New Acylphloroglucinol Derivatives with Diverse Architectures from Hypericum henryi

Hyperhenrones: Prenylated α-pyrones with anti-inflammatory activity from Hypericum henryi

Fourteen previously undescribed α-pyrone derivatives (1-14) together with four known analogs (15-18) were isolated from a traditional Chinese medicinal plant Hypericum henryi. Compounds (+)/(-)-1, 2, and 3 share a rare 6/6/4/6/6 polycyclic skeleton. Compound 14 was the first example of a 7,7-dimethyl-pyran-4-one moiety. Their structures were elucidated using comprehensive spectroscopic analyses and electronic circular dichroism calculations. The anti-inflammatory activities of 1-18 were screened in lipopolysaccharide-induced RAW264.7 cells. Among them, compounds 14, (+)-18, and (-)-18 exhibited inhibitory effects against nitric oxide production in LPS-induced RAW264.7 cells. Additionally, compound 14 suppressed the expression of cyclooxygenase-2 and inducible nitric oxide synthase in LPS-induced RAW264.7 cells. Furthermore, preliminary mechanism studies indicated that compound 14 suppressed the phosphorylation and degradation of the inhibitor of NF-κB, and this led to the inhibition of NF-κB activation.

Cytotoxic and Antibacterial Prenylated Acylphloroglucinols from Hypericum olympicum L

Two new bicyclo[3.3.1]nonane type bicyclic polyprenylated acylphloroglucinol derivatives (BPAPs), olympiforin A and B as well as three known prenylated phloroglucinols, were isolated from the aerial parts of Hypericum olympicum L. The structures of the isolated compounds were established by means of spectral techniques (HRESIMS and 1D and 2D NMR). All compounds were tested on a panel of human tumor (MDA-MB-231, EJ, K-562, HL-60 and HL-60/DOX) and non- tumorigenic (HEK-293 and EA.hy926) cell lines using the MTT assay. All tested compounds exerted significant in vitro cytotoxicity with IC₅₀ values ranging from 1.2 to 24.9 μM and from 0.9 to 34 μM on tumor and non-cancerous cell lines, respectively. Most of the compounds had good selectivity and were more cytotoxic to the tumor cell lines than to the normal ones. A degradation of the precursor caspase 9 for some of the compounds was observed; therefore, the intrinsic pathway of apoptosis is the most likely mechanism of cytotoxic activity. The BPAPs were examined for antibacterial and antibiofilm activity through the broth microdilution method and the protocol of Stepanović. They showed a moderate effect against Enterococcus faecalis and Streptococcus pyogenes but a very profound activity against Staphylococcus aureus with minimum inhibitory concentrations (MIC) in the range of 0.78-2 mg/L. Olympiforin B also had a great effect against methicillin-resistant S. aureus (MRSA) with an MIC value of 1 mg/L and a very significant antibiofilm activity on that strain with a minimum biofilm inhibition concentration (MBIC) value of 0.5 mg/L. The structures of the isolated compounds were in silico evaluated using ADME and drug likeness tests.

Synthesis of Polycyclic n/5/8 and n/5/5/5 Skeletons Using Rhodium-Catalyzed [5 + 2 + 1] Cycloaddition of Exocyclic-ene-vinylcyclopropanes and Carbon Monoxide

A rhodium-catalyzed [5 + 2 + 1] reaction of exocyclic-ene-vinylcyclopropanes (exo-ene-VCPs) and CO has been realized to access challenging tricyclic n/5/8 skeletons (n = 5, 6, 7), some of which are found in natural products. This reaction can be used to build tetracyclic n/5/5/5 skeletons (n = 5, 6), which are also found in natural products. In addition, 0.2 atm CO can be replaced by (CH₂O)_n as the CO surrogate to achieve the [5 + 2 + 1] reaction with similar efficiency.

