Eszter Riethmüller

Characterisation of Diarylheptanoid- and Flavonoid-type Phenolics in Corylus avellana L. Leaves and Bark by HPLC/DAD–ESI/MS

INTRODUCTION The leaves of Corylus avellana L. (common hazel, Betulaceae), a plant with a wide distribution in Europe, have been used in folk medicine for various diseases, but phytochemical exploration of C. avellana is still incomplete. To the best of our knowledge there is no previous report concerning diarylheptanoids in C. avellana, although these compounds show a frequent occurrence among Betulaceae plants. OBJECTIVE To improve existing online chromatographic methods for the investigation of the phenolic compounds in C. avellana leaves and bark, focusing on diarylheptanoid-type molecules. METHODS Dried and powdered leaves and bark of C. avellana were extracted with increasing polarity solvents (n-hexane, chloroform, ethyl acetate and methanol) in Soxhlet extractor apparatus. For the characterisation of the phenolic compounds in the ethyl acetate and methanolic extracts, UV spectral data, obtained by LC with a diode-array detector (DAD), accurate molecular mass and formula, acquired by LC and electrospray ionisation (ESI) with time-of-flight (TOF) MS and fragmentation pattern, given by LC-ESI/MS/MS analyses were used. Quantitation of the compounds was performed by LC-MS/MS. RESULTS In the methanolic and ethyl acetate extracts of C. avellana bark four flavonoid glycosides and a caffeoyl hexoside derivative were detected and characterised, while in C. avellana leaves, seven diarylheptanoid-type molecules were tentatively identified in addition to six flavonoid components. As far as we know this is the first study where the presence of diarylheptanoids in C. avellana is reported. CONCLUSION The improved HPLC/DAD-ESI/MS method was successfully utilised for the characterisation and quantitation of the phenolic compounds in C. avellana bark and leaves extracts.

First characterisation of flavonoid- and diarylheptanoid-type antioxidant phenolics in Corylus maxima by HPLC-DAD-ESI-MS

Corylus maxima Mill. (Betulaceae) leaves have been used in traditional medicine both internally and externally, nevertheless phytochemical exploration of the plant remains incomplete. In this study, the in vitro antioxidant activity and polyphenolic composition of the ethyl acetate and methanolic extracts of C. maxima leaves and bark are reported for the first time. The radical scavenging activities of the extracts were investigated by the ABTS and DPPH assays. All the extracts of C. maxima possessed notable antioxidant activity. By mean of a HPLC-DAD-ESI-TOF and a HPLC-DAD-ESI-MS/MS method, altogether twenty-two phenolics were tentatively characterised: one flavan derivative (1), seven flavonol derivatives (4, 6, 12, 13, 16, 20 and 21) and fourteen diarylheptanoids (2, 3, 5, 7-11, 14, 15, 17-19 and 22). The amount of the two main flavonoids - myricetin-3-O-rhamnoside (6) and quercetin-3-O-rhamnoside (13) - and two diarylheptanoids - oregonin (3) and hirsutenone (15) - in the extracts were determined by a validated HPLC-ESI-MS/MS method in multiple reaction monitoring (MRM) mode. Our results showed that C. maxima could be considered as a valuable source of pharmacologically important natural products that might contribute to the revaluation of the phytotherapeutical potential of the plant.

Blood-brain barrier specific permeability assay reveals N-methylated tyramine derivatives in standardised leaf extracts and herbal products of Ginkgo biloba

The linkage between the central nervous system availability and neuropharmacological activity of the constituents of Ginkgo biloba L. extracts (GBE) is still incomplete. In this study, the in vitro blood-brain barrier (BBB) permeability profile of the standardised GBE was investigated by the parallel artificial membrane permeability assay (PAMPA). Biomarkers, such as terpene trilactones, flavonoid aglycones and ginkgotoxin exerted moderate or good BBB-permeability potential (BBB+), while glycosides and biflavones were predicted as unable to pass the BBB. N-methyltyramine (NMT) and N,N-dimethyltyramine or hordenine (Hor) were identified among BBB+ compounds, while subsequent direct HRMS analysis revealed tyramine (Tyr) and N,N,N-trimethyltyramine or candicine (Can) in GBE as trace constituents. Distribution of Tyr, NMT, Hor and Can was determined by a validated ion-exchange mechanism-based liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) method in G. biloba samples, such as herbal drugs and dietary supplements. The total content of the four tyramine derivatives in various GBEs ranged from 7.3 up to 6357μg/g dry extract with NMT and Hor as most abundant ones. Considering the pharmacological activities and the revealed fluctuation in the concentration of the analysed adrenergic protoalkaloids, the presented rapid LC-ESI-MS method is proposed for monitoring of the levels of Tyr, NMT, Hor and Can in G. biloba products.

