Steroids, Tri- and Meroterpenoids with a Quinone Structure—A Review

Terpenoids with quinoid structures are found as natural products. This includes steroidal quinones, quinones with a secosteroid structure and meroterpenoid quinones. Importantly, catechol estrogens as endogenous metabolites of estradiol and estrone are precursors of reactive quinones and semiquinones, which are thought to contribute to estrogen-induced carcinogenesis. On the other hand, a number of quinones that include substituted naphthoquinones and anthraquinones are highly cytotoxic and have been used in cancer treatment. This makes the structures interesting synthetic targets. The following is a review of important natural and synthetic terpenoid and steroid quinone hybrids.

Meroterpenoids from Ganoderma Species:A Review of Last Five Years

Meroterpenoids are hybrid natural products that partially originate from the terpenoid pathway.Ganoderma meroterpenoids(GMs)are a type of meroterpenoids containing a 1,2,4-trisubstituted phenyl and a polyunsaturated terpenoid part.Over last 5 years,great efforts have been made to conduct phytochemistry research on the genus Ganoderma,which have led to the isolation and identification of a number of GMs.These newly reported GMs showed diverse structures and a wide range of biological activities.This review gives an overview of new GMs from genus Ganoderma and their biological activities and biosynthetic pathway,focusing on the period from 2013 until 2018.

Guajadials C-F, four unusual meroterpenoids from Psidium guajava

Guajadials C-F(1-4),four sesquiterpenoid-based meroterpenoids with unprecedented skeletons were isolated from the leaves of Psidium guajava.Their structures and relative configurations were established by extensive spectroscopic analysis.A possible biosynthetic pathway for 1-4 was also proposed.

Structurally Diverse Polymethylated Phloroglucinol Meroterpenoids from Baeckea frutescens

Phytochemical investigation of the MeOH extract of twigs and leaves of Baeckea frutescens led to the isolation of seven new polymethylated phloroglucinol meroterpenoids(PPMs),named baeckfrutones M-S(1-7).Their structures and absolute configurations were determined by spectroscopic analyses,chiral-phase HPLC analysis,and electronic circular dichroism(ECD)calculations.PPM 1 is a novel meroterpenoid possessing a 6/6/5/3 tetracyclic skeleton in PPMs,whereas 3 and 4 are the first hydroxytasmanone type phloroglucinol-monoterpene hybrids.(+)-2 and 7 displayed potent antiinflammatory activity with IC50 values of 20.86±0.60 and 36.21±1.18 lL,respectively.

Hyperlanins A and B, Two Highly Rearranged Meroterpenoids from Hypericum lancasteri

Hyperlanins A(1)and B(2),two highly rearranged polycyclic polyprenylated acylphloroglucinol(PPAP)-related meroterpenoids based on different new carbon skeletons,were isolated from Hypericum lancasteri.Compound 1 incorporates an unprecedented 5/6/7/5 ring system featuring a 3,13-dioxatetracyclo[9.2.1.12.5.01.8]pentadecane core.Compound 2 possesses a unique compact 6/6/5/6/6/5/6 ring system with a caged tetracyclo[6.2.1.13.8.05,11]dodecane motif.Their structures were established by spectroscopic data,X-ray diffraction,and computational approaches.Both compounds showed anti-inflammatory activity in vitro.Compounds 1 and 2 could decrease the lipopolysaccharide(LPS)-/nigericin-induced IL-1βrelease in THP-1 cells.Both compounds also showed inhibition in hypoxia-inducible factor-1α(HIF-1αa)pathway luciferase reporter assay.

Rapid discovery of two unprecedented meroterpenoids from Daphne altaica Pall.using molecular networking integrated with MolNetEnhancer and Network Annotation Propagation

Under the guidance of the approach which integrates molecular networking,MolNetEnhancer and Net-work Annotation Propagation(NAP),daphnaltaicanoids A and B(1 and 2)with unprecedented 9-oxa-tetracyclo[6.6.1.0^(2,6).0^(8,13)]pentadecane and tetracyclo[5.3.0.1^(2,5).2^(4,11)]tridecane central frameworks were iso-lated from Daphne altaica Pall.,representing two types of unparalleled meroterpenoid cores.Their struc-tures were elucidated by extensive spectroscopic analysis,nuclear magnetic resonance(NMR)calcula-tions,DP4+analysis and electronic circular dichroism(ECD)calculations.The plausible biosynthetic path-ways for 1 and 2 were postulated.Biologically,2 exerted potent neuroprotective activities which were su-perior to trolox at 12.5 and 25μmol/L.Moreover,1 and 2 exhibited more noticeable acetylcholinesterase inhibitory activities than donepezil.Molecular docking simulations were performed to explore the inter-molecular interaction of compounds 1 and 2 with acetylcholinesterase.The bioactivity evaluation results highlight the prospects of 1 and 2 as a novel category of neurological agents.

