Antifungal and Cytotoxic β-Resorcylic Acid Lactones from a Paecilomyces Species

A new resorcylic acid lactone from the endophytic fungus Chaetosphaeronema sp

A new 14-membered resorcylic acid lactone (RAL14), chaetolactone A (1), along with three known ones (2-4), was obtained from the fermentation of the soil-derived fungus Chaetosphaeronema sp. SSJZ001. Their structures were established based on extensive spectroscopic data analyses (UV, IR, HRESIMS, 1D, and 2D NMR),13C NMR chemical shifts calculations coupled with the DP4+ probability method, theoretical calculations of ECD spectra, as well as X-ray diffraction analysis. All compounds were evaluated for their cytotoxic effects against A549, HO-8910, and MCF-7 cell lines.

Total synthesis of 14-membered ring β-resorcylic acid lactone (+)-monocillin II

This study outlines the total synthesis of (+)-monocillin II, wherein a cis-isomer selectively produces a trans-isomer during the ring-closing metathesis. The Mitsunobu reaction conducted at -60 °C, facilitating the formation of an ester bond, was the key to completing the total synthesis, which was accomplished in the longest linear sequence of 10 steps with an overall yield of 9.3%.

Rhodium(III)-Catalyzed C-H/O2 Dual Activation and Macrocyclization: Synthesis and Evaluation of Pyrido[2,1-a]isoindole Grafted Macrocyclic Inhibitors for Influenza H1N1

The development of environment-friendly, step economic couplings to generate structurally diverse macrocyclic compounds is highly desirable but poses a marked challenge. Inspired by the C-H oxidation mechanism of cytochromes P450, an unprecedented and practical Rh^III -catalyzed acylmethylation macrocyclization via C-H/O₂ dual activation has been developed by us. The process of macrocyclization is facilitated by a synergic coordination from pyridine and ester group. Interestingly, the reaction mode derives from a three-component coupling which differs from established olefination and alkylation paths. Density functional theory (DFT) calculations and control experiments revealed the mechanism of this unique C-H/O₂ dual activation. The newly achieved acylmethylation macrocyclic products and their derivatives showed a potent anti-H1N1 bioactivity, which may provide an opportunity for the discovery of novel anti-H1N1 macrocyclic leading compounds.

The Effect of Cyclosporin A on Aspergillus niger and the Possible Mechanisms Involved

Aspergillus niger is one of the major pathogenic fungi causing postharvest grape decay. The development of antifungal agents is beneficial to reduce the loss of grapes during storage. The aim of this study was to investigate the antifungal mechanism of cyclosporin A (CsA). It was indicated that the rot development on grapes caused by A. niger was almost completely inhibited with CsA in vivo at a concentration of 200 mg/L. The transcriptomic analysis revealed that the expression levels of genes involved in rRNA processing and ribosome biogenesis were down-regulated, whereas those related to β-glucosidases and chitinases were up-regulated. The results implied that CsA may disturb rRNA and ribosome formation to obstruct protein synthesis, accelerate chitin and glucan degradation to destruct cell walls, and ultimately reduce postharvest decay caused by A. niger in grapes. This study evaluated the potential of CsA as a grape preservative and provided new insights into the mechanisms underlying the molecular response in A. niger with the treatment of CsA.

Resorcylic acid lactones from a Podospora sp. that induce apoptosis in activated T cells through MAPKs/AKT pathway

Podomycins A-L (1-12), 12 undescribed hypothemycin-type resorcylic acid lactones (RALs), were characterized from Podospora sp. G214, an endophyte harbored in the roots of Sanguisorba officinalis L. Their structures were addressed by spectroscopic data, X-ray crystallography, the modified Mosher's method, together with Mo₂(OAc)₄- and Rh₂(OCOCF₃)₄-induced electronic circular dichroism (ICD) experiments. Podomycins A-C (1-3) represent the first class of natural RALs with a 13-membered macrolactone ring, while 4-12 are rearranged methoxycarbonyl substituted RALs. Biologically, compounds 2, 6, 8, 10, and 12 displayed immunosuppressive activities against T cell proliferation with IC₅₀ values of 14.5-21.9 μM, and B cell proliferation with IC₅₀ values of 22.3-36.5 μM, respectively. Further mechanism of action research demonstrated that podomycin F (6) distinctly induced apoptosis in activated T cells via MAPKs/AKT pathway.

