Biyoulactones A-C, new pentacyclic meroterpenoids from Hypericum chinense

Structurally diverse spirocyclic polycyclic polyprenylated acylphloroglucinols from Hypericum ascyron linn. and their anti-tumor activity

Ten spirocyclic polycyclic polyprenylated acylphloroglucinols (PPAP), hunascynols A-J (1-10), and 12 known analogs were isolated from the aerial parts of Hypericum ascyron Linn. Compounds 1 and 2, which share a 1,2-seco-spirocyclic PPAP skeleton, could be derived from spirocyclic PPAP, with a common octahydrospiro[cyclohexan-1,5'-indene]-2,4,6-trione core, through a cascade of Retro-Claisen, keto-enol tautomerism, and esterification reactions. Aldolization of normal spirocyclic PPAP yielded 3, which has a caged framework with a 6/5/6/5/6 ring system. The structures of these compounds were determined using spectroscopy and X-ray diffraction. The inhibitory activities of all isolates were tested in three human cancer cell lines and a zebrafish model. Compounds 1 and 2 displayed moderate cytotoxicity against HCT116 cells (IC₅₀ 6.87 and 9.86 μM, respectively). The mechanisms of these compounds were evaluated using Western blot assays. Compounds 3 and 5 inhibited the growth of sub-intestinal vessels in zebrafish embryos. Further, the target genes were screened using real-time PCR.

Intramolecular Tricarbonyl‐Ene Reactions and α‐Hydroxy‐β‐Diketone Rearrangements Inspired by the Biosynthesis of Polycyclic Polyprenylated Acylphloroglucinols

Structurally unique natural products pose biosynthetic puzzles whose solution can inspire new chemical reactions. Herein, we propose a unified biosynthetic pathway towards some complex meroterpenoids—the hyperireflexolides, biyoulactones, hybeanones and hypermonones. This hypothesis led to the discovery of uncatalyzed, intramolecular carbonyl‐ene reactions that are spontaneous at room temperature. We also developed an anionic cascade reaction featuring an α‐hydroxy‐β‐diketone rearrangement and an intramolecular aldol reaction to access four distinct natural product scaffolds from a common intermediate.

Chemical constituents from the flowers of Hypericum monogynum L. with COX-2 inhibitory activity

Hypericum monogynum L. (Hypericaceae) has been used as a folk Chinese medicine for the treatment of inflammatory related diseases. Cyclooxygenase-2 (COX-2) is a crucial target for the development of agents to treat inflammation. To search for anti-inflammatory compounds from traditional Chinese medicines, a chemical constituent study along with COX-2 inhibitory activity analysis was performed for this plant. In this study, sixteen chemical monomers, including three undescribed oxidative degradation polycyclic polyprenylated acylphloroglucinols (PPAPs, hypemoins C-E), two undescribed PPAPs (hypemoins A and B), and 11 known compounds, were identified from the flowers of H. monogynum. Their structures were characterized by HRESIMS, NMR techniques, ECD, and single crystal X-ray diffraction. Four flavonoid derivatives showed remarkable COX-2 inhibitory activities, with IC₅₀ values ranging from 0.220 ± 0.006 to 1.655 ± 0.098 μM. Among these compounds, the possible recognition mechanism between quercetin 3-(6″-O-caffeoyl)-β-3-D-galactoside and COX-2 was predicted by molecular docking analysis. Moreover, the multidrug resistance reversal activities for the selected compounds were evaluated.

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.

Total Synthesis of the Meroterpenoid Manginoid A as Fueled by a Challenging Pinacol Coupling and Bicycle-forming Etherification

The manginoids are a unique collection of bioactive natural products whose structures fuse an oxa-bridged spirocyclohexanedione with a heavily substituted trans-hydrindane framework. Herein, we show that such architectures can be accessed through a strategy combining a challenging pinacol coupling and bicycle-forming etherification with several additional chemo- and regioselective reactions. The success of these key events proved to be highly substrate and condition specific, affording insights for their application to other targets. As a result, not only has a 19-step total synthesis of manginoid A been achieved, but a potential roadmap to access other members of the family and related natural products has also been identified.