Prenylated acylphloroglucinols from the fruits of Garcinia xanthochymus

Our continuous study of the dry fruits of Garcinia xanthochymus led to the isolation and structural characterization of four new prenylated acylphloroglucinols, xanthochymusones J-M (1-4), together with the known polycyclic polyprenylated acylphloroglucinols, garciniagifolone A (5) and garcinialiptone A (6). Their structures were elucidated by interpretation of NMR and MS spectroscopic data. Compound 1 bearing a similar core to that of hulupinic acid should be derived via oxidization and ring contraction of prenylated acylphloroglucinol. The inhibitory activities of all the compounds against three human hepatocellular carcinoma cell lines Huh-7, Hep 3B, and Hep G2 were evaluated, and compounds 4 and 5/6 exhibited moderate cytotoxic activities against Hep G2 cells with IC₅₀ values10.4 and 8.8 μM.

Polycyclic Polyprenylated Acylphloroglucinols Bearing a Lavandulyl-Derived Substituent from Garcinia xanthochymus Fruits

Many type B polycyclic polyprenylated acylphloroglucinols (PPAPs) bear a lavandulyl-derived substituent, and the configurational assignment of this side chain can be difficult and sometimes leads to erroneous conclusions. In this study, 21 PPAPs, including the new xanthochymusones A-I (1-9), have been isolated from the fruits of Garcinia xanthochymus and structurally characterized. The relative configuration of the C-30 stereocenter was assigned by a combination of chemical transformations, ¹H-¹H coupling constants, conformational analysis, and NOE experiments. The configurational assignment of compound 7 indicates that the relative configuration at C-30 of PPAPs is not always the same. The absolute configurations of the new compounds were assigned by ECD and X-ray diffraction data, as well as by biosynthetic considerations. Analysis of NMR data enabled the configurational revision of garcicowins C and D. All the isolated PPAPs were tested for antiproliferative activity against three human hepatocellular carcinoma cell lines, including Huh-7, Hep 3B, and HepG2. Compounds 5 and 6, 7-epi-isogarcinol (16), and coccinone C (17) exhibited moderate antiproliferative activity. Compounds 6 and 16 induced apoptosis and inhibited cell migration in Huh-7 cells, probably through downregulating the STAT3 signaling pathway. This study provides effective methods for configurational assignments of type B PPAPs.

Seco-polyprenylated acylphloroglucinols from Hypericum elodeoides induced cell cycle arrest and apoptosis in MCF-7 cells via oxidative DNA damage

Four undescribed seco-polyprenylated acylphloroglucinols (seco-PAPs), elodeoidesones A-D (1-4), were characterized from Hypericum elodeoides. Compound 1 represents the 1,6-seco-PAPs with fascinating 5/5 fused ring, while 2-4 possess a 1,2-seco-PAPs skeleton with a five-membered lactone core. Their structures including absolute configurations were established by spectroscopic analyses and quantum chemical computations. A possible biosynthetic pathway of 1-4 from normal PAPs was proposed. All the isolates were investigated for their cytotoxicity against tumor cells. Notably, 1 inhibited the proliferation of MCF-7 cells with the IC₅₀ value of 7.34 μM. Mechanism investigation indicated that 1 induced MCF-7 cells apoptosis by blocking cell cycle at S phase via inducing oxidative DNA damage.

(±)-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.

Photoredox-Catalyzed Cascade Reactions Involving Aryl Radical: Total Synthesis of (±)-Norascyronone A and (±)-Eudesmol

Herein, we have developed two types of photoredox-catalyzed cascade reactions using diaryliodonium salts for the concise synthesis of norascyronone A and β-eudesmol. A rationally designed photoredox-catalyzed arylation/cyclization/Friedel-Crafts cascade reaction of enone was exploited to generate the norascyronone polycyclic skeleton. A visible-light-induced radical cyclization/acyloxy-migration reaction was explored to forge the decalin skeleton of eudesmol, and mechanistic studies indicated the reaction was initiated by one-electron oxidation of the enol ester.