Natural resorcylic acid lactones: A chemical biology approach for anticancer activity

Resorcylic acid lactones (RALs) are fungal polyketides that consist of a β-resorcylic acid residue (2,4-dihydroxybenzoic acid) embedded in a macrolactone ring. RALs exhibit a broad range of biological activities, including anticancer activities. Following discovery of the selective Hsp90 inhibition activity of radicicol, the kinase inhibition activity of hypothemycin, monocillin II, 5Z-7-oxo-zeaenol, and L-783,277 RALs, and the nuclear factor kappa B (NF-κB) inhibition activity of the RAL zearalenone, have attracted great attention as potential therapeutics for cancer treatment. In this minireview, we focus on natural RALs that possess cytotoxic activities [IC₅₀ values < 10 μM (or 4-5 μg/ml)], discussing their structures, isolation, occurrence, biological activities, and anticancer molecular mechanisms.

Dihydrochalcones from the leaves of Lithocarpus litseifolius

Three new phlorizin derivatives, 6"-O-vanilloylphlorizin (1), 6"-O-(4-hydroxybenzoyl)phlorizin (2), 6"-O-feruloylphlorizin (3), along with four known dihydrochalcones, phlorizin (4), 3-hydroxyphlorizin, trilobatin, and 6"-O-acetylphlorizin were isolated from the leaves of Lithocarpus litseifolius. Their structures were established by analysis of extensive spectroscopic data. The new compounds were shown to be non-cytotoxic when tested against A549, HeLa, HepG2, and MCF-7 cell lines.

Anticancer activities, structure-activity relationship, and mechanism of action of 12-, 14-, and 16-membered macrolactones

Cancer remains one of the major causes of death worldwide despite the encouraging breakthroughs in the discovery of novel chemotherapeutic agents in recent years. The development of new effective anticancer candidates still represents a challenging endeavor due to the severe anticancer demands and the emergence of drug-resistant, especially multidrug-resistant, cancers. Macrolactones could regulate multiple signaling pathways in cancer cells and demonstrated potential anticancer effects, including inhibition of proliferation, metastasis, and angiogenic activity. Accordingly, macrolactones possess excellent efficacy against both drug-sensitive and drug-resistant cancer cells, and the rational design of macrolactones may provide valuable therapeutic interventions for cancers. The purpose of this review is as follows: (1) outline the recent advances made in the development of 12-, 14-, and 16-membered macrolactones with anticancer potential; (2) summarize the structure-activity relationship; and (3) discuss their anticancer mechanisms.

Hypothemycin-Type Resorcylic Acid Lactones with Immunosuppressive Activities from a Podospora sp

Twelve new hypothemycin-type resorcylic acid lactones, three 10-membered (1-3) and nine 14-membered (4-12), together with seven known analogues (13-19), were obtained from the solid rice-based culture of Podospora sp. G214. Their structures were elucidated utilizing spectroscopic analysis, and the absolute configurations were determined by modified Mosher's method, Mo2(OAc)4-induced electronic circular dichroism experiments, and single-crystal X-ray diffraction. Compounds 1, 5, 10, and 12-19 exhibited potent immunosuppressive activities against concanavalin A-induced T cell proliferation with IC50 values ranging from 6.0 to 25.1 μM and lipopolysaccharide-induced B cell proliferation with IC50 values ranging from 6.2 to 29.1 μM. Further studies revealed that 1 induced apoptosis in activated T cells through the JNK-mediated mitochondrial pathway.

