Chaetonigrisins A-L, a group of 3-Indole-1,2-Propanediol derived alkaloids from Chaetomium nigricolor YT-2.

Thirteen new alkaloids (1-13) as well as ten known compounds were isolated from the solid-state fermented rice medium of the fungus Chaetomium nigricolor YT-2. Their structures were elucidated on the basis of spectroscopic data, quantum calculations, and single crystal X-ray crystallographic analysis. Chaetonigrisin A (1) represents an unprecedented carbon skeleton featuring a polycyclic 1H-pyrano[3,2:3,4-]​furo[2,​3-​b]​indole. Chaetonigrisin B (2) displays a unique carbon skeleton with a 1,3­dioxolane bridged-ring. Chaetonigrisin C (3) is a spirocyclic indole alkaloid. Chaetonigrisins D-H (4-8) are a group of asymmetric dimers, formed with two 3-indol-3yl-1,2-propanediol (4-6) or with a 3-indol-3yl-1,2-propanediol and a 3-indol-2yl-1,2-propanediol (7-8) by a pyran ring. Chaetonigrisins I-L (9-12) each contains a 3-indol-3yl-1,2-propanediol or 3-indol-2yl-1,2-propanediol substructure. Chaetonigrisin M (13) is a new quinoline alkaloid. The neuroprotective activity assay showed that at the concentration of 40 µM, compounds (4-7, 11, and 12) improved the cell viability of PC12 cells were 49.26 %, 74.69 %, 74.76 %, 86.63 %, 66.89 %, and 69.92 %, respectively induced by 6-OHDA, compound 7 showed significant neuroprotective activity via upregulation of SOD1 mRNA and Bcl-2 mRNA.

Hexachlorophene, a selective SHP2 inhibitor, suppresses proliferation and metastasis of KRAS-mutant NSCLC cells by inhibiting RAS/MEK/ERK and PI3K/AKT signaling pathways.

Kirsten rat sarcoma viral oncogene homolog (KRAS) mutations account for 35% of the genetic alterations in non-small cell lung cancer (NSCLC). The Src-homology region 2-containing protein tyrosine phosphatase 2 (SHP2), encoded by PTPN11, is closely involved in RAS downstream pathways and development of many tumors by affecting cell proliferation, differentiation, and immunity. Targeting SHP2 with small molecules may be a promising avenue for the treatment of KRAS-mutant (mut) NSCLC. Herein, hexachlorophene (HCP) was identified as a SHP2 inhibitor with an IC50 value of 5.63 ± 0.75 µM through screening of the FDA-approved drug library. HCP specifically inhibited SHP2 rather than other phosphatases. Molecular docking showed that HCP displayed an orientation favorable for nucleophilic attack in the catalytic domain of SHP2. HCP suppressed viability of multiple KRAS-mut and KRAS-wild type cells and induced senescence and apoptosis in KRAS-mut cells. Moreover, HCP reversed epithelial-mesenchymal transition to suppress metastasis in KRAS-mut cells, and inhibited the RAS/MEK/ERK and PI3K/AKT signaling pathways by suppression of SHP2 phosphorylation and formation SHP2/Grb2/Gab1/SOS1 complex. In summary, HCP can act as a specific SHP2 inhibitor to inhibit KRAS-mut NSCLC cell proliferation and metastasis and induce senescence through suppression of the RAF/MEK/ERK and PI3K/AKT pathways. HCP warrants further investigation as a new compound skeleton for the development of selective SHP2 inhibitors for the treatment of NSCLC.

Steroidal alkaloids from the bulbs of Fritillaria pallidiflora Schrenk and their anti-inflammatory activity.

Steroidal alkaloids (1-11), including one new 24-hydroxylated cevanine-type steroidal alkaloid, named yibeinone F (1), were isolated from the bulbs of Fritillaria pallidiflora Schrenk. Their structures were elucidated by analyses of extensive spectroscopic data and comparison of the NMR data with those reported previously, and the structures of compounds 1, 7 and 11 were further confirmed by X-ray single crystal diffraction analyses. The anti-inflammatory effects of all the isolated alkaloids were evaluated in LPS-activated RAW264.7 macrophages. Among them, compounds 9 (stenanzine) and 10 (hapepunine) showed significant inhibitory effects against LPS-induced NO production with IC50 values of 8.04 µM and 20.85 µM, respectively. Furthermore, compound 9 effectively inhibited the release of cytokines such as interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), and prostaglandin E2 (PGE2), and suppressed the protein expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase 2 (COX2) in LPS-stimulated RAW264.7 cells. Further experiments revealed the underlying mechanism that 9 blocked LPS-induced phosphorylation and degradation of inhibitor-α of nuclear transcription factor κB (IκBα) and c-Jun N-terminal kinase (JNK) in RAW264.7 cells. Taken together, compound 9 may be a valuable candidate for the treatment of inflammatory diseases.

