Structure and anti-TB activity of trachylobanes from the liverwort Jungermannia exsertifolia ssp. cordifolia

Two new anti-inflammatory trachylobane diterpenoids from Euphorbia atoto

Two new rare trachylobane euphoratones A-B (1-2), together with five known diterpenoids (compounds 3-7), were isolated from the aerial parts of Euphorbia atoto. Their structures were unambiguously elucidated through HRESIMS, 1D and 2D NMR spectral analysis. Compounds 1, 3, 4 and 7 showed weak anti-inflammatory activities (IC50 77.49 ± 6.34, 41.61 ± 14.49, 16.00 ± 1.71 and 33.41 ± 4.52 μM, respectively), compared to the positive control quercetin (IC50 15.23 ± 0.65 μM).

Transcriptome Analysis and Identification of Sesquiterpene Synthases in Liverwort Jungermannia exsertifolia

The liverwort Jungermannia exsertifolia is one of the oldest terrestrial plants and rich in structurally specific sesquiterpenes. There are several sesquiterpene synthases (STSs) with non-classical conserved motifs that have been discovered in recent studies on liverworts; these motifs are rich in aspartate and bind with cofactors. However, more detailed sequence information is needed to clarify the biochemical diversity of these atypical STSs. This study mined J. exsertifolia sesquiterpene synthases (JeSTSs) through transcriptome analysis using BGISEQ-500 sequencing technology. A total of 257,133 unigenes was obtained, and the average length was 933 bp. Among them, a total of 36 unigenes participated in the biosynthesis of sesquiterpenes. In addition, the in vitro enzymatic characterization and heterologous expression in Saccharomyces cerevisiae showed that JeSTS1 and JeSTS2 produced nerolidol as the major product, while JeSTS4 could produce bicyclogermacrene and viridiflorol, suggesting a specificity of J. exsertifolia sesquiterpene profiles. Furthermore, the identified JeSTSs had a phylogenetic relationship with a new branch of plant terpene synthases, the microbial terpene synthase-like (MTPSL) STSs. This work contributes to the understanding of the metabolic mechanism for MTPSL-STSs in J. exsertifolia and could provide an efficient alternative to microbial synthesis of these bioactive sesquiterpenes.

Diterpenoids with anti-inflammatory activity from Euphorbia wallichii

The Euphorbia plants are the focus of natural product drug discovery because of their fascinating structural diversity and broad biological activities. Here we reported the discovery of eight undescribed diterpenoids, including two ent-trachylobanes, five ent-atisanes, and one ent-abietane, together with 15 known ones from the whole plant of Euphorbia wallichii. Their chemical structures were elucidated by detailed spectrometry data analysis and X-ray crystallography. Among them, wallichane G represents a rare ent-atisane type pentacyclic diterpenoid featuring a tetrahydrofuran moiety. Furthermore, bioassays indicated that jolkinolide B exhibited potent inhibitory activities on the production of NO, with an IC₅₀ value of 3.84 ± 0.25 μM. Meanwhile, the mechanistic study revealed that jolkinolide B could obviously downregulate the expression of iNOS, COX-2, NF-κB, and phosphorylated IκBα in a dose-dependent manner and strongly upregulate the expression of Nrf2 and HO-1 protein, thereby suppressing the inflammatory process in macrophage cells induced by LPS.

Total Synthesis and Late-Stage C-H Oxidations of ent-Trachylobane Natural Products

Herein, we present our studies to construct seven ent-trachylobane diterpenoids by employing a bioinspired two-phase synthetic strategy. The first phase provided enantioselective and scalable access to five ent-trachylobanes, of which methyl ent-trachyloban-19-oate was produced on a 300 mg scale. During the second phase, chemical C-H oxidation methods were employed to enable selective conversion to two naturally occurring higher functionalized ent-trachylobanes. The formation of regioisomeric analogs, which are currently inaccessible via enzymatic methods, reveals the potential as well as limitations of established chemical C-H oxidation protocols for complex molecule synthesis.