Radicicol, a Novel Lead Compound against the Migratory-Stage Schistosomula of Schistosoma japonicum

Schistosomiasis poses a serious threat to human health and remains a major tropical and parasitic disease in more than 70 countries. Praziquantel (PZQ) has been the primary treatment for schistosomiasis for nearly 4 decades. However, its efficacy against migratory-stage schistosomula is limited. Radicicol (RAD), a β-resorcylic acid lactone derived from Paecilomyces sp. strain SC0924, was investigated as an alternative treatment for Schistosoma japonicum In vitro tests showed that within 72 h, RAD (10 μmol/liter) completely killed schistosomula of both skin and liver stages with an efficacy significantly higher than that of PZQ, although it was less potent against adult worms than PZQ. In vivo, RAD reduced worm burdens and liver eggs by 91.18% and 86.01%, respectively, by killing migratory-stage schistosomula. Optical microscopy and scanning electron microscopy revealed that RAD damaged the epiderm and tegument morphology of S. japonicum worms at various stages and altered their motility to different degrees. RAD exhibited schistosomicidal effects at different stages in vitro and in vivo, especially at the migratory stage, implying that its mechanism could be different from that of PZQ. Collectively, these results showed that RAD is promising as a lead for the development of drugs to control the migratory-stage schistosomula of S. japonicum.

Total synthesis: the structural confirmation of natural products

This feature article highlights total synthesis as one of the reliable tools for the structural confirmation of natural products.

Secondary Metabolites and Their Bioactivities Produced by Paecilomyces

Paecilomyces, a common saprobic filamentous fungus, not only plays an important role in biological control, but also has applications in medicine, food, and environmental protection. In this paper, 223 secondary metabolites and their bioactivities from 13 known species and various unidentified strains of Paecilomyces are reviewed. Their structures can be described as polyketide, terpenoid, peptide, alkaloid, quinone, pyrone, sterol, and fatty acid. They have been demonstrated varying biological activities, including antimicrobial, antitumor, insecticidal, antiplasmodial, antimalarial, nematicidal, herbicidal, and enzyme-inhibiting. This review provides a comprehensive overview of secondary metabolites and their biological activities from strains of Paecilomyces.

Beta resorcylic acid lactones (RALs) from fungi: chemistry, biology, and biosynthesis

β-Resorcylic acid lactones (RALs) are one of the major polyketides produced by fungi, and some of them have a diverse array of biological activities. Most RALs feature a 14-membered macrocyclic ring fused to β-resorcylic acid (2,4-dihydroxybenzoic acid). In this review, more than 100 RAL-type of compounds are structurally classified into three groups; 14-membered RALs with 17R configuration, 14-membered RALs with 17S configuration, and benzopyranones/benzofuranones, and they are reviewed comprehensively in terms of chemistry, biological activities, and biosynthetic pathways.

Biological Evaluation of Selected Flavonoids as Inhibitors of MNKs Targeting Acute Myeloid Leukemia

Excessive eIF4E phosphorylation by mitogen-activated protein kinase (MAPK)-interacting kinases 1 and 2 (MNK1 and MNK2; collectively, MNKs) has been associated with oncogenesis. The overexpression of eIF4E in acute myeloid leukemia (AML) is related to cancer cell growth and survival. Thus, the inhibition of MNKs and eIF4E phosphorylation are potential therapeutic strategies for AML. Herein, a structure-based virtual screening approach was performed to identify potential MNK inhibitors from natural products. Three flavonoids, apigenin, hispidulin, and luteolin, showed MNK2 inhibitory activity with IC₅₀ values of 308, 252, and 579 nM, respectively. A structure-activity relationship analysis was performed to disclose the molecular interactions. Furthermore, luteolin exhibited substantial inhibitory efficacy against MNK1 (IC₅₀ = 179 nM). Experimental results from cellular assays showed that hispidulin and luteolin inhibited the growth of MOLM-13 and MV4-11 AML cells by downregulating eIF4E phosphorylation and arresting the cell cycle at the G0/G1 phase. Therefore, hispidulin and luteolin showed promising results as lead compounds for the potential treatment for AML.

