Immunosuppressive leucosesterterpane and penta-nor-leucosesterterpane sesterterpenoids from Leucosceptrum canum

Five undescribed leucosesterterpane sesterterpenoids, leucosceptrines A-E, two undescribed penta-nor-leucosesterterpane (C20) sesterterpenoids, nor-leucosceptrines A and B, and three known analogues, were obtained from the aerial parts of Leucosceptrum canum of Chinese origin. Leucosceptrines A-C are the first examples of leucosesterterpane-type sesterterpenoids with unclosed dihydropyran rings and reverse configurations at chiral centers C-4 and/or C-12. Nor-leucosceptrines A and B possesses an unusual penta-nor-leucosesterterpane skeleton. Their structures were unambiguously elucidated through comprehensive spectroscopic analyses and single-crystal X-ray diffraction. A plausible biogenetic pathway for these sesterterpenoids was proposed. The immunosuppressive effects of these isolates on the secretion of the cytokine IFN-γ by mouse splenocytes stimulated with anti-CD3/CD28 monoclonal antibodies were observed with different potencies.

Antimicrobial sesterterpenoids with a unique 5/8/6/5 tetracyclic carbon-ring-system and diepoxide polyketides from a deep sea-sediment-sourced fungus Chaetomium globosum SD-347

Two new sesterterpenoids, sesterchaetins A and B (1 and 2), and two new diepoxide polyketides, chaetoketoics A and B (3 and 4), were characterized from the culture extract of Chaetomium globosum SD-347, a fungal strain derived from deep sea-sediment. Their structures and absolute configurations were unambiguously determined by detailed NMR, mass spectra, and X-ray crystallographic analysis. Compounds 1 and 2 contained a distinctive 5/8/6/5 tetracyclic carbon-ring-system, which represented a rarely occurring natural product framework. The new isolates 1-4 exhibited selective antimicrobial activities against human and aquatic pathogenic bacteria and plant-pathogenic fungi.

Two Sesterterpene Synthases from Lentzea atacamensis Demonstrate the Role of Conformational Variability in Terpene Biosynthesis

Mining of two multiproduct sesterterpene synthases from Lentzea atacamensis resulted in the identification of the synthases for lentzeadiene (LaLDS) and atacamatriene (LaATS). The main product of LaLDS (lentzeadiene) is a new compound, while one of the side products (lentzeatetraene) is the enantiomer of brassitetraene B and the other side product (sestermobaraene F) is known from a surprisingly distantly related sesterterpene synthase. LaATS produces six new compounds, one of which is the enantiomer of the known sesterterpene Bm1. Notably, for both enzymes the products cannot all be explained from one and the same starting conformation of geranylfarnesyl diphosphate, demonstrating the requirement of conformational flexibility of the substrate in the enzymes' active sites. For lentzeadiene an intriguing thermal [1,5]-sigmatropic rearrangement was discovered, reminiscent of the biosynthesis of vitamin D3. All enzyme reactions and the [1,5]-sigmatropic rearrangement were investigated through isotopic labeling experiments and DFT calculations. The results also emphasize the importance of conformational changes during terpene cyclizations.

Ménage à trois: light, terpenoids, and quality of plants

In controlled environment agriculture (CEA), light is used to impact terpenoid production and improve plant quality. In this review we discuss various aspects of light as important regulators of terpenoid production in different plant organs. Spectral quality primarily modifies terpenoid profiles, while intensity and photoperiod influence abundances. The central regulator of light signal transduction elongated hypocotyl 5 (HY5) controls transcriptional regulation of terpenoids under UV, red (R), and blue (B) light. The larger the fraction of R and green (G) light, the more beneficial the effect on monoterpenoid and sesquiterpenoid biosynthesis, and such an effect may depend on the presence of B light. A large fraction of R light is mostly detrimental to tetraterpenoid production. We conclude that light is a promising tool to steer terpenoid production and potentially tailor the quality of plants.

Bioinspired Total Synthesis of Bipolarolides A and B

We have achieved the first total synthesis of bipolarolides A and B, which possess an intriguing and complex 5/6/6/6/5 caged pentacyclic skeleton with seven contiguous stereocenters. The synthesis features a lithium-halogen exchange/intermolecular nucleophilic addition to link two enantioenriched fragments, two ring-closing metathesis reactions to assemble the five- and eight-membered rings, and a bioinspired Prins reaction/ether formation cascade cyclization to construct the 5/6/6/6/5 caged skeleton.

