Hypatulins A and B, Meroterpenes from Hypericum patulum

(±)-Hypernumqulins A-H: Eight pairs of unexpected [2+2] cycloaddition sesquiterpenoid alkaloid with 6/6/6/4/10 ring system from Hypericum monogynum L

(±)-Hypernumqulins A-H (1-8), eight pairs of enantiomeric quinoline alkaloids fused with an isopentenyl and a germacrane-type sesquiterpenoid, featuring an unprecedented skeleton with 6/6/6/4/10 ring system, were isolated from Hypericum monogynum L. under the guidance of molecular networking strategy. Their structures including absolute configuration were elucidated by NMR spectroscopy analysis, X-ray crystallography and quantum chemical calculation. The proposed [2+2] cycloaddition may play a key biogenic step in building the unexpected skeleton. Most of the isolates exhibited cytotoxicity with IC50 values ranging from 2.82 ± 0.03 to 45.25 ± 1.26 μM against MCF-7, A549 or SGC7901 cells. Furthermore, compounds (±)-1 and (-)-1 could induce apoptosis by upregulating the protein expression level of Bax and downregulating of Bcl-2 in MCF-7 cells. These findings provided the first example of germacrane sesquiterpene quinoline alkaloids, and supported the possibilities for the development of new anti-tumor agents.

Formohyperins G-L, polycyclic prenylated benzoylphloroglucinols from the flowers of Hypericum formosanum

Phytochemical study on the flowers of Hypericum formosanum Maxim. (Hypericaceae) led to the isolation of formohyperins G-L (1-6), whose structures were assigned by detailed spectroscopic analysis. Formohyperins G-L (1-6) are new benzoylphloroglucinols substituted by a C10 unit, a prenyl group, and a methyl group. Formohyperins G-J (1-4) possess a 6/6/6-tricyclic structure, while formohyperins K (5) and L (6) have a unique 6/6/5/4-tetracyclic structure consisting of cyclohexadienone, dihydropyrane, cyclopentane, and cyclobutane rings. The absolute configurations of 1-6 were deduced by analysis of the ECD spectra. Formohyperins G-J (1-4) and L (6) were found to show potent inhibitory activities against IL-1β release from LPS-treated murine microglial cells with EC50 values of 5.0, 10.9, 6.3, 10.8, and 13.7 µM, respectively, without cytotoxicity. 6-O-Methylformohyperins G (1a) and I (3a) also exhibited the inhibitory activities with EC50 values of 4.7 and 2.7 µM, respectively, although they were cytotoxic against microglial cells.

Unique Reactivity of the 1,4-Bis(silyloxy)-1,3-cyclopentadiene Moiety: Application to the Synthesis of 7-Norbornanone Derivatives

We describe a method for the synthesis of various 2-silyloxy-2-norbornen-7-ones by exploiting the specific reactivity of the 1,4-bis(silyloxy)-1,3-cyclopentadiene framework, which is generated by the silylation of a 2,2-disubstituted-1,3-cyclopentanedione bearing a picolinoyloxy group at the 2' position of its C-2 side chain. The release of the acyloxy group during the reaction generates carbocations that are then attacked by silyloxy-substituted carbons in the 1,4-bis(silyloxy)-1,3-cyclopentadiene moiety skeleton, forming a 4,5-cis-fused ring skeleton. Skeletal rearrangement of the bicyclic core results in the formation of the corresponding 2-silyloxy-2-norbornen-7-one. This novel transformation of 1,3-cyclopentanedione moieties can be used to synthesise other cyclopentenone-fused bicyclic frameworks.

New Monoterpenoid Glycosides from the Fruits of Hypericum patulum Thunb

The whole Hypericum patulum Thunb. plant is utilized in traditional medicine for its properties of clearing heat, detoxifying, soothing meridians, relaxing the liver, and stopping bleeding. In folk medicine, it is frequently used to treat hepatitis, colds, tonsillitis, and bruises. Phytochemical investigation of a 30% ethanol extract of the fresh ripe fruits of H. patulum has resulted in the isolation of two new pinane-type monoterpenoid glycosides 1-2, named patulumside E-F, and three new chain-shaped monoterpenoid glycosides 3-5, named patulumside G-H, J. Their structures were determined using extensive spectroscopic techniques, such as HR-ESI-MS, 1D and 2D NMR spectroscopy, and electronic circular dichroism (ECD) calculation. The anti-inflammatory activities of these compounds were evaluated in the LPS-induced RAW264.7 cells. This research represents the inaugural comprehensive phytochemical study of H. patulum, paving the way for further exploration of monoterpenoid glycosides.

