β-Carboline Alkaloids from the Seeds of Peganum harmala and Their Anti-HSV-2 Virus Activities

Pegaharolines A - I, structurally novel indole alkaloids with anti-HSV-2 virus activities from Peganum harmala L. seeds

Leading by the antiviral activities against HSV-2 virus, bioactivity-guided the fraction of crude alkaloids from seeds of Peganum harmala led to the isolation of nine structurally novel indole alkaloids, pegaharolines A - I (1-9), and 11 known ones (10-20). Compound 3 was an unusual 6/5/5/5 spirotetracyclic indole-derived alkaloids featuring a classic bicyclic indole unit fused with an additional pyrrolizine ring via a spiral atom (C-3). Compound 4 was determined as a novel indole alkaloid, characterized with a rare hexacyclic 6/5/6/5-6/6 ring system, by a single-crystal X-ray diffraction. Compounds 5 and 6 were peculiar indole dimers featuring with the rare carbon skeleton of an octacyclic scaffold. Compounds 1-6 were six racemates. Most compounds exhibited different levels of antiviral activities against HSV-2. Especially, the anti-HSV-2 activity of compound 1 (IC50 = 0.90 ± 0.10 μM) was much better than that of the positive control (acyclovir, IC50 = 1.12 ± 0.15 μM). In this study, the discovery of anti-HSV-2 components from the seeds of P. harmala, could benefit development and utilization of this plant in antiviral medicinal products.

Design, Synthesis and Biological Activity Evaluation of β-Carboline Derivatives Containing Nitrogen Heterocycles

A series of β-carboline derivatives containing nitrogen heterocycles were designed and synthesized. All compounds were screened for their antitumor activity against four human tumor cell lines (A549, K562, PC-3, T47D). Notably, compound N-(4-(morpholinomethyl)phenyl)-2-((5-(1-(3,4,5-trimethoxyphenyl)-9H-pyrido[3,4-b]indol-3-yl)-1,3,4-oxadiazol-2-yl)thio)acetamide (8q) exhibited significant inhibitory activity against PC-3 cells with an IC50 value of 9.86 µM. Importantly, compound 8q effectively suppressed both the proliferation and migration of PC-3 cells. Mechanistic studies revealed that compound 8q induced cell apoptosis and caused the accumulation of reactive oxygen species (ROS), leading to cell cycle arrest in the G0/G1 phase in PC-3 cells.

Sustainable next-generation color converters from P. harmala seed extracts for solid-state lighting

Traditional solid-state lighting heavily relies on color converters, which often have a significant environmental footprint. As an alternative, natural materials such as plant extracts could be employed if their low quantum yields (QYs) in liquid and solid states were higher. With this motivation, here, we investigate the optical properties of aqueous P. harmala extract, develop efficient color-converting solids through a cost-effective and environmentally friendly method, and integrate them with light-emitting diodes (LEDs). To achieve high-efficiency solid hosts for P. harmala-based fluorophores, we optically and structurally compare two crystalline and two cellulose-based platforms. Structural analyses reveal that sucrose crystals, cellulose-based cotton, and paper platforms enable a relatively homogeneous distribution of fluorophores compared to KCl crystals. Optical characterization demonstrates that the extracted solution and the extract-embedded paper possess QYs of 75.6% and 44.7%, respectively, whereas the QYs of the cotton, sucrose, and KCl crystals remain below 10%. We demonstrated that the paper host with the highest efficiency causes a blueshift in the P. harmala fluorescence, whereas the cotton host induces a redshift. We attribute this to the passivation of nonradiative transitions related to the structure of the hosts. Subsequently, as a proof-of-concept demonstration, we integrate the as-prepared efficient solids of P. harmala for the first time with a light-emitting diode (LED) chip to produce a color-converting LED. The resulting blue-emitting LED achieves a luminous efficiency of 21.9 lm Welect -1 with CIE color coordinates of (0.139, 0.070). These findings mark a significant step toward the utilization of plant-based fluorescent biomolecules in solid-state lighting, offering promising environmentally friendly organic color conversion solutions for future lighting applications.

[4 + 2] Cyclization or Lossen Rearrangement: Rhodium-Catalyzed Divergent Synthesis of Carboline Derivatives with Anticancer Activity

An unusual rhodium-catalyzed C-H activation/Lossen rearrangement/oxa-Michael addition tandem cyclization has been achieved along with a tunable well-known C-H activation/[4 + 2] annulation, leading to regio-, chemo-, and diastereoselective access to diverse pentacyclic α-carbolines and β-carboline-1-one derivatives in moderate to good yields with significant anticancer activity.

