Spiroinonotsuoxotriols A and B, Two Highly Rearranged Triterpenoids from Inonotus obliquus

Bioassay-guided isolation and characterisation of α-glucosidase inhibitors from Sanghuangporus baumii

Bioassay-guided fractionation of the isopropanol extract of the medicinal mushroom Sanghuangporus baumii led to the isolation and characterisation of a new acorane-type sesquiterpenoid bauminene (1) and seven known compounds 2-8. The planar structure of 1 was elucidated on the basis of extensive spectroscopic analysis, including 1D, 2D NMR and HR-ESI-MS. The relative configuration of 1 was determined by a combination of ROESY experiment, density functional theory calculation of 13C NMR, and DP4+ probability analysis, while the absolute configuration of 1 was established by comparative electronic circular dichroism (ECD) spectra analysis. In the in vitro bioassay, compounds 1-8 exhibited potent to moderate α-glucosidase inhibitory activity with IC50 values ranging from 6.8 ± 0.68 to 221.4 ± 6.57 µM. The presences of these bioactive constituents in the sclerotia of S. baumii may be related to the use of the fungus as 'Sanghuang' for the adjuvant treatment of DM.

Lycocasine A, a Lycopodium Alkaloid from Lycopodiastrum casuarinoides and Its Acid-Sensing Ion Channel 1a Inhibitory Activity

A novel Lycopodium alkaloid, lycocasine A (1), and seven known Lycopodium alkaloids (2-8), were isolated from Lycopodiastrum casuarinoides. Their structures were determined through NMR, HRESIMS, and X-ray diffraction analysis. Compound 1 features an unprecedented 5/6/6 tricyclic skeleton, highlighted by a 5-aza-tricyclic[6,3,1,02,6]dodecane motif. In bioactivity assays, compound 1 demonstrated weak inhibitory activity against acid-sensing ion channel 1a.

Research Progress on Application of Inonotus obliquus in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is one of the prime causes of end-stage renal disease. At present, the treatment of DKD is mainly confined to inhibiting the renin-angiotensin-aldosterone system, but the therapeutic effects is not satisfactory. As a kind of very rare and precious medicinal fungi, Inonotus obliquus has a very high medicinal value. Due to its special hypoglycemic and pharmacological effect, researchers currently have attached great importance to it. In this paper, the biological activities, pharmacological effects and application status in the treatment of DKD-related diseases of Inonotus obliquus and the latest progress of metabolites isolated from it in DKD were summarized, thus providing detailed insights and basic understanding of the potential application prospects in DKD.

Secondary metabolites from Aspergillus terreus F6-3, a marine fungus associated with Johnius belengerii

Two new terrein derivatives asperterreinones A-B (1-2), one new octahydrocoumarin derivative (±)-asperterreinin A (6), along with seventeen known compounds, were isolated from Aspergillus terreus F6-3, a marine fungus associated with Johnius belengerii. The structures of 1, 2, and 6 were established on the basis of 1D and 2D NMR, mass spectroscopy, comparative electronic circular dichroism (ECD) spectra analysis, density functional theory calculation of 13C NMR, and DP4+ probability analysis. Among all the isolates, eurylene (7), a constituent of the Malaysian medicinal plant Eurycoma longifolia, was obtained from a microbial source for first time. In the in vitro bioassay, 11 and 13 showed potent inhibitory activity against the Escherichia coli β-glucuronidase (EcGUS) with IC50 values of 27.75 ± 0.73 and 17.73 ± 0.81 μM, respectively. It was the first time that questinol (11) and (±)-aspertertone B (13) were reported as potent EcGUS inhibitors.