Total Synthesis and Late-Stage C-H Oxidations of ent-Trachylobane Natural Products

Herein, we present our studies to construct seven ent-trachylobane diterpenoids by employing a bioinspired two-phase synthetic strategy. The first phase provided enantioselective and scalable access to five ent-trachylobanes, of which methyl ent-trachyloban-19-oate was produced on a 300 mg scale. During the second phase, chemical C-H oxidation methods were employed to enable selective conversion to two naturally occurring higher functionalized ent-trachylobanes. The formation of regioisomeric analogs, which are currently inaccessible via enzymatic methods, reveals the potential as well as limitations of established chemical C-H oxidation protocols for complex molecule synthesis.

The Potential of Natural Diterpenes Against Tuberculosis: An Updated Review

Every year, 10 million people are affected by tuberculosis (TB). Despite being a preventable and curable disease, 1.5 million people die from TB each year, making it the world's top infectious disease. Many of the frontline antibiotics cause painful and disagreeable side effects. To mitigate the side effects from the use of chemically synthesized or clinical anti-tubercular drugs, there are many research studies focussed on natural products as a source of potential anti-tuberculosis drugs. Among different phytoconstituents, several classes of diterpenoids exert significant antimicrobial effects. This review explores diterpenoids as potential anti-tubercular drugs from natural sources. A total of 204 diterpenoids isolated from medicinal plants and marine species are discussed that inhibit the growth of Mycobacterium tuberculosis. The literature from 1994-2018 is reviewed, and 158 diterpenoids from medicinal plants, as well as 40 diterpenoids from marines, are alluded to have antituberculosis properties. The antitubercular activities discussed in the review indicate that the type of diterpenoids, the Mtb strains, substituents attached to diterpenoids and their position in the diterpenoids general skeleton can change the compounds antimycobacterial inhibitory effects.

Antiproliferative and Antimicrobial Activities of Selected Bryophytes

One-hundred and sixty-eight aqueous and organic extracts of 42 selected bryophyte species were screened in vitro for antiproliferative activity on a panel of human gynecological cancer cell lines containing HeLa (cervix epithelial adenocarcinoma), A2780 (ovarian carcinoma), and T47D (invasive ductal breast carcinoma) cells using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and for antibacterial activity on 11 strains using the disc-diffusion method. A total of 99 extracts derived from 41 species exerted ≥25% inhibition of proliferation of at least one of the cancer cell lines at 10 μg/mL. In the cases of Brachythecium rutabulum, Encalypta streptocarpa, Climacium dendroides, Neckera besseri, Pleurozium schreberi, and Pseudoleskeella nervosa, more than one extract was active in the antiproliferative assay, whereas the highest activity was observed in the case of Paraleucobryum longifolium. From the tested families, Brachytheciaceae and Amblystegiaceae provided the highest number of antiproliferative extracts. Only 19 samples of 15 taxa showed moderate antibacterial activity, including the most active Plagiomnium cuspidatum, being active on 8 tested strains. Methicillin-resistant Staphylococcus aureus (MRSA) and Staphylococcus aureus were the most susceptible to the assayed species. This is the first report on the bioactivities of these 14 species.

Chemical Constituents of Bryophytes: Structures and Biological Activity

Comparatively little attention has been paid to the bryophytes for use in the human diet or medicine in spite of the presence of 23 000 species globally. Several hundred new compounds have been isolated from the liverworts (Marchantiophyta), and more than 40 new carbon skeletons of terpenoids and aromatic compounds were found. Most of the liverworts studied elaborate characteristic odiferous, pungent, and bitter-tasting compounds, of which many show antimicrobial, antifungal, antiviral, allergic contact dermatitis, cytotoxic, insecticidal, anti-HIV, plant growth regulatory, neurotrophic, NO production and superoxide anion radical release inhibitory, muscle relaxing, antiobesity, piscicidal, and nematocidal activities. The biological effects ascribed to the liverworts are mainly due to lipophilic sesqui- and diterpenoids, phenolic compounds, and polyketides, which are the principal constituents of their oil bodies. Some mosses and liverworts produce significant levels of vitamin B₂ and tocopherols, as well as prostaglandin-like highly unsaturated fatty acids. The most characteristic chemical phenomenon of the liverworts is that most of the sesqui- and diterpenoids are enantiomers of those found in higher plants. In this review, the chemical constituents and potential medicinal uses of bryophytes are discussed.