In Vitro Effect of 9,9'-Norharmane Dimer against Herpes Simplex Viruses

Herpes simplex virus (HSV) infections are highly widespread among humans, producing symptoms ranging from ulcerative lesions to severe diseases such as blindness and life-threatening encephalitis. At present, there are no vaccines available, and some existing antiviral treatments can be ineffective or lead to adverse effects. As a result, there is a need for new anti-HSV drugs. In this report, the in vitro anti-HSV effect of 9,9'-norharmane dimer (nHo-dimer), which belongs to the β-carboline (βC) alkaloid family, was evaluated. The dimer exhibited no virucidal properties and did not impede either the attachment or penetration steps of viral particles. The antiviral effect was only exerted under the constant presence of the dimer in the incubation media, and the mechanism of action was found to involve later events of virus infection. Analysis of fluorescence lifetime imaging data showed that the nHo-dimer internalized well into the cells when present in the extracellular incubation medium, with a preferential accumulation into perinuclear organelles including mitochondria. After washing the host cells with fresh medium free of nHo-dimer, the signal decreased, suggesting the partial release of the compound from the cells. This agrees with the observation that the antiviral effect is solely manifested when the alkaloid is consistently present in the incubation media.

Penigrines A-E: Five undescribed azepine-indole alkaloids from Penicillium griseofulvum

Penigrines A-E (1-5), five undescribed azepine-indole alkaloids, were isolated from the fungus Penicillium griseofulvum. Their structures with absolute configurations were determined by NMR, HRESIMS, ECD calculation, and X-ray diffraction experiments. Penigrine C (3) possesses an undescribed 6-oxa-8-azabicyclo[3.2.2]nonane-7,9-dione moiety that fused to an indole core, and penigrines D and E (4 and 5) are a pair of epimers. The plausible biosynthetic pathways of 1-5 are proposed. Penigrine A (1) shows the potential for heart failure treatment.

Discovery of cyperenoic acid as a potent and novel entry inhibitor of influenza A virus

Influenza therapeutics with new targets and modes of action are urgently needed due to the frequent emergence of mutants resistant to currently available anti-influenza drugs. Here we report the in vitro and in vivo anti-influenza A virus activities of cyperenoic acid, a natural compound, which was isolated from a Chinese medicine Croton crassifolius Geise. Cyperenoic acid could potently suppress H1N1, H3N2 and H9N2 virus replication with IC50 values ranging from 0.12 to 15.13 μM, and showed a low cytotoxicity against MDCK cells (CC50 = 939.2 ± 60.0 μM), with selectivity index (SI) values ranging from 62 to 7823. Oral or intraperitoneal treatment of cyperenoic acid effectively protected mice against a lethal influenza virus challenge, comparable to the efficacy of Tamiflu. Additionally, cyperenoic acid also significantly reduced lung virus titers and alleviated influenza-induced acute lung injury in infected mice. Mechanism-of-action studies revealed that cyperenoic acid exhibited its anti-influenza activity during the entry stage of viral replication by inhibiting HA-mediated viral fusion. Simulation docking analyses of cyperenoic acid with the HA structures implied that cyperenoic acid binds to the stalk domain of HA in a cavity near the fusion peptide. Collectively, these results demonstrate that cyperenoic acid is a promising lead compound for the anti-influenza drug development and this research provides a useful small-molecule probe for studying the HA-mediated viral entry process.

Bioinspired total synthesis and biological activity of Pegaharine A

BACKGROUND

Phytopathogens cause various diseases by parasitizing crops, reducing crop yield and resulting in substantial economic losses in agricultural production. A novel type isolated from the perennial herbaceous Peganum harmala L. seeds, β-carboline alkaloids pegaharine A (PA), has become a hot topic in developing plant-originated green pesticides owing to their significant physiological activities.

RESULTS

A scalable bioinspired total synthesis of PA is accomplished in the present work. The systematical biological assay study showed that PA exhibited moderate inhibitory activity against nine tested plant pathogenic fungi and showed significant inhibitory activity in vitro against the three tested plant pathogenic bacteria. Most noteworthy is the inhibitory rates of PA on Xanthomonas oryzae pv. oryzae (Xoo), X. oryzae pv. oryzicola (Xoc) and X. axonopodis pv. citri (Xac) of 93.6%, 92.1% and 86.1%, respectively, which are better than the control drug, bismerthiazol (63.4%, 61.2% and 53.7% at 100 μg mL-1 concentration). Furthermore, the EC50 value of PA against Xoo, Xoc and Xac was 52.2, 60.0 and 65.1 μg mL-1 , respectively, superior to 72.9, 64.2 and 70.1 μg mL-1 of the control drug. Moreover, the anti-Xoo mechanistic studies revealed that PA exerted its antibacterial effects by increasing the permeability of the bacterial membrane, reducing the extracellular polysaccharide content and inducing morphological changes in bacterial cells.

