Hyperprins A and B, Two Complex Meroterpenoids from Hypericum przewalskii

Filicinic Acid-Based Meroterpenoids with Antiproliferative Activity against Prostate Cancer PC-3 Cells from Dryopteris wallichiana

Nine new structurally diverse filicinic acid-based meroterpenoids (1-9) with four kinds of carbon skeletons were isolated from the rhizomes of Dryopteris wallichiana. Their structures, including the absolute configurations, were elucidated by comprehensive analysis of spectroscopic data, quantum chemical calculations, and single-crystal X-ray diffraction. Structurally, compounds 1-4 feature an unprecedented 6/6/5/6/6/6 hexacyclic system with a rare oxaspiro[4.5]decane core linking the filicinic acid and ent-kaurane-type diterpene moieties. Compounds 5-6 are rare hybrids of filicinic acid and carotane-type sesquiterpene. Compound 7 is an unusual rearranged filicinic acid-carotane-type sesquiterpene meroterpenoid. Compounds 8-9 are two enantiomeric pairs of new meroterpenoids constructed by filicinic acid and a germarane-type sesquiterpene. A plausible biosynthetic pathway for the nine compounds was proposed. Notably, compounds 5, 6, (+)/(-)-8, and (+)/(-)-9 were discovered to possess antiproliferative activity against PC-3 cells based on virtual screening, and in vitro bioassay. An interactive preprint version of the article can be found at https://www.authorea.com/doi/full/10.22541/au.172666991.17272585/v1.

Bicyclic polyprenylated acylphloroglucinol-related meroterpenoids as potent DRAK2 inhibitors from Hypericum patulum

As a both edible and medicinal plant, Hypericum patulum (Hypericaceae) is used as a natural herbal tea, scented tea, and folk medicine. In this study, eight undescribed bicyclic polyprenylated acylphloroglucinol-related meroterpenoids named hyperpatins A-H, along with eight known ones, were isolated from this plant. Their structures were elucidated on the basis of spectroscopic techniques, chemical method, X-ray crystallographic experiments, and electronic circular dichroism analyses. Hyperpatins A-H possess a characteristic pyran ring system diversely fused with the bicyclo[3.3.1]nonane-2,4,9-trione core, and hyperpatins C and D incorporate a unique α,β-unsaturated aldehyde moiety. Some of the isolates exhibited potent inhibitory effects on death-associated protein kinase-related apoptosis-inducing kinase 2 with IC50 values ranging from 2.60 ± 0.29 to 17.93 ± 3.08 μM. This is the first report of DRAK2 inhibitory activity for acylphloroglucinol-related meroterpenoids. The most active molecule hyperpatins C showed binding affinity with DRAK2 by hydrogen-bond and hydrophobic interactions in molecular docking and promoted the glucose-stimulated insulin secretion ability of primary islets.

(±)-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.

Formyl phloroglucinol meroterpenoids from the leaves of Eucalyptus globulus subsp. maidenii and their ATP-citrate lyase inhibitory activities

Three new formyl phloroglucinol meroterpenoids, eumaidials A-C (1-3), were isolated from the leaves of Eucalyptus globulus subsp. maidenii, along with ten known analogues (4-13). Their chemical structures were determined by various spectral data and electronic circular dichroism calculations. Eumaidial A (1) is the first β-caryophyllene-based formyl phloroglucinol meroterpenoids from the genus Eucalyptus. Compounds 1-4 and 10 exhibited ATP-citrate lyase inhibitory activities, and compounds 2 and 3 suppressed the hepatocyte lipogenesis.

Status of research on natural protein tyrosine phosphatase 1B inhibitors as potential antidiabetic agents: Update

Protein tyrosine phosphatase 1B (PTP1B) is a crucial therapeutic target for multiple human diseases comprising type 2 diabetes (T2DM) and obesity because it is a seminal part of a negative regulator in both insulin and leptin signaling pathways. PTP1B inhibitors increase insulin receptor sensitivity and have the ability to cure insulin resistance-related diseases. However, the few PTP1B inhibitors that entered the clinic (Ertiprotafib, ISIS-113715, Trodusquemine, and JTT-551) were discontinued due to side effects or low selectivity. Molecules with broad chemical diversity extracted from natural products have been reported to be potent PTP1B inhibitors with few side effects. This article summarizes the recent PTP1B inhibitors extracted from natural products, clarifying the current research progress, and providing new options for designing new and effective PTP1B inhibitors.

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.

Diverse polycyclic polyprenylated acylphloroglucinols with anti-neuroinflammatory activity from Hypericum beanii

A phytochemical investigation on the roots of Hypericum beanii resulted in the isolation of six new polycyclic polyprenylated acylphloroglucinols (PPAPs), hyperberlones A-F, along with fourteen known analogues. The structural characterization of these compounds was carried out by analyzing the HRESIMS data, 1D and 2D NMR spectroscopic data, electronic circular dichroism (ECD) calculations, and gauge-independent atomic orbital (GIAO) NMR calculations. Hyperberlone A (1) was a caged PPAP with a rare tricyclo[4.3.1.0^3,8]decane carbon skeleton. It was deduced to be biosynthetically generated from hyperbeanol C (8) through key Paternò-Büchi reaction, radical cascade cyclizations, and retro-aldol reaction. Compounds 4, 6, 7, 9, 14, and 16 exhibited significant nitric oxide (NO) production inhibitory effects in lipopolysaccharide (LPS)-induced BV-2 microglial cells with IC₅₀ values of 6.11-25.28 μM. Moreover, compound 4 significantly decreased the expression of cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in LPS-induced BV-2 microglia, as well as the phosphorylation of JNK.