Divergent total synthesis of marine meroterpenoids(+)-dysidavarones A–C

Here,we report a concise and divergent enantioselective total synthesis of marine sesquiterpene quinone meroterpenoids(+)-dysidavarones A–C(1–3)using predysidavarone 6 as a key common intermediate.The highly strained and bridged eight-membered carbocycle of predysidavarone 6 was constructed by a one-pot intermolecular alkylation and intramolecular arylation of Wieland–Miescher ketone derivative 11 and benzyl bromide 12.The total synthesis of(+)-dysidavarones A–C(1–3)was achieved from predysidavarone 6 in a divergent manner by a late-stage introduction of the ethoxy group,which reveals the possible source of the ethoxy group within(+)-dysidavarones A–C(1–3)and provides a late-stage modifiable route for the synthesis of dysidavarone analogs for further anti-cancer activity evaluation.

(+)/(-)-Gerbeloid A,a pair of unprecedented coumarin-based polycyclic meroterpenoid enantiomers from Gerbera piloselloides:Structural elucidation,semi-synthesis,and lipid-lowering activity

A pair of coumarin-based polycyclic meroterpenoid enantiomers(+)/(-)-gerbeloid A[(+)-1a and(-)-1b]were isolated from the medicinal plant Gerbera piloselloides,which have a unique caged oxatricyclo[4.2.2.0^(3,8)]decene scaffold.Their planar and three-dimensional structures were exhaustively characterized by comprehensive spectroscopic data and X-ray diffraction analysis.Guided by the hypothetical biosynthetic pathway,the biomimetic synthesis of racemic 1 was achieved using 4-hydroxy-5-methylcoumarin and citral as the starting material via oxa-6πelectrocyclization and intramolecular[2+2]photocycloaddition.Subsequently,the results of the biological activity assay demonstrated that both(+)-1a and(-)-1b exhibited potent lipid-lowering effects in 3T3-L1 adipocytes and the high-fat diet zebrafish model.Notably,the lipid-lowering activity of(+)-1a is better than that of(-)-1b at the same concentration,and molecular mechanism study has shown that(+)-1a and(-)-1b impairs adipocyte differentiation and stimulate lipolysis by regulating C/EBPα/PPARγsignaling and Perilipin signaling in vitro and in vivo.Our findings provide a promising drug model molecule for the treatment of obesity.

Dimericbiscognienynes B and C: New diisoprenyl-cyclohexene-type meroterpenoid dimers from Biscogniauxia sp.

Dimericbiscognienynes B and C(1 and 2), two new diisoprenyl-cyclohexene-type meroterpenoid dimers,were isolated from Biscogniauxia sp. 71-10-1-1. Their structures, including the absolute configurations,were determined by spectroscopic analyses and ECD experiments. Meroterpenoids are special natural products that originate from mixed terpenoid-nonterpenoid pathway. As a member of meroterpenoid family, diisoprenyl-cyclohexene/ane-type meroterpenoids composed of two isoprenyl chains(C5 unit)and a cyclohexene/ane moiety(C6 unit), featuring diverse skeleton structures with wide range of bioactivities. In these reported diisoprenyl-cyclohexene/ane-type meroterpenoids, only three dimers were identified. The discovery of the two new dimers added members of this rare class of meroterpenoids.

Euphoractone,a cytotoxic meroterpenoid with an unusual entabietane-phloroglucinol skeleton,from Euphorbia fischeriana Steud.

A novel meroterpenoid,euphoractone(1),was isolated from the extracts of the roots of Euphorbia fischeriana Steud.Its structure was determined by spectroscopic methods and X-ray crystallography.1 possesses an unusual ent-abietane-phloroglucinol skeleton.The plausible biosynthetic pathway for 1 was proposed.1 showed inhibitory activities against human lung cancer H23 and H460 cells with the IC_(50)values of 21.07±3.54 and 20.91±4.07 μmol/L.