CONCLUSION

A novel β-carboline alkaloid, PA, was prepared by biomimetic total synthesis. Its significant antibacterial activity was closely related to the permeation of bacterial cell membranes, which was confirmed by anti-Xoo mechanistic studies. More importantly, the structure could be regarded as a model for developing novel bactericides. © 2023 Society of Chemical Industry.

β-Carboline alkaloids from the roots of Peganum harmala L

This study reports the isolation of four new β-carboline alkaloids (1-4) and six previously identified alkaloids (5-10) from the roots of Peganum harmala L. Among these compounds, 1 and 2 were characterized as rare β-carboline-quinazoline dimers exhibiting axial chirality. Compound 3 possessed a unique 6/5/6/7 tetracyclic ring system with an azepine ring, and compound 4 was a novel annomontine β-carboline. The structures of these compounds were elucidated by spectroscopic data and quantum mechanical calculations. The biosynthetic pathways of 1-3 were proposed. Additionally, the cytotoxicity of some isolates against four cancer cell lines (HL-60, A549, MDA-MB-231, and DU145) was evaluated. Notably, compound 4 exhibited significant cytotoxicity against HL-60, A549, and DU145 cells with IC50 values of 12.39, 12.80, and 30.65 μmol·L-1, respectively. Furthermore, compound 2 demonstrated selective cytotoxicity against HL-60 cells with an IC50 value of 17.32 μmol·L-1.

Identification of 1,3,4-oxadiazolyl-containing β-carboline derivatives as novel α-glucosidase inhibitors with antidiabetic activity

In this study, we designed and synthesized a novel class of 1,3,4-oxadiazolyl-containing β-carboline derivatives, i.e., compounds f1∼f35 as potential α-glucosidase inhibitors. All the synthesized compounds possessed outstanding α-glucosidase inhibitory activity with the IC50 values in the range of 3.07-15.49 μM, representing that they are 36∼183-fold more active than a positive control, acarbose (IC50 = 564.28 μM). Among them, compound f26 exhibited the highest α-glucosidase inhibitory activity (IC50 = 3.07 μM) and was demonstrated to function as a reversible and noncompetitive inhibitor. Mechanistic studies by means of 3D fluorescence spectra, CD spectra and molecular docking suggested that complexation of compound f26 with α-glucosidase through hydrogen bonds and hydrophobic interactions, led to changes in the conformation and secondary strictures of α-glucosidase and further the inhibition of the enzymatic activity. In vivo results showed that oral administration of compound f26 (50 mg/kg/day) could obviously reduce the levels of fasting blood glucose and improve glucose tolerance and dyslipidemia in diabetic mice. The present findings suggest that compound f26 is exploitable as a potential lead compound for the development of new α-glucosidase inhibitors with antidiabetic activity.

Natural products as potential lead compounds to develop new antiviral drugs over the past decade

Virus infection has been one of the main causes of human death since the ancient times. Even though more and more antiviral drugs have been approved in clinic, long-term use can easily lead to the emergence of drug resistance and side effects. Fortunately, there are many kinds of metabolites which were produced by plants, marine organisms and microorganisms in nature with rich structural skeletons, and they are natural treasure house for people to find antiviral active substances. Aiming at many types of viruses that had caused serious harm to human health in recent years, this review summarizes the natural products with antiviral activity that had been reported for the first time in the past ten years, we also sort out the source, chemical structure and safety indicators in order to provide potential lead compounds for the research and development of new antiviral drugs.

