Diterpenoids from Isodon species: an update

Structurally diverse ent-clerodanoids from the aerial parts of Isodon scoparius

Scoparodane C (1), a diterpenoid with a rare 3,4-seco-3-nor-2,11-epoxy-ent-clerodane scaffold, was obtained from the aerial parts of Isodon scoparius, along with isocopariusines A-E (2-6), five ent-clerodanoids featuring a 5/6-fused ring system, and isocopariusines F-H (7-9), three common ent-clerodanoids. The structures of these previously undescribed compounds were established by a combination of spectroscopic analysis, X-ray diffraction, chemical derivatization, and quantum chemical calculation. Remarkably, isocopariusine B (3) showed strong resistance reversal activity against fluconazole-resistant Candida albicans.

Advances in the Structures, Pharmacological Activities, and Biosynthesis of Plant Diterpenoids

More and more diterpenoids have attracted extensive attention due to the diverse chemical structures and excellent biological activities, and have been developed into clinical drugs or consumer products. The vast majority of diterpenoids are derived from plants. With the long-term development of plant medicinal materials, the natural resources of many plant diterpenoids are decreasing, and the biosynthetic mechanism of key active components has increasingly become a research hotspot. Using synthetic biology to engineer microorganisms into "cell factories" to produce the desired compounds is an essential means to solve these problems. In this review, we depict the plant-derived diterpenoids from chemical structure, biological activities, and biosynthetic pathways. We use representative plant diterpenes as examples to expound the research progress on their biosynthesis, and summarize the heterologous production of plant diterpenoids in microorganisms in recent years, hoping to lay the foundation for the development and application of plant diterpenoids in the future.

Silvaticusins A-D: ent-kaurane diterpenoids and a cyclobutane-containing ent-kaurane dimer from Isodon silvaticus

Three new ent-kaurane diterpenoids, silvaticusins A-C (1-3), along with a new ent-kaurane dimer silvaticusin D (4) were isolated from the aerial parts of Isodon silvaticus. The structures of these new compounds were established mainly by comprehensive analysis of their NMR and MS data. The absolute configuration of compounds 1 and 4 were determined using a single-crystal X-ray diffraction and computational methods, respectively. Compounds 2 and 3 were found to exhibit remarkable cytotoxic effects against five human tumor cell lines (HL-60, A-549, SMMC-7721, MDA-MB-231, and SW-480), with IC50 values spanning from 1.27 ± 0.08 to 7.52 ± 0.33 μM.

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.

Total syntheses of (-)-macrocalyxoformins A and B and (-)-ludongnin C

The complex and diverse molecular architectures along with broad biological activities of ent-kauranoids natural products make them an excellent testing ground for the invention of synthetic methods and strategies. Recent efforts notwithstanding, synthetic access to the highly oxidized enmein-type ent-kauranoids still presents considerable challenges to synthetic chemists. Here, we report the enantioselective total syntheses of C-19 oxygenated enmein-type ent-kauranoids, including (-)-macrocalyxoformins A and B and (-)-ludongnin C, along with discussion and study of synthetic strategies. The enabling feature in our synthesis is a devised Ni-catalyzed decarboxylative cyclization/radical-polar crossover/C-acylation cascade that forges a THF ring concomitantly with the β-keto ester group. Mechanistic studies reveal that the C-acylation process in this cascade reaction is achieved through a carboxylation followed by an in situ esterification. Biological evaluation of these synthetic natural products reveals the indispensable role of the ketone on the D ring in their anti-tumor efficacy.

Six new diterpenoids with anti-inflammatory and cytotoxic activity from Isodon serra

Diterpenoids occupy an important slot of the natural products diversity space with wide ranges of bioactivities and complex structures, providing potential applications for the development of therapeutics. In this study, we reported four new abietane-type diterpenoids viroxocin B-E (1-4), a new totarane-type diterpenoid viroxocin F (5), and a new sempervirane-type diterpenoid viroxocin G (6) along with four known compounds (7-10), isolated and identified from a widely used Traditional Chinese Medicine, Isodon serra (I. serra). Their structures were established by spectroscopic data analysis, experimental and calculated electronic circular dichroism (ECD) data, as well as X-ray diffraction analysis. Compounds 2, 5, 7, 8 and 10 exhibited promising anti-inflammatory activities in lipopolysaccharide (LPS)-induced RAW 267.4 cells, and their inhibition rates on NO production were more than 60% at 10 μM. Compound 7 showed cytotoxicity against human renal cell carcinoma 769P at 20 μM, the inhibition rate was 52.66%.

Recent Developments in the Syntheses of C-20-Oxygenated ent-Kaurane Diterpenoids

Ent-kaurane diterpenes are a large group of natural products, with more than 1,000 compounds since their discovery. Due to their excellent biological activities and complex polycyclic structures, these compounds have attracted organic synthesis chemists around the world to be devoted to achieve their total synthesis. At present, the isolated C-20-oxygenated ent-kaurane diterpenes are the most abundant of these natural products, reaching more than 350 in number. However, only total syntheses of 3,20-epoxy, 7,20-epoxy and 19,20-lactone ent-kaurane diterpenes have been reported. In this review, we elaborate the synthesis of these three types of C-20 oxygenated ent-kaurane natural products, discuss these synthetic strategies in detail, and provide good guidance and reference for the synthesis of other C-20 oxygenated compounds.

Natural Product-Inspired Molecules for Covalent Inhibition of SHP2 Tyrosine Phosphatase

Natural products have been playing indispensable roles in the development of lifesaving drug molecules. They are also valuable sources for covalent protein modifiers. However, they often are scarce in nature and have complex chemical structures, which are limiting their further biomedical development. Thus, natural product-inspired small molecules which still contain the essence of the parent natural products but are readily available and amenable for structural modification, are important and desirable in searching for lead compounds for various disease treatment. Inspired by the complex and diverse ent-kaurene diterpenoids with significant biological activities, we have created a synthetically accessible and focused covalent library by incorporating the bicyclo[3.2.1]octane α-methylene ketone, which is considered as the pharmacophore of ent-kaurene diterpenoids, as half of the structure, and replacing the other half with much less complex but more druglike scaffolds. From this library, we have identified and characterized selective covalent inhibitors of protein tyrosine phosphatase SHP2, an important anti-cancer therapeutic target. The success of this study demonstrated the importance of creating and evaluating natural product-inspired library as well as their application in targeting challenging disease targets.