Synthesis and antitumor activity in vitro of novel berbamine derivatives.

A series of new berbamine derivatives were synthesized, and their cytotoxic activity was evaluated against Human T-cell lymphoma cell line H9 and multiple myeloma cell line RPMI8226 in vitro. Compared with berbamine, the cytotoxicity of the modified derivatives was enhanced, especially simultaneously substituted at OH and 5-position. Compounds 2a and 4b exhibited high antitumor activity. The IC50 value of compound 2a was 0.30 µM for RPMI8226 cells, and the IC50 value of compound 4b was 0.36 µM for H9 cells, whereas berbamine IC50 values were 4.0 µM for H9 cells and 6.19 µM for RPMI8226 cells, respectively.[Formula: see text].

Natural Polyketides Isolated from the Endophytic Fungus Phomopsis sp. CAM212 with a Semisynthetic Derivative Downregulating the ERK/IκBα Signaling Pathways.

Three previously undescribed natural products, phomopsinin A - C (1:  - 3: ), together with three known compounds, namely, cis-hydroxymellein (4: ), phomoxanthone A (5: ) and cytochalasin L-696,474 (6: ), were isolated from the solid culture of Phomopsis sp. CAM212, an endophytic fungus obtained from Garcinia xanthochymus. Their structures were determined on the basis of spectroscopic data, including IR, NMR, and MS. The absolute configurations of 1: and 2: were assigned by comparing their experimental and calculated ECD spectra. Acetylation of compound 1: yielded 1A: , a new natural product derivative that was tested together with other isolated compounds on lipopolysaccharide-stimulated RAW 264.7 cells. Cytochalasin L-696,474 (6: ) was found to significantly inhibit nitric oxide production, but was highly cytotoxic to the treated cells, whereas compound 1: slightly inhibited nitric oxide production, which was not significantly different compared to lipopolysaccharide-treated cells. Remarkably, the acetylated derivative of 1: , compound 1A: , significantly inhibited nitric oxide production with an IC50 value of 14.8 µM and no cytotoxic effect on treated cells, thereby showing the importance of the acetyl group in the anti-inflammatory activity of 1A: . The study of the mechanism of action revealed that 1A: decreases the expression of inducible nitric oxide synthase, cyclooxygenase 2, and proinflammatory cytokine IL-6 without an effect on IL-1ß expression. Moreover, it was found that 1A: exerts its anti-inflammatory activity in lipopolysaccharide-stimulated RAW 264.7 macrophage cells by downregulating the activation of ERK1/2 and by preventing the translocation of nuclear factor κB. Thus, derivatives of phomopsinin A (1: ), such as compound 1A: , could provide new anti-inflammatory leads.

Three new diterpenes from Dysoxylum lukii and their NO production inhibitory activity.

Three new diterpenes were isolated from the stems of Dysoxylum lukii Merr and characterized on the basis of spectral data. Neoclerod-13Z-ene-3α, 4ß, 15-triol (3) exhibited the inhibition of lipopolysaccharide-induced nitric oxide production in RAW264.7 macrophages with an IC50 value of 25.49 µM.[Formula: see text].

6-Hydroxy-3-O-methyl-kaempferol 6-O-glucopyranoside potentiates the anti-proliferative effect of interferon α/ß by promoting activation of the JAK/STAT signaling by inhibiting SOCS3 in hepatocellular carcinoma cells.

