Longisglucinols A-C, Structurally Intriguing Polycyclic Polyprenylated Acylphloroglucinols with Anti-inflammatory Activity from Hypericum longistylum

New α-Glucosidase Inhibitors from the Whole Plant of Hypericum beanii Based on Ligand Fishing and Molecular Networking Analysis

In this work, a new rapid and targeted method for screening α-glucosidase inhibitors from Hypericum beanii was developed and verified. Ten new polycyclic polyprenylated acylphloroglucinols (PPAPs), hyperlagarol A-J (1-10), and nine known PPAPs (11-19) were obtained from H. beanii. Their structures were identified by using comprehensive analyses involving mass spectrometry, ultraviolet spectroscopy, infrared spectroscopy, nuclear magnetic resonance spectroscopy, and electron capture dissociation calculations. 1 and 2 are two new rare 2,3-seco-spirocyclic PPAPs, 3 and 4 are two novel 12,13-seco-spirocyclic PPAPs, 5 and 6 are two novel spirocyclic PPAPs, 7 and 8 are two new unusual spirocyclic PPAPs with complex bridged ring systems, and 9 and 10 are two novel nonspirocyclic PPAPs. α-GC inhibitory activities of all isolated compounds were tested. Most of them displayed inhibitory activities against α-glucosidase, with the IC50 values ranging from 6.85 ± 0.65 to 112.5 ± 9.03 μM. Moreover, the inhibitory type and mechanism of the active compounds were further analyzed using kinetic studies and molecular docking.

Hyparillums A and B: polycyclic polyprenylated acylphloroglucinols from Hypericum patulum

Hyparillums A (1) and B (2), two previously unidentified polycyclic polyprenylated acylphloroglucinols (PPAPs) with intricate architectures, were isolated from Hypericum patulum Thunb. Hyparillum A was the first PPAP with eight-carbon rings based on an unprecedented 6/6/5/6/6/5/6/4 octocyclic system featuring a rare heptacyclo[10.8.1.11,10.03,8.08,21.012,19.014,17]docosane core. In contrast, hyparillum B featured a novel heptacyclic architecture (6/6/5/6/6/5/5) based on a hexacyclo[9.6.1.11,9.03,7.07,18.011,16]nonadecane motif. Furthermore, hyparillums A and B demonstrated promising inhibitory effects on the proliferation of murine splenocytes stimulated by anti-CD3/anti-CD28 monoclonal antibodies and lipopolysaccharide, exhibiting half-maximal inhibitory concentration (IC50) values ranging from 6.13 ± 0.86 to 12.69 ± 1.31 μmol·L-1.

Discovery of bioactive polycyclic polyprenylated acylphloroglucinols with adamantine/homoadamantane skeletons from Hypericum wilsonii

In this work, nine previous undescribed polycyclic polyprenylated acylphloroglucinols with adamantine/homoadamantane skeletons, cumilcinols A-I (1-9), along with six known analogues, were isolated and identified from the stems, leaves and flowers of Hypericum wilsonii. Their structures were determined by HRESIMS, NMR spectroscopic analysis, single-crystal X-ray crystallography as well as electronic circular dichroism calculations and comparisons. Compound 2 formed a unique furan ring bearing a rare acetal functionality. In bioassays, hyperacmosin G (13) could significantly inhibit the production of NO in LPS-stimulated RAW264.7 cell (IC50 = 4.350 ± 1.146 μM), and increased expression of related transcription factors at the gene level, inhibit the nuclear translocation of NF-κBp65, and reduce the protein expression of COX-2. Additionally, compound 5 showed significant inhibitory activity on Con A-induced T-lymphocyte proliferation (IC50 = 4.803 ± 3.149 μM), and treatment of 5 could reduce the increased ratio of CD4 and CD8 subpopulations induced by Con A in vitro. Those results indicated 13 possesses potential anti-inflammatory activity, and 5 exhibits a certain degree of immunosuppressive activity.

Maydistacins A-G, Terpestacin-type Sesterterpenoids with Anti-inflammatory Activity from the Phytopathogenic Fungus Bipolaris maydis

Seven undescribed terpestacin-type sesterterpenoids, maydistacins A-G (1-7), along with two known congeners (8 and 9), were isolated from the phytopathogenic fungus Bipolaris maydis collected from the leaves of Hypericum longistylum. The structures of 1-7 were elucidated based on extensive spectroscopic analysis, chemical methods, NMR calculations with DP4+ probability analysis, and comparison of experimental and calculated electronic circular dichroism (ECD) calculations. In vitro anti-inflammatory effects of these compounds were tested in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Compound 1 exhibited inhibition of the production of nitric oxide in LPS-induced macrophages, with an IC50 value of 19 ± 2 μM. A dexamethasone control displayed an IC50 value of 6.7 ± 0.6 μM. Compound 1 is the first terpestacin-type sesterterpenoid reported to display anti-inflammatory activity and may provide a novel chemical scaffold for the discovery of new anti-inflammatory drugs.