Dimeric ent-kauranoids isolated from Isodon japonica var. Glaucocalyx and their anti-inflammatory activities

The phytochemical investigation of the aerial parts of Isodon japonica var. glaucocalyx afforded four undescribed (glaucocalyxin O-R, 1-4) and six known ent-kauranoids (5-10). Their structures were established using NMR and MS measurements. Compounds 1 and 2 are dimeric ent-kaurane-type diterpenoids. Moreover, the plausible biogenetic pathways for compounds 1 and 2 were proposed as Michael addition between two monomers. Eight compounds were assayed for their anti-inflammatory activity by evaluating NO production in LPS-induced RAW 267.4 cells, and compounds 7, 8 and 9 exhibited relatively remarkable anti-inflammatory activities at 10 μM.

The intramolecular SN2 reaction tautomeric ent-Kauranoids isolated from the aerial parts of Isodon amethystoides

As our ongoing searching for the bioactive natural terpenoids, nine ent-kauranoids (1-9), including three previously undescribed ones (1, 2, and 9), were isolated from the aerial parts of Isodon amethystoides. Their structures were elucidated on the basis of spectroscopic data analysis, including NMR, MS, and ECD. Compounds 1 and 2 were a pair of tautomeric compounds, which was confirmed by the HPLC analysis and low temperature NMR testing. The underlying mechanism of the tautomer was proposed as an intramolecular SN2 reaction, which was explained by quantum chemical calculation. The HOMO-LUMO gap and the free energy revealed the spontaneous of the tautomeric of the 1 and 2. Additionally, the similar phenomena were also found in the two groups of known compounds 3 and 4 and 6 and 7, respectively. Apart from the tautomer, compounds 3 and 4 can be hydrolyzed into 5 through ester hydrolysis in CDCl3, while compounds 6, 7 can be hydrolyzed into 8 through ester hydrolysis. These phenomena were also confirmed through HPLC analysis and low temperature nuclear magnetic resonance tests and the mechanism was studied using quantum chemical calculation.

A novel selective ERK1/2 inhibitor, Laxiflorin B, targets EGFR mutation subtypes in non-small-cell lung cancer

Extracellular regulated protein kinases 1/2 (ERK1/2) are key members of multiple signaling pathways, including the ErbB axis. Ectopic ERK1/2 activation contributes to various types of cancer, especially drug resistance to inhibitors of RTK, RAF and MEK, and specific ERK1/2 inhibitors are scarce. In this study, we identified a potential novel covalent ERK inhibitor, Laxiflorin B, which is a herbal compound with anticancer activity. However, Laxiflorin B is present at low levels in herbs; therefore, we adopted a semi-synthetic process for the efficient production of Laxiflorin B to improve the yield. Laxiflorin B induced mitochondria-mediated apoptosis via BAD activation in non-small-cell lung cancer (NSCLC) cells, especially in EGFR mutant subtypes. Transcriptomic analysis suggested that Laxiflorin B inhibits amphiregulin (AREG) and epiregulin (EREG) expression through ERK inhibition, and suppressed the activation of their receptors, ErbBs, via a positive feedback loop. Moreover, mass spectrometry analysis combined with computer simulation revealed that Laxiflorin B binds covalently to Cys-183 in the ATP-binding pocket of ERK1 via the D-ring, and Cys-178 of ERK1 through non-inhibitory binding of the A-ring. In a NSCLC tumor xenograft model in nude mice, Laxiflorin B also exhibited strong tumor suppressive effects with low toxicity and AREG and EREG were identified as biomarkers of Laxiflorin B efficacy. Finally, Laxiflorin B-4, a C-6 analog of Laxiflorin B, exhibited higher binding affinity for ERK1/2 and stronger tumor suppression. These findings provide a new approach to tumor inhibition using natural anticancer compounds.

Current Advances in Japanese Encephalitis Virus Drug Development

Japanese encephalitis virus (JEV) belongs to the Flaviviridae family and is a representative mosquito-borne flavivirus responsible for acute encephalitis and meningitis in humans. Despite the availability of vaccines, JEV remains a major public health threat with the potential to spread globally. According to the World Health Organization (WHO), there are an estimated 69,000 cases of JE each year, and this figure is probably an underestimate. The majority of JE victims are children in endemic areas, and almost half of the surviving patients have motor or cognitive sequelae. Thus, the absence of a clinically approved drug for the treatment of JE defines an urgent medical need. Recently, several promising and potential drug candidates were reported through drug repurposing studies, high-throughput drug library screening, and de novo design. This review focuses on the historical aspects of JEV, the biology of JEV replication, targets for therapeutic strategies, a target product profile, and drug development initiatives.

Two new terpenoid glycosides from Isodon macrocalyx

One previously undescribed tricyclo-diterpenoid saponin (1), one undescribed dammarane triterpenoid saponin (2) and four known triterpenoids (3-6) were isolated from the aerial part of Isodon macrocalyx. Their structures were determined using 1 D- and 2 D-NMR, HRESIMS, and comparison of their spectroscopic data with previously reported data. The isolates were evaluated for their anti-HBV activity in vitro using the HBV transfected Hep G2.2.15 cell line. Compounds 2 and 3 exhibited moderate anti-HBV activity.