Suppressor of cytokine signaling 3 (SOCS3) is a key negative regulator of type I interferon (IFN α/ß) signaling. Inhibition of SOCS3 by small molecules may be a new strategy to enhance the efficacy of type I IFN and reduce its side effects. We established a cell-based screening assay using human hepatoma HepG2 cells stably transfected with a plasmid wherein the luciferase reporter activity was propelled by interferon α-stimulated response element (ISRE), which is a motif specifically recognized by type I IFN-induced activation of Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway. After screening our chemical library, 6-hydroxy-3-O-methyl-kaempferol 6-O-glucopyranoside (K6G) was identified to be a potent activator of type I IFN with EC50 value of 3.33±0.04µM. K6G enhanced the phosphorylation of JAK1, Tyk2, and STAT1/2 but decreased the phosphorylation of STAT3. K6G also promoted endogenous IFN-α-regulated genes expression. More interestingly, K6G significantly decreased the expression of SOCS3 without affecting the expression of SOCS1. Furthermore, K6G enhanced the anti-proliferative effect of IFN-α on hepatocellular carcinoma (HCC) cells. These results suggested that K6G potentiated the inhibitory effect of IFN-α on HCC cell proliferation through activation of the JAK/STAT signaling pathway by inhibiting SOCS3 expression. K6G warrants further investigation as a novel therapeutic method to enhance the efficacy of IFN-α/ß.

Nitric oxide production inhibition and mechanism of phenanthrene analogs in lipopolysaccharide-stimulated RAW264.7 macrophages.

Natural phenanthrene derivatives are considered to be important resource for the anti-inflammatory therapeutics, but their structure-activity relationship and mechanisms are still unknown. In this study we evaluated 20 synthesized phenanthrene analogs in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Compounds 10, 11 and 17 were found to inhibit the production of nitric oxide (NO) with IC50 values of 37.26µM, 5.05µM and 20.31µM, respectively. Compound 11 decreased LPS-induced expression of inducible NO synthase (iNOS), inhibited phosphorylation of p38 mitogen-activated protein kinase (MAPK) and serine/threonine kinase Akt. It also suppressed the phosphorylation and degradation of inhibitory kappa B-α (IκBα). Data obtained suggest that compound 11 exerts anti-inflammatory effects by inhibiting p38 MAPK and nuclear factor κB (NF-κB) pathways, which warrants further investigation as a new anti-inflammatory pharmaceutical tool.

Iridoid Glucosides and Diterpenoids from Caryopteris glutinosa.

Five new iridoid glucoside derivatives (1-5), three new diterpenoids (7, 12, and 15), and 11 known compounds were isolated from the aqueous EtOH extract of Caryopteris glutinosa. Cell-based estrogen biosynthesis assays indicated that caryopteriside C (3) and caryopterisoid B (12) promote the biosynthesis of estrogen E2, with EC50 values of 11.1 and 8.0 µM, respectively, in human ovarian granulosa-like KGN cells via upregulating the expression of aromatase.

Untargeted analysis of sesquiterpene pyridine alkaloids from the dried roots of Tripterygium wilfordii using high-performance liquid chromatography/electrospray ionization tandem mass spectrometry.

RATIONALE: Sesquiterpene pyridine alkaloids are a large group of highly oxygenated sesquiterpenoids that have attracted attention in the fields of medicine because of their significant biological activities. METHODS: Reference compounds including 14 sesquiterpene pyridine alkaloids and one dihydroagarofuran ester were analyzed by collision-induced dissociation tandem mass spectrometry (CID-MS/MS). A high-performance liquid chromatography/electrospray ionization (HPLC/ESI)-MS/MS method at two collision energies was adopted to investigate the botanical extracts of Tripterygium wilfordii. RESULTS: For 15 reference compounds, in the high mass range, the product ions were formed by the loss of side chains or H2 O. In the low mass range, the high-abundance product ions at m/z 206, 204, or 194 were the characteristic ions of the pyridine moiety. The characteristic product ion at m/z 310 was formed through an ion-neutral complex intermediate. Fifty-four sesquiterpenoid derivatives, including 50 sesquiterpene pyridine alkaloids, were identified or tentatively characterized in botanical extracts of T. wilfordii based on their elemental constituents, characteristic fragmentation patterns, and the major product ion profiles of the reference compounds ascertained with HPLC/ESI-MS/MS at two collision energies. It seems that isocratic energy was appropriate for the untargeted analysis of compounds with molecular weights exceeding 800 Da, whereas a linear gradient energy vs molecular weight was suitable for those compounds with molecular weights below 800 Da. CONCLUSIONS: The HPLC/ESI-MS/MS method, combining characteristic fragmentation patterns and the profiles of the product ions generated at different collision energies, is an effective technique for characterizing untargeted compounds.

