Isoxerophilusins A and B, Two Novel Polycyclic Asymmetric Diterpene Dimers from Isodon xerophilus: Structural Elucidation, Modification, and Inhibitory Activities against α-Glucosidase.

Isoxerophilusins A (1) and B (2), two unprecedented diterpene heterodimers biogenetically from ent-atisanes and abietanes, were isolated from the rhizomes of Isodon xerophilus. Their structures were determined by extensive spectroscopic analysis and single-crystal X-ray diffraction. Selective esterification of 1 generated 11 new derivatives. All derivatives showed excellent α-glucosidase inhibitory activity in comparison to acarbose. Compounds 12 and 13 demonstrated significant inhibition against α-glucosidase with IC50 values of 4.92 and 3.83 µM, respectively.

Recent advances in the application of [2 + 2] cycloaddition in the chemical synthesis of cyclobutane-containing natural products.

Cyclobutanes are distributed widely in a large class of natural products featuring diverse pharmaceutical activities and intricate structural frameworks. The [2 + 2] cycloaddition is unequivocally the primary and most commonly used method for synthesizing cyclobutanes. In this review, we have summarized the application of the [2 + 2] cycloaddition with different reaction mechanisms in the chemical synthesis of selected cyclobutane-containing natural products over the past decade.

Discovery and bioinspired total syntheses of unprecedented sesquiterpenoid dimers unveiled bifurcating [4 + 2] cycloaddition and target differentiation of enantiomers.

[4 + 2] cycloaddition has led to diverse polycyclic chiral architectures, serving as novel sources for organic synthesis and biological exploration. Here, an unprecedented class of cadinane sesquiterpene [4 + 2] dimers, henryinins A-E (1-5), with a unique 6/6/6/6/6-fused pentacyclic system, were isolated from Schisandra henryi. The divergent total syntheses of compounds 1-5 and their enantiomers (6-10) were concisely accomplished in eight linear steps using a protection-free approach. Mechanistic studies illustrated the origin of selectivity in the key [4 + 2] cycloaddition as well as the inhibition of reaction pathway bifurcation via desymmetrization. The chemical proteomics results showed that a pair of enantiomers shared common targets (PRDX5 C100 and BLMH C73) and had unique targets (USP45 C588 for 4 and COG7 C419 for 9). This work provides experimental evidence for the discovery of unprecedented cadinane dimers from selective Diels-Alder reaction and a powerful strategy to explore the biological properties of natural products.

Discovery of Natural Potent HMG-CoA Reductase Degraders for Lowering Cholesterol.

Exploitation of key protected wild plant resources makes great sense, but their limited populations become the major barrier. A particular strategy for breaking this barrier was inspired by the exploration of a resource-saving fungal endophyte Penicillium sp. DG23, which inhabits the key protected wild plant Schisandra macrocarpa. Chemical studies on the cultures of this strain afforded eight novel indole diterpenoids, schipenindolenes A-H (1-8), belonging to six diverse skeleton types. Importantly, semisyntheses suggested some key nonenzymatic reactions constructing these molecules and provided targeted compounds, in particular schipenindolene A (Spid A, 1) with low natural abundance. Remarkably, Spid A was the most potent HMG-CoA reductase (HMGCR) degrader among the indole diterpenoid family. It degraded statin-induced accumulation of HMGCR protein, decreased cholesterol levels and acted synergistically with statin to further lower cholesterol. Mechanistically, transcriptomic and proteomic profiling suggested that Spid A potentially activated the endoplasmic reticulum-associated degradation (ERAD) pathway to enhance the degradation of HMGCR, while simultaneously inhibiting the statin-activated expression of many key enzymes in the cholesterol and fatty acid synthesis pathways, thereby strengthening the efficacy of statins and potentially reducing the side effects of statins. Collectively, this study suggests the potential of Spid A for treating cardiovascular disease.

