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.

Cytotoxic C-20 non-oxygenated ent-kaurane diterpenoids from Isodon wardii.

Twenty new ent-kaurane diterpenoids, wardiisins A-T (1-20), along with two previously undescribed artefactual compounds (21 and 22) and twelve known analogues (23-34), were isolated from the aerial part of Isodon wardii. Their structures were elucidated by comprehensive analysis of spectroscopic data and single-crystal X-ray diffraction, and most of them were found to bear unusual C-12 oxygenation. Compounds 4, 7, 8, 19, 20, 21 exhibited remarkable cytotoxicity against the cancer cell lines HL-60, SMMC-7721, A-549, MDA-MB-231, and SW480, with IC50 values ranging from 0.3 to 5.2 µM. Moreover, 7 was found to induce G2/M cell cycle arrest and promote apoptosis in SW480 cell lines.

Lanicepines A and B, Sesquiterpenes with Amino Acid-Derived Substituents from the Flowering Aerial Parts of Saussurea laniceps.

Two new guaianolide sesquiterpenes, lanicepines A (1) and B (2), possessing unusual amino acid-derived substituents at C-13, were isolated from the flowering aerial parts of Saussurea laniceps, a traditional herbal medicine also known as "snow lotus". The structures of 1 and 2 were elucidated based on spectroscopic analysis including applications of the modified Mosher's method and Marfey's method as well as ECD calculations. Lanicepine A (1) contains a dihydropyridinone moiety with a carbamoyl and a hydroxymethyl group. This substituent was considered to consist of asparagine and a C4 unit. In contrast, lanicepine B (2) has a substituent that seems to be derived from l-proline and a C4 unit. Lanicepines A (1) and B (2) and two related known sesquiterpenes isolated from the same plant material, 11ß,13-dihydrodesacylcynaropicrin (3) and 11ß,13-dihydrodesacylcynaropicrin 8-O-ß-d-glucoside (4), demonstrated inhibitory activity against IL-1ß production from LPS-stimulated microglial cells.

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.

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.

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.

Chaetolactam A, an Azaphilone Derivative from the Endophytic Fungus Chaetomium sp. g1.

Chaetolactam A (1), an unprecedented azaphilone derivative bearing a unique 9-oxa-7-azabicyclo[4.2.1]octan-8-onering system, together with two new compounds, 11-epi-chaetomugilide B (2) and chaetomugilide D (3) was isolated from an endophytic fungus, Chaetomium sp. g1. Notably, extensive NMR data analyses, NMR calculations with DP4 and DP4+ analyses, ECD calculations, and the RDC method were employed to establish the structure of 1. Furthermore, 2 exhibited potent apoptosis induction activity by mediating caspase-3 activation and PARP degradation at 3 µM in HL-60.

3-Hydroxy-4-methyldecanoic Acid-Containing Cyclotetradepsipeptides from an Endolichenic Beauveria sp.

An investigation of an endolichenic Beauveria sp. led to the discovery of seven new cyclotetradepsipeptides, beauveamides A-G (2-8), along with the known beauverolide Ka (1). All incorporate a 3-hydroxy-4-methyldecanoic acid (HMDA) moiety in their structures. Their configuration was determined through Marfey's, J-based configuration analysis, and NMR computational methods, representing the first time that the stereostructures of HMDA-moiety-containing cyclotetradepsipeptides have been established. Compounds 1 and 2 exhibited protecting effects on HEI-OC1 cells at 10 µM, while 1, 4, and 5 could stimulate glucose uptake in cultured rat L6 myoblasts at 50 µM. Compound 1 showed dose-dependent activity in both L6 myoblasts and myotubes.

Neuroprotective schinortriterpenoids from Schisandra neglecta collected in Medog County, Tibet, China.

