Cytotoxic Guaianolide Sesquiterpenoids from Ainsliaea fragrans

Research Progress on Sesquiterpenes from the Genus Ainsliaea

Sesquiterpenes constitute the principal components of the genus Ainsliaea, encompassing guaiane, germacrane, eudesmane, and polymer sesquiterpene lactones types. These secondary metabolites exhibit diverse pharmacological activities, including antitumor, antibacterial, anti-inflammatory, antiviral, antioxidant, hepatoprotective, and neuroprotective effects. Through a comprehensive literature search of the Web of Science, PubMed, SciFinder, and CNKI databases, it was discovered that there are as many as 145 main sesquiterpenoids in the genus Ainsliaea. However, the nuclear magnetic resonance (NMR) data for the sesquiterpenes in this genus have not been systematically compiled and summarized. Therefore, this review aims to highlight the chemical structures, NMR data, and pharmacological activities of sesquiterpenes in Ainsliaea. By meticulously analyzing published scholarly literature, our goal is to provide a solid foundation for further exploration of new sesquiterpenes and extensive utilization of this genus.

Terricoxanthones A-E, unprecedented dihydropyran-containing dimeric xanthones from the endophytic fungus Neurospora terricola HDF-Br-2 associated with the vulnerable conifer Pseudotsuga gaussenii

An investigation on the secondary metabolites from a rice culture broth of the endophytic fungus Neurospora terricola HDF-Br-2 derived from the vulnerable conifer Pseudotsuga gaussenii led to the isolation and characterization of 34 structurally diverse polyketides (1-34). Seven of them are previously undescribed, including five unprecedented dihydropyran-containing (terricoxanthones A-E, 1-5, resp.) and one rare tetrahydrofuran-containing (terricoxanthone F, 6) dimeric xanthones. The structures were elucidated by spectroscopic methods and single-crystal X-ray diffraction analyses. Terricoxanthones each were obtained as a racemic mixture. Their plausible biosynthetic relationships were briefly proposed. Compounds 6, aspergillusone A (8), and alatinone (27) displayed considerable inhibition against Candida albicans with MIC values of 8-16 μg/mL. 4-Hydroxyvertixanthone (12) and 27 exhibited significant inhibitory activities against Staphylococcus aureus, with MIC values of 4-8 μg/mL. Furthermore, compounds 8 and 27 could disrupt biofilm of S. aureus and C. albicans at 128 μg/mL. The findings not only extend the skeletons of xanthone dimers and contribute to the diversity of metabolites of endophytes associated with the endangered Chinese conifer P. gaussenii, but could further reveal the important role of protecting plant species diversity in support of chemical diversity and potential sources of new therapeutics.

Sinoflavonoids NJ and NK, anti-inflammatory prenylated flavonoids from the fruits of Podophyllum hexandrum Royle

Two new prenylated flavonoids named sinoflavonoids NJ and NK (1-2), along with ten known compounds were isolated from the fruits of Podophyllum hexandrum Royle. The chemical structures were determined through NMR spectroscopic data and MS analysis. Sinoflavonoid NJ (1) with an unusual 5,11-dioxabenzo[b]fluoren-10-one skeleton was firstly reported from Berberidaceae. The isolated flavonoids were tested with LPS-induced RAW 264.7 mouse macrophages model for their anti-inflammatory activity. Sinoflavonoid NJ (1) showed the most potent inhibition on nitric oxide production with IC50 value as 0.06 μM.

Discovery of plant-derived anti-tumor natural products: Potential leads for anti-tumor drug discovery

Natural products represent a paramount source of novel drugs. Numerous plant-derived natural products have demonstrated potent anti-tumor properties, thereby garnering considerable interest in their potential as anti-tumor drugs. This review compiles an overview of 242 recently discovered natural products, spanning the period from 2018 to the present. These natural products, which include 69 terpenoids, 42 alkaloids, 39 flavonoids, 21 steroids, 14 phenylpropanoids, 5 quinolines and 52 other compounds, are characterized by their respective chemical structures, anti-tumor activities, and mechanisms of action. By providing an essential reference and fresh insights, this review aims to support and inspire researchers engaged in the fields of natural products and anti-tumor drug discovery.

Structurally Diverse Sesquiterpenoids from the Genus of Ainsliaea

The genus of Ainsliaea embraces approximately 70 recognized species, many of which have been used to treat various diseases in folklore medicines. As the main metabolites of Ainsliaea plants, Ainsliaea sesquiterpenoids have drawn considerable attention in related scientific communities due to their intriguing structures and a variety of bioactivities. In this review, we intend to provide a full-aspect coverage of sesquiterpenoids reported from the genus of Ainsliaea, including 145 monomeric sesquiterpenoids and 30 oligomeric ones. Multiple aspects will be summarized, including their classification, distributions, structures, bioactivities, and biomimetic syntheses. In addition, their possible biosynthetic pathway will be discussed in detail.