Activation of endoplasmic reticulum stress by harmine suppresses the growth of esophageal squamous cell carcinoma

The worldwide overall 5-year survival rate of esophageal squamous cell carcinoma (ESCC) patients is less than 20%, and novel therapeutic strategies for these patients are urgently needed. Harmine is a natural β-carboline alkaloid, which received great interest in cancer research because of its biological and anti-tumor activities. The aim of this study is to examine the effects of harmine on ESCC and its mechanism. We investigated the effects of harmine on proliferation, cell cycle, apoptosis, and tumor growth in vivo. RNA sequencing (RNA-seq), real-time PCR, and western blotting were used to detect the mechanism. Harmine inhibited ESCC cell growth in vitro and tumor growth in vivo. Differentially expressed genes in harmine-treated ESCC cells were mainly involved in protein processing in the endoplasmic reticulum (ER). Real-time PCR and western blotting confirmed harmine-induced cellular ER stress. CRISPR-Cas9 knockout of C/EBP homologous protein (CHOP) abolished harmine-induced expression of death receptor 5 and apoptosis. Harmine also induced the expression of CHOP-mediated sestrin-2, which in turn contributes to autophagosome formation via suppressing the AMP-activated protein kinase-protein kinase B-mammalian target of rapamycin signaling pathway. In conclusion, our results demonstrate that harmine inhibits the growth of ESCC through its regulation of ER stress, suggesting that it is a promising candidate for ESCC treatment.

Methodological Development and Applications of Tryptamine-Ynamide Cyclizations in Synthesizing Core Skeletons of Indole Alkaloids

Over the past two decades, synthetic strategies for synthesizing the skeletons of various indole alkaloids based on tryptamine-ynamide have been continuously developed and applied to the total syntheses or formal total syntheses of related molecules. In this synopsis, we summarized the cyclization pathways of tryptamine-ynamide under different catalytic conditions, emphasizing the reaction mechanism and applications in the syntheses of indole alkaloids.

A Novel Aniline Derivative from Peganum harmala L. Promoted Apoptosis via Activating PI3K/AKT/mTOR-Mediated Autophagy in Non-Small Cell Lung Cancer Cells

Non-small cell lung cancer (NSCLC) is a common clinical malignant tumor with limited therapeutic drugs. Leading by cytotoxicity against NSCLC cell lines (A549 and PC9), bioactivity-guided isolation of components from Peganum harmala seeds led to the isolation of pegaharoline A (PA). PA was elucidated as a structurally novel aniline derivative, originating from tryptamine with a pyrrole ring cleaved and the degradation of carbon. Biological studies showed that PA significantly inhibited NSCLC cell proliferation, suppressed DNA synthesis, arrested the cell cycle, suppressed colony formation and HUVEC angiogenesis, and blocked cell invasion and migration. Molecular docking and surface plasmon resonance (SPR) demonstrated PA could bind with CD133, correspondingly decreased CD133 expression to activate autophagy via inhibiting the PI3K/AKT/mTOR pathway, and increased ROS levels, Bax, and cleaved caspase-3 to promote apoptosis. PA could also decrease p-cyclinD1 and p-Erk1/2 and block the EMT pathway to inhibit NSCLC cell growth, invasion, and migration. According to these results, PA could inhibit NSCLC cell growth by blocking PI3K/AKT/mTOR and EMT pathways. This study provides evidence that PA has a promising future as a candidate for developing drugs for treating NSCLC.

Inspired by bis-β-carboline alkaloids: Construction and antitumor evaluation of a novel bis-β-carboline scaffold as potent antitumor agents

Bis-β-carboline alkaloids are widely distributed in natural products and represent a promising drug-like scaffold for discovering drugs and bioactive molecules. In this study, we utilized the structural simplification strategy to construct a novel bis-β-carboline scaffold via "one-pot" condensation-Mannich reaction. The simplified bis-β-carboline derivatives were obtained in good yield. Antitumor evaluation revealed most compounds, especially 3m, displayed potent antitumor activity (IC₅₀ values for 3m: 0.96 μM ∼ 1.52 μM). More importantly, 3m displayed valuable antitumor properties including anti-migration and anti-invasion activity against cancer cells, antiangiogenic and vascular-disrupting properties. Mechanistic studies revealed 3m potently inhibited both Top1 and Top2 activity, thus interfering with DNA synthesis in cancer cells. Taken together, this study developed a new synthetic methodology to construct a novel bis-β-carboline scaffold, which represents a promising lead structure for antitumor drug discovery.

