Total Synthesis of Grifolin, Grifolic Acid, LL-Z1272α, LL-Z1272β, and Ilicicolinic Acid A

The Discovery of Acremochlorins O-R from an Acremonium sp. through Integrated Genomic and Molecular Networking

The fermentation of a soil-derived fungus Acremonium sp. led to the isolation of thirteen ascochlorin congeners through integrated genomic and Global Natural Product Social (GNPS) molecular networking. Among the isolated compounds, we identified two unusual bicyclic types, acremochlorins O (1) and P (2), as well as two linear types, acremochlorin Q (3) and R (4). Compounds 1 and 2 contain an unusual benzopyran moiety and are diastereoisomers of each other, the first reported for the ascochlorins. Additionally, we elucidated the structure of 5, a 4-chloro-5-methylbenzene-1,3-diol with a linear farnesyl side chain, and confirmed the presence of eight known ascochlorin analogs (6-13). The structures were determined by the detailed interpretation of 1D and 2D NMR spectroscopy, MS, and ECD calculations. Compounds 3 and 9 showed potent antibacterial activity against Staphylococcus aureus and Bacillus cereus, with MIC values ranging from 2 to 16 μg/mL.

Asymmetric Total Syntheses of ent-Stachybotrin C and Its Congener

The asymmetric total syntheses of ent-stachybotrin C and its congener have been accomplished through a convergent approach in the longest linear sequence of 12 steps from commercially available materials, respectively. Noteworthy transformation of the synthesis involved a cascade Knoevenagel condensation/Hantzsch ester reduction/epoxide ring-opening/transetherification to construct the core pyran ring with two adjacent stereocenters.

Naturally Occurring Organohalogen Compounds-A Comprehensive Review

The present volume is the third in a trilogy that documents naturally occurring organohalogen compounds, bringing the total number-from fewer than 25 in 1968-to approximately 8000 compounds to date. Nearly all of these natural products contain chlorine or bromine, with a few containing iodine and, fewer still, fluorine. Produced by ubiquitous marine (algae, sponges, corals, bryozoa, nudibranchs, fungi, bacteria) and terrestrial organisms (plants, fungi, bacteria, insects, higher animals) and universal abiotic processes (volcanos, forest fires, geothermal events), organohalogens pervade the global ecosystem. Newly identified extraterrestrial sources are also documented. In addition to chemical structures, biological activity, biohalogenation, biodegradation, natural function, and future outlook are presented.

Albatrellus confluens (Alb. & Schwein.) Kotl. & Pouz.: Natural Fungal Compounds and Synthetic Derivatives with In Vitro Anthelmintic Activities and Antiproliferative Effects against Two Human Cancer Cell Lines

Neglected tropical diseases affect the world's poorest populations with soil-transmitted helminthiasis and schistosomiasis being among the most prevalent ones. Mass drug administration is currently the most important control measure, but the use of the few available drugs is giving rise to increased resistance of the parasites to the drugs. Different approaches are needed to come up with new therapeutic agents against these helminths. Fungi are a source of secondary metabolites, but most fungi remain largely uninvestigated as anthelmintics. In this report, the anthelmintic activity of Albatrellus confluens against Caenorhabditis elegans was investigated using bio-assay guided isolation. Grifolin (1) and neogrifolin (2) were identified as responsible for the anthelmintic activity. Derivatives 4-6 were synthesized to investigate the effect of varying the prenyl chain length on anthelmintic activity. The isolated compounds 1 and 2 and synthetic derivatives 4-6, as well as their educts 7-10, were tested against Schistosoma mansoni (adult and newly transformed schistosomula), Strongyloides ratti, Heligmosomoides polygyrus, Necator americanus, and Ancylostoma ceylanicum. Prenyl-2-orcinol (4) and geranylgeranyl-2-orcinol (6) showed promising activity against newly transformed schistosomula. The compounds 1, 2, 4, 5, and 6 were also screened for antiproliferative or cytotoxic activity against two human cancer lines, viz. prostate adenocarcinoma cells (PC-3) and colorectal adenocarcinoma cells (HT-29). Compound 6 was determined to be the most effective against both cell lines with IC₅₀ values of 16.1 µM in PC-3 prostate cells and 33.7 µM in HT-29 colorectal cells.