α-Glucosidase Inhibitors from Two Mangrove-Derived Actinomycetes

α-Glucosidase (AGS) inhibitors have been regarded as an ideal target for the management of type 2 diabetes mellitus (T2DM) since they can maintain an acceptable blood glucose level by delaying the digestion of carbohydrates and diminishing the absorption of monosaccharides. In the process of our endeavor in mining AGS inhibitors from natural sources, the culture broth of two mangrove-derived actinomycetes Streptomyces sp. WHUA03267 and Streptomyces sp. WHUA03072 exhibited an apparent inhibitory activity against AGS. A subsequent chemical investigation into the two extracts furnished 28 secondary metabolites that were identified by spectroscopic methods as two previously undescribed linear polyketides 1-2, four benzenoid ansamycins 3-6, fourteen cyclodipeptides 7-18, one prenylated indole derivative 19, two fusicoccane-type diterpenoids 20-21, two hydroxamate siderophore 22-23, and five others 24-28. Among all of the isolates, 11 and 24 were obtained from actinomycetes for the first time, while 20-21 had never been reported to occur in a marine-derived microorganism previously. In the in vitro AGS inhibitory assay, compounds 3, 8, 9, 11, 14, 16, and 17 exhibited potent to moderate activity with IC₅₀ values ranging from 35.76 ± 0.40 to 164.5 ± 15.5 μM, as compared with acarbose (IC₅₀ = 422.3 ± 8.4 μM). The AGS inhibitory activity of 3, 9, 14, 16, and 17 was reported for the first time. In particular, autolytimycin (3) represented the first ansamycin derivative reported to possess the AGS inhibitory activity. Kinetics analysis and molecular docking were performed to determine the inhibition types and binding modes of these inhibitors, respectively. In the MTT assay, 3, 8, 9, 11, 14, 16, and 17 exhibited no apparent cytotoxicity to the human normal hepatocyte (LO2) cells, suggesting satisfactory safety of these AGS inhibitors.

Triterpenoids as bivalent and dual inhibitors of acetylcholinesterase/butyrylcholinesterase from the fruiting bodies of Inonotus obliquus

Inonotus obliquus, an edible and medicinal mushroom parasitic on birches, has been used in human diet and for traditional therapies in the high latitude regions of Europe and Asia for a long time. Our phytochemical study of this fungus led to the identification of fourteen triterpenoids including four undescribed ones, and two pairs of undescribed phenolic enantiomers. The undescribed compounds were elucidated by extensive spectroscopic analysis including 1D and 2D NMR and HRESIMS, quantum chemical NMR and ECD calculations, as well as single-crystal X-ray diffraction analysis. Bioassays revealed that eight compounds showed dual inhibition against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) with IC₅₀ values ranging from 2.40 ± 0.05 to 28.72 ± 0.46 μM, while 3β-hydroxy-lanosra-8,24-dien-21-al and trametenolic acid only presented BuChE inhibitory activities with IC₅₀ values of 22.21 ± 1.01 and 7.68 ± 0.13 μM, respectively. In the kinetic studies, the most active three compounds acted as non-competitive inhibitors for both cholinesterases. Furthermore, molecular docking simulations revealed that three compounds demonstrated dual-sites bounding to AChE/BuChE. These triterpenoids emerged as bivalent and dual inhibitors of AChE/BuChE and could be effective drug candidates to prevent and treat Alzheimer's disease in the future.

Diverse diterpenoids with α-glucosidase and β-glucuronidase inhibitory activities from Euphorbia milii

Four undescribed regular rosane-type diterpenoids euphominoids M-P and three undescribed rearranged rosane-type diterpenoids euphomilones C-E were isolated from the whole plants of Euphorbia milii Des Moul., along with nine known compounds. Their structures were elucidated by detailed interpretation of the NMR and mass spectroscopy. The absolute configurations were established by single-crystal X-ray diffraction experiments, as well as comparative analyses of calculated and experimental ECD spectra. Euphominoid M featured a highly oxygenated ring A and a rare four-membered oxygen ring while euphomilones C-E possessed 7/5/6 or 5/7/6 fused ring systems, which were rarely occurring in rosane-type diterpenoids. In the in-vitro bioassays, 19-norrosa-1,3,5(10),15-tetraene-2,3-diol and antiquorin showed more potent α-glucosidase inhibitory activity than the positive control acarbose while euphominoid C exhibited significant inhibitory activity against both α-glucosidase and β-glucuronidase. To the best of our knowledge, it was the first time that rosane-type diterpenoids were reported as β-glucuronidase inhibitors.