Contribution of individual flavonoids in Lysimachia species to the antioxidant capacity based on HPLC-DPPH assay

Abstract Quantitative phytochemical characterisation of the chief flavonoid aglycones in the hydrolysed Lysimachia extracts revealed the dominance of kaempferol, quercetin and myricetin in L. vulgaris, L. nummularia, L. punctata, L. christinae, L. ciliata and L. clethroides, respectively. Due to the significant radical scavenging capacity of the samples, the contribution of the individual aglycones to the total antioxidant activity became of interest. Therefore, a HPLC method coupled to pre-column DPPH scavenging assay was developed. Differences in the six Lysimachia species’ phenolic composition regarding their participation to the antioxidant activity were revealed. The participation of the three investigated flavonoids to the radical quenching activity was the highest (91.2%) in the L. vulgaris sample, the lowest in L. christinae sample with 29.6%. In L. vulgaris sample, the 76.3% contribution of quercetin to the scavenger capacity was the highest peak area decrement ratio among the investigated samples.

Characterization of diarylheptanoids: An emerging class of bioactive natural products

HighlightsOverview of linear and cyclic diarylheptanoids phytochemistry was presented.Natural sources of diarylheptanoids were summarized.Main extraction and isolation strategies were reviewed.Analytical techniques used for diarylheptanoid characterization were discussed. ABSTRACT Diarylheptanoids are a class of secondary plant metabolites with a wide variety of bioactivity. Research on their phytochemistry and phytoanalysis is rapidly growing and the number of identified structures bearing the aryl‐C7‐aryl skeleton is at present approaching 500. Historically, the yellow pigment curcumin has been characterized as the first diarylheptanoid and the extensive research on naturally occurring analogues is still ongoing. In this review, studies dealing with the characterization of linear and cyclic derivatives are discussed from the phytoanalytical point of view. Isolation, fractionation and purification strategies from natural sources along with their chromatographic behavior and structural characteristics are discussed. The role of various techniques used for the extraction (such as Soxhlet extraction, sonication, maceration/percolation, microwave‐assisted extraction, supercritical carbon dioxide extraction); isolation (liquid–liquid extraction, column chromatographic techniques, preparative thin‐layer and high‐performance liquid chromatography, centrifugal partition chromatography, counter‐current chromatography); separation (thin‐layer chromatography, high‐performance liquid chromatography, gas chromatography, capillary electrophoresis) and structural characterization (UV/Vis spectroscopy, infrared spectroscopy, X‐ray crystallography, mass spectrometry, nuclear magnetic resonance spectroscopy and circular dichroism spectroscopy) are critically reviewed.

Three newly identified lipophilic flavonoids in Tanacetum parthenium supercritical fluid extract penetrating the Blood-Brain Barrier

HighlightsOptimized supercritical fluid extraction of lipohilic flavonoids and parthenolid from Tanacetum parthenium L.Three newly identified lipophilic flavonoids (aceronin, sudachitin, nevadensin) in Tanacetum parthenium L.PAMPA‐BBB penetration of flavonoids and sesquiterpene lactones from feverfew. ABSTRACT Feverfew (Tanacetum parthenium L.) as a perennial herb has been known for centuries due to its medicinal properties. The main sesquiterpene lactone, parthenolide is considered to be responsible for the migraine prophylactic effect, however the pharmacological benefits of the lipophilic flavonoid components can not be neglected. Supercritical fluid extraction (7% ethanol, 22 MPa, 64 °C) was carried out on the leaves of Tanacetum parthenium L. from which the presence of methylated flavonoids beside parthenolide and other sesquiterpene lactones were indicated by preliminary LC–MS analyses. Specific Parallel Artificial Membrane Permeability Assay (PAMPA) was applied to identify the components capable to cross the Blood‐Brain Barrier (BBB). Three lipophilic flavonoids were detected on the acceptor side, that were isolated (Prep‐HPLC) and identified as sudachitin, aceronin and nevadensin (LC–MS/MS, NMR). These flavonoids were also characterized individually by PAMPA‐BBB model. The presence of sudachitin and nevadensin was proven in the Asteraceae family, but neither of the three flavonoids were reported in Tanacetum parthenium L.

Application of Flow Chemistry to Macrocyclization of Crown Ethers

This paper reports a new continuous-flow synthesis of chiral and achiral pyridino-18-crown-6 ethers. Macrocyclizations have been performed in a packed-bed flow reactor where deprotonation of a bifunctional primary or a secondary alcohol takes place with potassium hydroxide as a heterogeneous base avoiding the use of stronger and more dangerous one, sodium hydride. Ditosylate derivatives of pyridine as precursors for the macrocyclization used in batch condition were replaced by the appropriate diiodides and optimization of the parameters provided higher yields in shorter reaction times. The setup presented here is suitable for the preparation of different ethers by Williamsontype syntheses in continuous-flow reactions.