Guajamers A-I, Rearranged Polycyclic Phloroglucinol Meroterpenoids from Psidium guajava Leaves and Their Antibacterial Activity

Eight new polycyclic phloroglucinol meroterpenoids guajamers A-H(1-8),a methylated benzoylphloroglucinol meroterpenoid guajamer I(9)representing a new skeleton,and two known analogues(10 and 11)were isolated from the leaves of Psidium guajava.The structures of new molecules were elucidated by detailed analysis of spectroscopic data,and those of 1,2,8,and 9 were unambiguously confirmed by single-crystal X-ray diffraction study.Structurally,compounds 1-8 were sesquiterpene and monoterpene-based meroterpenoids with rearranged skeletons,while compound 9 was the first case of 3-alkyl-5-formyl-benzoylphloroglucinol-coupled sesquiterpene containing an unusual C-l-spiro-fused 6/6/9/4 polycyclic skeleton.In addition,all the isolated compounds were evaluated for their antibacterial activity against three bacterial strains,and most of them(compounds 2-7,10,and 11)showed antibacterial activity against Staphylococcus aureus and Staphylococcus epidermidis with MIC values of 8-32 μmol/L.These findings suggested that meroterpenoids isolated from Psidium guajava can be considered as potential antibacterial leading compounds for pharmaceutical industry.

Hyperterpenoids A and B:Two pairs of unprecedented 6/6/4/6/6 polycyclic cyclobutane meroterpenoids with potent neuroprotective and anti-inflammatory activities from Hypericum beanii

Hyperterpenoid A(1)and B(2),two pairs of enantiomers,with an unprecedented 6/6/4/6/6 polycyclic skeleton,along with one known compoud hypermonone A(3)were isolated from Hypericum beanii.The racemate(±)-1 and(±)-2 were successfully separated into the two optically pure enantiomers(ee>99%)using a preparative HPLC system.Their absolute configurations were elucidated by extensive spectroscopic analyses and single-crystal X-ray diffraction method.The related plausible biogenetic pathways were pre sented.Compound 1-3 showed significant neuroprotective activity and potential antiinflammatory activity.The result that(+)-2 and(-)-2 presented different anti-inflammatory properties,may lead us to new discovery of structure activity relationship between racemates,enantiomers,and diastereomers,as well as further research regarding the binding of drugs to target proteins.

Meroterpenthiazole A, a unique meroterpenoid from the deep-sea-derived Penicillium allii-sativi, significantly inhibited retinoid X receptor (RXR)-α transcriptional effect

A novel meroterpenoid,named meroterpenthiazole A(1),was isolated from the deep-sea-derived Penicillium allii-sativi.Its structure was established by extensive spectroscopic and computational methods.Meroterpenthiazole A bears a rare benzothiazole moiety in nature.Compound 1 significantly inhibited retinoid X receptor(RXR)-α transcriptional effect(K_(D)=12.3 μmol/L) through a novel binding mechanism.

New meroterpenoid compounds from the culture of mushroom Panus lecomtei

Two new meroterpenoid compounds(1 and 2) together with five known meroterpenoid derivatives(3–7) were isolated from solid culture of mushroom Panus lecomtei. The structures of new compounds were confirmed by the analysis of NMR and HRESI-MS spectroscopic data. The biosynthetic pathway of 1–7 was postulated. All isolated compounds were evaluated for antibacterial activities against Staphylococcus aureus, Escherichia coli, Bacillus subtilis, Pseudomonas aeruginosa and Bacillus Calmette–Guérin.Compound 3 exhibited weak antibacterial activity against Bacillus Calmette–Guérin with the inhibition rate of 83.6% at 100 μmol·L-1.Other compounds showed no antibacterial activities against all tested pathogens at 100 μmol·L-1.