Structurally diverse polyprenylated acylphloroglucinols from Hypericum uralum Buch.-Ham. ex D. Don

Uralins A - D, four undescribed polycyclic polyprenylated acylphloroglucinols (PPAPs) featuring an unprecedented fused hexacyclic architecture, a unique monocyclic tetra-seco-tetranor-b-PPAP, an oxidative b-PPAP and a rare norspiroindane-type m-PPAP, respectively, were isolated from the aerial parts of Hypericum uralum, along with ten known PPAPs. Their structures and absolute configurations were elucidated by extensive spectroscopic techniques (MS, NMR, [α]_D, CD), conceivable biogenetic pathways and time-dependent density functional theory-based electronic circular dichroism (TDDFT-ECD) calculations. Biological assays showed three b-PPAPs had moderate antioxidative damage activities, while spiroindanes exhibited moderate cytotoxic effects.

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.

Nine prenylated acylphloroglucinols with potential anti-depressive and hepatoprotective activities from Hypericum scabrum

In our screening program for new biologically active secondary metabolites, nine new polycyclic polyprenyled acylphloroglucinols, hyperscabins D-L, together with three known compounds, were obtained from the aerial parts of Hypericum scabrum. The chemical structures of 1-9 were characterized by extensive spectroscopic analyses, nuclear magnetic resonance calculation with DP4+ probability analysis, and the electronic circular dichroism spectra were calculated. Compound 1 was an unusual prenylated acylphloroglucinol decorated with a 5-oxaspiro [4,5] deca-1,9-dione skeleton. Compound 2 was a newly identified spirocyclic polyprenylated acylphloroglucinol possessing a rare 5,5-spiroketal segment. Compounds 3, 8, and 10 (10 μM) exhibited pronounced hepatoprotective activity against d-galactosamine-induced WB-F344 cell damage in vitro assays. All test compounds (1, 3, and 7-12) demonstrated potential inhibitory effects at 10 μM against noradrenalinet ([³H]-NE) reuptake in rat brain synaptosome.

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

Longisglucinol A (1), a polycyclic polyprenylated acylphloroglucinol (PPAP) with a new skeleton, along with two new congeners, longisglucinols B (2) and C (3), were isolated from Hypericum longistylum. Compound 1 features an unparalleled 6/6/6/5 fused ring skeleton based on a unique 8-oxa-tetracyclo-[8.3.3.0^1,9.0^3,7]cetane core. Longisglucinol A showed remarkable anti-inflammatory activity by inducing macrophage M2 polarization through the suppression of NF-κB.

Dearomatized Isoprenylated Acylphloroglucinol Derivatives with Potential Antitumor Activities from Hypericum henryi

A series of dearomatized isoprenylated acylphloroglucinols derivatives, hyperhenols A-E (1-5), as well as seven known analogues (6-12), were characterized from Hypericum henryi. Their structures were determined by combination of NMR, ECD spectroscopy, and X-ray diffraction analysis. Compounds 1 and 6-8 were tested to exhibit potential antitumor properties, of which 6 and 7 inhibited cell growth through inducing apoptosis and cell cycle arrest. In addition, these compounds could induce autophagy and PINK1/Parkin-mediated mitophagy in cancer cell lines, as well as suppress lung cancer A549 cells metastasis in vitro.

Diverse Polyphenols from Hypericum faberi

Six new polyphenols with different isoprenylated xanthones, isoprenylated acylphloroglucinols, and chromone architectures, hyperfaberols A-F (1-6), were isolated from the whole plants of Hypericum faberi along with seven other related known compounds. In which hyperfaberols A/B (1/2) and 12-13 were isoprenylated xanthones, hyperfaberols C-E (3-5) and 8-11 were seven isoprenylated acylphloroglucinol derivatives, while 6-7 were two chromones. Their structures were elucidated by comprehensive analysis of their spectroscopic data as well as detailed comparison with the literature data. Compounds 1 and 11 showed cytotoxities against the human esophageal cancer cell line (ECA-109) and the pancreatic tumor cell line (PANC-1) in vitro, respectively.

