Immunomodulatory Biscembranoids and Assignment of Their Relative and Absolute Configurations: Data Set Modulation in the Density Functional Theory/Nuclear Magnetic Resonance Approach

Sokotrasterol Sulfate Suppresses IFN-γ-Induced PD-L1 Expression by Inhibiting JAK Activity

PD-1/PD-L1 monoclonal antibodies exhibit promising therapeutic effectiveness in multiple cancers. However, developing a simple and efficient non-antibody treatment strategy using the PD-1/PD-L1 signaling pathway still remains challenging. In this study, we developed a flow cytometry assay to screen bioactive compounds with PD-L1 inhibitory activity. A total of 409 marine natural products were screened, and sokotrasterol sulfate (SKS) was found to efficiently suppress the IFN-γ-induced PD-L1 expression. SKS sensitizes the tumor cells to antigen-specific T-cell killing in the T cell-tumor cell coculture system. Mechanistically, SKS directly targeted Janus kinase (JAK) to inhibit the downstream activation of signal transducer and activator of transcription (STAT) and the subsequent transcription of PDL1. Our findings highlight the immunological role of SKS that may act as a basis for a potential immunotherapeutic agent.

Aculeatiols A-G: Lovastatin Derivatives Extracted from Aspergillus aculeatus

In this study, we isolated lovastatin derivatives, including aculeatiols A-G (1-7) and three known compounds (8-10), from Aspergillus aculeatus. Their structures and absolute configurations were experimentally determined by high-resolution electrospray ionization mass spectrometry, nuclear magnetic resonance spectroscopy, and X-ray diffraction analyses, and the results were corroborated by quantum-chemical calculations. As members of the lovastatin derivatives, aculeatiols A-C (1-3) possess a γ-lactone functional group in the side chain. Compound 6 represents the first example that features an undescribed aromatized heterotetracyclic 6/6/6/6 ring system. Biologically, the lipid-lowering effects of all of these compounds were evaluated by analyzing the free fatty acid-induced intracellular lipid accumulation. In addition, compound 5, which regulated the transcription of genes associated with lipid uptake and synthesis, inhibited the accumulation of lipids.

Discovery of Michael reaction acceptors from the leaves of Ailanthus altissima by a modified tactic

Structural characteristics-guided investigation of Ailanthus altissima (Mill.) Swingle resulted in the isolation and identification of seven undescribed potential Michael reaction acceptors (1-7). Ailanlactone A (1) possesses an unusual 1,7-epoxy-11,12-seco quassinoid core. Ailanterpene B (6) was a rare guaianolide-type sesquiterpene with a 5/6/6/6-fused skeleton. Their structures were determined through extensive analysis of physiochemical and spectroscopic data, quantum chemical calculations, and single crystal X-ray crystallographic technology using Cu Kα radiation. The cytotoxic activities of isolates on HepG2 and Hep3B cells were evaluated in vitro. Encouragingly, ailanaltiolide K (4) showed significant cytotoxicity against Hep3B cells with IC50 values of 1.41 ± 0.21 μM, whose covalent binding mode was uncovered in silico.

A Drimane Meroterpenoid Borate as a Synchronous Ca+ Oscillation Inhibitor from the Coral-Associated Fungus Alternaria sp. ZH-15

Territrem F (1), a drimane meroterpenoid bearing a unique borate ring system, was isolated together with its diol precursor territrem B (2) from the fungus Alternaria sp. ZH-15 associated with the soft coral Lobophytum crassum collected in the South China Sea. The structure of the new compound was elucidated by spectroscopic analysis and an X-ray single-crystal diffraction study, representing a new type of boron-containing natural product. Both compounds significantly inhibited spontaneous synchronous Ca²⁺ oscillations (SCOs) and epileptic discharges induced by 4-aminopyridine, showing the potential for antiepileptic drug research. The 5,9-boronic ester derivative of 2 did not change its SCO inhibitory activity.