Diterpenes as lead molecules against neglected tropical diseases

Nowadays, neglected tropical diseases (NTDs) are reported to be present everywhere. Poor and developing areas in the world have received great attention to NTDs. Drug resistance, safety profile, and various challenges stimulate the search for alternative medications. Plant-based drugs are viewed with great interest, as they are believed to be devoid of side effects. Diterpenes, a family of essential oils, have showed attractive biological effects. A systematic review of the literature was carried out to summarize available evidences of diterpenes against NTDs. For this, databases were searched using specific search terms. Among the 2338 collected reports, a total of 181 articles were included in this review. Of them, 148 dealt with investigations using single organisms, and 33 used multiple organisms. No mechanisms of action were reported in the case of 164 reports. A total of 93.92% were related to nonclinical studies, and 4.42% and 1.66% dealt with preclinical and clinical studies, respectively. The review displays that many diterpenes are effective upon Chagas disease, chikungunya, echinococcosis, dengue, leishmaniasis, leprosy, lymphatic filariasis, malaria, schistosomiasis, and tuberculosis. Indeed, diterpenes are amazing drug candidates against NTDs. Copyright © 2016 John Wiley & Sons, Ltd.

Notolutesins A-J, dolabrane-type diterpenoids from the Chinese liverwort Notoscyphus lutescens

Ten new dolabrane-type diterpenoids, notolutesins A-J (1-10), were isolated from the Chinese liverwort Notoscyphus lutescens, along with four known compounds. The structures of the new compounds were established on the basis of extensive spectroscopic data, and that of 1 was confirmed by single-crystal X-ray crystallography. The absolute configuration of 1 was determined by comparing its experimental and calculated electronic circular dichroism spectra. All of the isolates were evaluated for their cytotoxicity against a small panel of human cancer cell lines, and compound 1 exhibited an IC50 value of 6.2 μM against the PC3 human prostate cancer cell line.

Evaluation of the anti-mycobacterium tuberculosis activity and in vivo acute toxicity of Annona sylvatic

Background

The recent emergence of extensively multidrug-resistant Mycobacterium tuberculosis strains has further complicated the control of tuberculosis. There is an urgent need for the development of new molecular candidates antitubercular drugs. Medicinal plants have been an excellent source of leads for the development of drugs. The aim of this study was to evaluate the in vitro activity of 28 alcoholic extracts and essential oils of native and exotic Brazilian plants against Mycobacterium tuberculosis and to further study these extracts through chemical fractionation, the isolation of their constituents, and an evaluation of the in vivo acute toxicity of the active extracts. To the best of our knowledge this is the first chemical characterization, antituberculosis activity and acute toxicity evaluation of Annona sylvatica.

Methods

The anti-mycobacterial activity of these extracts and their constituent compounds was evaluated using the resazurin reduction microtiter assay (REMA). To investigate the acute toxicity of these extracts in vivo, female Swiss mice were treated with the extracts at doses of 500, 1000 and 2000 mg · kg^-1 of body weight. The extracts were characterized by LC-MS, and the constituents were isolated and identified by chromatographic analysis of spectroscopic data.

Results

Of the 28 extracts, the methanol extract obtained from the leaves of Annona sylvatica showed anti-mycobacterial activity with an minimal inhibitory concentration (MIC) of 184.33 μg/mL, and the ethyl acetate fraction (EAF) resulting from liquid-liquid partitioning of the A. sylvatica extract showed an MIC of 115.2 μg/mL. The characterization of this extract by LC-MS identified flavonoids and acetogenins as its main constituents. The phytochemical study of the A. sylvatica EAF resulted in the isolation of quercetin, luteolin, and almunequin.