Syntheses of Amorfrutins and Derivatives via Tandem Diels-Alder and Anionic Cascade Approaches

We describe two complementary approaches based on a convergent [4+2] logic toward the synthesis of amorfrutins, cannabinoids, and related plant metabolites. An anionic cascade cyclization employing β-methoxycrotonates and β-chloro-α,β-unsaturated esters yielded amorfrutins in four linear steps and demonstrated utility of β-alkoxycrotonate-derived nucleophiles as functional equivalents of β-ketoester-derived dianions. Analogously, tandem Diels-Alder/retro-Diels-Alder cycloaddition of dimedone-derived bis(trimethylsiloxy)-dienes and α,β-alkynyl ester dienophiles provided facile access to resorcinol precursors of amorfrutins and cannabinoids, avoiding late-stage installation of prenyl or geranyl moieties as in previous approaches.

Polyketides and Meroterpenes from the Marine-Derived Fungi Aspergillus unguis 158SC-067 and A. flocculosus 01NT-1.1.5 and Their Cytotoxic and Antioxidant Activities

Ten secondary metabolites, including a new grifolin analog, grifolin B (1); a new homovalencic acid derivative, 12-hydroxyhomovalencic acid (7); and a compound isolated from a natural source for the first time (9), along with seven known compounds, grifolin (2), averantin (3), 7-chloroaverantin (4), 1′-O-methylaverantin (5), 7-hydroxy-2-(2-hydroxypropyl)-5-pentylchromone (6), homovalencic acid (8), and bekeleylactone E (10), were isolated from two fungal strains. The structures of 1–10 were identified by detailed analysis and comparison of their spectroscopic data with literature values. Compounds 9 and 10 showed moderate cytotoxic activity against a panel of cancer cell lines (PC-3, HCT-15, MDA-MB-231, ACHN, NCI-H23, NUGC-3), with the GI₅₀ values ranging from 1.1 µM to 3.6 µM, whereas 1 displayed a weak 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity without cytotoxicity against all tested cell lines.

Design and synthesis of water-soluble grifolin prodrugs for DNA methyltransferase 1 (DNMT1) down-regulation

DNA methylation and gene silencing play indispensable roles in the epigenetic landscape and gene expression. DNA methyltransferase 1 (DNMT1), a member of the DNMT family, which catalyzes the addition of methyl groups on DNA has been identified to have a close relationship with tumorigenesis. But DNMT1 inhibitors are rare except for the highly toxic nucleoside derivates. Grifolin is a unique natural product which down-regulates DNMT1 and has low toxicity. However, the poor solubility and stability of grifolin limit its application. Herein, we synthesized PEG5-Grifolin as a water-miscible prodrug of grifolin. The half-life of PEG5-Grifolin at 25 °C was considerably extended, revealing excellent stability. Meanwhile, PEG5-Grifolin suppressed tumor growth of by downregulating DNMT1 and reactivating the expression of several tumor suppressor genes in vivo. PEG5-Grifolin might be a promising demethylation agent for DNMT1 associated diseases and benefit much against various types of DNMT1 associated cancer.

In this work, a series of prodrugs of grifolin with much improved solubility and stability were designed and synthesis, which potently downregulated DNMT1 and inhibited tumor proliferation in vitro and in vivo.

Efficient Synthesis of Cannabigerol, Grifolin, and Piperogalin via Alumina-Promoted Allylation

The synthesis of three phenolic natural products has been accomplished with unprecedented efficiency using a new alumina-promoted regioselective aromatic allylation reaction. Cannabigerol and grifolin were prepared in one step from the inexpensive 5-alkyl-resorcinols olivetol and orcinol. Piperogalin was synthesized, for the first time, via two sequential allylations of orcinol with geraniol and prenol.