Discovery from Hypericum elatoides and synthesis of hyperelanitriles as α-aminopropionitrile-containing polycyclic polyprenylated acylphloroglucinols

The search for lead compounds with anti-neuroinflammatory activity from structurally 'optimized' natural products is a crucial and promising strategy in the quest to discover safe and efficacious agents for treating neurodegenerative diseases. A phytochemical investigation on the aerial portions of Hypericum elatoides led to the isolation of five nitrogenous polycyclic polyprenylated acylphloroglucinols (PPAPs), hyperelanitriles A-D (1-4) and hyperelamine A (5). Their structures were determined by spectroscopic analysis, ECD and NMR calculations, and X-ray crystallography. To the best of our knowledge, compounds 1-4 represent the first examples of acylphloroglucinols featuring an α-aminonitrile moiety, while 5 is a rare enamine-containing PPAP. Further, the synthesis of these naturally occurring PPAP-based nitriles or amines was accomplished. Compound 5 exhibited inhibitory activity against LPS-activated NO production in BV-2 cells, potentially through the suppression of TLR-4/NF-κB signaling. Here we show the isolation, structural elucidation, synthesis, and bioactive evaluation of compounds 1-5.

Prenyllongnols A-D, New Prenylated Acylphloroglucinols that Fight Concanavalin A-Induced Autoimmune Hepatitis

Autoimmune hepatitis is a serious hepatic disorder with unknown nosogenesis, and natural products have been deemed to be one of the most significant sources of new drugs against this disease. Prenyllongnols A-D (1-4), four undescribed prenylated acylphloroglucinols, were isolated from Hypericum longistylum. Compounds 1-4 exhibited remarkable immunosuppressive activities in murine splenocyte proliferation under the induction of concanavalin A (Con A), and IC50 values ranged from 2.98 ± 0.21 to 6.34 ± 0.72 μM. Furthermore, in a Con A-challenged autoimmune hepatitis mouse model, the mice in the group that were pretreated with isolate 2 significantly ameliorated liver injury and decreased proinflammatory cytokine production. Notably, natural product 2 was the first prenylated acylphloroglucinol to protect against concanavalin A-induced autoimmune hepatitis. This finding underscores the potential of prenylated acylphloroglucinol-type metabolites as promising candidates for designing novel immunosuppressors in the quest for new antiautoimmune hepatitis drugs.

Hyperelatolides A-D, Antineuroinflammatory Constituents with Unusual Carbon Skeletons from Hypericum elatoides

Four new δ- and γ-lactone derivatives, hyperelatolides A-D (1-4, respectively), were discovered from the aerial portions of Hypericum elatoides R. Keller. Their structures were elucidated by analysis of NMR spectra, HRESIMS, quantum chemical calculations of NMR and ECD spectra, and X-ray crystallographic data. Hyperelatolides A (1) and B (2) represent the first examples of δ-lactone derivatives characterized by a (Z)-(5,5-dimethyl-2-(2-oxopropyl)cyclohexylidene)methyl moiety and a benzoyloxy group attached to the β- and γ-positions of the δ-lactone core, respectively, while hyperelatolides C (3) and D (4) are unprecedented γ-lactone derivatives featuring substituents similar to those of 1 and 2. All compounds were tested for their inhibitory effects on NO production in LPS-activated BV-2 cells. Lactones 1 and 2 exhibited considerable antineuroinflammatory activity, with IC50 values of 5.74 ± 0.27 and 7.35 ± 0.26 μM, respectively. Moreover, the mechanistic study revealed that lactone 1 significantly suppressed nuclear factor kappa B signaling and downregulated the expression of inducible nitric oxide synthase and cyclooxygenase-2 in LPS-induced cells, which may contribute to its antineuroinflammatory 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.

(±)-Walskiiglucinol A, a pair of rearranged acylphloroglucinol derivative enantiomers from Hypericum przewalskii

(±)-Walskiiglucinol A (1a/1b), a pair of rearranged acylphloroglucinol derivatives with a new carbon skeleton, was obtained from Hypericum przewalskii. Compounds 1a/1b were the first examples of naturally occurring acylphloroglucinol derivatives possessing a unique 1-oxaspiro[4.4]nonane core bearing a new 5/5 ring system. Their planar and relative structures were identified by extensive spectroscopic analysis and NMR chemical shift calculations with DP4+ probability analysis, and their absolute configurations were determined by electronic circular dichroism (ECD) calculations. A plausible biogenetic pathway of 1a/1b was proposed in which the breakage of the C-2/C-3 linkage via a retro-Claisen reaction and the cyclization between C-3 and C-1 were proposed as key steps. The isolates were evaluated for cytotoxic activities against a panel of cancer cell lines and anti-inflammatory activities against lipopolysaccharide (LPS)-induced NO production, and compounds 1a/1b showed moderate cytotoxic activities with IC₅₀ values ranging from 9.72 to 36.75 μM.

