Pyridone and tetramic acid alkaloids from the spider pathogenic fungus Torrubiella sp. BCC 2165

Enantioselective Synthesis of the 1,3-Dienyl-5-Alkyl-6-Oxy Motif: Method Development and Total Synthesis

The 1,3-dienyl-5-alkyl-6-oxy motif is widely found in various types of bioactive natural products. However, present synthesis is mainly non-asymmetric which relied upon different olefination or transition metal-catalyzed cross-coupling reactions using enantioenriched precursors. Herein, based upon a newly developed enantioselective α-alkylation of conjugated polyenoic acids, a variety of 1,3-dienyl-5-alkyl-6-oxy motif (with E-configured internal olefin) was generated as the corresponding α-adducts in a highly enantioselective and diastereoselective manner. Utilizing 1,3-dienyl-5-alkyl-6-oxy motif as key intermediates, we further demonstrated their synthetic potential by expedient total syntheses of three types of natural products (glutarimide antibiotics, α-pyrone polyketides and Lupin alkaloids) within 4-7 steps.

Two New 4-Hydroxy-2-pyridone Alkaloids with Antimicrobial and Cytotoxic Activities from Arthrinium sp. GZWMJZ-606 Endophytic with Houttuynia cordata Thunb

Two new 4-hydroxy-2-pyridone alkaloids furanpydone A and B (1 and 2), along with two known compounds N-hydroxyapiosporamide (3) and apiosporamide (4) were isolated from the endophytic fungus Arthrinium sp. GZWMJZ-606 in Houttuynia cordata Thunb. Furanpydone A and B had unusual 5-(7-oxabicyclo[2.2.1]heptane)-4-hydroxy-2-pyridone skeleton. Their structures including absolute configurations were determined on the basis of spectroscopic analysis, as well as the X-ray diffraction experiment. Compound 1 showed inhibitory activity against ten cancer cell lines (MKN-45, HCT116, K562, A549, DU145, SF126, A-375, 786O, 5637, and PATU8988T) with IC₅₀ values from 4.35 to 9.72 µM. Compounds 1, 3 and 4 showed moderate inhibitory effects against four Gram-positive strains (Staphylococcus aureus, methicillin-resistant S. aureus, Bacillus Subtilis, Clostridium perfringens) and one Gram-negative strain (Ralstonia solanacarum) with MIC values from 1.56 to 25 µM. However, compounds 1-4 showed no obvious inhibitory activity against two Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) and two pathogenic fungi (Candida albicans and Candida glabrata) at 50 µM. These results show that compounds 1-4 are expected to be developed as lead compounds for antibacterial or anti-tumor drugs.

2-Pyridone natural products as inhibitors of SARS-CoV-2 main protease

The disease, COVID-19, is caused by the severe acute respiratory coronavirus 2 (SARS-CoV-2) for which there is currently no treatment. The SARS-CoV-2 main protease (M^pro) is an important enzyme for viral replication. Small molecules that inhibit this protease could lead to an effective COVID-19 treatment. The 2-pyridone scaffold was previously identified as a possible key pharmacophore to inhibit SARS-CoV-2 M^pro. A search for natural, antimicrobial products with the 2-pyridone moiety was undertaken herein, and their calculated potency as inhibitors of SARS-CoV-2 M^pro was investigated. Thirty-three natural products containing the 2-pyridone scaffold were identified from the literature. An in silico methodology using AutoDock was employed to predict the binding energies and inhibition constants (K_i values) for each 2-pyridone-containing compound with SARS-CoV-2 M^pro. This consisted of molecular optimization of the 2-pyridone compound, docking of the compound with a crystal structure of SARS-CoV-2 M^pro, and evaluation of the predicted interactions and ligand-enzyme conformations. All compounds investigated bound to the active site of SARS-CoV-2 M^pro, close to the catalytic dyad (His-41 and Cys-145). Thirteen molecules had predicted K_i values <1 μM. Glu-166 formed a key hydrogen bond in the majority of the predicted complexes, while Met-165 had some involvement in the complex binding as a close contact to the ligand. Prominent 2-pyridone compounds were further evaluated for their ADMET properties. This work has identified 2-pyridone natural products with calculated potent inhibitory activity against SARS-CoV-2 M^pro and with desirable drug-like properties, which may lead to the rapid discovery of a treatment for COVID-19.

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2-pyridone-scaffold is an inhibitory pharmacophore for SARS-CoV-2 M^pro.

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Thirty-three natural, antimicrobial products identified with 2-pyridone moiety.

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All 2-pyridone natural products bind to active site of SARS-CoV-2 M^proin silico.

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Thirteen molecules found to have potent inhibitory activity against SARS-CoV-2 M^pro.

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Inhibition of SARS-CoV-2 by natural 2-pyridones may lead to treatment of COVID-19.

