding makes P. cineraria an attractive source candidate for extraction of these nutraceuticals with a potential for development into functional food.     

Mesoionic compounds with antifungal activity against Fusarium verticillioides

Background

Fungi contaminate the food of humans and animals, are a risk to health, and can cause financial losses. In this work, the antifungal activities of 16 mesoionic compounds (MI 1–16) were evaluated against mycotoxigenic fungi, including Aspergillus spp., Fusarium verticillioides and Penicillium citrinum. Furthermore, the decreased ergosterol in the total lipid content of Fusarium verticillioides was investigated.

Results

F. verticillioides was the most sensitive fungus to the mesoionic compounds. Among the evaluated compounds, MI-11 and MI-16 presented higher antifungal effects against F. verticillioides, with MIC values of 7.8 μg/ml, and MI-2 and MI-3 followed, with MICs of 15.6 μg/ml. The most active compounds were those with heterocyclic ring phenyl groups substituted by electron donor moieties (MI-11 and MI-16). Among some compounds with higher activity (MI-2, MI-11 and MI-16), decreased ergosterol content in the total lipid fraction of F. verticillioides was demonstrated. MI-2 reduced the ergosterol content approximately 40% and 80% at concentrations of 7.8 μg/ml and 15.6 μg/ml, respectively, and MI-11 and MI-16 decreased the content by 30% and 50%, respectively, when at a concentration of 7.8 μg/ml.

Conclusion

These findings indicate that mesoionic compounds have significant antifungal activity against F. verticillioides.     

Laboratory assessment of entomopathogenic nematode symbiotic bacteria to control maize pest,Ostrinia furnacalis,and fungi diseases,Bipolaris maydis and Curvularia lunata

The application of entomopathogenic nematodes (EPN) and their symbiotic bacteria as biological control approaches depend on their lethal parasites to pest and antifungal activities against plant pathogenic fungi. We have collected 23 symbiotic bacterial strains from 23 EPN isolates gathered from different regions of China. In the present study, the insecticidal and antifungal activities of all these bacterial isolates were evaluated in the laboratory. Bioassay results showed that the broth and crude extract of all these 23 EPN symbiotic bacteria strains have, to a certain extent, oral insecticidal activity and/or growth inhibition to the larvae of Ostrinia furnacalis and antifungal activity against Bipolaris maydis and Curvularia lunata. Among these strains, SY5 exhibited highest insecticidal and antifungal activities to O. furnacalis, B. maydis and C. lunata. The adversity resistance of strain SY5 showed that the antifungal activity of the broth was more stable than the insecticidal activity, and the stability of antifungal activity to B. maydis and C. lunata was different.     

Lactobacillus coryniformis subsp. coryniformis Strain Si3 Produces a Broad-Spectrum Proteinaceous Antifungal Compound

The antifungal activity spectrum of Lactobacillus coryniformis subsp. coryniformis strain Si3 was investigated. The strain had strong inhibitory activity in dual-culture agar plate assays against the molds Aspergillus fumigatus, A. nidulans, Penicillium roqueforti, Mucor hiemalis, Talaromyces flavus, Fusarium poae, F. graminearum, F. culmorum, and F. sporotrichoides. A weaker activity was observed against the yeasts Debaryomyces hansenii, Kluyveromyces marxianus, and Saccharomyces cerevisiae. The yeasts Rhodotorula glutinis, Sporobolomyces roseus, and Pichia anomala were not inhibited. In liquid culture the antifungal activity paralleled growth, with maximum mold inhibition early in the stationary growth phase, but with a rapid decline in antifungal activity after 48 h. The addition of ethanol to the growth medium prevented the decline and gave an increased antifungal activity. The activity was stable during heat treatment and was retained even after autoclaving at 121°C for 15 min. Maximum activity was observed at pH values of between 3.0 and 4.5, but it decreased rapidly when pH was adjusted to a level between 4.5 and 6.0 and was lost at higher pH values. The antifungal activity was fully regained after readjustment of the pH to the initial value (pH 3.6). The activity was irreversibly lost after treatment with proteolytic enzymes (proteinase K, trypsin, and pepsin). The antifungal activity was partially purified using ion-exchange chromatography and (NH₄)₂SO₄ precipitation, followed by gel filtration chromatography. The active compound(s) was estimated to have a molecular mass of approximately 3 kDa. This is the first report of the production of a proteinaceous antifungal compound(s) from L. coryniformis subsp. coryniformis.     