In Vitro and In Vivo Anti-Cancer Activity of Lasiokaurin in a Triple-Negative Breast Cancer Model

Due to its intricate heterogeneity, high invasiveness, and poor prognosis, triple-negative breast cancer (TNBC) stands out as the most formidable subtype of breast cancer. At present, chemotherapy remains the prevailing treatment modality for TNBC, primarily due to its lack of estrogen receptors (ERs), progesterone receptors (PRs), and human epidermal growth receptor 2 (HER2). However, clinical chemotherapy for TNBC is marked by its limited efficacy and a pronounced incidence of adverse effects. Consequently, there is a pressing need for novel drugs to treat TNBC. Given the rich repository of diverse natural compounds in traditional Chinese medicine, identifying potential anti-TNBC agents is a viable strategy. This study investigated lasiokaurin (LAS), a natural diterpenoid abundantly present in Isodon plants, revealing its significant anti-TNBC activity both in vitro and in vivo. Notably, LAS treatment induced cell cycle arrest, apoptosis, and DNA damage in TNBC cells, while concurrently inhibiting cell metastasis. In addition, LAS effectively inhibited the activation of the phosphatidylinositol-3-kinase/protein kinase B/mammalian target of rapamycin (PI3K/Akt/mTOR) pathway and signal transducer and activator of transcription 3 (STAT3), thus establishing its potential for multitarget therapy against TNBC. Furthermore, LAS demonstrated its ability to reduce tumor growth in a xenograft mouse model without exerting detrimental effects on the body weight or vital organs, confirming its safe applicability for TNBC treatment. Overall, this study shows that LAS is a potent candidate for treating TNBC.

Phytochemical diversity impacts herbivory in a tropical rainforest tree community

Metabolomics provides an unprecedented window into diverse plant secondary metabolites that represent a potentially critical niche dimension in tropical forests underlying species coexistence. Here, we used untargeted metabolomics to evaluate chemical composition of 358 tree species and its relationship with phylogeny and variation in light environment, soil nutrients, and insect herbivore leaf damage in a tropical rainforest plot. We report no phylogenetic signal in most compound classes, indicating rapid diversification in tree metabolomes. We found that locally co-occurring species were more chemically dissimilar than random and that local chemical dispersion and metabolite diversity were associated with lower herbivory, especially that of specialist insect herbivores. Our results highlight the role of secondary metabolites in mediating plant-herbivore interactions and their potential to facilitate niche differentiation in a manner that contributes to species coexistence. Furthermore, our findings suggest that specialist herbivore pressure is an important mechanism promoting phytochemical diversity in tropical forests.

Guidongnins I-J: Two New 6,7-seco-7,20-Olide-ent-kaurene Diterpenes with Unusual Structures from Isodon rubescens

Two undescribed ent-kaurene diterpenes, named guidongnins I (1) and J (2), were isolated from the medicinal plant Isodon rubescens. Compound 1 was determined to contain an unprecedented 23 carbons in the skeleton by bearing an extra isopropyl group at C-17 out of the diterpenoid parent structure, and compound 2 was the first example of 6,7-seco-7,20-olide-ent-kaurenes with two fused-tetrahydrofuran rings formed between C-6 and C-19/C-20 through oxygen bridges. Their structures, including their absolute configurations, were determined using the analyses of the spectroscopic and X-ray diffraction data. Guidongnins I (1) and J (2) were assessed for their anti-cancer activities against the growth of various cancer cell lines, and 2 displayed cytotoxic potency against HepG2 at IC50 27.14 ± 3.43 μM.

Charting the Evolution of Chemoenzymatic Strategies in the Syntheses of Complex Natural Products

Bolstered by recent advances in bioinformatics, genetics, and enzyme engineering, the field of chemoenzymatic synthesis has enjoyed a rapid increase in popularity and utility. This Perspective explores the integration of enzymes into multistep chemical syntheses, highlighting the unique potential of biocatalytic transformations to streamline the synthesis of complex natural products. In particular, we identify four primary conceptual approaches to chemoenzymatic synthesis and illustrate each with a number of landmark case studies. Future opportunities and challenges are also discussed.

Network Pharmacology and Molecular Docking Reveal the Mechanism of Isodon ternifolius (D. Don) Kudo Against Liver Fibrosis

Aim

Many studies have demonstrated the hepatoprotective or anti-fibrotic effects of Isodon ternifolius, but its pharmacological basis and mechanism remain unclear. In this study, we used in vitro models to validate the predicted results and revealed the potential mechanism of action and active ingredients through network pharmacology methods and molecular docking.

Methods

The chemical components of Isodon ternifolius were identified by literatures. Potential targets of Isodon ternifolius were predicted by Swiss Target Prediction. The disease targets were collected through the databases of Gene Card. Common targets of Isodon ternifolius and liver fibrosis were obtained by online tool Venny 2.1. PPI protein interaction network was obtained using String database, and target protein interaction network was drawn using Cytoscape software. Signaling pathway enrichment analysis was performed on drug-disease targets with of DAVID database.

Results

Twenty-one potential active ingredients and 298 potential targets were predicted by Swiss Target Prediction platform. Ninety pathways related to liver fibrosis were obtained by KEGG enrichment. The TLR4, MAPK and PI3K-Akt signaling pathways are mostly associated with liver fibrosis. Molecular docking techniques were used to validate the core target proteins TNF, Akt1, MAPK1, EGFR and TLR4 binding to the ingredients of Isodon ternifolius, which showed that a multitude of ingredients of Isodon ternifolius were able to bind to the above target proteins, especially 2α-hydroxy oleanolic acid and (-)-Lambertic acid. Our experimental validation results showed that Isodon ternifolius inhibited the activation of PI3K-Akt and ERK1/2 signaling pathways.

Conclusion

Through a network pharmacology approach and in vitro cell assay, we predicted and validated the active compounds of Isodon ternifolius and its potential targets for LF treatment. The results suggest that the mechanism of Isodon ternifolius treating LF by inhibiting angiogenesis may be related to the ERK1/2 and PI3K/Akt signaling pathways.

ent-Kaurane-Type Diterpenes Induce ROS-Mediated Mitochondrial Dysfunction and Apoptosis by Suppress the Homologous Recombination DNA Repair in Triple-Negative Breast Cancer Cells

Six ent-kaurane-type diterpenes were isolated from the roots of Isodon ternifolia. Previous studies have shown that compounds 1 and 2 exhibited cytotoxicity against three human cancer cell lines (MCF-7, A549, and HCT116), but its molecular mechanism has not been studied yet. In the present study, the inhibited proliferation of compounds 1 and 2 of two triple-negative breast cancer (TNBC) cell lines (4T1 and MDA-MB-231) have been demonstrated by MTT and colony formation assay. Flow cytometry, western blotting, and qPCR were used to further demonstrate the apoptosis process in TNBCs. Importantly, the following mitochondrial membrane potential (MMP) decrease during apoptosis was demonstrated to correlate to reactive oxygen species (ROS) production. In addition, DNA damage induced by compounds 1 and 2 was illustrated by detect of homologous recombination (HR) DNA repair genes and proteins expression, such as RAD51. These results indicated that compounds 1 and 2 could trigger the TNBCs apoptosis mediated by ROS-induced mitochondrial dysfunction and induce DNA double-strand breaks (DSBs) by down regulating HR DNA repair. Furthermore, this research reveals that the mechanism between mitochondria dysfunction and DNA damage is deserved to be investigated for elucidating the dynamic signal transduction between the nucleus and the cellular matrix during apoptosis.