Steccherins A-D, chamigrane-type sesquiterpenes from the fungus Steccherinum ochraceum with selective inhibition on B lymphocyte proliferation.

Four previously undescribed chamigrane sesquiterpenes, namely steccherins A-D, have been isolated from the fungus Steccherinum ochraceum. Their structures were elucidated by extensive spectroscopic analysis, as well as computational methods and single crystal X-ray diffraction. Steccherins A and B possess previously undescribed backbones which might be derived from normal chamigrane sesquiterpenes, especially that steccherin A possesses a spiro[5.6]dodecane carbon skeleton via a ring-rearrangement. Steccherins A, C, and D showed immunosuppressive activity with IC50 values ranging from 6.2 to 37.8 µM. The data suggested that these chamigrane sesquiterpenes have potential selective inhibition on LPS-induced B lymphocyte proliferation.

Cyclobutane-Containing Meroditerpenoids, (+)-Isoscopariusins B and C: Structure Elucidation and Biomimetic Synthesis.

(+)-Isoscopariusins B (1) and C (2), two meroditerpenoids containing a 6/6/4 tricyclic carbon skeleton and seven continuous stereocenters, were identified from Isodon scoparius. The structures were determined by nuclear magnetic resonance analysis and concise biomimetic syntheses from readily available alkene 5 in seven and six steps, respectively. An intermolecular [2+2] photocycloaddition with cooperative catalysis of a Lewis acid and an Ir photocatalyst was used to construct a cyclobutane core with four stereogenic centers.

Baicalein ameliorates oxidative stress and brain injury after intracerebral hemorrhage by activating the Nrf2/ARE pathway via miR-106a-5p/PHLPP2 axis.

Intracerebral hemorrhage (ICH) is a devastating stroke subtype. Baicalein (BAI) has been reported to be effective in ischemic stroke. The aim of the present study was to investigate the mechanism of BAI on brain injury after ICH. Firstly, ICH mouse models were established by injecting collagenase into the right of basal ganglia, followed by detection of neurobehavioral scores, brain edema, oxidative stress (OS) level, neuronal apoptosis and pathological changes. Average neurologic scores, brain water content, and blood-brain barrier permeability and MDA level in ICH mice were reduced after BAI treatment, while serum SOD and GSH-Px levels were increased and neuronal apoptosis and pathological injury of the brain tissues were mitigated. miR-106a-5p downregulation averted the effect of BAI on ICH mice. miR-106a-5p targeted PHLPP2 and PHLPP2 overexpression reversed the effect of BAI on ICH mice. BAI activated the Nrf2/ARE pathway by inhibiting PHLPP2 expression. In conclusion, BAI inhibited OS and protected against brain injury after ICH by activating the Nrf2/ARE pathway through the miR-106a-5p/PHLPP2 axis.

Isolation and Bioinspired Total Synthesis of Rugosiformisin A, A Skeleton-Rearranged Abietane-Type Diterpenoid from Isodon rugosiformis.

Rugosiformisin A, a skeleton-rearranged abietane-type diterpenoid with a spiro[4.5]decane motif, was isolated from Isodon rugosiformis. Its structure was unambiguously established via NMR spectroscopic analysis and single-crystal X-ray diffraction. A bioinspired asymmetric synthesis of rugosiformisin A was achieved in 15 steps with 2.7% overall yield. The synthesis features an iridium-catalyzed asymmetric polyene cyclization and a semipinacol rearrangement.

Sis-25, a meroditerpenoid derivative with a cyclobutane scaffold, inhibits activated T cell proliferation by targeting GSK3ß in vitro and in vivo.