Indole Alkaloids from Chaetomium globosum.

Two new indole alkaloids chaetocochin J (1) and chaetoglobinol A (8), along with chetomin (2), chetoseminudin A (3), cochliodinol (9), and semicochliodinol (10), were isolated from the rice culture of the fungus Chaetomium globosum. Their structures were elucidated by spectral analysis. Three new epipolythiodioxopiperazines, chaetocochins G-I (5-7), were identified by the combination of UPLC and mass spectrometric analysis. Chaetocochin I contained two sulfur bridges, one formed by three sulfur atoms between C-3 and C-11a, and the other formed by four sulfur atoms between C-3' and C-6'. Chaetocochin I was readily transformed into chetomin (2), chetoseminudin A (3), chaetocochin D (4), chaetocochin G (5), and chaetocochin H (6) by losing sulfur atoms. Compounds 1-3, and 8 exhibited antibacterial activities against Bacillus subtilis with MICs of 25, 0.78, 0.78, and 50 µg/mL, respectively, but not against Gram-negative bacterium (Escherichia coli). Compounds 2 and 8 were inactive against Candida albicans, Fusarium graminearum, Fusarium vasinfectum, Saccharomyces cerevisiae, and Aspergillus niger even at the high concentrations of 200 and 100 µg/mL, respectively. Compound 8 showed free radical scavenging capacity against the 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and 2,2'-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid radical (ABTS(+•)), with IC50 values of 143.6 and 45.2 µM, respectively. The free radical scavenging capacity rates of compounds 1-3 on the DPPH and ABTS(+•) were less than 20% at the test concentrations (89.9-108.3 µM). The superoxide anion radical scavenging assay indicated that compounds 1-3, and 8 showed 14.8% (90.9 µM), 18.1% (90.9 µM), 51.5% (88.3 µM), and 30.4% (61.3 µM) superoxide anion radical scavenging capacity, respectively.

Novel stilbenes from Artocarpus nanchuanensis.

Four new stilbene derivatives, hypargystilbenes B-E (1-4), together with seven known compounds (5-11), were isolated from the stems of Artocarpus nanchuanensis S.S. Chang. Their structures were elucidated on the basis of spectral data. Hypargystilbene B, hypargystilbene D, and hypargystilbene E exhibited protein tyrosine phosphatase 1B inhibitory effects with corresponding IC50 values of 3.23, 37.31, and 2.53 nM.

Antioxidant compounds from ethanol extracts of bamboo (Neosinocalamus affinis) leaves.

Activity-guided fractionation of Neosinocalamus affinis leaves led to obtain two new flavonoids, 4'-O-((7″R,8″S)-8″-guaiacylglyceryl)-pleioside B (9) and apigenin 6-C-ß-d-fucopyranosyl-7-O-ß-d-glucopyranoside (10) along with eight known compounds. Their structures were elucidated on the basis of spectroscopic data (UV, IR, NMR, and MS). Among these 10 compounds, farobin A (4) and isoorientin (7) showed significant antioxidant activity evaluated by 1,1-diphenyl-2-picrylhydrazyl, 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid), superoxide anion and nitric oxide (NO) radical-scavenging assays.

Turn-on phosphorescent chemodosimeter for Hg2+ based on a cyclometalated Ir(III) complex and its application in time-resolved luminescence assays and live cell imaging.

A novel "turn-on" phosphorescent chemodosimeter based on a cyclometalated Ir(III) complex has been designed and synthesized, which displays high selectivity and sensitivity toward Hg(2+) in aqueous media with a broad pH range of 4-10. Furthermore, by time-resolved photoluminescence techniques, some interferences from the short-lived background fluorescence can be eliminated effectively and the signal-to-noise ratio of the emission detection can be improved distinctly by using the chemodosimeter. Finally, the chemodosimeter can be used to monitor Hg(2+) effectively in living cells by confocal luminescence imaging.

Natural products and their derivatives regulating the janus kinase/signal transducer and activator of transcription pathway.