Ternifolipyrons A-J: new cytotoxic α-pyrones from Isodon ternifolius (D. Don) Kudô

Isodon ternifolius (D.Don) Kudô is an important Asian herb used in traditional medicine against several diseases. Nineteen compounds were isolated from the dichloromethane-methanol (1 : 1) extract of I. ternifolius roots, including ten new α-pyrone derivatives, named ternifolipyrons A-J. The chemical structures of the isolates were determined by a combination of 1D and 2D NMR, along with LR- and HRMS spectroscopy. The absolute configurations of the α-pyrone derivatives were constructed based upon the X-ray signal crystal of the bromobenzoyl derivative of 1 as well as the electronic circular dichroism (ECD). All isolates (1-19) were investigated for their growth-inhibitory potential towards CCRF-CEM-leukemia cells at a fixed concentration of 30 μM. The compounds which exerted more than 50% inhibition at this concentration, compounds (7, 10, 12, 15-17), were tested at a different concentration range to determine their IC₅₀ values in CCRF-CEM leukemia, MDA-MB-231 triple-negative breast cancer, and MCF7 breast cancer cell lines. Ursolic acid (16) showed the most potent activity against the three cancer cell lines with IC₅₀ values of 8.37, 18.04, and 18.93 μM, respectively.

Ent-kaurane diterpenoids from the Annonaceae family: a review of research progress and call for further research

The Annonaceae is one of the plant families with members that are credited with numerous pharmacological functions. Among the group of compounds responsible for these bioactivities are the ent-kaurane diterpenoids. The ent-kauranes are a group of 20-Carbon, tetracyclic diterpenoids that are widely distributed in other plant families including the Annonaceae family. This mini-review focuses mainly on the ent-kaurane diterpenoids isolated from the Annonaceae family, delineates the various biological activities of these compounds, and highlights the research gaps that exist for further scientific scrutiny.

5-epi-ent-Kaurane diterpenoids from the aerial parts of Isodon eriocalyx and their anti-atherosclerotic potential

The phytochemical investigation of the EtOAc extract from the aerial parts of Isodon eriocalyx afforded seventeen diterpenoids, including eight undescribed compounds. Eriocalyxins H-L have unique structural characteristics featuring a 5-epi-ent-kaurane diterpenoid scaffold with eriocalyxins H-K also possess an unusual 6,11-epoxyspiro-lactone ring while eriocalyxin L, a 1,7:3,20-diepoxy-ent kaurene, features an 1,7-oxygen linkage. The structures of these compounds were elucidated by spectroscopic data interpretation, and the absolute configurations of eriocalyxins H, I, L, and M were confirmed by single-crystal X-ray diffraction. The isolates were screened for their inhibitory activities against VCAM-1 and ICAM-1 at 5 μM. While eriocalyxin O, coetsoidin A and laxiflorin P were found to significantly inhibit both VCAM-1 and ICAM-1, 8 (17),13-ent-labdadien-15 → 16-lactone-19-oic acid displayed evidently inhibitory effect against ICAM-1.

Enantioselective Total Syntheses of Grayanane Diterpenoids and (+)-Kalmanol: Evolution of the Bridgehead Carbocation-Based Cyclization and Late-Stage Functional Group Manipulation Strategies

Grayanane diterpenoids contain over 300 highly oxidized and structurally complex members, many of which possess important biological activities. Full details are provided for the development of the concise, enantioselective and divergent total syntheses of grayanane diterpenoids and (+)-kalmanol. The unique 7-endo-trig cyclization based on a bridgehead carbocation was designed and implemented to construct the 5/7/6/5 tetracyclic skeleton, demonstrating the practical value of the bridgehead carbocation-based cyclization strategy. Extensive studies of late-stage functional group manipulation were performed to forge the C1 stereogenic center, during which a photoexcited intramolecular hydrogen atom transfer reaction was discovered and the mechanism was further studied through density functional theory (DFT) calculations. The biomimetic 1,2-rearrangement from the grayanoid skeleton provided a 5/8/5/5 tetracyclic framework and resulted in the first total synthesis of (+)-kalmanol.

Recent advances in natural small molecules as drug delivery systems

Drug delivery systems (DDSs) are a multidisciplinary approach toward the effective delivery of drugs to their target sites. Natural small molecule (NSM) compounds with anticancer activity, self-assembly and co-assembly functions show great potential for application as novel DDSs in the biomedical field. NSMs are widely sourced, have many modification sites, and readily form hydrogen bonds, π-π interactions, van der Waals interactions, and other non-covalent bonds in solvents, resulting in ordered structures. Moreover, their good biocompatibility and bioactivity allow compositions based on these compounds to be used in life science applications such as tissue engineering, drug delivery and cell imaging, showing the potential medical value of NSMs as DDSs. In this review, we summarise the role, assembly principles and applications of natural products such as triterpenoids, diterpenoids, sterols, alkaloids and polysaccharides in the construction of small molecule systems, which are expected to provide an important reference for the development of more active natural nanomaterials and the study of single or multi-component interactions.

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.