A bivalent β-carboline derivative inhibits macropinocytosis-dependent entry of pseudorabies virus by targeting the kinase DYRK1A

Pseudorabies virus (PRV) has become a "new life-threatening zoonosis" since the human-originated PRV strain was first isolated in 2020. To identify novel anti-PRV agents, we screened a total of 107 β-carboline derivatives and found 20 compounds displaying antiviral activity against PRV. Among them, 14 compounds showed better antiviral activity than acyclovir. We found that compound 45 exhibited the strongest anti-PRV activity with an IC₅₀ value of less than 40 nM. Our in vivo studies showed that treatment with 45 significantly reduced the viral loads and protected mice challenged with PRV. To clarify the mode of action of 45, we conducted a time of addition assay, an adsorption assay, and an entry assay. Our results indicated that 45 neither had a virucidal effect nor affected viral adsorption while significantly inhibiting PRV entry. Using the FITC-dextran uptake assay, we determined that 45 inhibits macropinocytosis. The actin-dependent plasma membrane protrusion, which is important for macropinocytosis, was also suppressed by 45. Further, the kinase DYRK1A was predicted to be a potential target for 45. The binding of 45 to DYRK1A was confirmed by DARTS and CETSA. Further analysis revealed that knockdown of DYRK1A by siRNA suppressed PRV macropinocytosis and the TNFα-induced formation of protrusions. These results suggested that 45 could restrain PRV macropinocytosis by targeting DYRK1A. Together, these findings reveal a unique mechanism through which β-carboline derivatives restrain PRV infection, pointing to their potential value in the development of anti-PRV agents. Our data also reveal a potential target for designing novel macropinocytosis inhibitors.

Alkaloids as potential antivirals. A comprehensive review

Alkaloids are a diverse group of natural phytochemicals. These phytochemicals in plants provide them protection against pests, and herbivorous organisms and also control their development. Numerous of these alkaloids have a variety of biological effects, and some have even been developed into medications with different medicinal properties. This review aims to provide a broad overview of the numerous naturally occurring alkaloids (isolated from both terrestrial and aquatic species) along with synthetically produced alkaloid compounds having prominent antiviral properties. Previous reviews on this subject have focused on the biological actions of both natural and synthetic alkaloids, but they have not gone into comprehensive detail about their antiviral properties. We reviewed here several antiviral alkaloids that have been described in the literature in different investigational environments i.e. (in-vivo, in-ovo, in-vitro, and in-silico), and found that these alkaloid compounds have significant antiviral properties against several infectious viruses. These alkaloids repressed and targeted various important stages of viral infection at non-toxic doses while some of the alkaloids reported here also exhibited comparable inhibitory activities to commercially used drugs. Overall, these anti-viral effects of alkaloids point to a high degree of specificity, implying that they could serve as effective and safe antiviral medicines if further pursued in medicinal and pharmacological investigations.

A new amide from the marine sponge Haliclona baeri

A new amide, baeriamide (1), along with nine known diketopiperazines (2-10), was isolated from the marine sponge Haliclona baeri. Their structures were identified by the means of UV, IR, MS and NMR. The absolute configuration of 1 was established by Marfey's method and comparing the specific optical rotation with the known compound HCO-Val-Gly methyl ester. Compound 1 was derived from dehydration of formylated L-valine with γ-amino-butanoic acid methyl ester. Compounds 2-10 were isolated from the genus of Haliclona for the first time. The absolute confirmation of 7 was confirmed first by the means of single-crystal X-ray diffraction. The cytotoxic, antibacterial, antiviral and antifouling activities of these compounds were also tested. However, none of them exhibited significant bioactivities.

A gold(i)-catalysed approach towards harmalidine an elusive alkaloid from Peganum harmala

Upon gold catalysis, the 2,3-dihydropyrrolo[1,2-a]indole motif, encountered in few but interesting bioactive natural products, was efficiently obtained from N-aryl 2-alkynylazetidine derivatives. In an attempt to apply this methodology to the synthesis of harmalidine, isolated from the seeds of Peganum harmala, advanced amino 2,3-hydropyrrolo[1,2-a]indol(one) derivatives were readily obtained in only 11 steps from but-3-yn-1-ol. While the reported structure of harmalidine could not be reached from these intermediates, a surprising 12-membered diimino dimer was isolated. Extensive comparison of the reported harmalidine NMR data to the experimental and calculated data of our synthetic molecules, harmaline or the synthetised N-methylharmaline show discrepancies with the proposed natural product structure.

