New Insights into the Anti-Oomycete Mechanisms of a Leaf Extract from Glycyrrhiza glabra Against Pseudoperonospora cubensis

Cucurbit downy mildew, caused by Pseudoperonospora cubensis, is responsible for high economic losses worldwide in cucumber production. Synthetic pesticides or copper-based products are still important tools to manage the disease. However, the pathogen has developed resistance against common fungicides rather quickly, and there is a need for alternative plant-protecting agents. Glycyrrhiza glabra leaf extract is known for its antifungal activity and was highly effective in former bioassays and semi-commercial trials against downy mildew of cucumber. To elucidate the active ingredients and the mode of action, licorice leaf extract was here fractionated into five fractions (F1 to F5) with a newly developed and optimized separation process via flash chromatography. The crude extract (P1) and fraction F1 inhibited the zoospore release from sporangia, the zoospore germination, and germ tube development of P. cubensis almost completely on two cucumber cultivars, one tolerant and one susceptible to the pathogen. Infestation rates were reduced between 73 and 96%. F1 contained three previously reported antifungal polyphenols: glabranin, pinocembrin, and licoflavanon. Here, we report an additional new compound, naringenin. Furthermore, F5 is found here to show some protective effects against P. cubensis, based on either direct fungicidal or indirect effects via the host plant. The presented results show that licorice leaf extract can serve as an alternative plant protection agent, able to manage P. cubensis infestation on cucumber cultivars with differing levels of susceptibility by interfering with important early stages in the pathogen development.

Multi-dimensional preparation of Thymus quinquecostatus Celak. by normal-phase flash chromatography coupled to counter-current chromatography

In this study, a multi-dimensional chromatography system was developed by integrating normal-phase flash chromatography and counter-current chromatography to isolate flavonoids, phenylpropanoids, and thymol from the aerial parts of Thymus quinquecostatus Celak. In the online multi-dimensional switching system, a normal-phase flash chromatograph packed with 1.2 g of dry homogeneous silica gel mixture (containing 600 mg of methanol extract) was connected to counter-current chromatography via a six-port valve. Two two-dimensional separations were performed using n-heptane-ethyl acetate-methanol-water (6:4:6:4, v/v) and ethyl acetate-water solvent systems sequentially to separate the constituents of Thymus quinquecostatus Celak. The upper phase of the former solvent system was utilized as both elution solvent for flash chromatography and the stationary phase for counter-current chromatography, while the lower phase of the latter solvent system containing 10 mM trifluoroacetic acid was employed as elution solvent for flash chromatography and one mobile phase in pH gradient counter-current chromatography. Thymol (7) and xanthomicrol (8), two hydrophobic ingredients, were purified in the initial two-dimensional separation. The subsequent two-dimensional separation yielded six hydrophilic compounds, namely dihydrokaempferol-7-O-D-glucopyranoside (1), lithospermic acid (2), luteolin-7-O-glucuronide (3), rosmarinic acid (4), messerschmidin (5) and apigenin-7-O-D-glucuronide (6). This study represents the first documented use of online multi-dimensional normal-phase flash chromatography coupled to counter-current chromatography for separating constituents from Thymus quinquecostatus Celak.

Streptomyces sp. Strain PBR11, a Forest-Derived Soil Actinomycetia with Antimicrobial Potential

The Actinomycetia isolate PBR11 was isolated from the forest rhizosphere soil of Pobitora Wildlife Sanctuary (PWS), Assam, India. The isolate was identified as Streptomyces sp. with 92.91% sequence similarity to their closest type strain, Streptomyces atrovirens NRRL B-16357 DQ026672. The strain demonstrated significant antimicrobial activity against 19 test pathogens, including multidrug-resistant (MDR) clinical isolates and dermatophytes. Phenol, 2,5-bis(1,1-dimethylethyl), is the major chemical compound detected by gas chromatography-mass spectrometry in the ethyl acetate extract of PBR11 (EtAc-PBR11). The presence of the PKS type II gene (type II polyketide synthases) and chitinase gene suggested that it has been involved in the production of antimicrobial compounds. Metabolic profiling of the EtAc-PBR11 was performed by thin-layer chromatography and flash chromatography resulted in the extraction of two bioactive fractions, namely, PBR11Fr-1 and PBR11Fr-2. Liquid chromatography-tandem mass spectrometry analysis of both the fractions demonstrated the presence of significant antimicrobial compounds, including ethambutol. This is the first report on the detection of antituberculosis drug in the bioactive fractions of Streptomyces sp. PBR11. EtAc-PBR11 and PBR11Fr-1 showed the lowest MIC values (>0.097 and >0.048 μg/mL, respectively) against Candida albicans MTCC 227, whereas they showed the highest MIC values (>0.390 and >0.195 μg/mL, respectively) against Escherichia coli ATCC BAA-2469. The effects of PBR11Fr-1 were investigated on the pathogens by using a scanning electron microscope. The results indicated major morphological alterations in the cytoplasmic membrane. PBR11Fr-1 exhibited low cytotoxicity on normal hepatocyte cell line (CC-1) and the percent cell viability started to decline as the concentration increased from 50 μg/mL (87.07% ± 3.22%) to 100 μg/mL (81.26% ± 2.99%). IMPORTANCE Novel antibiotic breakthroughs are urgently required to combat antimicrobial resistance. Actinomycetia are the principal producers of antibiotics. The present study demonstrated the broad-spectrum antimicrobial potential of an Actinomycetia strain Streptomyces sp. strain PBR11 isolated from the PWS of Assam, India, which represents diverse, poorly screened habitats for novel microorganisms. The strain displayed 92.4% sequence similarity with genes of the closest type strain, indicating that the strain may represent a novel taxon within the phylum Actinomycetota. The metabolomics studies of EtAc-PBR11 revealed structurally diverse antimicrobial agents, including the detection of the antituberculosis drug ethambutol, in the bioactive fraction of Streptomyces sp. PBR11 for the first time. The PBR11 strain also yielded positive results for the antibiotic synthesis gene and the chitinase gene, both of which are responsible for broad-spectrum antimicrobial activity. This suggests that the untouched forest ecosystems have a tremendous potential to harbor potent actinomycetia for future drug discovery.