A series of novel scopariusicide derivatives were designed and synthesized starting from the main diterpenoid from the aerial parts of Isodon scoparius. Sis-25 was the most effective compound among them. The potential mechanism(s) of its immunosuppressive activity in vitro, as well as its effects on delayed type hypersensitivity (DTH) reaction and imiquimod-induced dermatitis in vivo were investigated in this study. Sis-25 inhibited anti-CD3/anti-CD28 mAbs, PHA or alloantigen-induced T cell proliferation without obvious cytotoxicity. Sis-25 was a highly selective inhibitor of GSK3-ß and inhibited the mTOR/p70S6K pathway but not the PI3K/Akt, p38 MAPK/ERK 1/2 and JAK3/STAT5 pathways. Furthermore, Sis-25 significantly inhibited IFN-γ, IL-6 and IL-17 expression but not IL-10 expression in activated T cells. Finally, Sis-25 treatment mitigated the DNFB-induced DTH reaction and ameliorated imiquimod-induced dermatitis. In summary, Sis-25 exerted significant immunosuppressive activity by targeting GSK3ß in vitro and in vivo. Sis-25 may guide the design of new drugs for more effective and safer treatments of autoimmune diseases and provide new insight into developing utilizations of Isodon scoparius.

Scopariusicides D-M, ent-clerodane-based isomeric meroditerpenoids with a cyclobutane-fused γ/δ-lactone core from Isodon scoparius.

Scopariusicides D-M (1-10), ten new ent-clerodane-based meroditerpenoids with a cyclobutane-fused γ/δ-lactone core, were isolated from Isodon scoparius. Their structures were determined by comprehensive analysis of spectroscopic data, single-crystal X-ray diffraction, chemical transformation, and TDDFT ECD calculation. A plausible biosynthetic pathway of 1-10 was proposed in which the asymmetrical cyclobutane ring was formed via a crossed "head-to-tail" intermolecular [2 + 2] cycloaddition in anti/syn facial approaches between an ent-clerodane lactone and a cis-4-hydroxycinnamic acid. Bioactivity evaluation manifested that 5 exhibited significant neuroprotective effect against corticosterone-induced injury in PC12 cells, while 6 and 7 exhibited moderate immunosuppressive activity against human T cell proliferation stimulated by anti-CD3/anti-CD28 mAb.

Cytochalasans from the Endophytic Fungus Phomopsis sp. shj2 and Their Antimigratory Activities.

Cytochalasans from the endophytic fungi featured structure diversity. Our previous study has disclosed that cytochalasans from the endophytic fungus Phomopsis sp. shj2 exhibited an antimigratory effect. Further chemical investigation on Phomopsis sp. shj2 has led to the discovery of seven new cytochalasans (1-7), together with four known ones. Their structures were elucidated through extensive spectroscopic data interpretation and single-crystal X-ray diffraction analysis. Compounds 1-3 and 8-11 exhibited antimigratory effects against MDA-MB-231 in vitro with IC50 values in the range of 1.01-10.42 µM.

Harnessing Natural Products by a Pharmacophore-Oriented Semisynthesis Approach for the Discovery of Potential Anti-SARS-CoV-2 Agents.

Natural products possessing unique scaffolds may have antiviral activity but their complex structures hinder facile synthesis. A pharmacophore-oriented semisynthesis approach was applied to (-)-maoelactone A (1) and oridonin (2) for the discovery of anti-SARS-CoV-2 agents. The Wolff rearrangement/lactonization cascade (WRLC) reaction was developed to construct the unprecedented maoelactone-type scaffold during semisynthesis of 1. Further mechanistic study suggested a concerted mechanism for Wolff rearrangement and a water-assisted stepwise process for lactonization. The WRLC reaction then enabled the creation of a novel family by assembly of the maoelactone-type scaffold and the pharmacophore of 2, whereby one derivative inhibited SARS-CoV-2 replication in HPA EpiC cells with a low EC50 value (19±1 nM) and a high TI value (>1000), both values better than those of remdesivir.

Structurally diverse diterpenoids from Isodon oresbius and their bioactivity.

