Mass spectrometry of 3,5- and 4,5-dicaffeoylquinic acids and selected derivatives

Hydroxycinnamic acids in sunflower leaves serve as UV-A screening pigments

Despite the weak absorption of hydroxycinnamic acids in the UV-A region, we found evidence that these compounds protect against damage induced by UV-A radiation in sunflowers.

Fragmentation of 2-aroylbenzofuran derivatives by electrospray ionization tandem mass spectrometry

We investigated the gas-phase fragmentation reactions of a series of 2-aroylbenzofuran derivatives by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The most intense fragment ions were the acylium ions m/z 105 and [M+H-C₆ H₆ ]⁺ , which originated directly from the precursor ion as a result of 2 competitive hydrogen rearrangements. Eliminations of CO and CO₂ from [M+H-C₆ H₆ ]⁺ were also common fragmentation processes to all the analyzed compounds. In addition, eliminations of the radicals •Br and •Cl were diagnostic for halogen atoms at aromatic ring A, whereas eliminations of •CH₃ and CH₂ O were useful to identify the methoxyl group attached to this same ring. We used thermochemical data, obtained at the B3LYP/6-31+G(d) level of theory, to rationalize the fragmentation pathways and to elucidate the formation of E, which involved simultaneous elimination of 2 CO molecules from B.

The effect of temperature and methanol-water mixture on pressurized hot water extraction (PHWE) of anti-HIV analogoues from Bidens pilosa

Background

Pressurized hot water extraction (PHWE) technique has recently gain much attention for the extraction of biologically active compounds from plant tissues for analytical purposes, due to the limited use of organic solvents, its cost-effectiveness, ease-of-use and efficiency. An increase in temperature results in higher yields, however, issues with degradation of some metabolites (e.g. tartrate esters) when PHWE is conditioned at elevated temperatures has greatly limited its use. In this study, we considered possibilities of optimizing PHWE of some specific functional metabolites from Bidens pilosa using solvent compositions of 0, 20, 40 and 60 % methanol and a temperature profile of 50, 100 and 150 °C.

Results

The extracts obtained were analyzed using UPLC-qTOF-MS/MS and the results showed that both temperature and solvent composition were critical for efficient recovery of target metabolites, i.e., dicaffeoylquinic acid (diCQA) and chicoric acid (CA), which are known to possess anti-HIV properties. It was also possible to extract different isomers (possibly cis-geometrical isomers) of these molecules. Significantly differential (p ≤ 0.05) recovery patterns corresponding to the extraction conditions were observed as recovery increased with increase in methanol composition as well as temperature. The major compounds recovered in descending order were 3,5-diCQA with relative peak intensity of 204.23 ± 3.16 extracted at 50 °C and 60 % methanol; chicoric acid (141.00 ± 3.55) at 50 °C and 60 % methanol; 4,5-diCQA (108.05 ± 4.76) at 150 °C and 0 % methanol; 3,4-diCQA (53.04 ± 13.49) at 150 °C and 0 % methanol; chicoric acid isomer (40.01 ± 1.14) at 150 °C and 20 % methanol; and cis-3,5-diCQA (12.07 ± 5.54) at 100 °C and 60 % methanol. Fitting the central composite design response surface model to our data generated models that fit the data well with R² values ranging from 0.57 to 0.87. Accordingly, it was possible to observe on the response surface plots the effects of temperature and solvent composition on the recovery patterns of these metabolites as well as to establish the optimum extraction conditions. Furthermore, the pareto charts revealed that methanol composition had a stronger effect on extraction yield than temperature.

Conclusion

Using methanol as a co-solvent resulted in significantly higher (p ≤ 0.05) even at temperatures as low as 50 °C, thus undermining the limitation of thermal degradation at higher temperatures during PHWE.