Discovery of Undescribed Monoterpenoid Polyprenylated Acylphloroglucinols with Immunosuppressive Activities from Hypericum longistylum

Acylphlorostylums A-G (1-7), seven undescribed monoterpenoid polyprenylated acylphloroglucinols, were isolated and identified from Hypericum longistylum. Significantly, acylphlorostylums A and B were the first monoterpenoid polyprenylated acylphloroglucinols possessing a dodecahydro-1H-benzo [b]cyclopenta [e]oxepine moiety bearing a 6/7/5 fused tricyclic ring system that assembled by the attack from 4-OH to C-13. In addition, acylphlorostylums A-G exhibited moderate in vitro immunosuppressive activity in anti-CD3/anti-CD28 monoclonal antibodies, lipopolysaccharide and concanavalin A-induced murine splenocyte proliferation, with IC₅₀ values ranging from 1.51 ± 0.12 to 18.49 ± 1.67 μM, underscoring those isolates as novel chemical templates in the development of novel immunosuppressors.

Norprzewalsone A, a Rearranged Polycyclic Polyprenylated Acylphloroglucinol with a Spiro[cyclopentane-1,3'-tricyclo[7.4.0.01,6]tridecane] Core from Hypericum przewalskii

Norprzewalsone A (1), a rearranged polyprenylated polycyclic acylphloroglucinol (PPAP) with a new carbon skeleton, along with a new congener, norprzewalsone B (2), were isolated from Hypericum przewalskii. Compound 1 possessed a new 5/6/5/6/6 pentacyclic ring system based on a spiro[cyclopentane-1,3'-tricyclo[7.4.0.0^1,6]tridecane] core, which might be derived from the common [3.3.1]-type bicyclic polyprenylated acylphloroglucinol (BPAP) via the key retro-Claisen, intramolecular cyclization, and Diels-Alder cyclization reactions. Their structures and absolute configurations were confirmed by spectroscopic data, calculated 1D NMR data with DP4+ probability analyses, and electronic circular dichroism calculations and comparison. More significantly, compound 1 exhibited a moderate inhibitory effect on NO production in lipopolysaccharide-stimulated RAW264.7 cells.

Discovery of 13,15-nor-polycyclic polyprenylated acylphloroglucinols from Hypericum longistylum with anti-inflammatory activity

Spihyperglucinols A (1) and B (2), the first 13,15-nor-polycyclic polyprenylated acylphloroglucinols (PPAPs) featuring a 7/6/5 tricyclic ring system based on an unexpected bicyclo[3.2.2]nonane core, along with three new congeners, spihyperglucinols C-E (3-5), were isolated from Hypericum longistylum. Importantly, 1 and 2 displayed potential inhibitory effects on the production of nitric oxide in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages, with IC50 values of (8.70 ± 1.18) and (9.23 ± 1.26) μM, respectively, comparable to the positive control, dexamethasone, with an IC50 value of (9.76 ± 1.13) μM.

Hyperispirones A and B, spiro-bridged polycyclic polyprenylated acylphloroglucinols with anti-angiogenesis activity from Hypericum beanii

Two unprecedented spiro-bridged polycyclic polyprenylated acylphloroglucinols (PPAPs), one with a caged heptacyclo[18.3.1.01,20.02,17.03,15.06,15.08,13]tetracosane core bearing a dual-bridged spiro central feature (1) and the other with an unusual 8-oxa-tetracyclo[7.4.2.01,9,03,7]cetane ring system (2),...

Survey of natural products reported by Asian research groups in 2020

The new natural products reported in 2020 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2020 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

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.

Hyperbeanone A, a 5,6-seco-spirocyclic polycyclic polyprenylated acylphloroglucinol derivative with an unprecedented skeleton from Hypericum beanii

Hyperbeanone A (1), a novel 5,6-seco-polycyclic PPAP derivative characterized by an undescribed benz[f]indene-1,9(4H)-dione ring system fused to a tricyclic γ-lactone unit via a ketone carbonyl, was isolated from the aerial parts of Hypericum beanii.

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 longisglucinol A from Hypericum longistylum.