Meroterpenes and prenylated benzoylphloroglucinol from the flowers of Hypericum formosanum

Formohyperins A-F, previously undescribed meroterpenes, and grandone, a prenylated benzoylphloroglucinol being considered to be one of their biogenetic precursors, were isolated from the flowers of a Hypericaceous plant, Hypericum formosanum Maxim. Detailed spectroscopic analyses showed that formohyperins A-D were meroterpenes with an enolized 3-phenylpropane-1,3-dione moiety. Formohyperins E and F were elucidated as meroterpenes having a 4-benzoyl-5-hydroxycyclopent-4-ene-1,3-dione moiety. Formohyperins A-C and E were optically active, and their absolute configurations were deduced by comparison of the experimental and TDDFT calculated ECD spectra. In contrast, formohyperin D was concluded to be a racemate. Formohyperins A-F and grandone were found to show inhibitory activities against LPS-stimulated IL-1β production from murine microglial cells with EC50 values of 13.2, 6.6, 8.5, 24.3, 4.1, 10.9, and 3.0 μM, respectively.

Hyperipersions A-C, three new acylphloroglucinols from the branches and leaves of Hypericum perforatum L. with antiangiogenic activities

Three new acylphloroglucinols were isolated from the branches and leaves of Hypericum perforatum L., named as hyperipersions A-C (1-3), together with three known compounds which were identified as elegaphenone (4), 2,6-dihydroxy-3,4-dimethylbenzoic acid methyl ester (5) and 2,3-methylenedioxyxanthone (6), respectively. The structures of isolated compounds were determined by UV, IR, HR-ESI-MS, NMR analysis. Their antiangiogenic activities were studied against HUVECs. The IC50 value of compound 3 was 2.39 ± 0.21 μM against HUVECs, which was stronger than vatalanib, and other compounds had moderate antiangiogenic activity.

Hypericum Genus as a Natural Source for Biologically Active Compounds

Hypericum L. genus plants are distributed worldwide, with numerous species identified throughout all continents, except Antarctica. These plant species are currently used in various systems of traditional medicine to treat mild depression, wounds and burns, diarrhea, pain, fevers, and their secondary metabolites previously shown, and the in vitro and/or in vivo cytotoxic, antimicrobial, anti-inflammatory, antioxidant, antihyperglycemic, and hepatoprotective activities, as well as the acetylcholinesterase and monoamine oxidase inhibitory activities. We conducted a systematic bibliographic search according to the Cochrane Collaboration guidelines to answer the question: "What is known about plants of Hypericum genus as a source of natural products with potential clinical biological activity?" We documented 414 different natural products with confirmed in vitro/in vivo biological activities, and 58 different Hypericum plant species as sources for these natural products. Phloroglucinols, acylphloroglucinols, xanthones, and benzophenones were the main chemical classes identified. The selective cytotoxicity against tumor cells, cell protection, anti-inflammatory, antimicrobial, antidepressant, anti-Alzheimer's, and adipogenesis-inhibition biological activities are described. Acylphloroglucinols were the most frequent compounds with anticancer and cell-protection mechanisms. To date, no work has been published with a full descriptive list directly relating secondary metabolites to their species of origin, plant parts used, extraction methodologies, mechanisms of action, and biological activities.

Synthesis of 3-epi-Hypatulin B Featuring a Late-Stage Photo-Oxidation in Flow

A synthesis of 3-epi-hypatulin B, a highly oxygenated and densely functionalized bicyclic scaffold, is reported. The carbon skeleton was prepared by functionalization of a cyclopentanone and an intramolecular Mukaiyama aldol reaction. Highlights include a late-stage photo-oxidation of a methoxyallene to provide an ester group. The problems encountered in the batch process were solved by translation into a flow protocol. Our synthesis highlights the value of flow chemistry to enable challenging late-stage transformations in natural product synthesis.