Schisdilactones K-U (1-11), a series of previously unreported 16,17-secopreschisanartane-type schinortriterpenoids (SNTs), were isolated from the leaves and stems of Schisandra neglecta A. C. Smith. Their structures were mainly established through analysis of their spectroscopic data. Besides, schisdilactones K (1), O (5) and R (8) were confirmed by single-crystal X-ray crystallographic analysis, and the configurations of schisdilactones T and U (10 and 11) were elucidated via quantum chemical calculation of their NMR chemical shifts and electronic circular dichroism (ECD) spectra. Schisdilactones L-S (2-8) and U (11) were found to exhibit moderate protective activities against corticosterone-induced apoptosis of PC12 cells at 20 µM, with cell viability in the range of 62.95-66.97%.

Synthesis of nigranoic acid and manwuweizic acid derivatives as HDAC inhibitors and anti-inflammatory agents.

As a successful anti-tumor drug target, the family of histone deacetylases (HDACs) is also a critical player in immune response, making the research of anti-inflammatory HDAC inhibitors an attractive new focus. In this report, triterpenoids nigranoic acid (NA) and manwuweizic acid (MA) were identified as HDAC inhibitors through docking-based virtual screening and enzymatic activity assay. A series of derivatives of NA and MA were synthesized and assessed for their biological effects. As a result, hydroxamic acid derivatives of NA and MA showed moderately increased activity for HDAC1/2/4/6 inhibition (the lowest IC50 against HDAC1 is 1.14 µM), with no activity against HDAC8. In J774A.1 macrophage, compound 1-3, 13 and 17-19 demonstrated inhibitory activity against lactate dehydrogenase (LDH) and IL-1ß production, without affecting cell viability. Compound 19 increased the histone acetylation level in J774A.1 cells, as well as inhibited IL-1ß maturation and caspase-1 cleavage. These results indicated that compound 19 blocks the activation of NLRP3 inflammasome, probably related to HDAC inhibition. This work provided a natural scaffold for developing low-cytotoxic and anti-inflammatory HDAC inhibitors, as well as a class of tool molecules for studying the relationship between HDACs and NLRP3 activation.

(-)-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.

Elucidation of the Structure of Pseudorubriflordilactone B by Chemical Synthesis.

Rubriflordilactone B (1) is a schinortriterpenoid isolated by Sun and colleagues, which possesses a tetrasubstituted benzene moiety and eight stereocenters. The previous synthesis of 1 by Li and co-workers uncovered the existence of its naturally occurring stereoisomer "pseudorubriflordilactone B". Here we report a collaborative study by the two groups that elucidates the structure of pseudorubriflordilactone B to be 16,17-bis-epi-rubriflordilactone B (26). Chemical synthesis served as an important tool in the structure determination. Taking advantage of a modular synthetic route, we systematically "mutated" the configurations of C-23, C-22, C-20, and C-16/C-17 located at the right-hand domain of 1, and thus prepared its 15 stereoisomers for spectrum comparison. The 1H NMR spectra of synthetic 26 in deuterated chloroform and pyridine were identical to those of authentic pseudorubriflordilactone B, respectively. This synthetic sample displayed anti-HIV activity (EC50 = 0.288 µM) in vitro.

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.

Acetyl-macrocalin B suppresses tumor growth in esophageal squamous cell carcinoma and exhibits synergistic anti-cancer effects with the Chk1/2 inhibitor AZD7762.

Natural products derived from herbal medicines have become a major focus of anti-cancer drug discovery studies. Acetyl-macrocalin B (A-macB) is an ent-diterpenoid isolated from Isodon silvatica. This study aimed to examine the effect and molecular action of A-macB in esophageal squamous cell carcinoma (ESCC) and explore possible drug synergistic modalities. A-macB induced cellular reactive oxygen species (ROS) generation, initiated the p38 mitogen-activated protein kinase (MAPK) signaling pathway, and triggered the caspase-9-dependent apoptosis cascade in ESCC cells. The ROS scavenger N-acetylcysteine (NAC) and the specific p38 inhibitor SB203580 reversed the effects of A-macB on the p38 network and thus rescued ESCC cells from apoptosis. The cellular ROS increase was at least partially due to the suppression of glutathione-S-transferase P1 (GSTP1) by A-macB. A-macB also upregulated the Chk1/Chk2-Cdc25C/Cdc2/Cyclin B1 axis to induce G2/M phase arrest. The cell growth inhibition induced by A-macB was further enhanced by AZD7762, a specific Chk1/Chk2 inhibitor, with a combination index (CI) of <1. Moreover, A-macB efficiently suppressed xenograft growth without inducing significant toxicity, and AZD7762 potentiated the effects of A-macB in the suppression of tumor growth in vivo. Taken together, A-macB is a promising lead compound for ESCC and exerts synergistic anti-cancer effects with AZD7762.