Hymoins A-D: Two Pairs of Polyprenylated Acylphloroglucinols from Hypericum monogynum and Their Light-Induced Transformation

Hymoins A-D (1-4), two pairs of light-induced transformative polyprenylated acylphloroglucinols with an unprecedented pentacyclic skeleton, were isolated from the flowers of Hypericum monogynum. The first decarbonylative ring contraction of complex natural products was investigated by light irradiation. Their structures were elucidated by nuclear magnetic resonance analysis, X-ray crystallography, and electronic circular dichroism calculations. In addition, compound 3 showed moderate inhibition efficacy of the platelet-activating-factor-induced aggregation of rabbit platelets.

Unusual derivatives from Hypericum scabrum

Three new compounds (1-3) with unusual skeletons were isolated from the n-hexane extract of the air-dried aerial parts of Hypericum scabrum. Compound 1 represents the first example of an esterified polycyclic polyprenylated acylphloroglucinol that features a unique tricyclo-[4.3.1.11,4]-undecane skeleton. Compound 2 is a fairly simple MPAP, but with an unexpected cycloheptane ring decorated with prenyl substituents, and compound 3 has an unusual 5,5-spiroketal lactone core. Their structures were determined by extensive spectroscopic and spectrometric techniques (1D and 2D NMR, HRESI-TOFMS). Absolute configurations were established by ECD calculations, and the absolute structure of 2 was confirmed by a single crystal determination. Plausible biogenetic pathways of compounds 1-3 were also proposed. The in vitro antiprotozoal activity of the compounds against Trypanosoma brucei rhodesiense and Plasmodium falciparum and cytotoxicity against rat myoblast (L6) cells were determined. Compound 1 showed a moderate activity against T. brucei and P. falciparum, with IC50 values of 3.07 and 2.25 μM, respectively.

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.

Phomeroids A and B: two novel cytotoxic meroterpenoids from the deep-sea-derived fungus Phomopsis tersa FS441

Phomeroids A (1) and B (2), two novel meroterpenoids representing two types of skeletons, together with one known homologous analogue (3) were isolated from the deep-sea-derived fungus Phomopsis tersa FS441.

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).

Cytotoxic Components from Hypericum elodeoides Targeting RXRα and Inducing HeLa Cell Apoptosis through Caspase-8 Activation and PARP Cleavage

To find small-molecule regulators of RXRα, a phytochemical study of Hypericum elodeoides was conducted. Fifteen compounds, including the new 1 and 6, were isolated from the whole plant of H. elodeoides. The absolute configuration of 1 was assigned by comparison of experimental and calculated ECD data. Compounds 1 and 6 exhibited concentration-dependent inhibitory effects on RXRα transcription and selectively inhibited the proliferation of HeLa cells. Western blot analysis suggested that 1 and 6 induced apoptosis of HeLa cells with time- and dose-dependent PARP cleavage. A caspase activation assay indicated that these two compounds triggered caspase-8 activation to induce apoptosis by the extrinsic pathway. Molecular docking results suggested that 1 and 6 interacted with the Arg319 moiety of RXRα-LBD. Ligands binding to RXRα have shown promise in the discovery of anticancer drugs. A fluorescence quenching assay indicated the binding of 1 and 6 to the RXRα with the binding constant ( K_D) fitted as 68.3 and 14.0 μM, respectively. A preliminary SAR study of the isolates was conducted to enhance the knowledge of the RXRα ligands. Thus, 1 and 6 might act as the small-molecule regulators of RXRα, which target RXRα and mediate HeLa cell apoptosis through the extrinsic pathways.

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.

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.

Cytotoxic Meroterpenoids with Rare Skeletons from Psidium guajava Cultivated in Temperate Zone

Three new meroterpenoids, guajavadials A-C (1-3), were isolated from Psidium guajava cultivated in temperate zone. Their structures were established by extensive spectroscopic evidence and electronic circular dichroism (ECD) calculations. Guajavadial A (1) represents a novel skeleton of the 3,5-diformylbenzyl phloroglucinol-coupled monoterpenoid, while guajavadials B (2) and C (3) are new adducts of the 3,5-diformylbenzyl phloroglucinol and a sesquiterpene with different coupling models. The plausible biosynthetic pathways as well as antimicrobial and cytotoxic activities of these meroterpenoids are also discussed. All these isolates exhibited moderate cytotoxicities against five human cancer cell lines, with 3 being most effective with an IC50 value of 3.54 μM toward SMMC-7721 cell lines.