Efficient purification of the diarylheptanoid oregonin from red alder (Alnus rubra) leaves and bark combining aqueous extraction, spray drying and flash-chromatography

INTRODUCTION

The diarylheptanoid xyloside oregonin ((5S)-1,7-bis(3,4-dihydroxyphenyl)-5-(β-d-xylopyranosyloxy)-heptan-3-one) has significant medicinal potential and is found at high concentration in leaves and bark of red alder (Alnus rubra).

OBJECTIVES

To establish inexpensive and easily scaled methods for the extraction and purification of oregonin from timber by-products.

METHODS

We developed a method combining aqueous extraction with spray drying of red alder extract into a powder, thus reducing the need for organic solvents used in traditional Soxhlet extraction or in solvent partitioning. Flash chromatography was utilised to purify oregonin from crude spray-dried alder extract.

RESULTS

Crude spray-dried alder extract was comprised of an average of 9% of the diarylheptanoid compound oregonin. Less than 10% thermal degradation of oregonin was observed using extraction temperatures between 25°C and 50°C, followed by spray drying. The structure of purified oregonin was validated using high-performance liquid chromatography (HPLC), mass spectrometry (MS), ultraviolet spectroscopy (UV), and nuclear magnetic resonance (NMR).

CONCLUSION

The developed method was robust, repeatable, and yielded purified oregonin of greater than > 95% purity (average of 95.8%). Our analysis represents the most complete NMR characterisation of oregonin reported to date.

Enzymatic Synthesis and Flash Chromatography Separation of 1,3-Diferuloyl-sn-Glycerol and 1-Feruloyl-sn-Glycerol

Ethyl ferulate was transesterified with Enova Oil (a soy-based vegetable oil containing 80-85% diacylglycerol) using Novozym 435 at 60 °C. The resultant feruloylated vegetable oil reaction product produced a precipitate (96.4 g, 4.02 wt%) after 7 d of standing at room temperature. Preliminary characterization of the precipitate identified the natural phenylpropenoids 1,3-diferuloyl-sn-glycerol (F2G) and 1-feruloyl-sn-glycerol (FG) as the major components. A flash chromatography method was developed and optimized (e.g., mass of sample load, flow rate, binary solvent gradient slope, and separation run length) using a binary gradient of hexane and acetone mobile phase and silica gel stationary phase to separate and isolate F2G and FG. The optimized parameters afforded F2G (1.188 ± 0.052 g, 39.6 ± 1.7%) and FG (0.313 ± 0.038 g, 10.4 ± 1.3%) from 3.0 g of the transesterification precipitate, n = 10 trials. Overall, all flash chromatography separations combined, F2G (39.1 g, 40.6%) and FG (9.4 g, 9.8%) were isolated in a combined yield of 48.5 g (51.4%), relative to the 96.4 g of transesterification precipitate collected. The optimized flash chromatography method was a necessary improvement over previously reported preparative HPLC and column chromatography methods used to purify milligram to low gram quantities of F2G and FG to be able to process ~100 g of material in a timely, efficient manner.