Syntheses of Linear Biosynthetic C25-Precursors of Leucosceptroids

An efficient synthetic approach was developed and applied to the syntheses of four linear biosynthetic C25-precursors of leucosceptroids. The synthesis features a Julia-Kocienski olefination and a late-stage bioinspired photo-oxidation as key steps. The immunosuppressive effects of all synthetic compounds on mouse T cells and macrophage RAW264.7 were determined.

Leucosceptrane Sesterterpenoids as a New Type of Natural Immunosuppressive Agents in Treating Sepsis

Intragastric administration of the total sesterterpenoid extract (TSE) of medicinal plant Leucosceptrum canum at 2.5 g/kg dose protected mice from LPS-induced sepsis. Phytochemical investigation led to the isolation and identification of 47 leucosceptrane sesterterpenoids (1-47) including 30 new compounds (1-30) with complicated oxygenation patterns. Biological screening indicated their immunosuppressive activity via inhibiting IFN-γ secretion and/or proliferation of T cells with different potencies. Mechanism study of compounds 9, 25, and 32 revealed that they inhibited the activations of AKT-mTOR, JNK, p38 MAPK or ERK pathway in T cells and macrophages. In addition, compounds 9 and 25 induced G0/G1 cell arrest of T cells. The major component, leucosceptroid N (32), significantly lowered the levels of IL-6 and TNF-α in peripheral blood serum, and ameliorated the multiorgan damages of LPS-induced sepsis mice at 25 mg/kg dose. These findings suggest that leucosceptrane sesterterpenoids are a new type of potential immunosuppressive agents for sepsis treatment.

Unprecedented sesterterpenoids, orientanoids A-C: discovery, bioinspired total synthesis and antitumor immunity

Sesterterpenoids are a very rare class of important natural products. Three new skeletal spiro sesterterpenoids, named orientanoids A-C (1-3), were isolated from Hedyosmum orientale. Their structures were determined by a combination of spectroscopic data, X-ray crystallography, and total synthesis. To obtain adequate materials for biological research, the bioinspired total syntheses of 1-3 were effectively achieved in 7-8 steps in overall yields of 2.3-6.4% from the commercially available santonin without using any protecting groups. In addition, this work also revised the stereochemistry of hedyosumins B (6) and C (10) as 11R-configuration. Tumor-associated macrophages (TAMs) have emerged as important therapeutic targets in cancer therapy. The in-depth biological evaluation revealed that these sesterterpenoids antagonized the protumoral and immunosuppressive functional phenotype of macrophages in vitro. Among them, the most potent and major compound 1 inhibited protumoral M2-like macrophages and activated cytotoxic CD8+ T cells, and consequently inhibited tumor growth in vivo.

Discovery of Unusual Sesterterpenoids from Colquhounia coccinea var. mollis and Their Metabolic Implications

Three unusual sesterterpenoids featuring unprecedented rearranged colquhounane (C25) and tetranorcolquhounane (C21) frameworks, colquhounoids E (1) and F (3) and norcolquhounoid F (2), were isolated from a Lamiaceae medicinal plant Colquhounia coccinea var. mollis. Their structures were elucidated by spectroscopic analysis and quantum chemical calculations. A biomimetic inspired regioselective cyclopropane cleavage was achieved under acidic conditions. The immunosuppressive activities of these new sesterterpenoids were also evaluated.

Exploring the Divergent Reactivity of Vinyl Radicals Emanating from Alkynes and Thiols via Photoredox Catalysis

Organic chemistry has seen a surge in visible-light-driven transformations, which offer unique reaction pathways and access to new synthetic possibilities. We aim to provide a comprehensive understanding of state-of-the-art photo-mediated alkyne functionalization, with a focus on the reactive behavior of vinyl radicals. This review outlines our contributions to the field, including developing new methods for forming carbon-carbon and carbon-heteroatom bonds.

Formation of a traditional Chinese medicine self-assembly nanostrategy and its application in cancer: a promising treatment

Traditional Chinese medicine (TCM) has been used for centuries to prevent and treat a variety of illnesses, and its popularity is increasing worldwide. However, the clinical applications of natural active components in TCM are hindered by the poor solubility and low bioavailability of these compounds. To address these issues, Chinese medicine self-assembly nanostrategy (CSAN) is being developed. Many active components of TCM possess self-assembly properties, allowing them to form nanoparticles (NPs) through various noncovalent forces. Self-assembled NPs (SANs) are also present in TCM decoctions, and they are closely linked to the therapeutic effects of these remedies. SAN is gaining popularity in the nano research field due to its simplicity, eco-friendliness, and enhanced biodegradability and biocompatibility compared to traditional nano preparation methods. The self-assembly of active ingredients from TCM that exhibit antitumour effects or are combined with other antitumour drugs has generated considerable interest in the field of cancer therapeutics. This paper provides a review of the principles and forms of CSAN, as well as an overview of recent reports on TCM that can be used for self-assembly. Additionally, the application of CSAN in various cancer diseases is summarized, and finally, a concluding summary and thoughts are proposed. We strongly believe that CSAN has the potential to offer fresh strategies and perspectives for the modernization of TCM.