Identification and functional characterization of three cytochrome P450 genes for the abietane diterpenoid biosynthesis in Isodon lophanthoides

We identify two ferruginol synthases and a 11-hydroxyferruginol synthase from a traditional Chinese medicinal herb Isodon lophanthoides and propose their involvement in two independent abietane diterpenoids biosynthetic pathways. Isodon lophanthoides is a traditional Chinese medicinal herb rich in highly oxidized abietane-type diterpenoids. These compounds exhibit a wide range of pharmaceutical activities, yet the biosynthesis is barely known. Here, we describe the screening and functional characterization of P450s that oxidize the abietane skeleton abietatriene. We mainly focused on CYP76 family and identified 12 CYP76AHs by mining the RNA-seq data of I. lophanthoides. Among the 12 CYP76AHs, 6 exhibited similar transcriptional expression features as upstream diterpene synthases, including root or leaf-preferential expression pattern and highly MeJA inducibility. These six P450s were considered as first-tier candidates and functionally characterized in yeast and plant cells. In yeast assays showed that both CYP76AH42 and CYP76AH43 were ferruginol synthases hydroxylating the C12 position of abietatriene, whereas CYP76AH46 was characterized as a 11-hydroxyferruginol synthase which catalyzes two successive oxidations at C12 and C11 of abietatriene. Heterologous expression of three CYP76AHs in Nicotiana benthamiana resulted in the formation of ferruginol. qPCR analysis showed CYP76AH42 and CYP76AH43 were mainly expressed in the root, which was consistent with the distribution of ferruginol in the root periderms. CYP76AH46 was primarily expressed in the leaves where barely ferruginol or 11-hydroxyferruginol was detected. In addition to distinct organ-specific expression pattern, three CYP76AHs exhibited different genomic structures (w or w/o introns), low protein sequence identities (51-63%) and were placed in separate subclades in the phylogenetic tree. These results suggest that the identified CYP76AHs may be involved in at least two independent abietane biosynthetic pathways in the aerial and underground parts of I. lophanthoides.

Diastereoselective Synthesis of trans-anti-Hydrophenanthrenes via Ti-mediated Radical Cyclization and Total Synthesis of Kamebanin

Ent-kaurenes consist of an ABC-ring based on a trans-anti-hydrophenanthrene skeleton and a D ring with an exomethylene. Highly oxygen-functionalized ent-kauren-15-ones have promising antiinflammatory pharmacological activity. In this study, we developed a novel diastereoselective synthesis of trans-anti-hydrophenanthrenes via a Ti-mediated reductive radical cyclization. We also demonstrated the applicability of this method by developing the first total synthesis of (±)-kamebanin (longest linear sequence; 17 steps, overall yield; 6.5 %). Furthermore, this synthesis provided a formal semi-pinacol rearrangement for the construction of the quaternary carbon at C8 and a novel Thorpe-Ziegler-type reaction for the construction of the D-ring.

A chromosome-level genome assembly reveals that tandem-duplicated CYP706V oxidase genes control oridonin biosynthesis in the shoot apex of Isodon rubescens

The ent-kaurenoids (e.g., oridonin and enmein) from the Isodon genus (Lamiaceae) are one class of diterpenoids with rich structural diversity and intriguing pharmaceutical activity. In contrast to the well-established gibberellin pathway, oxidative modifications diversifying the ent-kaurene skeleton in Isodon have remained undetermined for half a century. Here we report a chromosome-level genome assembly of I. rubescens, a well-recognized oridonin producer long favored by Asian people as a traditional herb with antitumor effects. The shoot apex was confirmed to be the actual region actively producing ent-kaurene diterpenoids. Through comparative genomics and phylogenetic analyses, we discovered a cluster of tandem-duplicated CYP706V oxygenase-encoding genes located on an ancient genomic block widely distributed in eudicots, whereas almost exclusively emerged in Isodon plants. In the shoot apex, IrCYP706V2 and IrCYP706V7 oxidized the ent-kaurene core in the initial stage of oridonin biosynthesis. Loss of CYP706Vs in other Lamiaceae plants offered an explanation for the specific kaurenoid production in Isodon plants. Moreover, we found that the Isodon genomes encode multiple diterpenoid synthases that are potentially involved in generating diterpenoid diversity. These findings provided new insights into the evolution of the lineage-specific diterpenoid pathway and laid a foundation for improving production of bioactive ent-kaurene-type diterpenoids by molecular breeding and synthetic biology approaches.

Exploring the effect of Weifuchun capsule on the toll-like receptor pathway mediated HES6 and immune regulation against chronic atrophic gastritis

ETHNOPHARMACOLOGICAL RELEVANCE

Weifuchun capsule (WFC) is a traditional Chinese patent medicine for chronic atrophic gastritis (CAG) in clinic. However, the mechanism of action of WFC for CAG still remains unclear due to its complex composition.

AIM OF THE STUDY

The study was projected to uncover the mechanism of action of WFC and the corresponding pharmacodynamic substance of WFC against CAG as well as providing a standard example for the research of traditional Chinese medicine (TCM) from the perspective of the network and the system.

MATERIALS AND METHODS

We identified the compounds of WFC through LC-MS/MS analysis and performed a systematic network targets analysis for WFC in the treatment of CAG which thoroughly described the mechanism of action of WFC for CAG. Based on analysis integrating omics data and algorithms, we focused on the specific immune regulatory role of WFC in the treatment of CAG, especially on a hub pathway, Toll-like receptor signaling pathway and thus deciphered the role of WFC in immune regulation, anti-inflammation and mediation of HES6. In experiments part, MNNG-GES-1-cell line and rat models were used to validate our findings.

RESULTS

In this study, compounds of WFC are identified through LC‒MS/MS and network target analysis is performed to dissect the specific immunoregulatory effect as well as mediation of HES6, a newly discovered biomolecule related to gastritis carcinoma progression, of WFC on CAG through the Toll-like receptor signaling pathway. Based on cell line and rat models, we verify the mechanism of action of WFC for CAG in inhibiting inflammatory cytokines, regulating immune cells like T cells and macrophages, related genes including TLR2 and CD14. It is also validated that WFC inhibits the expression of HES6 (P < 0.05).

CONCLUSION

Based on the combination of computational strategy and experiments, our study offers a comprehensive analysis to reveal the role of WFC in regulating immune response, inhibiting inflammation in the treatment of CAG, and provides a standard example for the research of TCM from the perspective of the network and the system.