(+)- and (-)-Alternarilactone A: Enantiomers with a Diepoxy-Cage-like Scaffold from an Endophytic Alternaria sp.

The enantiomers (+)- and (-)-alternarilactone A (1), the first examples of dibenzo-α-pyrones bearing a diepoxy-cage-like moiety, were isolated from the endophytic fungus Alternaria sp. hh930. The deficiency in 1H-1H COSY and HMBC correlations caused by the highly oxidized caged system of 1 and the deceptive and ambiguous signals such as "W" couplings in NMR data increased the risk of structure misassignment of 1. By performing a quantum chemical calculation of the NMR chemical shifts together with a DP4+ probability analysis and single-crystal X-ray crystallographic experiment, their structures were unambiguously determined, and their absolute configurations were determined by ECD calculations.

Isoscoparins R and S, two new ent-clerodane diterpenoids from Isodon scoparius.

Two new ent-clerodane diterpenoids, named isoscoparins R and S (1 and 2), were isolated from the aerial parts of Isodon scoparius. Their structures were characterized mainly by analyzing the NMR and HRESIMS data, and the relative configuration of compound 1 was determined by single-crystal X-ray diffraction. Compound 2 showed weak activity as an autophagic inhibitor.

7α,20-Epoxy-ent-kaurane Diterpenoids from the Aerial Parts of Isodon pharicus.

A phytochemical investigation of an ethyl acetate extract of the aerial parts of Isodon pharicus led to the isolation of 21 new 7α,20-epoxy-ent-kaurane diterpenoids, pharicins C-W (1-21), and 29 known (22-50) analogues. The structural characterization of 1-21 and assignment of their relative configurations were accomplished by spectroscopic data interpretation, while the structures of 1 and 16 were confirmed by X-ray crystallography. The absolute stereostructure of 1 was confirmed by electronic circular dichroism data analysis. Twenty-five of the diterpenoids were screened for their cytotoxic activities against a panel of tumor cell lines, including HL-60, SMMC-7721, A-549, MCF-7, and SW-480. Compounds 11, 16, 38, and 48 exhibited inhibitory activities against these tumor cell lines with IC50 values ranging from 1.01 to 9.62 µM, while 2, 15, 29, and 47 exhibited moderate cytotoxic potency.

Diterpenoids from Isodon species: an update.

Covering: December 2005 to June 2016. Previous review: Nat. Prod. Rep., 2006, 23, 673-698Over the last decade, great efforts have been made to conduct phytochemistry research on the genus Isodon, which have led to the isolation and identification of a number of diterpenoids. At the same time, these newly reported diterpenoids with diverse structures have led to new findings on their biological functions and chemical synthesis research. In this update, we review more than 600 new diterpenoids, including their structures, classifications, biogenetic pathways, bioactivities, and chemical synthesis.

Structurally Diverse Diterpenoids from Isodon scoparius and Their Bioactivity.

Fourteen new diterpenoids (1-14) based on four skeletal types and two known analogues (15 and 16) were isolated from the aerial parts of Isodon scoparius. Compound 2 is the first ent-kaurane diterpenoid featuring a 1,11-ether bridge, and the structures of these new compounds were established mainly by NMR and MS methods. The absolute configurations of 1 and 5 and the relative configuration of 3 were determined using single-crystal X-ray diffraction. The absolute configuration of 14 was determined by comparison of the experimental and calculated electronic circular dichroism spectra. Compounds 1, 4, and 15 were active against five human tumor cell lines (HL-60, SMMC-7721, A-549, MCF-7, and SW-480), and they also inhibited NO production in LPS-stimulated RAW264.7 cells, with IC50 values of 1.0, 3.1, and 1.8 µM, respectively.