A Monocarbocyclic Sesterterpenoid Biosynthetic Precursor of Leucosceptroids from Leucosceptrum canum and Its Metabolic Isomerization by a Specialist Insect

Pre-leucosceptroid (1), a rare monocarbocyclic sesterterpenoid featuring a cyclopentane ring with a terminal furan moiety, was isolated from the leaves of Leucosceptrum canum. Discovery of 1 suggested a two-step cyclization...

Application of Pauson-Khand reaction in the total synthesis of terpenes

The Pauson-Khand reaction (PKR) is a formal [2 + 2 + 1] cycloaddition involving an alkyne, an alkene and carbon monoxide mediated by a hexacarbonyldicobaltalkyne complex to yield cyclopentenones in a single step. This versatile reaction has become a method of choice for the synthesis of cyclopentenone and its derivatives since its discovery in the early seventies. The aim of this review is to point out the applications of PKR in the total synthesis of terpenes.

An Alternative Approach towards C-12 Functionalized Scalaranic Sesterterpenoids Synthesis of 17-Oxo-20-norscalaran-12α,19-O-lactone

Scalarane sesterterpenoids emerged as interesting bioactive natural products which were isolated extensively from marine sponges and shell-less mollusks. Some representatives were also reported recently from superior plants. Many scalarane sesterterpenoids displayed a wide spectrum of valuable properties, such as antifeedant, antimicrobial, antifungal, antitubercular, antitumor, anti-HIV properties, cytotoxicity and stimulation of nerve growth factor synthesis, as well as anti-inflammatory activity. Due to their important biological properties, many efforts have been undertaken towards the chemical synthesis of natural scalaranes. The main synthetic challenges are connected to their complex polycyclic framework, chiral centers and different functional groups, in particular the oxygenated functional groups at the C-12 position, which are prerequisites of the biological activity of many investigated scalaranes. The current work addresses this problem and the synthesis of 17-oxo-20-norscalaran-12α,19-O-lactone is described. It was performed via the 12α-hydroxy-ent-isocopal-13(14)-en-15-al obtained from (-)-sclareol as an accessible starting material. The tetracyclic lactone framework was built following an addition strategy, which includes the intramolecular Michael addition of a diterpenic acetoacetic ester and an intramolecular aldol condensation reaction as key synthetic steps. The structure and stereochemistry of the target compound have been proven by X-Ray diffraction method.

Visible-Light-Promoted Oxidative Annulation of Naphthols and Alkynes: Synthesis of Functionalized Naphthofurans

A visible-light-mediated site-selective oxidative annulation of naphthols with alkynes for the synthesis of functionalized naphthofurans has been developed. The reaction relies on the in situ formation of an electron donor acceptor pair between phenylacetylene and thiophenol as the light-absorbing system to obviate the requirement of an added photocatalyst. The protocol facilitates the transformation of 1-naphthol and 2-naphthol as well as 1,4-naphthoquinone into a wide variety of highly functionalized naphthofurans.

Spectanoids A-H: Eight undescribed sesterterpenoids from Aspergillus spectabilis

Ten sesterterpenoids, including eight undescribed ones named spectanoids A-H and two known analogs, were obtained from Aspergillus spectabilis. Their structures, including absolute configurations, were determined based on HRESIMS, NMR, ECD calculations and single-crystal X-ray diffraction analyses. Spectanoids A-G are tricyclic sesterterpenoids with an unusual 5/12/5 ring system, while spectanoid H possesses a 5/8/6/5 ring system. All of these compounds were evaluated for their cytotoxic activities against three human cancer cells, and spectanoid A, spectanoid C and spectanoid F exhibited moderate cytotoxic activities with IC₅₀ values ranging from 12.1 to 26.1 μM.