Fragmentation reactions using electrospray ionization mass spectrometry: an important tool for the structural elucidation and characterization of synthetic and natural products

Over the last decade, the number of studies reporting the use of electrospray ionization mass spectrometry (ESI-MS) in combination with collision cells (or other activation methods) to promote fragmentation of synthetic and natural products for structural elucidation purposes has considerably increased. However, the lack of a systematic compilation of the gas-phase fragmentation reactions subjected to ESI-MS/MS conditions still represents a challenge and has led to many misunderstood results in the literature. This review article exploits the most common fragmentation reactions for ions generated by ESI in positive and negative modes using collision cells in an effort to stimulate the use of this technique by non-specialists, undergraduate students and researchers in related areas.

Comparative cytotoxicity of artemisinin and cisplatin and their interactions with chlorogenic acids in MCF7 breast cancer cells

In parts of Africa and Asia, self-medication with a hot water infusion of Artemisia annua (Artemisia tea) is a common practice for a number of ailments including malaria and cancer. In our earlier work, such an extract showed better potency than artemisinin alone against both chloroquine-sensitive and -resistant parasites. In this study, in vitro tests of the infusion in MCF7 cells showed high IC₅₀ values (>200 μm). The combination of artemisinin and 3-caffeoylquinic acid (3CA), two major components in the extract, was strongly antagonistic and gave a near total loss of cytotoxicity for artemisinin. We observed that the interaction of 3CAs with another cytotoxic compound, cisplatin, showed potentiation of activity by 2.5-fold. The chelation of cellular iron by 3CA is hypothesized as a possible explanation for the loss of artemisinin activity.

The rolC gene increases caffeoylquinic acid production in transformed artichoke cells

Caffeoylquinic acids are found in artichokes, and they are currently considered important therapeutic or preventive agents for treating Alzheimer's disease and diabetes. We transformed artichoke [the cultivated cardoon or Cynara cardunculus var. altilis DC (Asteraceae)] with the rolC gene, which is a known inducer of secondary metabolism. High-performance liquid chromatography with UV and high-resolution mass spectrometry (HPLC-UV-HRMS) revealed that the predominant metabolites synthesized in the transgenic calli were 1,5-dicaffeoylquinic acid, 3,4-dicaffeoylquinic acid, and chlorogenic acid. The rolC-transformed calli contained 1.5% caffeoylquinic acids by dry weight. The overall production of these metabolites was three times higher than that of the corresponding control calli. The enhancing effect of rolC remained stable over long-term cultivation.

Anti-plasmodial polyvalent interactions in Artemisia annua L. aqueous extract--possible synergistic and resistance mechanisms

Artemisia annua hot water infusion (tea) has been used in in vitro experiments against P. falciparum malaria parasites to test potency relative to equivalent pure artemisinin. High performance liquid chromatography (HPLC) and mass spectrometric analyses were employed to determine the metabolite profile of tea including the concentrations of artemisinin (47.5±0.8 mg L(-1)), dihydroartemisinic acid (70.0±0.3 mg L(-1)), arteannuin B (1.3±0.0 mg L(-1)), isovitexin (105.0±7.2 mg L(-1)) and a range of polyphenolic acids. The tea extract, purified compounds from the extract, and the combination of artemisinin with the purified compounds were tested against chloroquine sensitive and chloroquine resistant strains of P. falciparum using the DNA-intercalative SYBR Green I assay. The results of these in vitro tests and of isobologram analyses of combination effects showed mild to strong antagonistic interactions between artemisinin and the compounds (9-epi-artemisinin and artemisitene) extracted from A. annua with significant (IC50 <1 μM) anti-plasmodial activities for the combination range evaluated. Mono-caffeoylquinic acids, tri-caffeoylquinic acid, artemisinic acid and arteannuin B showed additive interaction while rosmarinic acid showed synergistic interaction with artemisinin in the chloroquine sensitive strain at a combination ratio of 1:3 (artemisinin to purified compound). In the chloroquine resistant parasite, using the same ratio, these compounds strongly antagonised artemisinin anti-plasmodial activity with the exception of arteannuin B, which was synergistic. This result would suggest a mechanism targeting parasite resistance defenses for arteannuin B's potentiation of artemisinin.

