Chartspiroton, a Tetracyclic Spiro-naphthoquinone Derivative from a Medicinal Plant Endophytic Streptomyces

Irpexols A-C, xanthone derivatives from the endophyte fungus Irpex laceratus A878

Three new xanthone derivatives irpexols A-C (1-3) and five known xanthones including three dimeric ones were successfully isolated from Irpex laceratus A878, an endophytic fungus of the family Irpicaceae from the medicinal plant Pogostemon cablin (Blanco) Bentham (Lamiaceae). The structures of these compounds were elucidated by extensive spectroscopic analyses including ultraviolet-visible spectroscopy (UV), infrared spectroscopy (IR), mass spectrometry (MS), and nuclear magnetic resonance (NMR). All of the three new compounds (1-3) share a de-aromatic and highly‑oxygenated xanthone skeleton. In addition, the cytotoxic activity of compounds 1-8 were evaluated against SF-268, MCF-7, HepG2, and A549 tumor cell lines. The results revealed that compound 6 showed moderate cytotoxic activity with the IC50 values ranging from 24.83 to 45.46 μM, while the IC50 values of the positive control adriamycin was ranging from 1.11 to 1.44 μM.

Synthesis of the Tetracyclic Spiro-naphthoquinone Chartspiroton

Chartspiroton is a recently discovered naphthoquinone natural product that features a spiro-fused benzofuran lactone. We report its first synthesis via an 11-step linear sequence. The sterically hindered tetra-ortho-substituted biaryl subunit was installed by base-induced ring expansion of a readily available 1,3-indandione. This step also liberated the fully substituted naphthalene core unit at the same time. The unique spiro-fused benzofuran lactone of the natural product was constructed via late-stage oxidation of an advanced naphthoquinone.

Unlocking the potential of bacterial endophytes from medicinal plants for drug discovery

Among the plant-associated microorganisms, the so-called endophytes continue to attract much attention because of their ability not only to protect host plants from biotic and abiotic stress factors, but also the potential to produce bioactive secondary metabolites. The latter property can elicit growth-promoting effects on plants, as well as boost the production of plant-specific secondary metabolites with valuable pharmacological properties. In addition, endophyte-derived secondary metabolites may be a rich source for the discovery of drugs to treat various diseases, including infections and cancer. However, the full potential of endophytes to produce bioactive secondary metabolites is often not revealed upon conventional cultivation in the laboratory. New advances in genomics and metabolic engineering offer exciting opportunities for the exploration and exploitation of endophytes' biosynthetic potential. This review focuses on bacterial endophytes of medicinal plants, some of their secondary metabolites and recent advances in deciphering their biosynthesis. The latter may assist in genetic engineering efforts aimed at the discovery of novel bioactive compounds with the potential to be developed into drugs.

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.

Harnessing the action mechanisms of microbial endophytes for enhancing plant performance and stress tolerance: current understanding and future perspectives

Microbial endophytes are microorganisms that reside within plant tissues without causing any harm to their hosts. These microorganisms have been found to confer a range of benefits to plants, including increased growth and stress tolerance. In this review, we summarize the recent advances in our understanding of the mechanisms by which microbial endophytes confer abiotic and biotic stress tolerance to their host plants. Specifically, we focus on the roles of endophytes in enhancing nutrient uptake, modulating plant hormones, producing secondary metabolites, and activating plant defence responses. We also discuss the challenges associated with developing microbial endophyte-based products for commercial use, including product refinement, toxicology analysis, and prototype formulation. Despite these challenges, there is growing interest in the potential applications of microbial endophytes in agriculture and environmental remediation. With further research and development, microbial endophyte-based products have the potential to play a significant role in sustainable agriculture and environmental management.