Enantioselective Total Synthesis of Cerorubenic Acid-III via Type II [5+2] Cycloaddition Reaction

The first enantioselective total synthesis of cerorubenic acid-III is described in detail. Different strategies and attempts, based on a type II [5+2] cycloaddition reaction, leading to the bicyclo[4.4.1] ring system with a strained bridgehead double bond, are depicted. Furthermore, sodium naphthalenide was found to be efficient in the chemoselective reduction of 8-oxabicyclo[3.2.1]octene, with three transformations completed in one operation. An unusual S_N1 transannular cyclization reaction was applied to construct the synthetically challenging vinylcyclopropane moiety. This strategy enabled the total synthesis of cerorubenic acid-III in 19 steps.

Mining methods and typical structural mechanisms of terpene cyclases

Terpenoids, formed by cyclization and/or permutation of isoprenes, are the most diverse and abundant class of natural products with a broad range of significant functions. One family of the critical enzymes involved in terpenoid biosynthesis is terpene cyclases (TCs), also known as terpene synthases (TSs), which are responsible for forming the ring structure as a backbone of functionally diverse terpenoids. With the recent advances in biotechnology, the researches on terpene cyclases have gradually shifted from the genomic mining of novel enzyme resources to the analysis of their structures and mechanisms. In this review, we summarize both the new methods for genomic mining and the structural mechanisms of some typical terpene cyclases, which are helpful for the discovery, engineering and application of more and new TCs.

Immunosuppressive gentianellane-type sesterterpenoids from the traditional Uighur medicine Gentianella turkestanorum

Whole plants of Gentianella turkestanorum are commonly used as a traditional Uighur medicine. A phytochemical investigation led to the isolation of eight undescribed gentianellane-type sesterterpenoids (18-epi-nitidasin, gentianelloids D-F, and 18-epi-gentianelloids C-F), one undescribed 11,12-seco-gentianellane (18-epi-alborosin), and three known analogs (nitidasin, gentianelloid C and alborosin) among which gentianelloid C was found for the first time from a natural source. The structures of these compounds were elucidated by extensive spectroscopic analyses (including 1D and 2D NMR, HRMS, IR, and specific rotation) and in the case of 18-epi-gentianelloid C by the single-crystal X-ray diffraction analysis. A putative biosynthetic route for these sesterterpenoids was proposed. The immunosuppressive activity of the isolated compounds was also evaluated by their ability to inhibit the proliferation of T cells and T cell cytokine IFN-γ production. Nitidasin suppressed IFN-γ production with an IC₅₀ value of 16.50 μM, while gentianelloid F and alborosin inhibited the proliferation of and IFN-γ production in T cells with IC₅₀ values of 12.40-14.66 μM.

Genome-guided investigation of anti-inflammatory sesterterpenoids with 5-15 trans-fused ring system from phytopathogenic fungi

Fungal terpenoids catalyzed by bifunctional terpene synthases (BFTSs) possess interesting bioactive and chemical properties. In this study, an integrated approach of genome mining, heterologous expression, and in vitro enzymatic activity assay was used, and these identified a unique BFTS sub-clade critical to the formation of a 5-15 trans-fused bicyclic sesterterpene preterpestacin I (1). The 5-15 bicyclic BFTS gene clusters were highly conserved but showed relatively wide phylogenetic distribution across several species of the diverged fungal classes Dothideomycetes and Sordariomycetes. Further genomic organization analysis of these homologous biosynthetic gene clusters from this clade revealed a glycosyltransferase from the graminaceous pathogen Bipolaris sorokiniana isolate BS11134, which was absent in other 5-15 bicyclic BFTS gene clusters. Targeted isolation guided by BFTS gene deletion led to the identification of two new sesterterpenoids (4, and 6) from BS11134. Compounds 2 and 4 showed moderate effects on LPS-induced nitrous oxide production in the murine macrophage-like cell line RAW264.7 with in vitro inhibition rates of 36.6 ± 2.4% and 24.9 ± 2.1% at 10 μM, respectively. The plausible biosynthetic pathway of these identified compounds was proposed as well. This work revealed that phytopathogenic fungi can serve as important sources of active terpenoids via systematic analysis of the genomic organization of BFTS biosynthetic gene clusters, their phylogenetic distribution in fungi, and cyclization properties of their metabolic products. KEY POINTS: • Genome mining of the first BFTS BGC harboring a glycosyltransferase. • Gene-deletion guided isolation revealed three novel 5-15 bicyclic sesterterpenoids. • Biosynthetic pathway of isolated sesterterpenoids was proposed.