Asymmetric Divergent Synthesis of ent-Kaurane-, ent-Atisane-, ent-Beyerane-, ent-Trachylobane-, and ent-Gibberellane-type Diterpenoids

A unified strategy toward asymmetric divergent syntheses of nine C8-ethano-bridged diterpenoids A1-A9 (candol A, powerol, sicanadiol, epi-candol A, atisirene, ent-atisan-16α-ol, 4-decarboxy-4-methyl-GA₁₂, trachinol, and ent-beyerane) has been developed based on late-stage transformations of common synthons having ent-kaurane and ent-trachylobane cores. The expeditious assembly of crucial advanced ent-kaurane- and ent-trachylobane-type building blocks is strategically explored through a regioselective and diastereoselective Fe-mediated hydrogen atom transfer (HAT) 6-exo-trig cyclization of the alkene/enone and 3-exo-trig cyclization of the alkene/ketone, showing the multi-reactivity of densely functionalized polycyclic substrates with π_C═C and π_C═O systems in HAT-initiated reactions. Following the rapid construction of five major structural skeletons (ent-kaurane-, ent-atisane-, ent-beyerane-, ent-trachylobane-, and ent-gibberellane-type), nine C8-ethano-bridged diterpenoids A1-A9 could be accessed in the longest linear 8 to 11 steps starting from readily available chiral γ-cyclogeraniol 1 and known chiral γ-substituted cyclohexenone 2, in which enantioselective total syntheses of candol A (A1, 8 steps), powerol (A2, 9 steps), sicanadiol (A3, 10 steps), epi-candol A (A4, 8 steps), ent-atisan-16α-ol (A6, 11 steps), and trachinol (A8, 10 steps) are achieved for the first time.

Seco- and isopimarane diterpenoids from Kaempferia marginata rhizomes and their NO inhibition activities

Three undescribed 9,10-seco-isopimarane diterpenoids, marginols I-K, and an unprecedent isopimara-8(9),15-diene diterpene, 14-epi-boesenberol F, together with a known 9,10-seco-isopimarane diterpenoid, kaemgalangol A, were isolated from the rhizomes of Vietnamese Kaempferia marginata. Marginols I and J contained a naturally very rare 6-oxabicyclo[3.2.1]octane-5-ol ring, while marginol K had a naturally rare oxepan-2-one ring in its structure. The unprecedented structures were elucidated by spectroscopic techniques, including HR-ESI-TOF-MS, UV, IR, and 1D and 2D NMR. The absolute configurations of marginols I-K and 14-epi-boesenberol F were determined by ECD calculations. The NO production inhibitory assay revealed that the isolated compounds, except marginol J, exhibited NO inhibitory activities with IC₅₀ values ranging from 65.06 to 87.70 μM against lipopolysaccharide (LPS)-induced RAW264.7 cells.

[2 + 2]-Cycloaddition-derived cyclobutane natural products: structural diversity, sources, bioactivities, and biomimetic syntheses

This review summarizes the structural diversity, bioactivities, and biomimetic synthesis of [2 + 2]-type cyclobutane natural products, along with discussion of their biosynthesis, stereochemical analysis, racemic occurrence, and biomimetic synthesis.

Dearomative logic in natural product total synthesis

Covering: 2011 to 2022The natural world is a prolific source of some of the most interesting, rare, and complex molecules known, harnessing sophisticated biosynthetic machinery evolved over billions of years for their production. Many of these natural products represent high-value targets of total synthesis, either for their desirable biological activities or for their beautiful structures outright; yet, the high sp3-character often present in nature's molecules imparts significant topological complexity that pushes the limits of contemporary synthetic technology. Dearomatization is a foundational strategy for generating such intricacy from simple materials that has undergone considerable maturation in recent years. This review highlights the recent achievements in the field of dearomative methodology, with a focus on natural product total synthesis and retrosynthetic analysis. Disconnection guidelines and a three-phase dearomative logic are described, and a spotlight is given to nature's use of dearomatization in the biosynthesis of various classes of natural products. Synthetic studies from 2011 to 2021 are reviewed, and 425 references are cited.

Comparative analysis of medicinal plant Isodon rubescens and its common adulterants based on chloroplast genome sequencing

Isodon rubescens (Hemsley) H. Hara is the source of Donglingcao under the monograph Rabdosiae Rubescentis Herba in Chinese Pharmacopoeia. In the local marketplace, this medicine can be accidentally contaminated, deliberately substituted, or mixed with other related species. The contaminants of herbal products are a threat to consumer safety. Due to the scarcity of genetic information on Isodon plants, more molecular markers are needed to avoid misidentification. In the present study, the complete chloroplast (cp) genome of seven species of Isodon was sequenced, de novo assembled and characterized. The cp genomes of these species universally exhibited a conserved quadripartite structure, i.e., two inverted repeats (IRs) containing most of the ribosomal RNA genes and two unique regions (large single copy and small single copy). Moreover, the genome structure, codon usage, and repeat sequences were highly conserved and showed similarities among the seven species. Five highly variable regions (trnS-GCU-trnT-CGU, atpH-atpI, trnE-UUC-trnT-GGU, ndhC-trnM-CAU, and rps15-ycf1) might be potential molecular markers for identifying I. rubescens and its contaminants. These findings provide valuable information for further species identification, evolution, and phylogenetic research of Isodon.

Multi-omics analysis the differences of VOCs terpenoid synthesis pathway in maintaining obligate mutualism between Ficus hirta Vahl and its pollinators

INRODUCTION

Volatile organic compounds (VOCs) emitted by the receptive syconia of Ficus species is a key trait to attract their obligate pollinating fig wasps. Ficus hirta Vahl is a dioecious shrub, which is pollinated by a highly specialized symbiotic pollinator in southern China. Terpenoids are the main components of VOCs in F. hirta and play ecological roles in pollinator attraction, allelopathy, and plant defense. However, it remains unclear that what molecular mechanism difference in terpenoid synthesis pathways between pre-receptive stage (A-phase) and receptive stage (B-phase) of F. hirta syconia.

METHODS

Transcriptome, proteome and Gas Chromatography-Mass Spectrometer (GC-MS) were applied here to analyze these difference.