Extraction, structural characterization, and biological activities of a new glucan from Codonopsis pilosula

In this study, a powerful and rapid aqueous two-phase system (ATPS) method was used to extract polysaccharides from Codonopsis pilosula. The ATPS process was investigated with response surface methodology (RSM). At an ammonium sulfate concentration of 17%, ethanol concentration of 30%, and extraction temperature of 40 °C at pH 6, the total extraction yield of polysaccharides reached (31.57 ± 1.28)%. After separation and purification, a homogenized polysaccharide CPP 2-4 with molecular weight of 3.9 × 10⁴ kDa was obtained from the bottom phase. The physicochemical properties and structural features confirmed that CPP 2-4 was an α-1,6-glucan. Activity studies showed that the IC₅₀ of CPP 2-4 for DPPH radical scavenging was 0.105 mg/mL. The FRAP and ABTS assays showed that CPP 2-4 had strong antioxidant activity in a dose-dependent manner. Furthermore, CPP 2-4 inhibited NO release in RAW264.7 cells induced by lipopolysaccharide, which indicated a certain anti-inflammatory effect. This study improved the extraction rate of polysaccharides from C. pilosula and identified a glucan for the first time, that can contribute to a better understanding of the composition and structure of polysaccharides from C. pilosula and provide data support for the medicine and food homology of C. pilosula.

Structure Elucidation and Anti-Tumor Activities of Trichothecenes from Endophytic Fungus Fusariumsporotrichioides

The secondary metabolites of Fusarium sporotrichioides, an endophytic fungus with anti-tumor activity isolated from Rauvolfia yunnanensis Tsiang, were investigated. Five trichothecenes, including one previously undescribed metabolite, were isolated and identified. Their structures were elucidated by means of extensive spectroscopic methods; the absolute configuration of compound 1 was determined by the ECD method. Surprisingly, 8-n-butyrylneosolaniol (3) exhibited stronger anti-tumor activity than T-2 toxin against Huh-7 cell line, with an IC₅₀ value of 265.9 nM. 8-n-butyrylneosolaniol (3) promoted apoptosis induction in Huh-7 cells. Moreover, cell cycle analysis showed that cell cycle arrest caused by 8-n-butyrylneosolaniol (3) at the G2/M phase resulted in cell proliferation inhibition and pro-apoptotic activity. Further studies showed a significant decrease in mitochondrial membrane permeabilization and a significant increase in ROS generation, which led to the activation of caspase cascades and subsequent cleavage of PARP fragments. In conclusion, 8-n-butyrylneosolaniol (3) induced cell apoptosis in Huh-7 cells via the mitochondria-mediated apoptotic signaling pathway, which could be a leading compound for anti-tumor agents.

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.

Survey of natural products reported by Asian research groups in 2020

The new natural products reported in 2020 in peer-reviewed articles in journals with good reputations were reviewed and analyzed. The advances made by Asian research groups in the field of natural products chemistry in 2020 were summarized. Compounds with unique structural features and/or promising bioactivities originating from Asian natural sources were discussed based on their structural classification.

Dendrocrepidamine, a novel octahydroindolizine alkaloid from the roots of Dendrobium crepidatum

A novel octahydroindolizine alkaloid, named dendrocrepidamine (1) with an unusual 18,19,19'-cyclopropanone-dendrocrepine skeleton, was isolated from the ethanol extract of the roots of Dendrobium crepidatum, along with six known compounds (2-7). The structure of 1 was elucidated through HR-ESIMS, NMR spectroscopic data and computational calculations. All compounds were examined for their inhibitory effects on nitric oxide (NO) production induced by lipopolysaccharide (LPS) in RAW264.7 cells with IC₅₀ values in the range of 3.04-54.89 µM. In vivo, crepidatin (6) (80, 40 and 10 mg/kg) showed a significant protective effect against LPS-induced acute lung injury (ALI) in mice.

Structurally Diverse Polycyclic Salicylaldehyde Derivative Enantiomers from a Marine-Derived Fungus Eurotium sp. SCSIO F452

To enlarge the chemical diversity of Eurotium sp. SCSIO F452, a talented marine-derived fungus, we further investigated its chemical constituents from a large-scale fermentation with modified culture. Four pairs of new salicylaldehyde derivative enantiomers, euroticins F-I (1–4), as well as a known one eurotirumin (5) were isolated and characterized. Compound 1 features an unprecedented constructed 6/6/6/5 tetracyclic structures, while 2 and 3 represent two new types of 6/6/5 scaffolds. Their structures were established by comprehensive spectroscopic analyses, X-ray diffraction, ¹³C NMR, and electronic circular dichroism calculations. Selected compounds showed significant inhibitory activity against α-glucosidase and moderate cytotoxic activities against SF-268, MCF-7, HepG2, and A549 cell lines.