Anti-Adipogenic Lanostane-Type Triterpenoids from the Edible and Medicinal Mushroom Ganoderma applanatum

Our previous research has shown that lanostane triterpenoids from Ganoderma applanatum exhibit significant anti-adipogenesis effects. In order to obtain more structurally diverse lanostane triterpenoids to establish a structure–activity relationship, we continued the study of lanostane triterpenoids from the fruiting bodies of G. applanatum, and forty highly oxygenated lanostane-type triterpenoinds (1–40), including sixteen new compounds (1–16), were isolated. Their structures were elucidated using NMR spectra, X-ray crystallographic analysis, and Mosher’s method. In addition, some of their parts were evaluated to determine their anti-adipogenesis activities in the 3T3-L1 cell model. The results showed that compounds 16, 22, 28, and 32 exhibited stronger anti-adipogenesis effects than the positive control (LiCl, 20 mM) at the concentration of 20 μM. Compounds 15 and 20 could significantly reduce the lipid accumulation during the differentiation process of 3T3-L1 cells, comparable to the untreated group. Their IC₅₀ values were 6.42 and 5.39 μM, respectively. The combined results of our previous and present studies allow us to establish a structure-activity relationship of lanostane triterpenoids, indicating that the A-seco-23→26 lactone skeleton could play a key role in anti-adipogenesis activity.

α-Glucosidase and Bacterial β-Glucuronidase Inhibitors from the Stems of Schisandra sphaerandra Staph

α-Glucosidase (AGS) is a therapeutic target for Type 2 diabetes mellitus (T2DM) that tends to complicate with other diseases. Some medications for the treatment of T2DM complications have the risk of inducing severe adverse reactions such as diarrhea via the metabolism of intestinal bacterial β-glucuronidase (BGUS). The development of new AGS and/or BGUS inhibitors may improve the therapeutic effects of T2DM and its complications. The present work focused on the isolation and characterization of AGS and/or BGUS inhibitors from the medicinal plant Schisandra sphaerandra. A total of eight compounds were isolated and identified. Sphaerandralide A (1) was obtained as a previously undescribed triterpenoid, which may have chemotaxonomy significance in the authentication of the genus Schisandra and Kadsura. 2′-acetyl-4′,4-dimethoxybiphenyl-2-carbaldehyde (8) was obtained from a plant source for the first time, while compounds 2–7 were isolated from S. sphaerandra for the first time. In the in vitro assay, compounds 1–5 showed potent to moderate activity against AGS. Interestingly, compound 3 also exhibited significant BGUS inhibitory activity, demonstrating the potential of being developed as a bifunctional inhibitor that may find application in the therapy of T2DM and/or the diarrhea induced by medications for the treatment of T2DM complications.

Neuroprotective effects of a new triterpenoid from edible mushroom on oxidative stress and apoptosis through the BDNF/TrkB/ERK/CREB and Nrf2 signaling pathway in vitro and in vivo

Inonotus obliquus (Fr.) Pilat is an edible mushroom which is used to produce tea and syrup due to its medicinal properties.

Tetrodecadazinone, a novel tetrodecamycin-pyridazinone hybrid with anti-liver fibrosis activity from Streptomyces sp. HU051

Tetrodecadazinone (1), a novel tetrodecamycin-pyridazinone hybrid possessing a new 1,2-dimethyl-1-(2-methylnonyl)decahydronaphthalene skeleton, and 4-hydroxydihydrotetrodecamycin (2) were separated from a culture of Streptomyces sp. HU051, together with a known compound, dihydrotetrodecamycin (3). Diverse spectroscopic approaches were applied to assign the structures of 1-3, and the structure of 1 was further confirmed by single crystal X-ray diffraction analysis. Compound 1 is the first example of a pyridazinone-containing natural product. Biosynthetically, 1 is proposed to be derived from a Michael addition reaction of a PKS-derived tetrodecamycin and a piperazic-acid-derived pyridazinone. Biological evaluation revealed 1 could reduce the expressions of extracellular matrix proteins (fibronectin and collagen I) and α-smooth muscle actin (α-SMA) in transforming growth factor-β (TGF-β1)-activated LX-2 cells. Preliminary mechanism study showed 1 exerted its anti-liver fibrosis effect by regulating TGF-β1/Smad2/3 signaling pathway.

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.