Rapid screening and identification of caffeic acid and its esters in Erigeron breviscapus by ultra-performance liquid chromatography/tandem mass spectrometry

Caffeic acid and its esters (CAEs) are widely distributed in the plant kingdom and have been reported to elicit a wide range of exceptional biological activities. Present methods for screening and characterization of CAEs normally need the use of liquid chromatography diode-array detection/multistage mass spectrometry (LC-DAD/MS(n)). In this report, a rapid and efficient method coupling ultra-performance liquid chromatography (UPLC) with fragment-targeted multi-reaction monitoring (MRM) has been developed for screening CAEs in a crude extract of Erigeron breviscapus, while a UPLC/quasi-MS(n) method has been applied in the structural identification of these compounds. Furthermore, a simple quasi-UPLC/MS/MS method based on in-source collision-induced dissociation (CID) has been proposed for rapid identification of the CAEs. As a result, a total of more than 34 CAEs were detected and their structures characterized. Nine of them were reported from E. breviscapus for the first time. Applications of these strategies in the chemical investigation of an injection of E. breviscapus resulted in the identifications of 16 CAEs. These strategies, if appropriate modifications are made, will be very useful in screening and characterization not only of CAEs, but of other structural types of compounds in various complex matrices.

Comparison of major phenolic constituents and in vitro antioxidant activity of diverse Kudingcha genotypes from Ilex kudingcha, Ilex cornuta, and Ligustrum robustum

A total of seven Kudingcha genotypes from three plant species (Ilex kudingcha, Ilex cornuta, and Ligustrum robustum) with different geographic origins in China were investigated for their major phenolic compounds, individual and total phenolics contents, and in vitro antioxidant properties (ABTS, DPPH, FRAP, and OH assays). LC-PDA-APCI-MS analysis showed that Kudingcha genotypes from Ilex and Ligustrum had entirely different phenolic profiles. Major phenolics in Kudingcha genotypes from two Ilex species were mono- and dicaffeoylquinic acids, whereas those in a Kudingcha genotype from Ligustrum were phenylethanoid and monoterpenoid glycosides. All Kudingcha genotypes of Ilex exhibited significantly stronger antioxidant capacities than that of Ligustrum. Within six Ilex genotypes, great variation existed in their composition of individual phenolic compounds and their antioxidant properties. The comparative data and LC fingerprints obtained in this study may provide useful information for screening and breeding of better Kudingcha genotypes and also for their authentication and quality control.

Analysis of caffeic acid derivatives from Osmanthus yunnanensis using electrospray ionization quadrupole time-of-flight mass spectrometry

A series of six caffeic acid derivatives (1-6) in Osmanthus yunnanensis were investigated by electrospray quadrupole time-of-flight tandem mass spectrometry (ESI-QToF-MS/MS) in both negative- and positive-ion modes. High-quality MS/MS spectra of [M + H](+) are generated from high-abundance protonated parent ions obtained by addition of ammonium chloride to the solutions. Fragmentation mechanisms of [M - H](-) and [M + H](+) precursor ions were proposed and elemental compositions of most of the product ions were confirmed on the basis of the high-resolution ESI-collision-induced dissociation (CID)- MS/MS spectra. It was found that the fragment ions at m/z 179, m/z 161, m/z 135 and m/z 134 in negative-ion mode and at m/z 163, m/z 145 and m/z 135 in positive mode should be the characteristic ions of caffeic acid. In addition, the radical fragment ions with high abundance were observed for many caffeic acid derivatives especially for 4. The structural elements of unknown compounds 7 and 8 were tentatively identified on based on tandem mass spectra of known ones.