Conclusions

Among the compounds isolated from the EAF, luteolin and almunequin were the most promising, with MICs of 236.8 μg/mL (827.28 μM) and 209.9 μg/mL (328.48 μM), respectively. The acute administration of the EAF fraction in doses of 500, 1000, and 2000 mg · kg^-1 of body weight did not cause signs of toxicity in the treated animals.

Chlorinated coumarins from the polypore mushroom Fomitopsis officinalis and their activity against Mycobacterium tuberculosis

An EtOH extract of the polypore mushroom Fomitopsis officinalis afforded two new naturally occurring chlorinated coumarins, which were identified as the previously synthesized compounds 6-chloro-4-phenyl-2H-chromen-2-one (1) and ethyl 6-chloro-2-oxo-4-phenyl-2H-chromen-3-carboxylate (2). The structures of the two isolates were deduced by ab initio spectroscopic methods and confirmed by chemical synthesis. In addition, an analogue of each was synthesized as 7-chloro-4-phenyl-2H-chromen-2-one (3) and ethyl 7-chloro-2-oxo-4-phenyl-2H-chromen-3-carboxylate (4). All four compounds were characterized physicochemically, and their antimicrobial activity profiles revealed a narrow spectrum of activity with lowest MICs against the Mycobacterium tuberculosis complex.

Relaxant effect of Ent-7α-hydroxytrachyloban-18-oic acid, a trachylobane diterpene from Xylopia langsdorfiana A. St-Hil. & Tul., on tracheal smooth muscle

Ent-7α-hydroxytrachyloban-18-oic acid, a trachylobane diterpene from Xylopia langsdorfiana, has previously been shown to relax the guinea-pig trachea in a concentration-dependent manner. In this study we aimed to elucidate the mechanisms underlying this action and so contribute to the discovery of natural products with therapeutic potential. A possible interaction between diterpene and the Ca²⁺-calmodulin complex was eliminated as chlorpromazine (10^-6 M), a calmodulin inhibitor, did not significantly alter the diterpene-induced relaxation (pD₂ = 4.38 ± 0.07 and 4.25 ± 0.07; mean ± S.E.M., n=5). Trachylobane-318 showed a higher relaxant potency when the trachea was contracted by 18 mM KCl than it did with 60 mM KCl (pD₂ = 4.90 ± 0.25 and 3.88 ± 0.01, n=5), suggesting the possible activation of K⁺ channels. This was confirmed, as in the presence of 10 mM TEA⁺ (a non-selective K⁺ channel blocker), diterpene relaxation potency was significantly reduced (pD₂ = 4.38 ± 0.07 to 4.01 ± 0.06, n=5). Furthermore, K⁺ channel subtypes K_ATP, K_V, SK_Ca and BK_Ca seem to be modulated positively by trachylobane-318 (pD₂ = 3.91 ± 0.003, 4.00 ± 0.06, 3.45 ± 0.14 and 3.80 ± 0.05, n=5) but not the K_ir subtype channel (pD₂ = 4.15 ± 0.10, n=5). Cyclic nucleotides were not involved as the relaxation due to aminophylline (pD₂ = 4.27 ± 0.09, n=5) was not altered in the presence of 3 × 10^-5 M trachylobane-318 (pD₂ = 4.46 ± 0.08, n=5). Thus, at a functional level, trachylobane-318 seems to relax the guinea-pig trachea by positive modulation of K⁺ channels, particularly the K_ATP, K_V, SK_Ca and BK_Ca subtypes.