The In Vitro Antifungal Activity of Sudanese Medicinal Plants against Madurella mycetomatis,the Eumycetoma Major Causative Agent

Eumycetoma is a debilitating chronic inflammatory fungal infection that exists worldwide but it is endemic in many tropical and subtropical regions. The major causative organism is the fungus Madurella mycetomatis. The current treatment of eumycetoma is suboptimal and characterized by low cure rate and high recurrence rates. Hence, an alternative therapy is needed to address this. Here we determined the antifungal activity of seven Sudanese medicinal plant species against Madurella mycetomatis. Of these, only three species; Boswellia papyrifera, Acacia nubica and Nigella sativa, showed some antifungal activity against M. mycetomatis and were further studied. Crude methanol, hexane and defatted methanol extracts of these species were tested for their antifungal activity. B. papyrifera had the highest antifungal activity (MIC50 of 1 ug/ml) and it was further fractionated. The crude methanol and the soluble ethyl acetate fractions of B. papyrifera showed some antifungal activity. The Gas-Liquid-Chromatography hybrid Mass-Spectrophotometer analysis of these two fractions showed the existence of beta-amyrin, beta-amyrone, beta-Sitosterol and stigmatriene. Stigmatriene had the best antifungal activity, compared to other three phytoconstituents, with an MIC-50 of 32 μg/ml. Although the antifungal activity of the identified phytoconstituents was only limited, the antifungal activity of the complete extracts is more promising, indicating synergism. Furthermore these plant extracts are also known to have anti-inflammatory activity and can stimulate wound-healing; characteristics which might also be of great value in the development of novel therapeutic drugs for this chronic inflammatory disease. Therefore further exploration of these plant species in the treatment of mycetoma is encouraging.     

Synthesis and antifungal activity of benzofuran-5-ols

Benzofuran-5-ol derivatives were synthesized and tested for in vitro antifungal activity against Candida, Aspergillus species, and Cryptococcus neoformans. Among them tested, many benzofuran-5-ols showed good antifungal activity. The results suggest that benzofuran-5-ols would be promising antifungal agents.     

The influence of the rolC gene on isoflavonoid production in callus cultures of Maackia amurensis

The polyphenolic complex of Maackia amurensis, as well as a complex of isoflavonoids from M. amurensis callus cultures, display strong hepatoprotective effects in experimental animal and human studies. To increase the yield of polyphenols in cultures of M. amurensis, calli were transformed with the rolC gene as well as with an empty vector that was used as a control. HPLC analysis revealed that the transgenic cultures produced the same complex of isoflavonoids. The complex consisted of 20 compounds, including isoflavones and their glucosides as well as pterocarpans and their glucosides. The cultures transformed with either the empty vector or the rolC gene construct produced on average 1.22 % dry weight (DW) and 1.39 % DW of isoflavonoids, respectively. Isoflavonoid production in the transformed callus lines carrying the empty vector and the rolC gene construct reached 106 and 146 mg/L, respectively. Moreover, the rolC gene construct promoted cell growth and overall cell productivity. The transgenic callus lines expressing the rolC gene exhibited higher levels of the following six isoflavonoids: daidzein, calycosin, formononetin, 4′-Ο-β-glucopyranosyldaidzin, maackiain and 6′-O-malonyl-3-O-β-D-glucopyranosylmaackiain. However, lower levels of genistin were observed in rolC calli than in those carrying the empty vector.