The untapped potential of plant sesterterpenoids: chemistry, biological activities and biosynthesis

Covering: 1969 up to 2021Sesterterpenoids, biosynthetically derived from the precursor, namely geranylfarnesyl diphosphate (GFDP) are amongst the rarest of all isoprenoids with approximately 1300 compounds known. Most sesterterpenoids originate from marine organisms (especially sponges), while only about 15% of these compounds are isolated from several families of plants such as Lamiaceae, Gentianaceae, and Nartheciaceae. Many plant sesterterpenoids possess highly oxygenated and complex cyclic skeletons and exhibit remarkable biological activities involving cytotoxic, anti-inflammatory, antimicrobial, and antifeedant properties. Thus, due to their intrinsic chemical complexity and intriguing biological profiles, plant sesterterpenoids have attracted continuing interest from both chemists and biologists. However, the biosynthesis and distribution of sesterterpenoids in the plant kingdom still remain elusive, although substantial progress has been achieved in recent years. This review provides an overall coverage of sesterterpenoids originating from plant sources, followed by a classification of their chemical skeletons, which summarizes the distribution, chemistry, biological activities, biosynthesis and evolution of plant sesterterpenoids, aiming at strengthening the research efforts toward the untapped great potential of these unique natural product resources.

Bacterial terpenome

Covering: up to mid-2020 Terpenoids, also called isoprenoids, are the largest and most structurally diverse family of natural products. Found in all domains of life, there are over 80 000 known compounds. The majority of characterized terpenoids, which include some of the most well known, pharmaceutically relevant, and commercially valuable natural products, are produced by plants and fungi. Comparatively, terpenoids of bacterial origin are rare. This is counter-intuitive to the fact that recent microbial genomics revealed that almost all bacteria have the biosynthetic potential to create the C5 building blocks necessary for terpenoid biosynthesis. In this review, we catalogue terpenoids produced by bacteria. We collected 1062 natural products, consisting of both primary and secondary metabolites, and classified them into two major families and 55 distinct subfamilies. To highlight the structural and chemical space of bacterial terpenoids, we discuss their structures, biosynthesis, and biological activities. Although the bacterial terpenome is relatively small, it presents a fascinating dichotomy for future research. Similarities between bacterial and non-bacterial terpenoids and their biosynthetic pathways provides alternative model systems for detailed characterization while the abundance of novel skeletons, biosynthetic pathways, and bioactivies presents new opportunities for drug discovery, genome mining, and enzymology.

Sesterterpenoids: chemistry, biology, and biosynthesis

Covering: July 2012 to December 2019Over the last seven years, expanding research efforts focused on sesterterpenoids has led to the isolation, identification, and characterization of numerous structurally novel and biologically active sesterterpenoids. These newly reported sesterterpenoids provide diverse structures that often incorporate unprecedented ring systems and new carbon skeletons, as well as unusual functional group arrays. Biological activities of potential biomedical importance including suppression of cancer cell growth, inhibition of enzymatic activity, and modulation of receptor signaling, as well as ecologically important functions such as antimicrobial effects and deterrence of herbivorous insects have been associated with a variety of sesterterpenoids. There has also been a rapid growth in our knowledge of the genomics, enzymology, and specific pathways associated with sesterterpene biosynthesis. This has opened up new opportunities for future sesterterpene discovery and diversification through the expression of new cryptic metabolites and the engineered manipulation of associated biosynthetic machinery and processes. In this paper we reviewed 498 new sesterterpenoids, including their structures, source organisms, country of origin, relevant bioactivities, and biosynthesis.

Cytotoxic Scalarane Sesterterpenes from the Sponge Hyrtios erectus

Twelve new sesterterpenes along with eight known sesterterpenes were isolated from the marine sponge Hyrtios erectus collected off the coast of Chuuk Island, the Federated State of Micronesia. Based upon a combination of spectroscopic and computational analyses, these compounds were determined to be eight glycine-bearing scalaranes (1–8), a 3-keto scalarane (9), two oxidized-furan-bearing scalaranes (10 and 11), and a salmahyrtisane (12). Several of these compounds exhibited weak antiproliferation against diverse cancer cell lines as well as moderate anti-angiogenesis activities. The antiproliferative activity of new compound 4 was found to be associated with G0/G1 arrest in the cell cycle.