RESULTS AND DISCUSSION

Compared to A-phase syconia, the genes (ACAT2, HMGR3, GGPS2, HDR, GPS2, TPS2, TPS4, TPS10-4, TPS14) related to the terpenoid synthesis pathway had higher expression level in receptive syconia (B-phase) according to transcriptome sequencing. Seven differentially expressed transcription factors were screened, namely bHLH7, MYB1R1, PRE6, AIL1, RF2b, ANT, VRN1. Specifically, bHLH7 was only specifically expressed in B-phase. 235 differentially expressed proteins (DEPs) were mainly located in the cytoplasm and chloroplasts. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis showed that the DEPs were mainly enriched in the metabolic process. A total of 9 terpenoid synthesis proteins were identified in the proteome. Among them, 4 proteins in methylerythritol phosphate (MEP) pathway were all down-regulated. Results suggested the synthesis of terpenoids precursors in B-phase bracts were mainly accomplished through the mevalonic acid (MVA) pathway in cytoplasm. Correlation analysis between the transcriptome and proteome, we detected a total of 1082 transcripts/proteins, three of which are related to stress. From the VOCs analysis, the average percent of monoterpenoids emitted by A-phase and B-phase syconia were 8.29% and 37.08%, while those of sesquiterpenes were 88.43% and 55.02% respectively. Monoterpenes (camphene, myrcene, camphor, menthol) were only detected in VOCs of B-phase syconia. To attract pollinators, B-phase syconia of F. hirta need more monoterpenoids and less sesquiterpenes. We speculate that transcription factor bHLH7 may regulate the terpenoid synthesis pathway between A- and B-phase syconia. Our research provided the first global analysis of mechanism differences of terpenoid synthesis pathways between A and B phases in F. hirta syconia.

Bioactive isopimarane and 3,4-seco isopimarane diterpenoids from Isodon amethystoides

Isodon amethystoides (Lamiaceae) is a popular plant in folk medicine in the southern provinces of China. Our phytochemical investigation of the twigs and leaves of this plant led to the discovery of five new diterpenoids with isopimarane and 3,4-seco isopimarane scaffolds [isoamethinols A–E (1–5)], along with the known compound 3,4-seco isopimara-4(18),7,15-triene-3-oic acid methylester (6). The chemical structures of these compounds, including the absolute configurations of the new diterpenoids, were determined by comprehensive spectroscopic analyses and single crystal X-ray diffraction measurements. These compounds were evaluated for their biological activities against a panel of human cancer cell lines, gram-positive bacterial strains and HIV. Notably, the 3,4-seco-isopimarane isoamethinol D (4) showed toxicity to the cervical Hela cancer (Hela) cells with an IC50 value of 27.21 μM and the lung (A549) cancer cells with an IC50 value of 21.47 μM. Compound 4 also exhibited mild antimicrobial activity against the oral bacterial strain Streptococcus mutans. These findings suggested that the diterpenoids with a 3,4-seco-isopimarane diterpenoids isolated from I. amethystoides could provide a novel structure scaffold for the discovery of anticancer and antimicrobial compounds.

Graphical Abstract

Design, Synthesis and Biological Evaluation of Lophanic Acid Derivatives as Antifungal and Antibacterial Agents

In order to discover more promising antifungal and antibacterial agents, a series of new derivatives were designed and synthesized by structure modification based on the naturally occurring antimicrobial compound lophanic acid. The structures of all the target compounds were well characterized by spectroscopic data. The stereochemistry of these compounds was further determined through the X-ray diffraction analysis of 6a. The synthetic compounds were evaluated for their antimicrobial activities against filamentous fungi (T. rubrum, T. mentagrophytes), yeasts (C. neoformans, C. albicans) and Gram-positive and Gram-negative bacteria (MRSA, S. mutans, S. sobrinus, and E. coli). Among them, 3d and 3i are found as the most promising leads that showed potent inhibitory effects against all the tested fungal and bacterial strains except for E. coli. The presence of the C-20 carboxylic ester groups and the free hydroxy group at C-13 was found to be essential for the antifungal and antibacterial activities of the lophanic acid derivatives.

Euphorbia diterpenoids: isolation, structure, bioactivity, biosynthesis, and synthesis (2013-2021)

Covering: 2013 to 2021As the characteristic metabolites of Euphorbia plants, Euphorbia diterpenoids have always been a hot topic in related science communities due to their intriguing structures and broad bioactivities. In this review, we intent to provide an in-depth and extensive coverage of Euphorbia diterpenoids reported from 2013 to the end of 2021, including 997 new Euphorbia diterpenoids and 78 known ones with latest progress. Multiple aspects will be summarized, including their occurrences, chemical structures, bioactivities, and syntheses, in which the structure-activity relationship and biosynthesis of this class will be discussed for the first time.

Plastome sequences fail to resolve shallow level relationships within the rapidly radiated genus Isodon (Lamiaceae)

As one of the largest genera of Lamiaceae and of great medicinal importance, Isodon is also phylogenetically and taxonomically recalcitrant largely ascribed to its recent rapid radiation in the Hengduan Mountains. Previous molecular phylogenetic studies using limited loci have only successfully resolved the backbone topology of the genus, but the interspecific relationships suffered from low resolution, especially within the largest clade (Clade IV) which comprises over 80% species. In this study, we attempted to further elucidate the phylogenetic relationships within Isodon especially Clade IV using plastome sequences with a broad taxon sampling of ca. 80% species of the genus. To reduce systematic errors, twelve different plastome data sets (coding and non-coding regions with ambiguously aligned regions and saturated loci removed or not) were employed to reconstruct phylogeny using maximum likelihood and Bayesian inference. Our results revealed largely congruent topologies of the 12 data sets and recovered major lineages of Isodon consistent with previous studies, but several incongruences are also found among these data sets and among single plastid loci. Most of the shallow nodes within Clade IV were resolved with high support but extremely short branch lengths in plastid trees, and showed tremendous conflicts with the nrDNA tree, morphology and geographic distribution. These incongruences may largely result from stochasticity (due to insufficient phylogenetic signal) and hybridization and plastid capture. Therefore, the uniparental-inherited plastome sequences are insufficient to disentangle relationships within a genus which has undergone recent rapid diversification. Our findings highlight a need for additional data from nuclear genome to resolve the relationships within Clade IV and more focused studies to assess the influences of multiple processes in the evolutionary history of Isodon. Nevertheless, the morphology of the shape and surface sculpture/indumentum of nutlets is of systematic importance that they can distinguish the four major clades of Isodon.