Alternative oxidase inhibitors: Mitochondrion-targeting as a strategy for new drugs against pathogenic parasites and fungi

The alternative oxidase (AOX) is a ubiquitous terminal oxidase of plants and many fungi, catalyzing the four-electron reduction of oxygen to water alongside the cytochrome-based electron transfer chain. Unlike the classical electron transfer chain, however, the activity of AOX does not generate adenosine triphosphate but has functions such as thermogenesis and stress response. As it lacks a mammalian counterpart, it has been investigated intensely in pathogenic fungi. However, it is in African trypanosomes, which lack cytochrome-based respiration in their infective stages, that trypanosome alternative oxidase (TAO) plays the central and essential role in their energy metabolism. TAO was validated as a drug target decades ago and among the first inhibitors to be identified was salicylhydroxamic acid (SHAM), which produced the expected trypanocidal effects, especially when potentiated by coadministration with glycerol to inhibit anaerobic energy metabolism as well. However, the efficacy of this combination was too low to be of practical clinical use. The antibiotic ascofuranone (AF) proved a much stronger TAO inhibitor and was able to cure Trypanosoma vivax infections in mice without glycerol and at much lower doses, providing an important proof of concept milestone. Systematic efforts to improve the SHAM and AF scaffolds, aided with the elucidation of the TAO crystal structure, provided detailed structure-activity relationship information and reinvigorated the drug discovery effort. Recently, the coupling of mitochondrion-targeting lipophilic cations to TAO inhibitors has dramatically improved drug targeting and trypanocidal activity while retaining target protein potency. These developments appear to have finally signposted the way to preclinical development of TAO inhibitors.

Grifolic acid induces GH3 adenoma cell death by inhibiting ATP production through a GPR120-independent mechanism

BACKGROUND

Grifolic acid is a derivative of grifolin, an antitumor natural compound, and it was reported as an agonist of free fatty acid receptor GPR120. Little is known about its antitumor effects and the involvement of GPR120.

METHODS

GH3 cells, the rat anterior pituitary adenoma cells, were cultured and the cell death was measured by MTT assay and Annexin V/PI staining. The mitochondrial membrane potential (MMP) of GH3 cells was measured by JC-1 staining. Cellular ATP levels and the intracellular NAD/NADH ratio were measured. GPR120 expression in GH3 cells was observed by RT-PCR and Western Blot, and siRNA was used to inhibit GPR120 expression in GH3 cells.

RESULTS

Grifolic acid dose- and time-dependently induced the necrosis of GH3 cells. Grifolic acid significantly reduced the mitochondrial membrane potential (MMP) and decreased cellular ATP levels in GH3 cells. In contrast, the MMP of isolated mitochondria was not decreased by grifolic acid. The intracellular NAD/NADH ratio was significantly increased by grifolic acid. GPR120 is expressed in GH3 cells, but GPR120 agonists such as EPA, GW9508 and TUG891 did not affect the viability of GH3 cells. Moreover, GPR120 siRNA knockdown showed no significant influence on grifolic acid-induced GH3 cell death.

CONCLUSION

Grifolic acid induces GH3 cell death by decreasing MMP and inhibiting ATP production, which may be due to the inhibition of NADH production through a GPR120-independent mechanism.

Grifolic acid causes osteosarcoma cell death in vitro and in tumor-bearing mice

Grifolic acid is a natural compound isolated from the fungus Albatrellus confluens. In the present study, we assessed the effects of grifolic acid on human osteosarcoma cells. We found that grifolic acid dose- and time-dependently induced cell death in the U-2 OS, MG-63, Saos-2, and 143B human osteosarcoma cell lines. Grifolic acid decreased osteosarcoma cell mitochondrial membrane potential, ATP production, and cellular NADH levels, but did not impact mitochondrial membrane potential in isolated mitochondria from human osteosarcoma cells. Intratumoral injection of grifolic acid also promoted tumor cell death and prolonged survival in nude mice bearing human osteosarcoma xenografts. Grifolic acid had no obvious toxicity in mice, with no histological changes in liver, kidney, lung, or heart, and no changes in blood cell counts or levels of plasma total protein, alanine aminotransferase, or aspartate aminotransferase. These results show that grifolic acid induces osteosarcoma cell death by inhibiting NADH generation and ATP production without obvious toxicity. Intratumoral injection of grifolic acid may be a promising anti-osteosarcoma therapeutic option in patients.