Hyperpatulones C-G, new spirocyclic polycyclic polyprenylated acylphloroglucinols from the leaves of Hypericum patulum

Five new spirocyclic polycyclic polyprenylated acylphloroglucinols, Hyperpatulones C-G (1-5), were obtained from the leaves of Hypericum patulum. Their structures were characterized by the comprehensive analysis of their IR, NMR, CD spectra and HRESIMS data. All the new compounds were evaluated for the α-glycosidase inhibitory activities. Among them, compounds 3-5 showed α-glucosidase inhibitory activities, with IC₅₀ values of 14.06-37.69 μM.

Characteristic metabolites of Hypericum plants: their chemical structures and biological activities

Plants belonging to the genus Hypericum (Hypericaceae) are recognized as an abundant source of natural products with interesting chemical structures and intriguing biological activities. In the course of our continuing study on constituents of Hypericum plants, aiming at searching natural product-based lead compounds for therapeutic agents, we have isolated more than 100 new characteristic metabolites classified as prenylated acylphloroglucinols, meroterpenes, ketides, dibenzo-1,4-dioxane derivatives, and xanthones including prenylated xanthones, phenylxanthones, and xanthonolignoids from 11 Hypericum plants and one Triadenum plant collected in Japan, China, and Uzbekistan or cultivated in Japan. This review summarizes their chemical structures and biological activities.

Diverse Polycyclic Polyprenylated Acylphloroglucinol Congeners with Anti-Nonalcoholic Steatohepatitis Activity from Hypericum forrestii

The new polycyclic polyprenylated acylphloroglucinols, hyperforcinols A-J (1-10), were isolated from the fruits of Hypericum forrestii, together with 30 biogenetic congeners of known structures. The structures of hyperforcinols A-J were determined by HRESIMS and 1D/2D NMR spectroscopic analysis, and their absolute configurations were determined by a combination of the electronic circular dichroism (ECD) exciton chirality method, ECD calculations, and X-ray diffraction analysis. A selection of 25 isolates, possessing seven types of carbon skeletons, were assessed for their in vitro effects against nonalcoholic steatohepatitis (NASH) using a free fatty acid-induced L02 cell model. Compounds 20 and 40 significantly decreased intracellular lipid accumulation. QRT-PCR analyses revealed that compounds 20 and 40 regulate the expression of lipid metabolism-related genes, including CD36, FASN, PPARα, and ACOX1.

Neuraminidase Inhibitors from the Roots of Caragana sinica

Two new oligostilbenes, caragasinins D and E, along with four known compounds, kobophenol A, α-viniferin, wistin, and 5-hydroxy-2-[(4-hydroxyphenyl)acetyl]-3-methoxybenzoic acid, were isolated from the roots of Caragana sinica. These compounds were spectroscopically analyzed for their structures and configurations and compared with existing data. The configurations of caragasinins D and E were elucidated by ¹ H-NMR spectroscopy, CD spectroscopy, and time-dependent density-functional theory simulated ECD spectral data. All six compounds were evaluated for their inhibitory activity against neuraminidase (NA) from Clostridium perfringens. Among the tested compounds, 5-hydroxy-2-[(4-hydroxyphenyl)acetyl]-3-methoxybenzoic acid demonstrated statistically significant NA inhibitory activity, which was comparable to the positive control, mangiferin.

Enantiomeric chromene derivatives with anticancer effects from Mallotus apelta

Mallotusapelta(Lour.) Müll.Arg has been used in traditional medicine for the treatment of chronic hepatitis. Six new chromene derivatives, malloapeltas C-H (1-6) and one known compound, malloapelta B (7) were isolated and structured from the leaves of M.apelta. Two pairs of enantiomers (1a/1b and 2a/2b) were successfully separated by chiral high-pressure liquid chromatography (HPLC). The structures and absolute configurations of compounds were determined using spectroscopic methods, including 1D, 2D NMR, and MS and quantum chemical calculation methods. All compounds were evaluated for cytotoxic activity using cell counting kit-8 (CCK-8) assay against ovariancancer cell line (TOV-21G). Compounds 1-5 and 7 exhibited significant growth and viability inhibitory effects with GI₅₀ values ranging from 0.06 to 10.39 μM and IC₅₀ values ranging from 1.62 to 10.42 μM on ovarian cancer cell line, TOV-21G. The most cytotoxic compounds 2, 3, and 7 were chosen for studying in apoptosis mechanism. Compounds 2, 3, and 7-induced apoptosis as evidenced by activated caspase 8, caspase 9, and PARP, increased Bak and Bax, and decreased Bcl-xL and survivin. Moreover, compounds 2, 3, and 7 significantly inhibited the NF-κB signaling pathway. Taken together, our findings propose the potential application of compounds 2, 3, and 7 for treating cancer via modulating NF-κB activity.