Structurally Diverse Diterpenes from the South China Sea Soft Coral Sarcophyton trocheliophorum

The present investigation of the South China Sea soft coral Sarcophyton trocheliophorum resulted in the discovery of six new polyoxygenated diterpenes, namely sartrocheliols A-E (1, 3, 5-8) along with four known ones, 2, 4, 9, and 10. Based on extensive spectroscopic data analysis, sartrocheliol A (1) was identified as an uncommon capnosane diterpene, while sartrocheliols B-E (3, 5-8) were established as cembrane diterpenes. They displayed diverse structural features not only at the distinctly different carbon frameworks but also at the various types of heterocycles, including the epoxide, γ-lactone, furan, and pyran rings. Moreover, their absolute configurations were determined by a combination of quantum mechanical-nuclear magnetic resonance (QM-NMR) approach, modified Mosher's method, and X-ray diffraction analysis. In the anti-tumor bioassay, compound 4 exhibited moderate cytotoxic activities against A549, H1975, MDA-MB-231, and H1299 cells with the IC₅₀ values ranging from 26.3 to 47.9 μM.

Cembrane Diterpenes Possessing Nonaromatic Oxacycles from the Hainan Soft Coral Sarcophyton mililatensis

Documents on the chemical composition of the soft coral Sarcophyton mililatensis are sparse. The present investigation of the Hainan soft coral S. mililatensis resulted in the discovery of six new cembrane diterpenes, sarcoxacyclols A-F (1-6) and four known analogs (7-10). Their structures were elucidated by extensive spectroscopic analysis along with a comparison with the data in current literature. The nonaromatic oxacycles in their structures were the rarely found tetrahydrofuran ether across C-1 and C-12 and tetrahydropyran ether across C-1 and C-11, respectively. Moreover, the absolute configuration of compound 4 was established unambiguously by X-ray diffraction analysis using Ga Kα radiation (λ = 1.34139 Å). Based on the biogenetical consideration, the absolute configurations of other five new compounds were tentatively assumed. Assessment of the bioactivity for these secondary metabolites revealed that compound 1 exhibited significant tumor necrosis factor (TNF)-α inhibitory activity (IC₅₀ = 9.5 μmol/L), similar to the positive control dexamethasone (IC₅₀ = 8.7 μmol/L), but no obvious cytotoxicity towards RAW264.7 cells (CC₅₀ > 50 μmol/L). The preliminary molecular docking suggested the crucial roles of the hydroxyl and acetoxyl groups in the computational prediction of the binding mode between the diterpene and the protein.

The Soft Coral Sarcophyton trocheliophorum: A Warehouse of Terpenoids with Structural and Pharmacological Diversity

The soft coral Sarcophyton trocheliophorum, which was frequently encountered on Indo-Pacific and Red Sea coral reefs, furnished a wealth of secondary metabolites. Notably, terpenoids dominated the chemical profile of this species. In this review, we summarized the discovery of 156 terpenoids from the soft coral S. trocheliophorum specimens in different geographical areas. The structures comprised 13 terpenoidal classes with various functionalities. We covered the era from the first report of S. trocheliophorum-derived metabolites in 1976 up to October 2022. The biological effects of these chemical compositions on a vast array of potential pharmacological activities such as protein tyrosine phosphatase 1B (PTP1B) inhibitory, neuroprotective, cytotoxic, anti-inflammatory, antibacterial, antivirus, and immunomodulatory activities were also presented. This review also revealed an immense demand to explore the terpene biosynthetic gene clusters of this species besides the chemo- and bio-investigations.