Kiiacylphnols A-H, eight undescribed polycyclic polyprenylated acylphloroglucinols with anticancer activities from Hypericum przewalskii Maxim

Kiiacylphnols A-H, eight previously undescribed polycyclic polyprenylated acylphloroglucinols (PPAPs), along with two known congeners (hyperforcinol F and oxepahyperforin), were obtained from Hypericum przewalskii Maxim. The structures of these metabolites were confirmed by spectroscopic analyses, quantum-chemical ¹H and ¹³C NMR calculations with DP4+ analyses, electronic circular dichroism (ECD) comparisons and calculations. Kiiacylphnols A and B were the first [3.3.1]-type PPAPs with an unusual octahydrooxireno[2,3-i]chromene scaffold bearing a rare 6/6/6/3 ring system. More significantly, kiiacylphnol A and oxepahyperforin displayed cytotoxicity against acute myeloid leukemia and diffuse large B-cell lymphoma cell lines by inducing cell apoptosis.

(±)-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.

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.

Enantiomeric pairs of meroterpenoids with 11/5/6 spiro-heterocyclic systems from Hypericum kouytchense

Undescribed enantiomeric pairs of acylphloroglucinol related meroterpenoids with 11/5/6 spiro-heterocyclic systems were isolated from Hypericum kouytchense.

Probing Indole Diketopiperazine-Based Hybrids as Environmental-Induced Products from Aspergillus sp. EGF 15-0-3

Comprehensive analyses of the metabolite spectra of Aspergillus sp. EGF 15-0-3 under different culture conditions revealed the presence of unique environmental-induced metabolites exclusively from the rice medium. Subsequent target isolation afforded four unprecedented indole diketopiperazine-based hybrids with a pyrano[3',2':7,8]isochromeno[4,3-b]pyrazino[2,1-i]indole core (1 and 2) or a spiro[piperazine-2,2'-pyrano[3,4,5-de]chromene] scaffold (3 and 4). Putative biosynthetic pathways for 1-4, with Diels-Alder cycloadditions as key steps, were proposed. 1-4 exhibited selective cytotoxicities among several human cancer cells.

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.

(±)-hyperzewalsins A-D, four pairs of nor-monocyclic polyprenylated acylphloroglucinols with immunosuppressive activity from hypericum przewalskii maxim

Three pairs of previously undescribed 2,3-nor-monocyclic polyprenylated acylphloroglucinols (MPAPs), (±)-hyperzewalsins A-C, a pair of 1,2,3,4-nor-MPAPs, (±)-hyperzewalsins D, along with one undescribed precursor, hyperzewalsin E, were isolated and identified from the aerial parts of Hypericum przewalskii Maxim. (Hypericaceae), and their structures were confirmed by extensive spectroscopic analyses, and quantum-chemical calculations including electronic circular dichroism calculations and NMR calculations with a DP4+ analysis. Significantly, (±)-hyperzewalsins A-D represented the first nor-MPAPs bearing carbon chain constitutions based on diverse highly degraded phloroglucinols. (±)-Hyperzewalsins A-C were the rare nor-MPAPs characterized by degradations of C-2 and C-3 in the core decorated by scissions of C-3/C-4 and C-1/C-2 bonds through Retro-Claisen reactions. (±)-Hyperzewalsins D were the first examples of naturally occurring MPAPs with the loss of C-1/2/3/4 in the phloroglucinol ring formed by cleavages of C-3/C-4 and C-1/C-6 bonds via Retro-Claisen and decarboxylation reactions. Plausible biogenetic pathways for the isolates were proposed. The isolates were evaluated for their immunosuppressive activity in lipopolysaccharide-stimulated murine splenocytes.

Meroterpenoids: A Comprehensive Update Insight on Structural Diversity and Biology

Meroterpenoids are secondary metabolites formed due to mixed biosynthetic pathways which are produced in part from a terpenoid co-substrate. These mixed biosynthetically hybrid compounds are widely produced by bacteria, algae, plants, and animals. Notably amazing chemical diversity is generated among meroterpenoids via a combination of terpenoid scaffolds with polyketides, alkaloids, phenols, and amino acids. This review deals with the isolation, chemical diversity, and biological effects of 452 new meroterpenoids reported from natural sources from January 2016 to December 2020. Most of the meroterpenoids possess antimicrobial, cytotoxic, antioxidant, anti-inflammatory, antiviral, enzyme inhibitory, and immunosupressive effects.

Polyprenylated acylphloroglucinol meroterpenoids with PTP1B inhibition from Hypericum forrestii

Three new polyprenylated acylphloroglucinol meroterpenoids, hyperiforins A-C (1-3), were isolated from Hypericum forrestii (Chittenden) N. Robson, together with twelve known analogues (4-15). Their structures were established by extensive physical and spectroscopic data analysis. Compounds 1, 2, 5, 7, and 13-15 showed potent inhibitory effects on protein tyrosine phosphatase 1B with IC₅₀ values from 6.63 ± 2.40 to 14.21 ± 3.51 μM.

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 sporormielone A from a Sporormiella species.