Leucosceptroid B from glandular trichomes of Leucosceptrum canum reduces fat accumulation in Caenorhabditis elegans through suppressing unsaturated fatty acid biosynthesis

Obesity that is highly associated with numerous metabolic diseases has become a global health issue nowdays. Plant sesterterpenoids are an important group of natural products with great potential; thus, their bioactivities deserve extensive exploration. RNA-seq analysis indicated that leucosceptroid B, a sesterterpenoid previously discovered from the glandular trichomes of Leucosceptrum canum, significantly regulated the expression of 10 genes involved in lipid metabolism in Caenorhabditis elegans. Furthermore, leucosceptroid B was found to reduce fat storage, and downregulate the expression of two stearoyl-CoA desaturase (SCD) genes fat-6 and fat-7, and a fatty acid elongase gene elo-2 in wild-type C. elegans. In addition, leucosceptroid B significantly decreased fat accumulation in both fat-6 and fat-7 mutant worms but did not affect the fat storage of fat-6; fat-7 double mutant. These findings indicated that leucosceptroid B reduced fat storage depending on the downregulated expression of fat-6, fat-7 and elo-2 and thereby inhibiting the biosynthesis of the corresponding unsaturated fatty acid. These findings provide new insights into the development and utilization of plant sesterterpenoids as potential antilipemic agents.

Roquefornine A, a sesterterpenoid with a 5/6/5/5/6-fused ring system from the fungus Penicillium roqueforti YJ-14

Roquefornine A, a sesterterpenoid with an unprecedented 5/6/5/5/6-membered pentacyclic system, was characterized from Penicillium roqueforti YJ-14.

Sesterterpenoids

Sesterterpenoids are known as a relatively small group of natural products. However, they represent a variety of simple to more complex structural types. This contribution focuses on the chemical structures of sesterterpenoids and how their structures are constructed in Nature.

Ophiobolin-Type Sesterterpenoids from the Mangrove Endophytic Fungus Aspergillus sp. ZJ-68

Eleven new ophiobolin-type sesterterpenoids, asperophiobolins A-K (1-11), along with 12 known analogues (12-23) were isolated from the cultures of the mangrove endophytic fungus Aspergillus sp. ZJ-68. The structures of the new compounds were elucidated through spectroscopic analyses, and their absolute configurations were assigned by a combination of Mo₂(AcO)₄-induced electronic circular dichroism spectra and quantum chemical calculations. Asperophiobolins A-D (1-4) represent the first examples possessing a five-membered lactam unit between C-5 and C-21 in ophiobolin derivatives. In the bioactivity assays, compounds 8-10 and 14-17 exhibited inhibitory effects on lipopolysaccharide-induced nitric oxide production in RAW 264.7 macrophage cells with IC₅₀ values ranging from 9.6 to 25 μM, and compound 8 was found to show comparable inhibition of Mycobacterium tuberculosis protein tyrosine phosphatase B with an IC₅₀ value of 19 μM.

A new family of sesterterpenoids isolated around the Pacific Rim

Covering: 2009 up to the end of 2017 There has been a recent eruption in the number of known marine sesterterpenoids which have been isolated from Pacific Rim marine organisms. These compounds have novel and unusual structures that exhibit incredibly potent and varied bioactivities. This review details the isolation, biological testing and prospects for this exciting new family with discussion of their potential biogenetic origins.

Unusual and Highly Bioactive Sesterterpenes Synthesized by Pleurotus ostreatus during Coculture with Trametes robiniophila Murr

Candida albicans and Cryptococcus neoformans, human-pathogenic fungi found worldwide, are receiving increasing attention due to high morbidity and mortality in immunocompromised patients. In the present work, 110 fungus pairs were constructed by coculturing 16 wood-decaying basidiomycetes, among which coculture of Trametes robiniophila Murr and Pleurotus ostreatus was found to strongly inhibit pathogenic fungi through bioactivity-guided assays. A combination of metabolomics and molecular network analysis revealed that 44 features were either newly synthesized or produced at high levels in this coculture system and that 6 of the features that belonged to a family of novel and unusual linear sesterterpenes contributed to high activity with MICs of 1 to 32 μg/ml against pathogenic fungi. Furthermore, dynamic ¹³C-labeling analysis revealed an association between induced features and the corresponding fungi. Unusual sesterterpenes were ¹³C labeled only in P. ostreatus in a time course after stimulation by the coculture, suggesting that these sesterterpenes were synthesized by P. ostreatus instead of T. robiniophila Murr. Sesterterpene compounds 1 to 3 were renamed postrediene A to C. Real-time reverse transcription-quantitative PCR (RT-qPCR) analysis revealed that transcriptional levels of three genes encoding terpene synthase, farnesyl-diphosphate farnesyltransferase, and oxidase were found to be 8.2-fold, 88.7-fold, and 21.6-fold higher, respectively, in the coculture than in the monoculture, indicating that biosynthetic gene cluster 10 was most likely responsible for the synthesis of these sesterterpenes. A putative biosynthetic pathway of postrediene A to postrediene C was then proposed based on structures of sesterterpenes and molecular network analysis.IMPORTANCE A number of gene clusters involved in biosynthesis of secondary metabolites are presumably silent or expressed at low levels under conditions of standard laboratory cultivation, resulting in a large gap between the pool of discovered metabolites and genome capability. This work mimicked naturally occurring competition by construction of an artificial coculture of basidiomycete fungi for the identification of secondary metabolites with novel scaffolds and excellent bioactivity. Unusual linear sesterterpenes of postrediene A to C synthesized by P. ostreatus not only were promising lead drugs against human-pathogenic fungi but also highlighted a distinct pathway for sesterterpene biosynthesis in basidiomycetes. The current work provides an important basis for uncovering novel gene functions involved in sesterterpene synthesis and for gaining insights into the mechanism of silent gene activation in fungal defense.