Polycyclic polyprenylated acylphloroglucinols from Hypericum choisianum

Twenty-one polycyclic polyprenylated acylphloroglucinols, including three new compounds named as hyperichoisins A (3), B (14) and C (21), were isolated from the aerial parts of Hypericum choisianum. The structures of those new compounds were elucidated by analysis of mass, NMR data, and chiroptical properties. A bioassay showed that otogirinin B had significant inhibitory effect on cell proliferation of A549.

Prenylated Acylphloroglucinols from Hypericum faberi

The isolation and structure elucidation of six new prenylated acylphloroglucinols, faberiones A-F, from the whole plant of Hypericum faberi is reported. Faberiones A-D (1-4) share a rare styrene substituent and may be biosynthetically generated via further acylation of the acylphloroglucinols. By analyzing the MS and NMR data, the structures of the new isolates were established. Faberiones B (2) and C (3) showed moderate cytotoxicity against the pancreatic cell line (PANC-1) with IC₅₀ values of 6.2 and 9.0 μM, respectively.

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.

Garsubelone A, the First Dimeric Polycyclic Polyprenylated Acylphloroglucinols with Complicated Heptacyclic Architecture from Garcinia subelliptica

Garsubelone A (1), the first dimeric polycyclic polyprenylated acylphloroglucinols type metabolite featuring a complicated 6/6/6/6/6/6/6 heptacyclic architecture containing 10 stereogenic centers, was isolated from Garcinia subelliptica. Biogenetically, this compound was constructed by the plausible monomeric precursor, garsubelone B (2) and secohyperforin, via a key Diels-Alder cycloaddition to form an unique 2-oxabicyclo[3.3.1]nonane core. Their structures and absolute configurations were determined by comprehensive spectroscopic and X-ray diffraction techniques. The cytotoxic activities of these isolates were also evaluated.

Structural diversity and biological activities of phloroglucinol derivatives from Hypericum species

Plants of the genus Hypericum (Hypericaceae) are used in folk medicine all over the world, H. perforatum being the most well-known species. Standardized extracts of this plant are commercially-available to treat mild to moderate depression cases. The present review summarizes the literature published up to 2016 concerning the phloroglucinol derivatives isolated from Hypericum species, together with their structural features and biological activities. These phytochemical studies led to the isolation of 101 prenylated phloroglucinols, chromanes and chromenes, 35 dimeric acylphloroglucinols, 235 polycyclic polyprenylated acylphloroglucinols, 25 simple benzophenones and 33 phloroglucinol-terpene adducts. These compounds show a diverse range of biological activities, such as antimicrobial, cytotoxic, antinociceptive and antidepressant-like effects.

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.

Tricyclic Polyprenylated Acylphloroglucinols from St John's Wort, Hypericum perforatum

The new polyprenylated acylphloroglucinol derivatives 1-15 and the known furohyperforin (16) were isolated from the stems and leaves of Hypericum perforatum. Their structures were determined by analyses of NMR and HRESIMS data. Their absolute configurations were elucidated by a combination of electronic circular dichroism (ECD) and Rh₂(OCOCF₃)₄-induced ECD, as well as X-ray diffraction crystallography. The new hyperforatin F (9) contains a unique acetyl functionality at C-1 of the bicyclo[3.3.1]nonane core. Hyperforatins G (10) and H (11) are similarly the first examples of naturally occurring [3.3.1]-type polycyclic prenylated acylphloroglucinols possessing a carbonyl functionality at C-32. The compounds were tested for their acetylcholinesterase (AChE) inhibitory activities and cytotoxic activities against a panel of human tumor cell lines. Compounds 3, 5, 6, 8, and 9 exerted moderate inhibitory activities (IC₅₀ 3.98-9.13 μM) against AChE.