Involucratusins A-H: Unusual Cadinane Dimers from Stahlianthus involucratus with Multidrug Resistance Reversal Activity

Three novel cadinane dimers, involucratusins A–C (1–3), five unique nor-cadinane-dimers, involucratusins D–H (4–8), together with a known compound (9) were isolated from the rhizomes of Stahlianthus involucratus. Their challenging structures and absolute configurations were determined by spectroscopic data, CD experimentation, chemical conversions and single-crystal X-ray diffraction. Compounds 1–3 are unusual cadinane dimers with new connection and novel cores. Compound 4 is a unique nor-cadinane-dimer, and 5 and 6 are two pairs of hemiketal racemates with novel dinor-cadinane-dimer backbone. Compounds 7 and 8 represent unusual dodecanor-cadinane-dimer and tetradecanor-cadinane-dimer carbon skeletons, respectively. The possible biogenetic pathways of 1–8 were proposed, involving nucleophilic addition, S_N2 nucleophilic displacement, [3 + 3] benzannulation, oxidative cleavage, decarboxylation, and oxidative phenol coupling reactions. Multidrug resistance (MDR) reversal activity assay of the isolates were evaluated in doxorubicin-resistant human breast cancer cells (MCF-7/DOX). The combined use of these novel cadinane dimers at a concentration of 10 μM increased the cytotoxicity of doxorubicin by 2.2–5.8-fold. It is the first report about the MDR reversal activity of cadinane dimers.

Prenylated benzophenones from Triadenum japonicum

Six new prenylated benzophenones, (-)-nemorosonol (1) and trijapins A-E (2-6), were isolated from the aerial parts of Triadenum japonicum. (-)-Nemorosonol (1) and trijapins A-C (2-4) have a common tricyclo[4.3.1.0(3,7)]decane skeleton, while 1 is an enantiomer of (+)-nemorosonol previously isolated from Clusia nemorosa. The absolute configuration of (-)-nemorosonol (1) was assigned by ECD spectroscopy. Trijapins A-C (2-4) are analogues of 1 possessing an additional tetrahydrofuran ring. Trijapins D (5) and E (6) are prenylated benzophenones with a 1,2-dioxane moiety and a hydroperoxy group, respectively. (-)-Nemorosonol (1) exhibited antimicrobial activity against Escherichia coli (MIC, 8 μg/mL), Staphylococcus aureus (MIC, 16 μg/mL), Bacillus subtilis (MIC, 16 μg/mL), Micrococcus luteus (MIC, 32 μg/mL), Aspergillus niger (IC50, 16 μg/mL), Trichophyton mentagrophytes (IC50, 8 μg/mL), and Candida albicans (IC50, 32 μg/mL), while trijapin D (5) showed antimicrobial activity against C. albicans (IC50, 8 μg/mL).

Synthesis of the furo[2,3-b]chromene ring system of hyperaspindols A and B

The synthesis of the unique furo[2,3-b]chromene ring system found in hyperaspidinols A and B, acylphloroglucinols from Hypericum chinense has been achieved in twelve steps. By comparison of the NMR spectra of the synthesized compounds with those of the natural products, a relative stereochemistry is suggested, especially that of the ketal carbon.

Hikiokoshins A-I, diterpenes from the leaves of Isodon japonicus

Diterpenes, hikiokoshins A-I, and twelve known diterpenes were isolated from the leaves of Isodon japonicus (Burm. f.) H. Hara (Lamiaceae). The hikiokoshins A-I possess various skeletons such as ternifonane {hikiokoshin A}, ent-6,7:8,15-diseco-6,8-cyclokauran-7,20-olide {hikiokoshin B}, ent-6,7-secokauran-7,20-olide {hikiokoshin C}, and ent-7,20-epoxykaurane {hikiokoshins D-I}. Their structures were elucidated on the basis of spectroscopic analysis. Antimicrobial activities of hikiokoshins A and B were evaluated.