Online identification of chlorogenic acids, sesquiterpene lactones, and flavonoids in the Brazilian arnica Lychnophora ericoides Mart. (Asteraceae) leaves by HPLC-DAD-MS and HPLC-DAD-MS/MS and a validated HPLC-DAD method for their simultaneous analysis

Lychnophora ericoides Mart. (Asteraceae, Vernonieae) is a plant, endemic to Brazil, with occurrence restricted to the "cerrado" biome. Traditional medicine employs alcoholic and aqueous-alcoholic preparations of leaves from this species for the treatment of wounds, inflammation, and pain. Furthermore, leaves of L. ericoides are also widely used as flavorings for the Brazilian traditional spirit "cachaça". A method has been developed for the extraction and HPLC-DAD analysis of the secondary metabolites of L. ericoides leaves. This analytical method was validated with 11 secondary metabolites chosen to represent the different classes and polarities of secondary metabolites occurring in L. ericoides leaves, and good responses were obtained for each validation parameter analyzed. The same HPLC analytical method was also employed for online secondary metabolite identification by HPLC-DAD-MS and HPLC-DAD-MS/MS, leading to the identification of di- C-glucosylflavones, coumaroylglucosylflavonols, flavone, flavanones, flavonols, chalcones, goyazensolide, and eremantholide-type sesquiterpene lactones and positional isomeric series of chlorogenic acids possessing caffeic and/or ferulic moieties. Among the 52 chromatographic peaks observed, 36 were fully identified and 8 were attributed to compounds belonging to series of caffeoylferuloylquinic and diferuloylquinic acids that could not be individualized from each other.

Identification of antioxidant phenolic compounds in feverfew (Tanacetum parthenium) by HPLC-ESI-MS/MS and NMR

Antioxidant polyphenolic acids in the medicinal herb feverfew (Tanacetum parthenium) were isolated through in vitro bioassay-orientated antioxidant tests in response to 1,1-diphenyl-2-picrylhydrazyl (DPPH*) free radical scavenging and Fe(2+)-chelating activities. Purification of the active compounds and their structural elucidation involved a variety of techniques including open-column chromatography, HPLC, GC-MS, LC-MS and NMR. Major compounds with potent DPPH* scavenging activities were characterised as 3,5-, 4,5- and 3,4-di-O-caffeoylquinic acids (DCQAs). This is the first report of DCQAs found in feverfew.

Identification and characterization of major flavonoids and caffeoylquinic acids in three Compositae plants by LC/DAD-APCI/MS

In this study, a liquid chromatography/diode array detector-atmospheric pressure chemical ionization/mass spectrometry (LC/DAD-APCI/MS) was successfully developed to identify and characterize the main flavonoids and caffeoylquinic acids (CQAs) of three common Compositae plants (Chrysanthemum morifolium Raman, Artemisia annua, and Chrysanthemum coronarium) which have been used as herbal medicine. Identifications were performed by comparing the retention time, UV and mass spectra of samples with standards or/and earlier publications. The crude methanolic extracts of these plants were assayed directly using LC/MS without any further pretreatment. The proposed method is rapid and reproducible and is useful for characterization and evaluation of different plant flavonoids and CQAs. A total of 41 different flavonoids and 6 CQAs were identified and confirmed by APCI-MS. The main components of three Compositae plants were also compared. Although there exist some similarities in the flavonoidic content of the leaf and flower of C. morifolium, significant variations in their varieties and concentrations were observed. Artemisia annua processes substantial amount of alkylated derivatives of flavones and Chrysanthemum coronarium contains only CQAs. These findings suggest that although all the plants studied are from the same Compositae family, their flavonoids and phenolic compositions are markedly different. The proposed method is useful for further chromatographic fingerprinting of plant flavonoids.

A novel inhibitor of respiratory syncytial virus isolated from ethnobotanicals

A novel low molecular weight compound, CJ 4-16-4, isolated from ethnobotanicals using bioassay-guided fractionation, was found to be a potent inhibitor of respiratory syncytial virus (RSV) in vitro and in vivo. In vitro, a very low micromolar efficacious dose was obtained against at least four of subtype A (RSV-Long, RSV A2, and RSV A6 57754) and one of subtype B (Washington) RSV strains without seeing any significant cytotoxicity to Hep-2, MDCK or Vero cell lines. The drug inhibits growth of RSV in Hep-2 cells maintained in tissue culture at a very low concentration (approximately 0.07 microM) with cell toxicity >400 microM (TI>5880). In a cotton rat model of RSV infection, the drug was able to reduce viral titers by approximately 1 log at dose 12.5 and 25 mg/kg/day, and by >2 log at 100 mg/kg/day. This antiviral activity was specific as influenza A and B and herpes simplex 1 and 2 viruses were not inhibited. The results obtained indicate that CJ 4-16-4 warrants clinical development.