Twelve new diterpenoids, isoresbins A-L (1-12), together with twenty-eight known ones, were isolated from the aerial parts of Isodon oresbius. Their diverse structures included 6,7-seco-ent-kaurane, 7,20-epoxy-ent-kaurane, 6,7:8,15-diseco-ent-kaurane, and abietanes skeletons, which were elucidated by spectroscopic data interpretation, single-crystal X-ray diffraction, and quantum chemical calculation. Isoresbins A (1) and B (2) possessed a new rearranged 15(8 â†’ 11)-abeo-6,7-seco-ent-kaurane skeleton. 1 and 5 promoted lysosomal function, which was evaluated by LysoTracker Red staining and DQ-ovalbumin dequenching assay. 1 showed cytotoxicity against six human tumor cell lines with IC50 values in 2.07-4.04 µM range. Moreover, 1 induced damage of mitochondrial membrane potential, G2/M cell cycle arrest and apoptosis in SW480 cells.

Long Non-Coding RNA Small Nucleolar RNA Host Gene 5 (SNHG5) Regulates Renal Tubular Damage in Diabetic Nephropathy via Targeting MiR-26a-5p.

The study explored the diagnostic value of SNHG5 in diabetic nephropathy (DN) and investigated the role and mechanism on DN via establishing the in vitro HK2 cell model. This study recruited 62 types 2 diabetes mellitus (T2DM) patients, 58 DN patients and 60 healthy controls (HC). The expressions of serum SNHG5 and miR-26a-5p were measured by RT-qPCR analysis. The diagnostic value of SNHG5 in DN was assessed by ROC curve. The in vitro cell model was built to estimate the effects of SNHG5 on cell viability, cell apoptosis, inflammation response and oxidative stress. Serum SNHG5 was increased in DN patients (relative expression: 2.04±0.34) and had the diagnostic value in DN. After HK2 cells were treated with high glucose, the cell viability decreased and apoptosis increased, and the production of inflammatory cytokines and ROS enhanced significantly. It was noticed that inhibition of SNHG5 could reverse the above phenomenon caused by high glucose. Besides, serum miR-26a-5p was diminished in DN patients, and luciferase reporter gene revealed that miR-26a-5p is direct target of SNHG5. These results indicated that inhibition of SNHG5 may mitigate HG-induced renal tubular damage via targeting miR-26a-5p, which providing a new insight into the mechanism of renal tubule damage in DN patients.

Spiro ent-Clerodane Dimers: Discovery and Green Approaches for a Scalable Biomimetic Synthesis.

Scospirosins A (1) and B (2), two unprecedented spiro ent-clerodane dimers with 6/6/10/6 and 6/6/6/6/6 ring systems, respectively, were isolated from Isodon scoparius. Their structures were unambiguously established by spectroscopic, X-ray crystallographic, and chemical approaches. A bioinspired protecting-group-free strategy for their synthesis was achieved on a gram scale and featured the application of green methods, including neat reaction, sensitized photooxygenation, and electrochemical oxidation. 2 exhibited selective immunosuppressive activity against the proliferation of T lymphocytes (IC50 = 1.42 µM).

Tangutidines A-C, Three Amphoteric Diterpene Alkaloids from Aconitum tanguticum.

Three new diterpene alkaloids, tangutidines A-C (1-3), and four known alkaloids (4-7) were isolated from the whole plant of Aconitum tanguticum, from which amphoteric diterpene alkaloids (1-3) were obtained for the first time. The structures of 1-3 were elucidated by detailed interpretation of spectroscopic data, including MS and NMR data. All of them were evaluated for their cytotoxic activities.

(-)-Isoscopariusin†A, a Naturally Occurring Immunosuppressive Meroditerpenoid: Structure Elucidation and Scalable Chemical Synthesis.