Activation of an unconventional meroterpenoid gene cluster in Neosartorya glabra leads to the production of new berkeleyacetals

Fungal genomes carry many gene clusters seemingly capable of natural products biosynthesis,yet most clusters remain cryptic or down-regulated. Genome mining revealed an unconventional paraherquonin-like meroterpenoid biosynthetic gene cluster in the chromosome of Neosartorya glabra.The cryptic or down-regulated pathway was activated by constitutive expression of pathway-specific regulator gene ber A encoded within ber biosynthetic gene cluster. Chemical analysis of mutant Ng-OE:ber A extracts enabled the isolation of four berkeleyacetal congeners, in which two of them are new. On the basis of careful bioinformatic analysis of the coding enzymes in the ber gene cluster, the biosynthetic pathway of berkeleyacetals was proposed. These results indicate that this approach would be valuable for discovery of novel natural products and will accelerate the exploitation of prodigious natural products in filamentous fungi.

Hyperinoids A and B,two polycyclic meroterpenoids from Hypericum patulum

Hyperinoids A(1)and B(2),two prenylated acylphloroglucinol related meroterpenoids,were isolated from Hypericum patulum.Compound 1 incorporates an unprecedented 11,12-dioxatetracyclo[5.4.3.01,7.04,14]tetradecane system,while 2 possesses a unique 10,11-dioxatetracyclo[5.3.3.01,7.04,13]tridecane syste m.Their structures were established by spectro scopic analysis and X-ray crystallographic data.Compounds 1 and 2 were identified as potent NF-κB inhibitors and suppressed the LPS-induced inflammatory responses in RAW 246.7 macrophages and primary mouse BMDM cells.

Psiguamers A-C, three cytotoxic meroterpenoids bearing a methylated benzoylphloroglucinol framework from Psidium guajava and total synthesis of 1 and 2

Three sesquiterpene-based meroterpenoids psiguamers A-C(1-3)with new skeletons were isolated from Psidium guajava leaves.Compounds(±)-1 and(±)-2 were two pairs of humulene-de「ived meroterpenoids bearing a rare methylated benzoylphloroglucinol unit,while 3 was an unprecedented adduct of bicyclogermacrene and methylated benzoylphloroglucinol.Their structures were determined based on comprehensive analyses of spectroscopic data,calculated electronic circular dichroism(ECD)spectra,total synthesis,and X-ray crystallographic data.The biomimetic synthesis of(±)-1 and(±)-2 was achieved.Compound(+)-1 exhibited cytotoxic activities against five human tumor cell lines(HCT-116,HepG2,BGC-823,A549,and U251),with IC_(50) values of 2.94,9.01,6.45,5.42,and 5.33 μmol/L,respectively.

Arnequinol A and arnequinone A, two unique meroterpenoids from Arnebia euchroma

Arnequinol A(1),featuring an unprecedented 6/6/3 tricyclic carbon skeleton fused with a heptatomic oxo-bridge,together with arnequinone A(2)bearing a highly conjugated methyl-shifting benzogeijerene skeleton,were isolated from Arnebia euchroma.Their structures were elucidated by extensive spectro-scopic methods and quantum chemical calculations of the 13 C nuclear magnetic resonance(NMR)data and electronic circular dichroism(ECD)spectra.The plausible biosynthetic pathways for 1 and 2 were presented.In in vitro test,compound 2 showed potent neuroprotective activity against serum-deprivation induced PC12 cell damage at a concentration of 10μmol/L.

Periconones B-E,new meroterpenoids from endophytic fungus Periconia sp.

Periconones B-E（1-4）,four new polyketide-terpenoid hybrid molecules were isolated from the endophytic fungus Periconia sp.F-31.Their structures and absolute configurations were established by extensive spectroscopic data analysis and electronic circular dichroism（ECD）.Compound 4 exhibited in vitro cytotoxic activity against the human MCF-7 tumor cell line with an IC_（50） value of 4.2 μmol/L,and compound 1 displayed anti-HIV activity with an IC_（50） value of 18.0 μmol/L.

Amphichoterpenoids A-C,unprecedented picoline-derived meroterpenoids from the ascidian-derived fungus Amphichorda felina SYSU-MS7908

Amphichoterpenoids A-C(1-3),unprecedented picoline-derived meroterpenoids possessing a pyrano[3,2-c]pyridinyl-g-pyranone scaffold,were characterized from the ascidian-derived fungus Amphichorda felina SYSU-MS7908.Their structures were elucidated by spectroscopic methods,X-ray diffraction and electronic circular dichroism(ECD)calculations.A plausible biosynthetic pathway was proposed.The isolated compounds displayed moderate inhibitory activity against acetylcholinesterase with 50%inhibiting concentration(IC_(50))values of 18.8-53.2 mmol/L.