MS/MS Molecular Networking Unveils the Chemical Diversity of Biscembranoid Derivatives, Neutrophilic Inflammatory Mediators from the Cultured Soft Coral Sarcophyton trocheliophorum

Biscembranoids are the distinctive tetraterpenoids owing a 14/6/14 membered tricyclic scaffold that have been mainly discovered in the soft corals, especially the genera Sarcophyton, Lobophytum and Sinularia. Recent findings have demonstrated the great anti-inflammatory potential of biscembranoid analogues in human neutrophils, motivating more chemical and biological explorations targeting these marine-derived natural products. In the current study, the chemical diversity of biscembranoids derived from the cultured-type Sarcophyton trocheliophorum von Marenzeller was illustrated through MS/MS molecular networking (MN) profiling approach. Based on the MN patterns, the prioritization of unknown biscembranoid derivatives was putatively analyzed. As a result, the biscembrane targeting isolation afforded two new metabolites, sarcotrochelides A (1) and B (2), along with six known analogues (3-8). Their structures and relative configurations were determined by spectroscopic methods. In vitro neutrophil inflammatory inhibition was further investigated for all isolates based on reduced superoxide anion (O₂^•-) generation detections. Compounds 5-8 showed significant dose-dependently inhibitory effects, suggesting the cruciality of 6,7-dihydrooxepin-2(5H)-one moiety and saturated γ-lactone ring in their reactive oxygen species (ROS)-dependent anti-inflammatory properties.

Bistrochelides H-L: Biscembranoids from the south China sea soft coral Sarcophyton serenei

Five undescribed biscembranoids, bistrochelides H-L, along with four known biscembranoids, glaucumolides A-B and bistrochelides A-B, were isolated from the soft coral Sarcophyton serenei collected off the Xisha Island in the South China Sea. The structures of these compounds were elucidated by HRESIMS (high-resolution electrospray ionization mass spectroscopy) spectrometry, NMR (nuclear magnetic resonance) spectroscopy, X-ray diffraction analysis, electronic circular dichroism (ECD), and the comparison of their spectroscopic data with those reported in the literature. In bioassay, some compounds showed a strong inhibitory effect on osteoclast precursor cells at the concentration of 10 μM. Additionally, all compounds exhibited weakly antimicrobial activity against Vibrio harveyi.

Biogenetic and biomimetic synthesis of natural bisditerpenoids: hypothesis and practices

Covering: up to March 2022Bisditerpenoids, or diterpenoid dimers, are a group of natural products with high structural variance, deriving from homo- or hetero-dimeric coupling of two diterpenoid units. They usually possess complex architectures resulting from the diversity of monomeric diterpenoids as building blocks and the dimerization processes. These compounds have attracted the attention of synthetic and biological scientists owing to the rarity of their natural origin and their significant biological activities. Herein, we provide a review highlighting some of the interesting bisditerpenoids reported since 1961 and showcase the chemical diversity in both their structures and biosynthesis, as well as their biological functions. This review focuses on the biosynthetic dimerization pathways of interesting molecules and their biomimetic synthesis, which may act as useful inspiration for the discovery and synthesis of more bisditerpenoids and further pharmacological investigations.

Diterpenes and sterols from the Red Sea soft coral Sarcophyton trocheliophorum and their cytotoxicity and anti-leishmanial activities

The ethyl acetate and dichloromethane-soluble fractions, from a soft coral Sarcophyton trocheliophorum total methanolic extract, exhibited significant anti-leishmanial and cytotoxic activities. These active fractions yielded a new cembranoid diterpene (1), two known analogues [sarcotrocheliol (2) and sarcophine (3)], and two sterols [(24S)-24-methylcholesterol (4) and gorgosterol (5)]. The structure of the new diterpene (1) was determined via a detailed analysis of its spectroscopic data. Compounds 3 and 5 demonstrated noticeable cytotoxicity on A549 (IC₅₀ 17.4 ± 1.9 µg/ml) and HepG2 (IC₅₀ 17.7 ± 1.5 µg/ml) cell lines, respectively. None of the isolates 1‒5 showed detectable anti-leishmanial activity (IC₅₀ >100 µg/ml).