Endophytic Microbes from Medicinal Plants in Fenghuang Mountain as a Source of Antibiotics

One of the largest concerns with world health today is still antibiotic resistance, which is making it imperative to find efficient alternatives as soon as possible. It has been demonstrated that microbes are reliable sources for the creation of therapeutic antibiotics. This research intends to investigate the endophytic microorganisms from several medicinal plants in Fenghuang Mountain (Jiangsu Province, China) and to discover new antibiotics from their secondary metabolites. A total of 269 endophytic strains were isolated from nine distinct medicinal plants. Taxonomic analysis revealed that there were 20 distinct species among these endophytes, with Streptomyces being the most common genus. Three of the target strains were chosen for scale-up fermentation after preliminary screening of antibacterial activities and the metabolomics investigation using LC-MS. These strains were Penicillium sp. NX-S-6, Streptomyces sp. YHLB-L-2 and Streptomyces sp. ZLBB-S-6. Twenty-three secondary metabolites (1-23), including a new sorbicillin analogue (1), were produced as a result of antibacterial activity-guided isolation. Through spectroscopic analysis using MS and NMR, the structures of yield compounds were clarified. According to antibacterial data, S. aureus or B. subtilis were inhibited to varying degrees by sorrentanone (3), emodic acid (8), GKK1032 B (10), linoleic acid (14), toyocamycin (17) and quinomycin A (21). The most effective antimicrobial agent against S. aureus, B. subtilis, E. coli and A. baumannii was quinomycin A (21). In addition, quinomycin A showed strong antifungal activity against Aspergillus fumigatus, Cryptococcus neoformans, and two clinical isolated strains Aspergillus fumigatus #176 and #339, with MIC as 16, 4, 16 and 16 µg/mL, respectively. This is the first time that bioprospecting of actinobacteria and their secondary metabolites from medicinal plants in Fenghuang Mountain was reported. The finding demonstrates the potential of endophytic microbes in medical plants to produce a variety of natural products. Endophytic microbes will be an important source for new antibiotics.

Targeted isolation of diterpenoids and sesquiterpenoids from Daphne gemmata E. Pritz. ex Diels using molecular networking together with network annotation propagation and MS2LDA

Investigation of the whole plant of Daphne gemmata E. Pritz. ex Diels (Thymelaeaceae) using molecular networking coupled to Network Annotation Propagation (NAP) and unsupervised substructure annotation (MS2LDA) led to the discovery of five tigliane diterpenoids, 14 guaiane sesquiterpenoids, one rhamnofolane diterpenoid and three carotene sesquiterpenoids. The structures of the eight undescribed compounds, daphnorbol A and daphnegemmatoids A-G, were characterized by detailed spectroscopic analyses, NMR and ECD calculations, application of Snatzke's method and single-crystal X-ray diffraction analysis. All isolated compounds were evaluated for their cytotoxic activities against HepG2, A549, and MCF-7 cells by MTT assay. Daphnorbol A exhibited significant cytotoxic activity against HepG2 and A549 cells with IC50 values of 4.06 μM and 6.35 μM, respectively. Prostratin showed potent cytotoxic activity against HepG2 and A549 cells with IC50 values of 6.06 μM and 5.45 μM, respectively. Further Hoechst 33,258 and AO-EB staining assays indicated that daphnorbol A and prostratin could induce apoptosis in HepG2 and A549 cells.

Huoshanmycins A‒C, New Polyketide Dimers Produced by Endophytic Streptomyces sp. HS-3-L-1 From Dendrobium huoshanense

Three new polyketide dimers named huoshanmycins A‒C (1–3) were isolated from a plant endophytic Streptomyces sp. HS-3-L-1 in the leaf of Dendrobium huoshanense, which was collected from the Cultivation base in Jiuxianzun Huoshanshihu Co., Ltd. The dimeric structures of huoshanmycins were composed of unusual polyketides SEK43, SEK15, or UWM4, with a unique methylene linkage. Their structures were elucidated through comprehensive 1D-/2D-NMR and HRESIMS spectroscopic data analysis. The cytotoxicity against MV4-11 human leukemia cell by the Cell Counting Kit-8 (CCK8) method was evaluated using isolated compounds with triptolide as positive control (IC₅₀: 1.1 ± 0.4 μM). Huoshanmycins A and B (1, 2) displayed moderate cytotoxicity with IC₅₀ values of 32.9 ± 7.2 and 33.2 ± 6.1 μM, respectively.

Biomimetic Synthesis of Lavandiolides H, I, and K and Artematrolide F via Diels-Alder Reaction

The biomimetic synthesis of guaianolide dimers lavandiolides H, I, and K and artematrolide F containing a spirolactone moiety has been accomplished for the first time from naturally abundant arglabin in four to six steps with an overall yield up to 60%, and a series of natural product-like guaianolide dimers, trimer, and tetramer were also successfully synthesized. Notably, the trimeric compound exhibited antihepatoma cytotoxicity more potent than that of sorafenib with IC₅₀ values of 6.2 μM (HepG2), 6.8 μM (Huh7), and 7.2 μM (SK-HEP-1).