Cytotoxic Guaianolide Sesquiterpenoids from Ainsliaea fragrans

Twelve guaianolide-type sesquiterpene oligomers with diverse structures were isolated from the whole plants of Ainsliaea fragrans, including a novel trimer (1) and two new dimers (2, 3). The chemical structures of the new compounds were elucidated through spectroscopic data interpretation and computational calculations. Ainsfragolide (1) is an unusual guaianolide sesquiterpene trimer generated with a novel C-C linkage at C_2'-C_15″, which may be biosynthesized prospectively through a further Michael addition. Cytotoxicity results showed that ainsfragolide (1) was the most potent compound against five cancer cell lines with IC₅₀ values in the range of 0.4-8.3 μM.

Achyrophenols A-F: Polycyclic Polyphenol Lactone Skeletons and a Nor-Ursane-Type Triterpenoid from Achyrocline Satureioides

Two novel derivatives of 2-methyl-1-(2,3,4,6-tetrahydroxyphenyl)propan-1-one and (S)-2-methyl-1-(2,3,4,6-tetrahydroxyphenyl)butan-1-one (1 and 2), four novel six-membered lactone phenols (3-6), and a nor-ursane type triterpenoid (7) named Achroacid, were isolated from the aerial part of Achyrocline satureioides. The absolute configurations of 1-7 are presented by spectroscopic data and X-ray crystallographic analysis. A DP4plus evaluation was applied to determine the final stereochemistry for 1 and 2. The biosynthesis pathway of 1 and 2 was proposed. 1 has potential on anti-Gram-negative bacteria. Both 1 and 2 exhibited a significant impact on anti-H1299 cells. Compounds 3-7 showed moderate cancer cell lethality and significant anti-inflammatory activities.

Lonicerin targets EZH2 to alleviate ulcerative colitis by autophagy-mediated NLRP3 inflammasome inactivation

Aberrant activation of NLRP3 inflammasome in colonic macrophages strongly associates with the occurrence and progression of ulcerative colitis. Although targeting NLRP3 inflammasome has been considered to be a potential therapy, the underlying mechanism through which pathway the intestinal inflammation is modulated remains controversial. By focusing on the flavonoid lonicerin, one of the most abundant constituents existed in a long historical anti-inflammatory and anti-infectious herb Lonicera japonica Thunb., here we report its therapeutic effect on intestinal inflammation by binding directly to enhancer of zeste homolog 2 (EZH2) histone methyltransferase. EZH2-mediated modification of H3K27me3 promotes the expression of autophagy-related protein 5, which in turn leads to enhanced autophagy and accelerates autolysosome-mediated NLRP3 degradation. Mutations of EZH2 residues (His129 and Arg685) indicated by the dynamic simulation study have found to greatly diminish the protective effect of lonicerin. More importantly, in vivo studies verify that lonicerin dose-dependently disrupts the NLRP3–ASC–pro-caspase-1 complex assembly and alleviates colitis, which is compromised by administration of EZH2 overexpression plasmid. Thus, these findings together put forth the stage for further considering lonicerin as an anti-inflammatory epigenetic agent and suggesting EZH2/ATG5/NLRP3 axis may serve as a novel strategy to prevent ulcerative colitis as well as other inflammatory diseases.

Terragines F-G produced by endophytic Bacillus sp. SH-1.2-ROOT-18 from Dendrobium officinale

Two new terragine analogs (1‒2) with special succinimide and aminopentane moieties were isolated from the fermentation broth of Bacillus sp. SH-1.2-ROOT-18, an endophyte previously discovered from the root of Dendrobium officinale. The structures were elucidated base on comprehensive 1 D/2D NMR and MS data analysis. Complete NMR assignments for the first reported naturally occurring metabolite 3 was also provided.

Hot off the Press

A personal selection of 32 recent papers is presented covering various aspects of current developments in bioorganic chemistry and novel natural products such as baphicacanthcusine A from Baphicacanthus cusia.