Isolation and on-line identification of antioxidant compounds from three Baccharis species by HPLC-UV-MS/MS with post-column derivatisation

The aqueous extracts of aerial parts of Baccharis trimera (Less.) DC., B. crispa Spreng. and B. usterii Heering (Asteraceae) displayed significant radical scavenging activity in a diphenylpicrylhydrazole (DPPH)/TLC assay. In order to rapidly identify the active principles, the crude extracts were analysed by HPLC-UV, and an HPLC-micro-fractionation of the extract of B. usterii was performed. Six quinic acids derivatives (1-6) were isolated from B. usterii by MPLC. The fractions were monitored by DPPH/TLC assay and a series of radical-scavenging quinic acid derivatives could be identified. The comparison of the HPLC profiles of the extracts of B. usterii, B. trimera and B. crispa was performed. In order to obtain complementary on-line structural information for all peaks of interest, HPLC-MS/MS together with HPLC-UV involving post-column addition of UV shift reagents was undertaken on the crude extract. The interpretation of these data permitted the on-line identification of known compounds, some of which are reported for the first time in this plant.

Oxidative metabolism of 5-o-caffeoylquinic acid (chlorogenic acid), a bioactive natural product, by metalloporphyrin and rat liver mitochondria

Synthetic metalloporphyrins, in the presence of monooxygen donors, are known to mimic the various reactions of cytochrome P450 enzymes systems in the oxidation and oxygenation of various drugs and biologically active compounds. This paper reports an HPLC-MS-MS investigation of chlorogenic acid (CGA) oxidation by iodosylbenzene using iron(III) tetraphenylporphyrin chloride as catalyst. The oxidation products have been detected by sequential MS analyses. In addition, CGA was submitted to an in vitro metabolism assay employing isolated rat liver mitochondria. The single oxidized product obtained from mitochondrial metabolism corresponds to the major product formed by the metalloporphyrin-catalyzed reaction. These results indicate that biomimetic oxidation reactions, in addition to in vitro metabolism assays employing isolated organs/organelles, could replace some in vivo metabolism studies, thus minimizing the problems related to the use of a large number of living animals in experimental research.

Analgesic activity of di-caffeoylquinic acids from roots of Lychnophora ericoides (Arnica da serra)

The Brazilian medicinal plant Lychnophora ericoides Mart. (Asteraceae) has been used in traditional medicine to treat wounds, pain and inflammation. As part of our continuing investigation of this commercial phytomedicine, we focused on the polar fractions of the plant, since it is employed as alcoholic and hydroalcoholic preparations. The analgesic bioguided fractionation of the root polar extract yielded 3,5-di-O-[E]-caffeoylquinic acid, 4,5-di-O-[E]-caffeoylquinic acid and 3,4,5-tri-O-[E]-caffeoylquinic acid. The n-butanol fraction and the di-caffeoylquinic acids showed significant analgesic activity in the acetic acid-induced mouse writhing test at low but not at high doses. These findings support, at least in part, the validity of the use of Lychnophora ericoides roots in traditional medicine.