Enrichment and Assessment of the Contributions of the Major Polyphenols to the Total Antioxidant Activity of Onion Extracts: A Fractionation by Flash Chromatography Approach

The present study extensively fractionated crude red onion extract in order to identify the polyphenols which contributed most in the total antioxidant capacity of the onion extract using a flash chromatography system. The flash separations produced 70 fractions which were tested for their total phenol content, total flavonoid content, and antioxidant capacities as measured by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. Out of these 70 fractions, four fractions which were representatives of the four major peaks of the flash chromatograms, were further analysed for their constituent polyphenols using liquid chromatography tandem mass spectrometry (LC-MS/MS). The main contributor of onion antioxidant capacity is quercetin glycoside followed by quercetin aglycone although quercetin aglycone had higher antioxidant capacity than its glycosidic counterparts. High abundance of quercetin glycosides such as quercetin-3,4′-diglucoside and quercetin-4′-glucoside had compensated for their relatively low antioxidant capacities. A Higher degree of glycosylation resulted in lower antioxidant capacity. The fractionation approach also contributed in enrichment of the onion antioxidant polyphenols. A >9 folds enrichment was possible by discarding the early fractions (fractions 1–15) which contained the main bulk of the extracts, predominantly sugars.

Influence of Environmental Factors on the Production of Penitrems A-F by Penicillium crustosum

Filamentous fungi produce a multitude of secondary metabolites, some of them known as mycotoxins, which are toxic to vertebrates and other animal groups in low concentrations. Among them, penitrems, which belong to the group of indole-diterpene mycotoxins, are synthesized by Penicillium and Aspergillus genera and exhibit potent tremorgenic effects. This is the first complex study of the penitrems A-F production under the influence of different abiotic factors, e.g., media, incubation time, temperature, pH, light, water activity, and carbon and nitrogen source as well as oxidative and salt stress. For this purpose, penitrems A-F were isolated from Penicillium crustosum cultures and used as analytical standards. Among the carbon sources, glucose supplemented to the media at the concentration of 50 g/L, showed the strongest inducing effect on the biosynthesis of penitrems. Among nitrogen sources, glutamate was found to be the most favorable supplement, significantly increasing production of these secondary metabolites. CuSO4-promoted oxidative stress was also shown to remarkably stimulate biosynthesis of all penitrems. In contrast, the salt stress, caused by the elevated concentrations of NaCl, showed an inhibitory effect on the penitrem biosynthesis. Finally, cheese model medium elicited exceptionally high production of all members of the penitrems family. Obtained results give insides into the biosynthesis of toxicologically relevant penitrems A-F under different environmental factors and can be utilized to prevent food contamination.

Hydroxybenzoic Acids Are Significant Contributors to the Antioxidant Effect of Borututu Bark, Cochlospermum angolensis Welw. ex Oliv

Borututu (Cochlospermum angolensis) is an African tree whose bark has recently emerged as a herbal dietary supplement with claims for antioxidant activity. In order to substantiate the claimed activity of borututu supplements, we performed an activity-guided fractionation of the total extract utilizing a 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay. Subsequent flash and centrifugal chromatography resulted in the isolation of gallic acid (1) and protocatechuic acid (2) as the main antioxidant constituents. Two apocarotenoids and one flavonoid were also isolated from the chloroform fraction and were identified as cochloxanthin (3), dihydrocochloxanthin (4), and 7,4′-dimethyltaxifolin (5), respectively. A High-performance liquid chromatography (HPLC) method was also developed for fingerprinting borututu samples, with Compounds 1–4 suggested as chemical markers for quality control purposes.

Characterisation of the antiproliferative constituents and activity of Ficus exasperata (Vahl) on ovarian cancer cells -a preliminary investigation

Ovarian cancer is one of the most common gynaecological cancers today. This study therefore investigates the anticancer effects of Ficus exasperata extracts and fractions on ovarian cancer cells. The antiproliferative activity of the crude extracts (1 mg/mL) was assessed using the MTT assay on A2780 (ovarian cancer) cell line. Bio-activity guided fractionation was performed and preliminary identification was further achieved using high resolution mass spectrometry and nuclear magnetic resonance spectroscopy. All crude extracts tested exhibited antiproliferative activity except for the methanol extract which interestingly showed proliferative effects. Five fatty acids were identified from the active fractions (FB1-10 and FB1-12). FB1-12 exhibited an IC₅₀ value of 15.20 μg/mL. The least potent fraction (FB1-4 + 5) had an IC₅₀ value of 34.51 μg/mL. H1-HEX and H1-MET exhibited 97.2 and 97.9%, respectively, compared to control. This study therefore provides proof-of-principle that fatty acids of Ficus exasperata exhibit significant antiproliferative effects on ovarian cancer cells.

The weight of flash chromatography: A tool to predict its mass intensity from thin-layer chromatography

Purification by flash chromatography strongly impacts the greenness of a process. Unfortunately, due to the lack of the relevant literature data, very often this impact cannot be assessed thus preventing the comparison of the environmental factors affecting the syntheses. We developed a simple mathematical approach to evaluate the minimum mass intensity of flash chromatography from the retention factor values determined by thin-layer chromatography.