Effective Search of Triterpenes with Anti-HSV-1 Activity Using a Classification Model by Logistic Regression

Natural products are an excellent source of skeletons for medicinal seeds. Triterpenes and saponins are representative natural products that exhibit anti-herpes simplex virus type 1 (HSV-1) activity. However, there has been a lack of comprehensive information on the anti-HSV-1 activity of triterpenes. Therefore, expanding information on the anti-HSV-1 activity of triterpenes and improving the efficiency of their exploration are urgently required. To improve the efficiency of the development of anti-HSV-1 active compounds, we constructed a predictive model for the anti-HSV-1 activity of triterpenes by using the information obtained from previous studies using machine learning methods. In this study, we constructed a binary classification model (i.e., active or inactive) using a logistic regression algorithm. As a result of the evaluation of predictive model, the accuracy for the test data is 0.79, and the area under the curve (AUC) is 0.86. Additionally, to enrich the information on the anti-HSV-1 activity of triterpenes, a plaque reduction assay was performed on 20 triterpenes. As a result, chikusetsusaponin IVa (11: IC₅₀ = 13.06 μM) was found to have potent anti-HSV-1 with three potentially anti-HSV-1 active triterpenes. The assay result was further used for external validation of predictive model. The prediction of the test compounds in the activity test showed a high accuracy (0.83) and AUC (0.81). We also found that this predictive model was found to be able to successfully narrow down the active compounds. This study provides more information on the anti-HSV-1 activity of triterpenes. Moreover, the predictive model can improve the efficiency of the development of active triterpenes by integrating many previous studies to clarify potential relationships.

Inhibitory effect of triterpenoids from the mushroom Inonotus obliquus against α-glucosidase and their interaction: Inhibition kinetics and molecular stimulations

Bioassay-guided fractionation led to the isolation of a series of triterpenoids (1-46) including 12 new ones (1-12) from the mushroom Inonotus obliquus. The structures of all the compounds were elucidated by spectroscopic analysis as well as by comparison with literature data. Triterpenoids 1-3, 6, 7, 16, 24, 25, 27, 38, 43, 44 and 46 showed strong α-glucosidase inhibition, with IC₅₀ values from 11.5 to 81.8 μM. Their structure-activity relationships were discussed. Inonotusol F (24) showed the strongest inhibitory activity and it presented noncompetitive inhibition against α-glucosidase. Molecular docking and molecular dynamics stimulation further demonstrated that GLU302 and PHE298 were key amino acids for the inhibition of inonotusol F (24) towards α-glucosidase. This study indicates the vital role of triterpenoids in explaining hypoglycemic effect of Inonotus obliquus and provides important evidence for further development and utilization of this mushroom.

Biotransformation of Oleanane and Ursane Triterpenic Acids

Oleanane and ursane pentacyclic triterpenoids are secondary metabolites of plants found in various climatic zones and regions. This group of compounds is highly attractive due to their diverse biological properties and possible use as intermediates in the synthesis of new pharmacologically promising substances. By now, their antiviral, anti-inflammatory, antimicrobial, antitumor, and other activities have been confirmed. In the last decade, methods of microbial synthesis of these compounds and their further biotransformation using microorganisms are gaining much popularity. The present review provides clear evidence that industrial microbiology can be a promising way to obtain valuable pharmacologically active compounds in environmentally friendly conditions without processing huge amounts of plant biomass and using hazardous and expensive chemicals. This review summarizes data on distribution, microbial synthesis, and biological activities of native oleanane and ursane triterpenoids. Much emphasis is put on the processes of microbial transformation of selected oleanane and ursane pentacyclic triterpenoids and on the bioactivity assessment of the obtained derivatives.

Modified lanostane-type triterpenoids with neuroprotective effects from the fungus Inonotus obliquus

Six undescribed lanostane triterpenoids (1-6), together with three known compounds (7-9) were isolated from Inonotus obliquus. Compounds 3-5 are the rare natural compounds featuring a 4,5-seco-lanostane core with a 5,7,9-trien-21,24-cyclopentane moiety. The structure elucidation of the compounds was conducted by spectroscopic techniques and the ECD method. The absolute configuration of compound 1 was confirmed by single-crystal X-ray diffraction analysis. All isolated compounds were assayed for their neuroprotective activity against H₂O₂-induced cell injury using human neuroblastoma SH-SY5Y cells. Compound 9 exhibited the most potent neuroprotective activity and the flow cytometry analysis indicated that 9 could protect SH-SY5Y cells from oxidative damage by inhibiting cell apoptosis.

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.