Asperunguisins A-F, Cytotoxic Asperane Sesterterpenoids from the Endolichenic Fungus Aspergillus unguis

Six new asperane-type sesterterpenoids, asperunguisins A-F (1-6), were isolated from the endolichenic fungus Aspergillus unguis, together with a known analogue, aspergilloxide (7); these are rare asperane-type sesterterpenoids, characterized by a unique hydroxylated 7/6/6/5 tetracyclic system. The structures of asperunguisins A-F (1-6) were elucidated on the basis of spectroscopic methods (NMR and HRESIMS), X-ray single-crystal diffraction analysis, ECD calculations, and biogenetic considerations. Asperunguisin C (3) showed cytotoxicity against the human cancer cell line A549 with an IC₅₀ value of 6.2 μM. Further investigation revealed that the observed cell death was a result of G0/G1 cell cycle arrest via DNA damage followed by cellular apoptosis.

Sesterterpene MHO7 suppresses breast cancer cells as a novel estrogen receptor degrader

Breast cancer, the most prevalent cancer in women, remains the second in the list of cancer mortality, the majority of these fatalities resulted from estrogen receptor alpha (ERα) positive disease. ERα is well known for its function on breast cancer initiation and development and has become the most successful biomarker in breast cancers. Ophiobolins are sesterterpene compounds with a distinct tricyclic 5-8-5 ring and have presented anti-cancer activities. MHO7(6-epi-ophiobolin G)was isolated from products of a mangrove fungus in our previous research and demonstrated robust activity against breast cancer cells (BCCs). The investigation on the precise mechanism of MHO7 shows that MHO7 acts as a novel ERα down regulator different from the known molecules in ER + breast cancer cells. A whole-genome transcriptomic analysis on MCF-7 cells treated with MHO7 revealed the estrogen signaling pathway was the most affected pathway, and further evidence showed the de novo synthesis of ESR1 mRNA was inhibited. In addition, MHO7 down-regulated ERα at the protein level through multiple approaches. It not only bound to ERα, pushing helix 11 away in the agonist conformation but also increased the ERα degradation through the ubiquitin-proteasome system. These effects consequently caused decreasing of the transcriptional activity of ER modulation which was confirmed by the decreasing of estrogen receptor element (ERE) activity as well as downstream genes expressions like GREB1, BRCA1, MUC1 and CCND1. Combination of tamoxifen and MHO7 yield a synergistic effect on the inhibition of MCF-7 cells when treated around the IC₅₀ values. Our results suggest that MHO7 is a very promising drug candidate and provides a novel drug version on ERα down-regulation to fighting with breast cancer.

Identifying and engineering the ideal microbial terpenoid production host

More than 70,000 different terpenoid structures are known so far; many of them offer highly interesting applications as pharmaceuticals, flavors and fragrances, or biofuels. Extraction of these compounds from their natural sources or chemical synthesis is—in many cases—technically challenging with low or moderate yields while wasting valuable resources. Microbial production of terpenoids offers a sustainable and environment-friendly alternative starting from simple carbon sources and, frequently, safeguards high product specificity. Here, we provide an overview on employing recombinant bacteria and yeasts for heterologous de novo production of terpenoids. Currently, Escherichia coli and Saccharomyces cerevisiae are the two best-established production hosts for terpenoids. An increasing number of studies have been successful in engineering alternative microorganisms for terpenoid biosynthesis, which we intend to highlight in this review. Moreover, we discuss the specific engineering challenges as well as recent advances for microbial production of different classes of terpenoids. Rationalizing the current stages of development for different terpenoid production hosts as well as future prospects shall provide a valuable decision basis for the selection and engineering of the cell factory(ies) for industrial production of terpenoid target molecules.