Catalytic potential of a fungal indole prenyltransferase toward β-carbolines, harmine and harman, and their prenylation effects on antibacterial activity

The prenylation of compounds has attracted much attention, since it often adds bioactivity to non-prenylated compounds. We employed an enzyme assay with CdpNPT, an indole prenyltransferase from Aspergillus fumigatus with two naturally occurring β-carbolines, harmine (3) and harman (4) as prenyl acceptors, in the presence of dimethylallyl diphosphate (DMAPP) as the prenyl donor. The enzyme accepted these two prenyl acceptor substrates to produce 6-(3',3'-dimethylallyl)harmine (5) from 3 and 9-(3',3'-dimethylallyl)harman (6) and 6-(3',3'-dimethylallyl)harman (7) from 4. The X-ray crystal structure analysis of the CdpNPT (38-440) truncated mutant complexed with 4, and docking simulation studies of DMAPP to the crystal structure of the CdpNPT (38-440) mutant, suggested that CdpNPT could employ the two-step prenylation mechanism to produce 7, while the enzyme produced 6 with either one- or two-step prenylation mechanisms. Furthermore, the antibacterial assays revealed that the 3',3'-dimethylallylation of 3 and 4, as well as harmol (1), at C-6 enhanced the activities against Staphylococcus aureus and Bacillus subtilis.

Antibacterial, Antifungal, Antiviral, and Antiparasitic Activities of Peganum harmala and Its Ingredients: A Review

Infectious diseases have always been the number one enemy threatening health and well-being. With increasing numbers of infectious diseases, growing resistance of pathogens, and declining roles of antibiotics in the treatment of infectious diseases, it is becoming increasingly difficult to treat new infectious diseases, and there is an urgent need to develop new antibiotics to change the situation. Natural products tend to exhibit many special biological properties. The genus Peganum (Zygophyllaceae) has been used, for a long time, to treat cough, asthma, lumbago, hypertension, diabetes, and Alzheimer’s disease. Over the past two decades, a growing number of studies have shown that components from Peganum harmala Linn and its derivatives can inhibit a variety of microorganisms by inducing the accumulation of ROS in microorganisms, damaging cell membranes, thickening cell walls, disturbing cytoplasm, and interfering with DNA synthesis. In this paper, we provide a review on the antibacterial, antifungal, antiviral, and antiparasitic activities of P. harmala, with a view to contribute to research on utilizing P. harmala for medicinal applicaitons and to provide a reference in the field of antimicrobial and a basis for the development of natural antimicrobial agents for the treatment of infectious diseases.

(±)-Pheharmines A–B, two pairs of racemic alkaloids with a morpholino[4,3,2-hi]β-carboline core, from the roots of Peganum harmala

Two pairs of unprecedented β-carboline-phenylpropanoid alkaloids, (±)-pheharmines A–B (1–4), characterized by a morpholino[4,3,2-hi]β-carboline core with two chiral centers, were isolated from the roots of Peganum harmala.

From natural products to HDAC inhibitors: An overview of drug discovery and design strategy

Histone deacetylases (HDACs) play a key role in the homeostasis of protein acetylation in histones and have recently emerged as a therapeutic target for numerous diseases. The inhibition of HDACs may block angiogenesis, arrest cell growth, and lead to differentiation and apoptosis in tumour cells. Thus, HDAC inhibitors (HDACi) have received increasing attention and many of which are developed from natural sources. In the past few decades, naturally occurring HDACi have been identified to have potent anticancer activities, some of which have demonstrated promising therapeutic effects on haematological malignancies. In this review, we summarized the discovery and modification of HDAC inhibitors from natural sources, novel drug design that uses natural products as parent nuclei, and dual target design strategies that combine HDAC with non-HDAC targets.

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.

Nitrogenous Compounds from the Antarctic Fungus Pseudogymnoascus sp. HSX2#-11

The species Pseudogymnoascus is known as a psychrophilic pathogenic fungus which is ubiquitously distributed in Antarctica. While the studies of its secondary metabolites are infrequent. Systematic research of the metabolites of the Antarctic fungus Pseudogymnoascus sp. HSX2#-11 led to the isolation of one new pyridine derivative, 4-(2-methoxycarbonyl-ethyl)-pyridine-2-carboxylic acid methyl ester (1), together with one pyrimidine, thymine (2), and eight diketopiperazines, cyclo-(dehydroAla-l-Val) (3), cyclo-(dehydroAla-l-Ile) (4), cyclo-(dehydroAla-l-Leu) (5), cyclo-(dehydroAla-l-Phe) (6), cyclo-(l-Val-l-Phe) (7), cyclo-(l-Leu-l-Phe) (8), cyclo-(l-Trp-l-Ile) (9) and cyclo-(l-Trp-l-Phe) (10). The structures of these compounds were established by extensive spectroscopic investigation, as well as by detailed comparison with literature data. This is the first report to discover pyridine, pyrimidine and diketopiperazines from the genus of Pseudogymnoascus.