Ethnopharmacology of Hypericum species in China: A comprehensive review on ethnobotany, phytochemistry and pharmacology

ETHNOPHARMACOLOGICAL RELEVANCE

Hypericum species have been used traditionally as astringent, antipyretic, diuretic, antiphlogistic, analgesic, and antidepressant in Europe, America, Africa, and Asia. One of the most extensively investigated medicinal herbs, H. perforatum L. (St. John's wort), is widely used in many countries to treat mild to moderate mental depression. Hypericum species are abundant throughout China, including 30 used as ethnomedicines. There are limited publications describing the ethnobotanical uses and biological activities associated with Hypericum species in China. Some reported activities include the treatment of wounds and bruises, irregular menstruation, dysentery, hepatitis, mastitis, jaundice, hemoptysis, and epistaxis.

AIM OF THE REVIEW

This review aims to critically examine how Hypericum species are used ethnomedicinally in China, to see if the ethnobotanical data may be useful to help prioritize Hypericum species and certain phytochemical constituents that may be new drug leads, and consider the focus and lack of the phytopharmacological study on Hypericum species in China.

MATERIALS AND METHODS

Classic medicinal books and ethnomedicinal publications were reviewed for the genus Hypericum (called jin si tao in Chinese). In addition, relevant information about ethnobotany, phytochemistry, and pharmacology were from online databases including SciFinder, Science Direct, PubMed, Google Scholar, and China National Knowledge Infrastructure (CNKI). "Hypericum", "", "ethnobotany", "traditional use", "ethnomedicine", "phytochemistry", "pharmacology" and "bioactivity" were used as keywords when searching the databases. Thus, available articles from 1959 to 2019 were collected and analyzed.

RESULTS

Among 64 Hypericum species recorded in China, 30 have been used as ethnomedicines by 15 linguistic groups such as Dai, Dong, Han, Miao, and Mongolian people. Hypericum species in China possess traditional uses which are also mirrored in Europe, America, Africa, and other countries in Asia. However, there are some unique ethnomedicinal uses in China. For example, several Hypericum species are used as a local remedy in southwest China, and H. attenuatum Fisch. ex Choisy is used to treat cardiac disorders in northeast China. Antitumor, anti-inflammatory, antimicrobial, neuroprotective, antidepressant, hepatoprotective, cardioprotective, and antiviral activities have been reported in numerous biological studies. The main phytochemical constituents in Hypericum consist of phloroglucinols, naphthodianthrones, xanthones, flavonoids, and terpenoids.

CONCLUSIONS

There is a rich traditional knowledge regarding the ethnomedicinal uses of Hypericum species in China. Through phytochemical and pharmacological studies, several medicinal Hypericum from China have yielded many bioactive phytochemicals, possessing antitumor, anti-inflammatory, antimicrobial, and neuroprotective properties. Hypericum species from China are potential sources of drugs to fight cancer and other chronic diseases. Remarkably, nearly half of Hypericum species in China have rarely been studied, and their ethnomedicinal potential have not been scientifically evaluated. Thus, in vitro mechanistic studies, in vivo pharmacology, and clinical efficacy are all needed, prioritizing those studies that relate most closely with their traditional uses. In addition, a comprehensive plant-resource evaluation, quality control, and toxicology studies are needed.

Hypericum spp.: An Update on the Biological Activities and Metabolic Profiles

Plants from the genus Hypericum, one genus of the Hypericaceae family, have attracted a lot of attention for their potential pharmaceutical applications. Most of the studies in the literature focus on H. perforatum L. (common St. John's wort), whose complex spectrum of bioactive compounds makes this species one of the top herbal remedies and supplements in the world. It is also important to compare the studies on other Hypericum species, both from the phytochemical and biological point of view. The aim of this review was to provide an update of most recent studies about biological investigations of plants belonging to Hypericum genus. The metabolic profiles of Hypericum spp. were also discussed in order to present a spectrum of secondary metabolites not previously identified in this genus.