Janus kinase/signal transducer and activator of transcriptions (JAK/STAT) signaling pathway is one of the major signaling pathways involved in a variety of human physiological and pathological process. The proteins of JAK/STAT pathway or interferon response element (such as JAK, STAT, Src, SOCS, 2'5'-OAS, and ISRE) might be as drug targets for the study of physiological processes and treatment of related diseases, including cell proliferation, differentiation, apoptosis and immune processes, inflammation, cancer, arthritis, asthma, diabetes, and other diseases. This review attempts to summarize the current status of natural products and their derivatives (2002-2013) regulating the proteins or transcription elements of JAK/STAT signaling pathway to supply a new direction or drug targets for the discovery of new drugs.

Sulforaphane decreases oxidative stress and inhibits NLRP3 inflammasome activation in a mouse model of ulcerative colitis.

Excessive oxidative stress and NLRP3 inflammasome activation are considered the main drivers of inflammatory bowel disease (IBD), and inhibition of inflammasomes ameliorates clinical symptoms and morphological manifestations of IBD. Herein, we examined the roles of NLRP3 activation in IBD and modulation of NLRP3 by sulforaphane (SFN), a compound with multiple pharmacological activities that is extracted from cruciferous plants. To simulate human IBD, we established a mouse colitis model by administering dextran sodium sulfate in the drinking water. SFN (25, 50 mg·kg-1·d-1, ig) or the positive control sulfasalazine (500 mg/kg, ig) was administered to colitis-affected mice for 7 days. Model mice displayed pathological alterations in colon tissue as well as classic symptoms of colitis beyond substantial tissue inflammation. Expression of NLRP3, ASC, and caspase-1 was significantly elevated in the colonic epithelium. The expression of NLRP3 inflammasomes led to activation of downstream proteins and increases in the cytokines IL-18 and IL-1ß. SFN administration either fully or partially reversed these changes, thus restoring IL-18 and IL-1ß, substantially inhibiting NLRP3 activation, and decreasing inflammation. SFN alleviated the inflammation induced by LPS and NLRP3 agonists in RAW264.7 cells by decreasing the levels of reactive oxygen species. In summary, our results revealed the pathological roles of oxidative stress and NLRP3 in colitis, and indicated that SFN might serve as a natural NLRP3 inhibitor, thereby providing a new strategy for alternative colitis treatment.

Luteolin and its analog luteolin-7-methylether from Leonurus japonicus Houtt suppress aromatase-mediated estrogen biosynthesis to alleviate polycystic ovary syndrome by the inhibition of tumor progression locus 2.

ETHNOPHARMACOLOGICAL RELEVANCE: Leonurus japonicus Houtt (L. japonicus, Chinese motherwort), known as Yi Mu Cao which means "good for women", has long been widely used in China and other Asian countries to alleviate gynecological disorders, often characterized by estrogen dysregulation. It has been used for the treatment of polycystic ovary syndrome (PCOS), a common endocrine disorder in women but the underlying mechanism remains unknown. AIM OF THE STUDY: The present study was designed to investigate the effect and mechanism of flavonoid luteolin and its analog luteolin-7-methylether contained in L. japonicus on aromatase, a rate-limiting enzyme that catalyzes the conversion of androgens to estrogens and a drug target to induce ovulation in PCOS patients. MATERIALS AND METHODS: Estrogen biosynthesis in human ovarian granulosa cells was examined using ELISA. Western blots were used to explore the signaling pathways in the regulation of aromatase expression. Transcriptomic analysis was conducted to elucidate the potential mechanisms of action of compounds. Finally, animal models were used to assess the therapeutic potential of these compounds in PCOS. RESULTS: Luteolin potently inhibited estrogen biosynthesis in human ovarian granulosa cells stimulated by follicle-stimulating hormone. This effect was achieved by decreasing cAMP response element-binding protein (CREB)-mediated expression of aromatase. Mechanistically, luteolin and luteolin-7-methylether targeted tumor progression locus 2 (TPL2) to suppress mitogen-activated protein kinase 3/6 (MKK3/6)-p38 MAPK-CREB pathway signaling. Transcriptional analysis showed that these compounds regulated the expression of different genes, with the MAPK signaling pathway being the most significantly affected. Furthermore, luteolin and luteolin-7-methylether effectively alleviated the symptoms of PCOS in mice. CONCLUSIONS: This study demonstrates a previously unrecognized role of TPL2 in estrogen biosynthesis and suggests that luteolin and luteolin-7-methylether have potential as novel therapeutic agents for the treatment of PCOS. The results provide a foundation for further development of these compounds as effective and safe therapies for women with PCOS.