(-)-Isoscopariusin A was isolated from the aerial parts of Isodon scoparius. Chemical synthesis and spectroscopic analysis established its structure as an unsymmetrical meroditerpenoid bearing a sterically congested 6/6/4 tricyclic carbon skeleton with seven continuous stereocenters. A gram-scale synthesis was achieved in 12 steps from commercially available (+)-sclareolide. A cobalt catalyzed, hydrogen atom transfer-based olefin isomerization was used to prepare a trisubstituted alkene, which underwent stereoselective [2+2] cycloaddition with a substituted keteniminium ion generated in situ from the corresponding amide. The cyclobutanone product was further elaborated into the fully substituted cyclobutane core through face-selective homologation, and the two side chains were installed by using nickel-catalyzed cross-electrophile coupling and carbodiimide-mediated esterification, respectively. (-)-Isoscopariusin A displayed selective inhibition of T-cell proliferation.

High-content screening of diterpenoids from Isodon species as autophagy modulators and the functional study of their antiviral activities.

Autophagy is a conserved lysosomal degradation process, and abnormal autophagy has been associated with various pathological processes, e.g., neurodegeneration, cancer, and pathogen infection. Small chemical modulators of autophagy show the potential to treat autophagy-associated diseases. Diterpenoids, nature products found in various plants, exhibit a wide range of bioactivity, and we have recently isolated and characterized over 150 diterpenoids from Isodon species distributed in China. Here, we applied a high-content fluorescence imaging-based assay to assess these diterpenoids' ability to affect autophagic flux in HeLa cells. We found that enanderinanin J, an ent-kauranoid dimer, is an autophagy inhibitor, manifested by its ability to increase lysosomal pH and inhibit the fusion between autophagosomes and lysosomes. Autophagy has been shown to be either positively or negatively involved in the life cycle of Zika virus (ZIKV), Japanese encephalitis virus (JEV), Dengue virus (DENV), and enterovirus-A71 (EV-A71). We found that enanderinanin J significantly inhibited the infection of ZIKV, DENV, JEV, or EV-A71. Interestingly, although ATG5 knockdown inhibited ZIKV or JEV infection, enanderinanin J further inhibited the infection of ZIKV or JEV in ATG5-knockdown cells. Taken together, our data indicate that enanderinanin J inhibits autophagosome-lysosome fusion and is a potential antiviral agent.

ent-Kaurane-Based Diterpenoids, Dimers, and Meroditerpenoids from Isodon xerophilus.

Eight new diterpenoids (1-8) with varied structures were isolated from the aerial parts of Isodon xerophilus. Among them, xerophilsin A (1) was found to be an unusual meroditerpenoid representing a hybrid of an ent-kauranoid and a long-chain aliphatic ester, xerophilsins B-D (2-4) are dimeric ent-kauranoids, while xerophilsins E-H (5-8) are new ent-kauranoids. The structures of 1-8 were elucidated mainly through the analyses of their spectroscopic data. The absolute configurations of 2, 6, and 8 were confirmed by single-crystal X-ray diffraction, and the configuration of C-16 in 7 was established through quantum chemical calculation of NMR chemical shifts, as well as modeling of key interproton distances. Bioactivity evaluation of all isolated compounds revealed that 2, 3, and 5 inhibited NO production in LPS-stimulated RAW264.7 cells.

Neuroprotective schinortriterpenoids with diverse scaffolds from Schisandra henryi.

Eleven undescribed schinortriterpenoids (SNTs) and one known analogue (12) were isolated from the stems and leaves of Schisandra henryi. Their diverse structures included preschisanartane (1), 18-norschiartane (2-5, 12), schiartane (6 and 7), and schisanartane (8-11) skeletons, which were elucidated by comprehensive NMR, MS, electronic circular dichroism analyses, single crystal X-ray diffraction and biogenetic considerations. 1 was the first case of preschisanartane-type SNT with six-membered lactone ring, and 2 was one of the most highly oxygenated 18-norschiartane SNTs. Three types of the highly oxygenated SNTs, 1, 4, 10 and 11, effectively prevent apoptosis induced by corticosterone in PC12 cells. In addition, 11 showed neurite outgrowth-promoting activity.