Hypascyrins A-E, Prenylated Acylphloroglucinols from Hypericum ascyron

Six new prenylated acylphloroglucinols with menthane moieties, hypascyrins A-E (1-5) and ent-hyphenrone J (6), together with four known analogues, were isolated from Hypericum ascyron roots. Detailed spectroscopic data analyses resulted in the assignment of their structures. The absolute configuration of 1 was deduced by experimental and calculated ECD data, while those of 2-6 were assigned by ECD data analyses as well as chemical conversions. Hypascyrins A (1), C (3), and E (5) and ent-hyphenrone J (6) exhibited antimicrobial activity against MRSA (MIC₅₀ values of 4.0, 8.0, 2.0, and 4.0 μM, respectively) and Bacillus subtilis (MIC values of 4.0, 4.0, 2.0, and 4.0 μM, respectively).

FgaPT2, a biocatalytic tool for alkyl-diversification of indole natural products

Demonstration of FgaPT2 catalyzed alkyl-diversification of indole containing natural products.

Aromatic prenyltransferases from natural product biosynthetic pathways display relaxed specificity for their aromatic substrates. While a growing body of evidence suggests aromatic prenyltransferases to be more tolerant towards their alkyl-donor substrates, most studies aimed at probing their donor-substrate specificity are limited to only a small set of alkyl pyrophosphate donors, restricting their broader utility as biocatalysts for synthetic applications. Here, we assess the donor substrate specificity of an l-tryptophan C4-prenyltransferase, also known as C4-dimethylallyltryptophan synthase, FgaPT2 from Aspergillus fumigatus, using an array of 34 synthetic unnatural alkyl-pyrophosphate analogues, and demonstrate FgaPT2 can catalyze the transfer of 25 of the 34 non-native alkyl groups from their corresponding synthetic alkyl-pyrophosphate analogues at N1, C3, C4 and C5 position of tryptophan in a normal and reverse manner. The kinetic studies and regio-chemical analysis of the alkyl-l-tryptophan products suggest that the alkyl-donor transfer by FgaPT2 is a function of the stability of the carbocation and the steric factors in the active site of the enzyme. Further, to demonstrate the biocatalytic utility of FgaPT2, this study also highlights the FgaPT2-catalyzed synthesis of a small set of alkyl-diversified indolocarbazole analogues. These results reveal FgaPT2 to be more tolerant to diverse non-native alkyl-donor substrates beyond their known acceptor substrate promiscuity and set the stage for its development as a novel biocatalytic tool for the differential alkylation of natural products for drug discovery and other synthetic applications.

Hyperpatulones A-F, polycyclic polyprenylated acylphloroglucinols from Hypericum patulum and their cytotoxic activities

Six new compounds, hyperpatulones A-F (1-6), along with ten additional known related derivatives (7-16), were isolated from Hypericum patulum (Guttiferae). Their structures were elucidated by extensive analysis of spectroscopic data (IR, UV, HRESIMS, 1D and 2D NMR), X-ray crystallography, electronic circular dichroism (ECD) spectroscopy and Rh2(OCOCF3)4-induced ECD. All compounds were tested for their cytotoxic activities on human HepG-2, HeLa, MCF-7, and A549 cell lines via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Compound 5 exhibited significant cytotoxicities against HepG-2, HeLa and A549 cell lines with IC50 values of 9.52 ± 0.27, 11.87 ± 0.22 and 12.63 ± 0.12 μM, respectively.

Hyperdioxane A, a Conjugate of Dibenzo-1,4-dioxane and Sesquiterpene from Hypericum ascyron

Two new dibenzo-1,4-dioxane derivatives, hyperdioxanes A (1) and B (2), were isolated from the roots of a Hypericaceous plant, Hypericum ascyron. Hyperdioxane A (1) is a conjugate of dibenzo-1,4-dioxane and sesquiterpene with an unprecedented heptacyclic ring system. The structures of 1 and 2 were assigned by detailed spectroscopic analyses, including application of a modified Mosher's method. A possible biogenetic pathway of hyperdioxane A (1) from hyperdioxane B (2) and a sesquiterpene, eremophil-9,11(13)-dien-8β,12-olide (3), is presented.