Pitfalls in the structural elucidation of small molecules. A critical analysis of a decade of structural misassignments of marine natural products

Covering: July 2010 to August 2021This article summarizes more than 200 cases of misassigned marine natural products reported between July 2010 and August 2021, sorting out errors according to the structural elements. Based on a comparative analysis of the original and the revised structures, major pitfalls still plaguing the structural elucidation of small molecules were identified, emphasizing the role of total synthesis, crystallography, as well as chemical- and biosynthetic logic to complement spectroscopic data. Distinct "trends" in natural product misassignment are evident between compounds of marine and plant origin, with an overall much lower incidence of "impossible" structures within misassigned marine natural products.

Fluvirucins B7-B10, new antifungal macrolactams from a marine-derived Nonomuraea sp. MYH522

Marine rare actinomycetes are an important source of secondary metabolites. From a marine-derived actinomycete Nonomuraea sp. MYH522, four new macrolactams, fluvirucins B7-B10, together with known fluvirucin B6 were isolated. Their structures were determined based on comprehensive analysis of HRESIMS and NMR spectroscopic data as well as by comparing 13C NMR resonances and optical rotation values with those for related congeners. Fluvirucins are characterized by a 14-membered macrolactam attached by an aminosugar moiety. The discovery of fluvirucins B6-B10 enriched the N-acetylated derivatives of fluvirucins. The diverse alkyl substituents at C-2 and C-6 implied substrate promiscuity in fluvirucin polyketide biosynthesis. These compounds didn't exhibit any antibacterial or antifungal activities when used alone, which suggested the importance of the free amino group in the antimicrobial activity of fluvirucins. However, fluvirucins B6, B9, and B10 showed synergistic antifungal activity with fluconazole against fluconazole-resistant isolates of Candida albicans.

Cembranolides and Related Constituents from the Soft Coral Sarcophyton cinereum

In an attempt to explore the bioactive metabolites of the soft coral Sarcophyton cinereum, three new cembranolides, cinerenolides A–C (1–3), and 16 known compounds were isolated and identified from the EtOAc extract. The structures of the new cembranolides were elucidated on the basis of spectroscopic analysis, and the NOE analysis of cinerenolide A (1) was performed with the assistance of the calculated lowest-energy molecular model. The relative configuration of cinerenolide C (3) was determined by the quantum chemical NMR calculation, followed by applying DP4+ analysis. In addition, the cytotoxic assays disclosed that some compounds exhibited moderate to potent activities in the proliferation of P388, DLD-1, HuCCT-1, and CCD966SK cell lines.

Isolation, Structure Determination of Sesquiterpenes from Neurolaena lobata and Their Antiproliferative, Cell Cycle Arrest-Inducing and Anti-Invasive Properties against Human Cervical Tumor Cells

Seven new germacranolides (1–3, 5–8), among them a heterodimer (7), and known germacranolide (4), eudesmane (9) and isodaucane (10) sesquiterpenes were isolated from the aerial parts of Neurolaena lobata. Their structures were determined by using a combination of different spectroscopic methods, including HR-ESIMS and 1D and 2D NMR techniques supported by DFT-NMR calculations. The enantiomeric purity of the new compounds was investigated by chiral HPLC analysis, while their absolute configurations were determined by TDDFT-ECD and OR calculations. Due to the conformationally flexible macrocycles and difficulties in assigning the relative configuration, ¹³C and ¹H NMR chemical shift and ECD and OR calculations were performed on several stereoisomers of two derivatives. The isolated compounds (1–10) were shown to have noteworthy antiproliferative activities against three human cervical tumor cell line with different HPV status (HeLa, SiHa and C33A). Additionally, lobatolide C (6) exhibited substantial antiproliferative properties, antimigratory effect, and it induced cell cycle disturbance in SiHa cells.