Asymmetric Total Synthesis of Cerorubenic Acid-III

The first asymmetric total synthesis of the highly strained compound cerorubenic acid-III is reported. A type II intramolecular [5 + 2] cycloaddition allowed efficient and diastereoselective construction of the synthetically challenging bicyclo[4.4.1] ring system with a strained bridgehead (anti-Bredt) double bond in the final product. A unique transannular cyclization installed the vinylcyclopropane moiety with retention of the desired stereochemistry.

Atolypenes, Tricyclic Bacterial Sesterterpenes Discovered Using a Multiplexed In Vitro Cas9-TAR Gene Cluster Refactoring Approach

Most natural product biosynthetic gene clusters identified in bacterial genomic and metagenomic sequencing efforts are silent under laboratory growth conditions. Here, we describe a scalable biosynthetic gene cluster activation method wherein the gene clusters are disassembled at interoperonic regions in vitro using CRISPR/Cas9 and then reassembled with PCR-amplified, short DNAs, carrying synthetic promoters, using transformation assisted recombination (TAR) in yeast. This simple, cost-effective, and scalable method allows for the simultaneous generation of combinatorial libraries of refactored gene clusters, eliminating the need to understand the transcriptional hierarchy of the silent genes. In two test cases, this in vitro disassembly-TAR reassembly method was used to create collections of promoter-replaced gene clusters that were tested in parallel to identify versions that enabled secondary metabolite production. Activation of the atolypene ( ato) gene cluster led to the characterization of two unprecedented bacterial cyclic sesterterpenes, atolypene A (1) and B (2), which are moderately cytotoxic to human cancer cell lines. This streamlined in vitro disassembly- in vivo reassembly method offers a simplified approach for silent gene cluster refactoring that should facilitate the discovery of natural products from silent gene clusters cloned from either metagenomes or cultured bacteria.

Biosynthesis of an anti-tuberculosis sesterterpenoid asperterpenoid A

Biosynthesis of a potent MptpB inhibitor asperterpenoid A by a sesterterpene cyclase AstC and a multifunctional P450 enzyme AstB.

Total synthesis of sesterterpenoids

Total syntheses of biologically and structurally fascinating sesterterpenoids published between Jan. 2012 and Jan. 2018 are summarized and discussed here.

Asymmetric total synthesis of (+)-astellatol and (−)-astellatene

Here we describe the full account of the total synthesis of (+)-astellatol, as well as the first total synthesis of (−)-astellatene.

Isolation and Absolute Configurations of Diversiform C17, C21 and C25 Terpenoids from the Marine Sponge Cacospongia sp

Chemical investigation of MeOH extract of a South China Sea sponge Cacospongia sp. yielded 15 terpenoids belonging to three different skeleton-types, including the unusual C₁₇γ-lactone norditerpenoids (1–3), the rare C₂₁ pyridine meroterpenoid (7), and the notable C₂₅ manoalide-type sesterterpenoids (4–6, 8–10). Compounds 1–5 were initially obtained as enantiomers, and were further separated to be optically pure compounds (1a, 1b, 2a, 2b, 3a-r, 3b-r, 4a, 4b, 5a and 5b) by chiral HPLC, with a LiAlH₄ reduction aid for 3. Compounds 3a/3b (a pair of inseparable enantiomers), 4a, 5a, 6, and 7 were identified as new compounds, while 1a/1b and 2a/2b were obtained from a natural source and were determined for their absolute configurations for the first time. This is also the first time to encounter enantiomers of the well-known manoalide-type sesterterpenoids from nature. The structures with absolute configurations of the new compounds were unambiguously determined by comprehensive methods including HR-ESI-MS and NMR data analysis, optical rotation comparison, experimental and calculated electronic circular dichroism (ECD), and Mo₂(OAc)₄ induced circular dichroism (ICD) methods. The cytotoxicity of the isolates against selected human tumor cell lines was evaluated, however, the tested compounds showed no activity against selected cell lines.

Stereoselective Synthesis of the ABC Ring System of Aspterpenacids

Aspterpenacids A and B are sesterterpenoids that possess a unique and highly congested 5/3/7/6/5 fused ring system. These compounds also contain a sterically encumbered isopropyl trans-hydrindane motif and a cyclopropane motif bearing two quaternary centers, which make them remarkably challenging synthetic targets. Herein, we report the successful construction of the key highly substituted ABC ring system in a stereoselective manner.