Research Progress of Polycyclic Polyprenylated Acylphloroglucinols

Polycyclic polyprenylated acylphloroglucinols (PPAPs) are a class of hybrid natural products sharing the mevalonate/methylerythritol phosphate and polyketide biosynthetic pathways and showing considerable structure and bioactivity diversity. This review discusses the progress of research into the chemistry and biological activity of 421 natural PPAPs in the past 11 years as well as in-depth studies of biological activities and total synthesis of some PPAPs isolated before 2006. We created an online database of all PPAPs known to date at http://www.chem.uky.edu/research/grossman/PPAPs . Two subclasses of biosynthetically related metabolites, spirocyclic PPAPs with octahydrospiro[cyclohexan-1,5'-indene]-2,4,6-trione core and complicated PPAPs produced by intramolecular [4 + 2] cycloadditions of MPAPs, are brought into the PPAP family. Some PPAPs' relative or absolute configurations are reassigned or critically discussed, and the confusing trivial names in PPAPs investigations are clarified. Pharmacologic studies have revealed a new molecular mechanism whereby hyperforin and its derivatives regulate neurotransmitter levels by activating TRPC6 as well as the antitumor mechanism of garcinol and its analogues. The antineoplastic potential of some type B PPAPs such as oblongifolin C and guttiferone K has increased significantly. As a result of the recent appearances of innovative synthetic methods and strategies, the total syntheses of 22 natural PPAPs including hyperforin, garcinol, and plukenetione A have been accomplished.

Survey of natural products reported by Asian research groups in 2016

The new natural products reported in peer-reviewed articles in 2016 in journals with good reputations were reviewed and analyzed. The advances that Asian research groups made in the field of natural products chemistry in 2016 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on structural classification.

Chemical Components from Phaeanthus vietnamensis and Their Inhibitory NO Production in BV2 Cells

Phaeanthus vietnamensis Bân is a well-known medicinal plant which has been used for the treatment of various inflammatory diseases in traditional medicine. Using various chromatographic methods, three new compounds, (7S,8R,8'R)-9,9'-epoxy-3,5,3',5'-tetramethoxylignan-4,4',7-triol (1), 8α-hydroxyoplop-11(12)-en-14-one (5), and (1R,2S,4S)-4-acetyl-2-[(E)-(cinnamoyloxy)]-1-methylcyclohexan-1-ol (12) along with twelve known compounds were isolated from the leaves of P. vietnamensis. Their chemical structures were elucidated by physical and chemical methods. All compounds were evaluated for the inhibitory activities of nitric oxide production in LPS-stimulated BV2 cells. As the results, compound 6 showed the most potent inhibitory activity on LPS-stimulated NO production in BV2 cells with the IC₅₀ values of 15.7 ± 1.2 μm. Compounds 2, 7, and 8 significantly inhibited inflammatory NO production with IC₅₀ values ranging from 22.6 to 25.3 μm.

Sesquiterpene derivatives from marine sponge Smenospongia cerebriformis and their anti-inflammatory activity

Using various chromatographic methods, five new sesquiterpene derivatives named smenohaimiens A-E (1-5) and five known, 19-hydroxy-polyfibrospongol B (6), ilimaquinone (7), dictyoceratin C (8), polyfibrospongol A (9), and polyfibrospongol B (10) were isolated from the marine sponge Smenospongia cerebriformis Duchassaing & Michelotti, 1864. Their structures were assigned by 1D, 2D NMR spectroscopic analysis, HR ESI MS, and calculations of the electron circular dichroism spectra. All compounds were evaluated for the inhibitory activity against NO production in lipopolysaccharide-stimulated in BV2 microglia cells. As the results, compound 7 significantly inhibited NO production with the IC₅₀ value of 10.40±1.28µM. The remaining compounds showed moderate inhibitory NO production activities with IC₅₀ values ranging from 24.37 to 30.43µM.

Hot off the press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as hitorin A from Chloranthus japonicus.