Skeleton Reassignment of Type C Polycyclic Polyprenylated Acylphloroglucinols

The previous assignment of the type C skeleton of polycyclic polyprenylated acylphloroglucinols (PPAPs) was controversial and proved to be incorrect in this study. The structures of the type C PPAPs (3-6) were revised to corresponding type A structures (3a-6a) via ¹³C NMR spectroscopic analysis and a quantum computational chemistry method. Therefore, only types A and B PPAPs are likely present in plants of the family Clusiaceae.

Furanmonogones A and B: two rearranged acylphloroglucinols with a 4,5-seco-3(2H)-furanone core from the flowers of Hypericum monogynum

Rearranged acylphloroglucinols with an unprecedented 4,5-seco-3(2H)-furanone skeleton, furanmonogones A (1) and B (2), were isolated from the flowers of Hypericum monogynum.

Norsampsone E, an unprecedented decarbonyl polycyclic polyprenylated acylphloroglucinol with a homoadamantyl core from Hypericum sampsonii

Norsampsone E, an unprecedented polycyclic polyprenylated acylphloroglucinol from Hypericum sampsonii, featured a homoadamantyl skeleton with the loss of the C-4 carbonyl.

Chiral separation and absolute configurations of two pairs of racemic polyprenylated benzophenones from Hypericum sampsonii

(±) Sampsonins A-B (1-2), two pairs of racemic polyprenylated benzophenones, were isolated from the aerial parts of Hypericum sampsonii and successfully separated by chiral HPLC column. Their structures were elucidated by spectroscopic analyses, X-ray diffraction analysis, and quantum chemical calculation of ECD method. Besides, the plausible biogenetic pathways of 1-2 were proposed, and all of them were evaluated for RXRα transcriptional-inhibitory activities and cytotoxicity against HeLa cells.

Hyperjapones A-E, Terpenoid Polymethylated Acylphloroglucinols from Hypericum japonicum

Hyperjapones A-E (1-5), novel terpenoid polymethylated acylphloroglucinols (TPAPs) with unusual architectures, were characterized from Hypericum japonicum. Their structures and absolute configurations were determined by comprehensive spectroscopic data and X-ray diffractions. Compound 1 was obtained as a racemic mixture and was separated by a column coated with cellulose tris(4-methylbenzoate) after attempts with various chiral materials. Compounds 1, 2, and 4 exhibited moderate antitumor activities in vitro.

Sampbenzophenones A–G, prenylated benzoylphloroglucinol derivatives from Hypericum sampsonii

Seven prenylated benzoylphloroglucinol derivatives, named sampbenzophenones A–G (1–7), together with two known analogues (8 and 9), were isolated from the aerial parts of Hypericum sampsonii.

Hypersampsones S–W, new polycyclic polyprenylated acylphloroglucinols from Hypericum sampsonii

Five new polycyclic polyprenylated acylphloroglucinols (1–5) with a bicyclo[3.3.1]nonane skeleton, along with five known analogues (6–10), were isolated from the aerial parts of Hypericum sampsonii.

1,9-seco-Bicyclic Polyprenylated Acylphloroglucinols from Hypericum uralum

Hyperuralones C-H (1-6), six new 1,9-seco-bicyclic polyprenylated acylphloroglucinols (1,9-seco-BPAPs) derived from the normal polyprenylated acylphloroglucinols with a bicyclo[3.3.1]nonane-2,4,9-trione core, together with six known analogues, were isolated from the aerial parts of Hypericum uralum. The structures of 1-6 were elucidated on the basis of the interpretation of NMR and MS spectroscopic data. The structure of attenuatumione B, a known compound isolated from H. attenuatum, was revised to that of a 1,9-seco-BPAP by NMR spectroscopic analysis and previous biomimetic synthesis methods. The inhibitory activities of these isolates on acetylcholinesterase were tested, and compounds 1 and 2 exhibited moderate activities with IC50 values of 9.6 and 7.1 μM, respectively.