Analysis of mexicanolide- and phragmalin-type limonoids from Heynea trijuga using high-performance liquid chromatography/electrospray tandem mass spectrometry.

RATIONALE: Limonoids, a class of tetranortriterpenoids, exhibit various biological effects, including acting as potent antifeedants and insect growth-regulators against various pests. The analysis of phragmalin- and mexicanolide-type limonoids by collision-induced dissociation tandem mass spectrometry (CID-MS/MS) has not been reported. METHODS: A high-performance liquid chromatography/electrospray ionization (HPLC/ESI)-MS/MS method was developed to investigate the fragmentation patterns of [M+NH4 ](+) ions for nine reference phragmalin- and mexicanolide-type limonoids. The method was also used in the identification of limonoid compounds in botanic extracts of Heynea trijuga. RESULTS: The losses of side chains and the furan part were the major fragmentation patterns. However, there was variation in the relative abundances of product ions resulting from the same fragmentation pathways. A total of 89 phragmalin- and mexicanolide-type limonoids in botanic extracts of Heynea trijuga were detected and 50 of these compounds were identified or tentatively characterized based on elemental constituents, fragmentation pathways, and the profile of the major product ions of reference compounds. In addition, the isomers could be tentatively distinguished. CONCLUSIONS: An HPLC/ESI-MS/MS method was developed and could be used to simultaneously identify and screen phragmalin- and mexicanolide-type limonoids in botanic extracts of Heynea trijuga.

Evaluation of relative isotopic abundance measurements in a quadrupole time-of-flight mass spectrometer for elemental composition determination of natural products in traditional Chinese medicine.

The relative isotopic abundance (RIA) measurement errors of a quadrupole time-of-flight (Q-ToF) instrument incorporating analog-to-digital converter detectors were systemically evaluated by stochastically collecting about 200 data in positive ion mass spectrometry (MS) mode. Errors varied with peak intensities at definite spectral acquisition rates but were very close, even if peak intensities changed sharply at different spectral acquisition rates with the same concentration. Intensity thresholds were systematically defined at 1 Hz of spectral acquisition rates. RIA measurement errors were also evaluated using peak area. It seemed that peak area was better adapted for the high-intensity ions while peak intensity was suited for very low-intensity ions. Several known compounds were selected for RIA measurements for product ions in tandem mass spectropmetry (MS/MS) mode. An extract of a representative traditional Chinese medicinal, Paederia scandens was analyzed with high-performance liquid chromatography-electrospray ionization-QToF-MS/MS. The unique elemental compositions of some compounds could not be identified even with exact masses and MS/MS spectra of measured and reference compounds. RIA errors, especially of (M+2)M(-1), provided vital information for determining the elemental composition.

Analyses of the iridoid glucoside dimers in Paederia scandens using HPLC-ESI-MS/MS.

INTRODUCTION: Many dimers consisting of structurally similar monomers are difficult to be identified even using NMR. Rapid structural identification of iridoid glycoside dimers, especially isomeric dimers in a complicated matrix, remains desirable. OBJECTIVE: To develop a rapid, sensitive analytical method for structural elucidation of trace iridoid glycoside isomers in a complicated extract. METHODS: Three isomeric iridoid glucoside dimers, paederoscandoside, saprosmoside E and saprosmoside D, were isolated and further analysed by electrospray ionisation quadrupole time-of-flight tandem mass spectrometry (ESI-QTOF-MS/MS) in positive-ion mode. Energy-resolved mass spectrometry (ERMS) was used to provide information on the relative intensity of ions versus collision energy. The crude extract of Paederia scandens was analysed by HPLC-ESI-MS/MS. RESULTS: The relative abundance of product ions in the MS/MS spectra from ammonium adduct ions varied greatly for the three isomers. The energy-resolved experiments enhanced differences among the three isomers. A total of 13 iridoid glucoside dimers (three groups of isomers) in the extract of P. scandens were identified or tentatively characterised by using HPLC-ESI-QTOF based on the tandem mass spectra of references. CONCLUSION: Linkage sites between different hydroxyl groups on the sugar and carboxyl groups for the three groups of isomers are confirmed. The reason for fragmentation differences might be that cleavage of the glycosidic bond accompanies the active H in vicinal hydroxyl rearrangement. The MS method is a useful tool for the analysis of isomers, especially trace isomers in a complicated extract.