Phytochemical and biological studies of bryophytes

The bryophytes contain the Marchantiophyta (liverworts), Bryophyta (mosses) and Anthocerotophyta (hornworts). Of these, the Marchantiophyta have a cellular oil body which produce a number of mono-, sesqui- and di-terpenoids, aromatic compounds like bibenzyl, bis-bibenzyls and acetogenins. Most sesqui- and di-terpenoids obtained from liverworts are enantiomers of those found in higher plants. Many of these compounds display a characteristic odor, and can have interesting biological activities. These include: allergenic contact dermatitis, antimicrobial, antifungal and antiviral, cytotoxic, insecticidal, insect antifeedant, superoxide anion radical release, 5-lipoxygenase, calmodulin, hyaluronidase, cyclooxygenase, DNA polymerase β, and α-glucosidase and NO production inhibitory, antioxidant, piscicidal, neurotrophic and muscle relaxing activities among others. Each liverwort biosynthesizes unique components, which are valuable for their chemotaxonomic classification. Typical chemical structures and biological activity of the selected liverwort constituents as well as the hemi- and total synthesis of some biologically active compounds are summarized.

Ent-pimarane and ent-trachylobane diterpenoids from Mitrephora alba and their cytotoxicity against three human cancer cell lines

Bioassay-guided fractionation of the hexane extract of the branches of Mitrephora alba led to the isolation of five diterpenoids: ent-8β-hydroxypimar-15-en-18-oic acid, ent-15,16-dihydroxypimar-8(14)-en-18-oic acid, ent-3β-hydroxytrachyloban-18-oic acid, ent-3β-hydroxytrachyloban-18-al and methyl ent-3β-hydroxytrachyloban-18-oate, together with five related known diterpenoids. The structures were elucidated by spectroscopic analysis and comparison with literature data. All isolated compounds were evaluated for their cytotoxic activities against three human cancer cell lines. The results showed that three ent-trachylobane diterpenes had moderate cytotoxicity against NCI-H187 cancer cells.

NMR-based conformational analysis of perezone and analogues

Complete assignment of the (1)H NMR chemical shift and coupling constant values of perezone (1), O-methylperezone (2) and 6-hydroxyperezone (3) was carried out by total-line-shape-fitting calculations using the PERCH iterative spectra analysis software (PERCH Solutions Ltd., Kuopio, Finland). The resulting simulated spectra for the three compounds showed strong similarity to their corresponding experimental spectra. Particularly, all vicinal, allylic and homoallylic coupling constant values for the side chain of the three compounds were very similar, thus revealing that the conformation of these three molecules in solution is indeed almost identical. This fact is in agreement with extended side chain conformations over folded chain conformations because 1, 2 and 3 undergo completely different intramolecular cycloaddition reactions. In addition, results of double pulsed field gradient spin echo NOESY 1D experiments performed on perezone (1) were unable to provide evidence for folded conformers.

Absolute configuration and 1H NMR characterization of rosmaridiphenol diacetate

The correction of patented structure 1 of rosmaridiphenol, an antioxidant isolated from rosemary, Rosmarinus officinalis, was made recently. The correct structure is proposed as 11,12-dihydroxy-8,11,13-icetexatrien-1-one (2a) based on 2D NMR data. In order to further support the structure, this work reports the single-crystal X-ray analysis, the complete (1)H NMR assignment by full spin-spin simulation, and the absolute configuration of the diacetate 2b derived via vibrational circular dicroism measurements in comparison with density functional theory calculated data.

Stereochemical analysis of leubethanol, an anti-TB-active serrulatane, from Leucophyllum frutescens

Bioactivity-guided fractionation of the methanolic root bark extract of Leucophyllum frutescens led to the identification of leubethanol (1), a new serrulatane-type diterpene with activity against both multi-drug-resistant and drug-sensitive strains of virulent Mycobacterium tuberculosis. Leubethanol (1) was identified by 1D/2D NMR data, as a serrulatane closely related to erogorgiane (2), and exhibited anti-TB activity with minimum inhibitory concentrations in the range 6.25-12.50 μg/mL. Stereochemical evidence for 1 was gleaned from 1D and 2D NOE experiments, from 1H NMR full spin analysis, and by comparison of the experimental vibrational circular dichroism (VCD) spectrum to density functional theory calculated VCD spectra of two diastereomers.