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

Fungal Pigments and Their Prospects in Different Industries

The public's demand for natural, eco-friendly, and safe pigments is significantly increasing in the current era. Natural pigments, especially fungal pigments, are receiving more attention and seem to be in high demand worldwide. The immense advantages of fungal pigments over other natural or synthetic pigments have opened new avenues in the market for a wide range of applications in different industries. In addition to coloring properties, other beneficial attributes of fungal pigments, such as antimicrobial, anticancer, antioxidant, and cytotoxic activity, have expanded their use in different sectors. This review deals with the study of fungal pigments and their applications and sheds light on future prospects and challenges in the field of fungal pigments. Furthermore, the possible application of fungal pigments in the textile industry is also addressed.

Structural Simplification of Natural Products

Natural products (NPs) are important sources of clinical drugs due to their structural diversity and biological prevalidation. However, the structural complexity of NPs leads to synthetic difficulties, unfavorable pharmacokinetic profiles, and poor drug-likeness. Structural simplification by truncating unnecessary substructures is a powerful strategy for overcoming these limitations and improving the efficiency and success rate of NP-based drug development. Herein, we will provide a comprehensive review of the structural simplification of NPs with a focus on design strategies, case studies, and new technologies. In particular, a number of successful examples leading to marketed drugs or drug candidates will be discussed in detail to illustrate how structural simplification is applied in lead optimization of NPs.

Total synthesis of natural productsviairidium catalysis

An overview of the highlights in total synthesis of natural products using iridium as a catalyst is given.

Risks of Mycotoxins from Mycoinsecticides to Humans

There are more than thirty mycotoxins produced by fungal entomopathogens. Totally, they belong to two classes, NRP and PK mycotoxins. Most of mycotoxins have not been paid sufficient attention yet. Generally, mycotoxins do not exist in mycoinsecticide and might not be released to environments unless entomogenous fungus proliferates and produces mycotoxins in host insects or probably in plants. Some mycotoxins, destruxins as an example, are decomposed in host insects before they, with the insect's cadavers together, are released to environments. Many species of fungal entomopathogens have the endophytic characteristics. But we do not know if fungal entomopathogens produce mycotoxins in plants and release them to environments. On the contrary, the same mycotoxins produced by phytopathogens such as Fusarium spp. and Aspergillus spp. have been paid enough concerns. In conclusion, mycotoxins from mycoinsecticides have limited ways to enter environments. The risks of mycotoxins from mycoinsecticides contaminating foods are controllable.

Capturing Biological Activity in Natural Product Fragments by Chemical Synthesis

Natural products have had an immense influence on science and have directly led to the introduction of many drugs. Organic chemistry, and its unique ability to tailor natural products through synthesis, provides an extraordinary approach to unlock the full potential of natural products. In this Review, an approach based on natural product derived fragments is presented that can successfully address some of the current challenges in drug discovery. These fragments often display significantly reduced molecular weights, reduced structural complexity, a reduced number of synthetic steps, while retaining or even improving key biological parameters such as potency or selectivity. Examples from various stages of the drug development process up to the clinic are presented. In addition, this process can be leveraged by recent developments such as genome mining, antibody–drug conjugates, and computational approaches. All these concepts have the potential to identify the next generation of drug candidates inspired by natural products.

Torrubiellone E, an Antimalarial N-Hydroxypyridone Alkaloid from the Spider Pathogenic Fungus Torrubiella longissima BCC 2022

Torrubiellone E (1), a new N-hydroxypyridone alkaloid, was isolated from the spider pathogenic fungus Torrubiella longissima BCC 2022, together with the known compounds, torrubiellones A (2) and B (3), and JBIR-130 (4). Compound 1 exhibited antimalarial activity against Plasmodium falciparum K1 with an IC50 value of 3.2 μg/mL, while it also showed weak cytotoxic activities.

Naturally occurring tetramic acid products: isolation, structure elucidation and biological activity

Natural products containing the tetramic acid core scaffold have been isolated from an assortment of terrestrial and marine species and often display wide ranging and potent biological activities including antibacterial, antiviral and antitumoral activities.

Metacridamides A and B, macrocycles from conidia of the entomopathogenic fungus Metarhizium acridum

Metarhizium acridum, an entomopathogenic fungus, has been commercialized and used successfully for biocontrol of grasshopper pests in Africa and Australia. Its conidia produce two novel 17-membered macrocycles, metacridamides A and B, which consist of a Phe unit condensed with a nonaketide. Planar structures were elucidated by a combination of mass spectrometric and NMR techniques. Following hydrolysis of 1, chiral amino acid analysis assigned the L-configuration to the Phe unit. A crystal structure established the absolute configuration of the eight remaining stereogenic centers in 1. Metacridamide A showed cytotoxicity to three cancer lines with IC₅₀'s of 6.2, 11.0, and 10.8 μM against Caco-2 (epithelial colorectal adenocarcinoma), MCF-7 (breast cancer), and HepG2/C3A (hepatoma) cell lines, respectively. In addition, metacridamide B had an IC₅₀ of 18.2 μM against HepG2/C3A, although it was inactive at 100 μM against Caco-2 and MCF-7. Neither analogue showed antimicrobial, phytotoxic, or insecticidal activity.