Phenolic compounds from the leaf extract of artichoke (Cynara scolymus L.) and their antimicrobial activities

A preliminary antimicrobial disk assay of chloroform, ethyl acetate, and n-butanol extracts of artichoke (Cynara scolymus L.) leaf extracts showed that the n-butanol fraction exhibited the most significant antimicrobial activities against seven bacteria species, four yeasts, and four molds. Eight phenolic compounds were isolated from the n-butanol soluble fraction of artichoke leaf extracts. On the basis of high-performance liquid chromatography/electrospray ionization mass spectrometry, tandem mass spectrometry, and nuclear magnetic resonance techniques, the structures of the isolated compounds were determined as the four caffeoylquinic acid derivatives, chlorogenic acid (1), cynarin (2), 3,5-di-O-caffeoylquinic acid (3), and 4,5-di-O-caffeoylquinic acid (4), and the four flavonoids, luteolin-7-rutinoside (5), cynaroside (6), apigenin-7-rutinoside (7), and apigenin-7-O-beta-D-glucopyranoside (8), respectively. The isolated compounds were examined for their antimicrobial activities on the above microorganisms, indicating that all eight phenolic compounds showed activity against most of the tested organisms. Among them, chlorogenic acid, cynarin, luteolin-7-rutinoside, and cynaroside exhibited a relatively higher activity than other compounds; in addition, they were more effective against fungi than bacteria. The minimum inhibitory concentrations of these compounds were between 50 and 200 microg/mL.

Identification of isomeric dicaffeoylquinic acids from Eleutherococcus senticosus using HPLC-ESI/TOF/MS and 1H-NMR methods

Liquid chromatography-electrospray time-of-flight mass spectrometry (HPLC-ESI/TOF/MS) and a novel NMR technique, developed to maximise the sensitivity obtained from the standard NMR spectrometer, have been applied to the identification of the phenolic constituents of Eleutherococcus senticosus. In addition, molecular modelling and dihedral bond angle calculations based on the vicinal 3JHH-coupling constants have been used in the unambiguous assignment of signals in the 1H-NMR spectra. 5'-O-Caffeoylquinic acid and three isomeric compounds, 1',5'-O-dicaffeoylquinic acid, 3',5'-O-dicaffeoylquinic acid and 4',5'-O-dicaffeoylquinic acid, have been isolated and identified from a sample. The isolation and structure determination of the latter two compounds are reported for the first time from this plant.

A new dicaffeoylquinic acid butyl ester from Isertia pittieri

A new 4,5-di-O-caffeoylquinic acid butyl ester (1) was isolated from an ethyl acetate soluble fraction of Isertia pittieri stems, along with three known compounds, 1,5-di-O-caffeoylquinic acid (2), 3,4-di-O-caffeoylquinic acid (3) and 4,5-di-O-caffeoylquinic acid (4).

Tandem mass spectrometry studies of green tea catechins. Identification of three minor components in the polyphenolic extract of green tea

Liquid chromatography/electrospray ionization mass and tandem mass spectrometry (MS/MS) techniques were used to identify two minor components and one new compound in the polyphenolic extract of green tea (Camellia sinensis). Identification and structure assignments were based on previously reported sub-structural features in the MS/MS product, precursor and neutral loss scans of reference samples. The structures of two minor components, related to the known green tea components epicatechin gallate (ECG, 5) and epigallocatechin gallate (EGCG, 6), are formed by methylation at the 3"-O-position of the gallic acid moiety. The new compound contained a gallic acid ester group, but had only one phenolic group in either the A- or B-ring, relative to the structure of 5. High-resolution mass measurements supported the empirical formula assigned to the new compounds. An important fragmentation for defining the position of methylation of the ester function involves ionization of the phenolic group at the 4"-position of the gallic acid, followed by elimination of the ester function as a neutral with concomitant formation of the m/z 169 ion. If the 4"-position is blocked by methylation, the formation of m/z 169 incorporating the gallic acid group would be blocked. Thus, the presence of an ion representing the ester group indicates a free 4"-phenol and the absence of this ion would signify the 4"-position as a site of methylation. The operation of this mechanism should be general and useful in assigning the site of methylation of any polyphenolic ester group in natural products. A similar conclusion can be drawn concerning alkylation or esterification of the 4'-position of the catechins, i. e. blocking the 4'-phenol would prevent formation of the m/z 125 ion common to all of the catechin compounds thus far examined. Therefore, mass spectral data are of considerable importance in deducing the sites of alkylation or esterification in the structures of the components of green tea.