Cembranoids of Soft Corals: Recent Updates and Their Biological Activities

Soft corals are well-known as excellent sources of marine-derived natural products. Among them, members of the genera Sarcophyton, Sinularia, and Lobophytum are especially attractive targets for marine natural product research. In this review, we reported the marine-derived natural products called cembranoids isolated from soft corals, including the genera Sarcophyton, Sinularia, and Lobophytum. Here, we reviewed 72 reports published between 2016 and 2020, comprising 360 compounds, of which 260 are new compounds and 100 are previously known compounds with newly recognized activities. The novelty of the organic molecules and their relevant biological activities, delivered by the year of publication, are presented. Among the genera presented in this report, Sarcophyton spp. produce the most cembranoid diterpenes; thus, they are considered as the most important soft corals for marine natural product research. Cembranoids display diverse biological activities, including anti-cancer, anti-bacterial, and anti-inflammatory. As cembranoids have been credited with a broad range of biological activities, they present a huge potential for the development of various drugs with potential health and ecological benefits.

Immunosuppressive 9,10-Secosteroids from the Gorgonian Verrucella umbraculum Collected in the South China Sea

Four new 9,10-secosteroids, verrucellols A-D (1-4), together with 12 known derivatives (5-16) were isolated from the gorgonian Verrucella umbraculum collected in the South China Sea. The structures of the new compounds were established by spectroscopic analysis and comparison with reported data. These compounds exhibited significant suppressive effects on CD4+ T lymphocyte cell differentiation in an in vitro bioassay. This is the first report of 9,10-secosteroids exhibiting immunomodulation activity.

Neuronal Modulators from the Coral-Associated Fungi Aspergillus candidus

Three new p-terphenyl derivatives, named 4″-O-methyl-prenylterphenyllin B (1) and phenylcandilide A and B (17 and 18), and three new indole-diterpene alkaloids, asperindoles E-G (22-24), were isolated together with eighteen known analogues from the fungi Aspergillus candidus associated with the South China Sea gorgonian Junceela fragillis. The structures and absolute configurations of the new compounds were elucidated on the basis of spectroscopic analysis, and DFT/NMR and TDDFT/ECD calculations. In a primary cultured cortical neuronal network, the compounds 6, 9, 14, 17, 18 and 24 modulated spontaneous Ca²⁺ oscillations and 4-aminopyridine hyperexcited neuronal activity. A preliminary structure-activity relationship was discussed.

Further new cembranoids from the South China Sea soft coral Sarcophyton trocheliophorum

Two new cembranoids, ximaosarcophytols A (1) and B (2), together with three related known ones (3-5), were isolated from the soft coral Sarcophyton trocheliophorum collected off the Ximao Island, Hainan Province, China. Their structures including the absolute configurations were elucidated by extensive spectroscopic analysis, TDDFT/ECD (time-dependent density functional theory/electronic circular dichroism) calculations and comparison with the reported data.

Discovery of Venturicidin Congeners and Identification of the Biosynthetic Gene Cluster from Streptomyces sp. NRRL S-4

Chemical screening of Streptomyces sp. NRRL S-4 with liquid chromatography-mass spectrometry (LC-MS) and the following chromatographic isolation led to the discovery of four 20-membered macrolides, venturicidin A (4) and three new congeners venturicidins D-F (1-3). Genome sequencing of strain S-4 revealed the presence of a biosynthetic gene cluster (BGC) encoding glycosylated type I polyketides (PKS). The BGC designated to venturicidin biosynthesis (ven) was supported by the proposed biosynthetic pathway and confirmed by inactivation of the core PKS gene of venK. Bioinformatic analyses on the conserved motifs and known stereospecificities in PKS modules are consistent with the structure and absolute configuration. This is the first report of venturicidin BGC since the discovery of the macrolide in 1961. In the biological assays, venturicidin A (4) and E (2) displayed a high selective cytotoxicity against acute monocytic leukemia MV-4-11 cells with IC₅₀ values of 0.09 and 0.94 μM, respectively. Venturicidin A (4) also showed a weak inhibitory activity on FMS-like-tyrosine kinase.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 440 papers for 2019), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Methods used to study marine fungi and their chemical diversity have also been discussed.