A Systematic Review on Secondary Metabolites of Paecilomyces Species: Chemical Diversity and Biological Activity

Fungi are well known for their ability to synthesize secondary metabolites, which have proven to be a rich resource for exploring lead compounds with medicinal and/or agricultural importance. The genera Aspergillus, Penicillium, and Talaromyces are the most widely studied fungal groups, from which a plethora of bioactive metabolites have been characterized. However, relatively little attention has been paid to the genus Paecilomyces, which has been reported to possess great potential for its application as a biocontrol agent. Meanwhile, a wide structural array of metabolites with attractive bioactivities has been reported from this genus. This review attempts to provide a comprehensive overview of Paecilomyces species, with emphasis on the chemical diversity and relevant biological activities of these metabolic products. Herein, a total of 148 compounds and 80 references are cited in this review, which is expected to be beneficial for the development of medicines and agrochemicals in the near future.

Resorcylic Acid Lactones from an Ilyonectria sp

Twelve new resorcylic acid lactones (RALs) including three new 16-membered RALs (1a, 1b and 2), eight new 14-membered RALs (3-10), and one new 12-membered RAL (11), along with five known 14-membered RALs (12-16), were identified from the fermentation of the soil-derived fungus Ilyonectria sp. sb65. Their structures were established by detailed analyses of 1D and 2D NMR, HRESIMS, and X-ray diffraction crystallography. All new compounds were evaluated for their cytotoxic effects against three human cancer cell lines, along with their potential as TRAIL sensitizers in TRAIL-resistant A549 human lung adenocarcinoma cells and their in vitro immunosuppressive effects against ConA-induced T-cell and LPS-induced B-cell proliferation.

Unraveling Plant Natural Chemical Diversity for Drug Discovery Purposes

The screening and testing of extracts against a variety of pharmacological targets in order to benefit from the immense natural chemical diversity is a concern in many laboratories worldwide. And several successes have been recorded in finding new actives in natural products, some of which have become new drugs or new sources of inspiration for drugs. But in view of the vast amount of research on the subject, it is surprising that not more drug candidates were found. In our view, it is fundamental to reflect upon the approaches of such drug discovery programs and the technical processes that are used, along with their inherent difficulties and biases. Based on an extensive survey of recent publications, we discuss the origin and the variety of natural chemical diversity as well as the strategies to having the potential to embrace this diversity. It seemed to us that some of the difficulties of the area could be related with the technical approaches that are used, so the present review begins with synthetizing some of the more used discovery strategies, exemplifying some key points, in order to address some of their limitations. It appears that one of the challenges of natural product-based drug discovery programs should be an easier access to renewable sources of plant-derived products. Maximizing the use of the data together with the exploration of chemical diversity while working on reasonable supply of natural product-based entities could be a way to answer this challenge. We suggested alternative ways to access and explore part of this chemical diversity with in vitro cultures. We also reinforced how important it was organizing and making available this worldwide knowledge in an "inventory" of natural products and their sources. And finally, we focused on strategies based on synthetic biology and syntheses that allow reaching industrial scale supply. Approaches based on the opportunities lying in untapped natural plant chemical diversity are also considered.

Total Synthesis of trans-Resorcylide via Macrocyclic Stille Carbonylation

The resorcylic macrolides are important natural products with a wide range of remarkable biological activities. So far, most of the reported resorcylic macrolide syntheses use either macrolactonization or ring closing metathesis to build the corresponding macrocycle. In continuation of our efforts in developing novel carbonylation reactions to facilitate natural product total synthesis, we report herein a total synthesis of trans-resorcylide (1) featuring a palladium-catalyzed macrocyclic Stille carbonylation to build its 12-membered macrocycle.