Stereoselective Synthesis and Application of Gibberellic Acid-Derived Aminodiols

A series of gibberellic acid-based aminodiols was designed and synthesized from commercially available gibberellic acid. Exposure of gibberellic acid to hydrochloric acid under reflux conditions resulted in aromatization followed by rearrangement to form allo-gibberic acid. The key intermediate, ethyl allo-gibberate, was prepared according to literature methods. Epoxidation of key intermediate and subsequent ring-opening of the corresponding epoxide with different nucleophiles resulted in N-substituted aminodiols. The regioselective ring closure of N-benzyl-substituted aminodiol with formaldehyde was also investigated. All aminodiol derivatives were well characterized using modern spectroscopic techniques and evaluated for their antiproliferative activity against a panel of human cancer cell lines. In addition, structure–activity relationships were examined by assessing substituent effects on the aminodiol systems. The results indicated that aminodiols containing aromatic rings on their nitrogen substituents displayed significant cytotoxic effects. Among these agents, N-naphthylmethyl-substituted aminodiols were found to be the most potent candidates in this series. One of these molecules exhibited a modest cancer selectivity determined by non-cancerous fibroblast cells. A docking study was also made to exploit the observed results.

Selective Oxidations in the Synthesis of Complex Natural ent-Kauranes and ent-Beyeranes

Syntheses of two natural products derived from the ent-kaurene kaurenoic acid are described for the first time using regio- and diastereoselective oxidations. Palladium- and manganese-mediated oxidations were used to accomplish the syntheses of two ent-beyerane metabolites. The use of the White-Gormisky-Zhao catalyst Mn(CF₃-PDP) enabled the first application of a nondirected metal-catalyzed oxidation in an unactivated C-H bond in a total synthesis.

Efficient production of clerodane and ent-kaurane diterpenes through truncated artificial pathways in Escherichia coli

The clerodane and ent-kaurane diterpenoids are two typical categories of diterpenoid natural products with complicated polycyclic carbon skeletons and significant pharmacological activities. Despite exciting advances in organic chemistry, access to these skeletons is still highly challenging. Using synthetic biology to engineer microbes provides an innovative alternative to bypass synthetic challenges. In this study, we constructed two truncated artificial pathways to efficiently produce terpentetriene and ent-kaurene, two representative clerodane and ent-kaurane diterpenes, in Escherichia coli. Both pathways depend on the exogenous addition of isoprenoid alcohol to reinforce the supply of IPP and DMAPP via two sequential phosphorylation reactions. Optimization of these constructs provided terpentetriene and ent-kaurene titers of 66 ± 4 mg/L and 113 ± 7 mg/L, respectively, in shake-flask fermentation. The truncated pathways to overproduce clerodane and ent-kaurane skeletons outlined here may provide an attractive route to prepare other privileged diterpene scaffolds.

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.

Glaucocalyxin A impairs tumor growth via amplification of the ATF4/CHOP/CHAC1 cascade in human oral squamous cell carcinoma

ETHNOPHARMACOLOGICAL RELEVANCE

The natural extract glaucocalyxin A (GLA), purified from the aboveground sections of the Chinese traditional medicinal herb Rabdosia japonica (Burm. f.) Hara var. glaucocalyx (Maxim.) Hara, has various pharmacological benefits, such as anti-bacterial, anti-coagulative, anti-neoplastic, and anti-inflammatory activities. Although GLA has shown anti-tumor activity against various cancers, the therapeutic potential and biological mechanisms of GLA remain to be further explored in oral squamous cell carcinoma (OSCC).

AIM OF THE STUDY

This study aimed to elucidate the therapeutic potential and regulatory mechanisms of GLA in OSCC.

MATERIALS AND METHODS

The cell proliferation and apoptosis effects of GLA were analyzed by CCK-8, clone formation, Annexin V/PI staining, and apoptotic protein expression in vitro. An OSCC xenograft model was applied to confirm the anti-neoplastic effect in vivo. Furthermore, the changes of reactive oxygen species (ROS) were determined by DCFH-DA probe and GSH/GSSG assay, and inhibited by the pan-caspase inhibitor Z-VAD(OMe)-FMK and the ROS scavenger N-acetylcysteine (NAC). The modulation of GLA on mitochondria and ER-dependent apoptosis pathways was analyzed by JC-1 probe, quantitative real-time PCR, and Western blot. Finally, public databases, clinical samples, and transfection cells were analyzed to explore the importance of GLA's indirect targeting molecule CHAC1 in OSCC.

RESULTS

GLA significantly inhibited cell proliferation and induced apoptosis in vitro and in vivo. GLA perturbed the redox homeostasis, and cell apoptosis was totally rescued by Z-VAD(OMe)-FMK and NAC. Furthermore, GLA activated the mitochondrial apoptosis pathway. Simultaneously, the overexpression and knockdown of CHAC1 dramatically affected GLA-mediated apoptosis. The endoplasmic reticulum stress-associated ATF4/CHOP signal was identified to participate in GLA-upregulated CHAC1 expression. Finally, we found that CHAC1 expression was lower in OSCC compared with normal tissues and positively correlated with 4-Hydroxynonenal (4-HNE) level. High CHAC1 expression also indicated better overall survival. Moreover, CHAC1 selectively regulated the viability of oral cancer cells.

CONCLUSION

GLA is a promising therapeutic agent that activates the ROS-mediated ATF4/CHOP/CHAC1 axis in OSCC patients.

Total Synthesis of the Alleged Structure of (+)-Fimbricalyxoid A

An enantioselective total synthesis of the alleged structure of (+)-fimbricalyxoid A is reported. The synthetic strategy features a pyridine-N-oxidate-mediated S_N2' reaction to introduce an oxygen functionality at position C3 of the A-ring and a sequential three-step process via the cleavage of the C-O bonds and hemiketalization to form the 3,20-oxybridge. With this strategy, the target molecule was synthesized in 19% overall yield and 12 steps from our previously synthesized cis-fused octahydrophenanthrene (+)-6.