Micaryolanes A and B, Two New Caryolane-Type Sesquiterpenoids from Marine Streptomyces sp. AH25

Caryolanes, known as β-caryophyllene alcohols, are widely occurring sesquiterpenes in plants. From the cultures of marine Streptomyces sp. AH25, two new caryolane sesquiterpenes, micaryolanes A and B (1 and 2), together with caryolan-1,9β-diol (3) were isolated. Their structures were elucidated by extensive analyses of HR-MS and NMR spectroscopic data. The absolute configurations were assigned via the CD data of the in situ formed [Rh₂ (OCOCF₃ )₄ ] complex and supported by comparison of experimental and calculated specific rotation values. Compounds 1-3 exhibited no activities against Hep3B or MG-63 cell lines or against Gram-positive and Gram-negative bacteria. The results not only enriched the caryolane family, but also proved bacteria as a productive source of terpene metabolites.

New Biscembranoids Sardigitolides A-D and Known Cembranoid-Related Compounds from Sarcophyton digitatum: Isolation, Structure Elucidation, and Bioactivities

Chemical examination from the cultured soft coral Sarcophyton digitatum resulted in the isolation and structural identification of four new biscembranoidal metabolites, sardigitolides A-D (1-4), along with three previously isolated biscembranoids, sarcophytolide L (5), glaucumolide A (6), glaucumolide B (7), and two known cembranoids (8 and 9). The chemical structures of all isolates were elucidated on the basis of 1D and 2D NMR spectroscopic analyses. Additionally, in order to discover bioactivity of marine natural products, 1-8 were examined in terms of their inhibitory potential against the upregulation of inflammatory factor production in lipopolysaccharide (LPS)-stimulated murine macrophage J774A.1 cells and their cytotoxicities against a limited panel of cancer cells. The anti-inflammatory results showed that at a concentration of 10 µg/mL, 6 and 8 inhibited the production of IL-1β to 68 ± 1 and 56 ± 1%, respectively, in LPS-stimulated murine macrophages J774A.1. Furthermore, sardigitolide B (2) displayed cytotoxicities toward MCF-7 and MDA-MB-231 cancer cell lines with the IC50 values of 9.6 ± 3.0 and 14.8 ± 4.0 µg/mL, respectively.

Osteoclastogenesis Modulatory Steroids from the South China Sea Gorgonian Coral Iciligorgia sp

A new 9,11-secosteroid, (22R)-22-acetoxy-3β,6α,11-trihydroxy-9,11-seco-5α-cholest-7-en-9-one, along with twelve known analogues were isolated from the South China Sea gorgonian coral Iciligorgia sp. Their structures were determined by the spectroscopic analysis and comparison with reported data. In an in vitro test of osteoclastic differentiation, three compounds exhibited significant down-regulating effect whereas two compounds showed significant up-regulating effect at 0.5 and 1.0 μm. This is the first report of the chemical investigation of the gorgonian Iciligorgia sp. The acetoxy substitution at C-22 seems to play an important role in the regulating activity.

Alternarin A, a Drimane Meroterpenoid, Suppresses Neuronal Excitability from the Coral-Associated Fungi Alternaria sp. ZH-15

Alternarin A (1), a rearranged drimane meroterpenoid characterized by a thioglycerate moiety, was isolated together with two known analogues from the coral-associated fungi Alternaria sp. ZH-15. Its structure was determined based on spectroscopic analysis, modified Mosher's method, and TDDFT/ECD calculations. In a primary cultured cortical neuronal network, compound 1 effectively inhibited the activity of spontaneous synchronous Ca²⁺ oscillations and 4-aminopyridine induced epileptic discharges in the low micromolar concentration range.