Polymethoxyflavones Isolated from the Peel of Miaray Mandarin (Citrus miaray) Have Biofilm Inhibitory Activity in Vibrio harveyi

Citrus fruits are a good source of bioactive compounds with numerous beneficial biological activities. In the present study, fruits of the unexplored Miaray mandarin were used for the isolation of 10 bioactive compounds. Dried peels were sequentially extracted with hexane and chloroform in a Soxhlet-type apparatus for 8 h. The extracts were concentrated under vacuum and separated by flash chromatography to obtain nine polymethoxyflavones and a limonoid. The purity of each compound was analyzed by high-performance liquid chromatography (HPLC), and the compounds were identified by spectral analysis using MALDI-TOF-MS and NMR. The isolated compounds were identified as 5-hydroxy-3,7,3',4'-tetramethoxyflavone, 5,6,7,8,4'-pentamethoxyflavone (tangeretin), 3,5,6,7,8,3',4'-heptamethoxyflavone, 5,6,7,8,3',4'-hexamethoxyflavone (nobiletin), 3,5,7,8,3',4'-hexamethoxyflavone, 3,5,7,3',4'-pentamethoxyflavone (pentamethylquercetin), 5,7,4'-trimethoxyflavone, 5,7,8,4'-tetramethoxyflavone, 5,7,8,3',4'-pentamethoxyflavone, and limonin. These compounds were further tested for their ability to inhibit cell-cell signaling and biofilm formation in Vibrio harveyi. Among the evaluated polymethoxyflavones, 3,5,6,7,8,3',4'-heptamethoxyflavone and 3,5,7,8,3',4'-hexamethoxyflavone inhibited autoinducer-mediated cell-cell signaling and biofilm formation. These results suggest that Miaray mandarin fruits are a good source of polymethoxyflavones. This is the first report on the isolation of bioactive compounds from Miaray mandarin and evaluation of their biofilm inhibitory activity as well as isolation of pentamethylquercetin from the Citrus genus.

Synthesis and evaluation of ¹⁸F labeled FET prodrugs for tumor imaging

INTRODUCTION

O-(2-[(18)F]fluoroethyl)-L-tyrosine (FET, [(18)F]1) is a useful amino-acid-based imaging agent for brain tumors. This paper reports the synthesis and evaluation of three FET prodrugs, O-(2-[(18)F]fluoroethyl)-L-tyrosyl-L-glycine (FET-Gly, [(18)F]2), O-(2-[(18)F]fluoroethyl)-L-tyrosyl-L-alanine (FET-Ala, [(18)F]3) and N-acetyl O-(2-[(18)F]fluoroethyl)-L-tyrosine (AcFET, [(18)F]4), which could be readily hydrolyzed to FET in vivo for tumor imaging. We investigated their metabolism in the blood and imaging properties in comparison to FET ([(18)F]1).

METHODS

Three new [(18)F]FET derivatives, 2-4, were prepared from their corresponding tosylate-precursors through nucleophilic fluorination and subsequent deprotection reactions. In vitro uptake studies were carried out in 9L glioma cancer cell lines. In vitro and in vivo hydrolysis studies were conducted to evaluate the hydrolysis of FET prodrugs in blood and in Fisher 344 rats. Biodistribution and PET imaging studies were then performed in rats bearing 9L tumors.

RESULTS

New FET prodrugs were prepared with 3-28% decay corrected radiochemical yields, good enantiomeric purity (>95%) and high radiochemical purity (>95%). FET-Gly ([(18)F]2), FET-Ala ([(18)F]3), and AcFET ([(18)F]4) exhibited negligible uptake in comparison to the high uptake of FET ([(18)F]1) in 9L cells. Metabolism studies of FET-Gly ([(18)F]2), FET-Ala ([(18)F]3), and AcFET ([(18)F]4) in rat and human blood showed that FET-Ala ([(18)F]3) was hydrolyzed to FET ([(18)F]1) faster than FET-Gly ([(18)F]2) or AcFET ([(18)F]4). Most of the FET-Ala (79%) was converted to FET ([(18)F]1) within 5min in blood in vivo. Biodistribution studies demonstrated that FET-Ala ([(18)F]3) displayed the highest tumor uptake. The tumor-to-background ratios of FET-Ala ([(18)F]3) and FET ([(18)F]1) were comparable and appeared to be better than those of FET-Gly ([(18)F]2) and AcFET ([(18)F]4). PET imaging studies showed that both FET ([(18)F]1) and FET-Ala ([(18)F]3) could visualize tumors effectively, and that they share similar imaging characteristics.

CONCLUSIONS

FET-Ala ([(18)F]3) demonstrated promising properties as a prodrug of FET ([(18)F]1), which could be used in PET imaging of tumor amino acid metabolism.