A New SV2A Ligand for Epilepsy.

Since the 1970s, racetams have been in use as cognitive enhancers. Levetiracetam was discovered to have antiseizure activity in animal models and was then found to bind to SV2A in synaptic and endocrine vesicles. Brivaracetam, an analog of levetiracetam, was identified in a medicinal chemistry campaign with the objective of discovering analogs with higher affinity at racetam-binding sites and greater antiseizure potency.

Total Syntheses of the Structures Assigned to Denigrins A, B, C, F, and G, 3,4-Diaryl-Pyrrole and -Pyrrolidinone Alkaloids, and the Conversion of Congener B into the Co-metabolite Spirodactylone.

The title marine natural products have been prepared by total synthesis and in the case of congeners 3, 6, and 7 for the first time. Each of these was obtained by manipulation of readily prepared denigrin B (2). The structure, 3, assigned to denigrin C is shown to be incorrect. Reaction of compound 2 with DDQ has led, in high yield, to the related natural product spirodactylone (16), while treating the corresponding permethyl ether 15 with PIFA/BF3·Et2O provides compound 20, embodying an isomeric framework.

Bioactivity-Based Molecular Networking-Guided Isolation of Epicolidines A-C from the Endophytic Fungus Epicoccum sp. 1-042.

Bioactivity-based molecular networking-guided fractionation enabled the isolation of three new polycyclic tetramic acids bearing cis-decalin, epicolidines A-C (1-3), along with one known compound, PF 1052 (4), from the endophytic fungus Epicoccum sp. 1-042 collected in Tibet, China. Their structures were assigned on the basis of extensive spectroscopic data, partial hydrolysis, advanced Marfey's method, quantum chemistry calculations, and X-ray diffraction analysis. Compounds 2-4 displayed promising activities against Gram-positive bacteria in vitro. Particularly, compound 4 displayed remarkable potential against vancomycin-resistant Enterococcus faecium (VRE) with an MIC value of 0.25 µg/mL, lower than the MIC (0.5 µg/mL) of the antibiotic combination quinupristin/dalfopristin (Q/D). In a further in vivo study, compound 4 increased the survival rate to 100% in the VRE-G. mellonella infection model at a concentration of 10 mg/kg.

Aurantoside L, a New Tetramic Acid Glycoside with Anti-Leishmanial Activity Isolated from the Marine Sponge Siliquariaspongia japonica.

A new tetramic acid glycoside, aurantoside L (1), was isolated from the sponge Siliquariaspongia japonica collected at Tsushima Is., Nagasaki Prefecture, Japan. The structure of aurantoside L (1) composed of a tetramic acid bearing a chlorinated polyene system and a trisaccharide part was elucidated using spectral analysis. Aurantoside L (1) showed anti-parasitic activity against L. amazonensis with an IC50 value of 0.74 µM.

Catalytic enantioselective 1,6-conjugate additions of propargyl and allyl groups.

Conjugate (or 1,4-) additions of carbanionic species to α,ß-unsaturated carbonyl compounds are vital to research in organic and medicinal chemistry, and there are several chiral catalysts that facilitate the catalytic enantioselective additions of nucleophiles to enoates. Nonetheless, catalytic enantioselective 1,6-conjugate additions are uncommon, and ones that incorporate readily functionalizable moieties, such as propargyl or allyl groups, into acyclic α,ß,γ,δ-doubly unsaturated acceptors are unknown. Chemical transformations that could generate a new bond at the C6 position of a dienoate are particularly desirable because the resulting products could then be subjected to further modifications. However, such reactions, especially when dienoates contain two equally substituted olefins, are scarce and are confined to reactions promoted by a phosphine-copper catalyst (with an alkyl Grignard reagent, dialkylzinc or trialkylaluminium compounds), a diene-iridium catalyst (with arylboroxines), or a bisphosphine-cobalt catalyst (with monosilyl-acetylenes). 1,6-Conjugate additions are otherwise limited to substrates where there is full substitution at the C4 position. It is unclear why certain catalysts favour bond formation at C6, and-although there are a small number of catalytic enantioselective conjugate allyl additions-related 1,6-additions and processes involving a propargyl unit are non-existent. Here we show that an easily accessible organocopper catalyst can promote 1,6-conjugate additions of propargyl and 2-boryl-substituted allyl groups to acyclic dienoates with high selectivity. A commercially available allenyl-boron compound or a monosubstituted allene may be used. Products can be obtained in up to 83 per cent yield, >98:2 diastereomeric ratio (for allyl additions) and 99:1 enantiomeric ratio. We elucidate the mechanistic details, including the origins of high site selectivity (1,6- versus 1,4-) and enantioselectivity as a function of the catalyst structure and reaction type, by means of density functional theory calculations. The utility of the approach is highlighted by an application towards enantioselective synthesis of the anti-HIV agent (-)-equisetin.

Structure of CC chemokine receptor 2 with orthosteric and allosteric antagonists.

CC chemokine receptor 2 (CCR2) is one of 19 members of the chemokine receptor subfamily of human class A G-protein-coupled receptors. CCR2 is expressed on monocytes, immature dendritic cells, and T-cell subpopulations, and mediates their migration towards endogenous CC chemokine ligands such as CCL2 (ref. 1). CCR2 and its ligands are implicated in numerous inflammatory and neurodegenerative diseases including atherosclerosis, multiple sclerosis, asthma, neuropathic pain, and diabetic nephropathy, as well as cancer. These disease associations have motivated numerous preclinical studies and clinical trials (see http://www.clinicaltrials.gov) in search of therapies that target the CCR2-chemokine axis. To aid drug discovery efforts, here we solve a structure of CCR2 in a ternary complex with an orthosteric (BMS-681 (ref. 6)) and allosteric (CCR2-RA-[R]) antagonist. BMS-681 inhibits chemokine binding by occupying the orthosteric pocket of the receptor in a previously unseen binding mode. CCR2-RA-[R] binds in a novel, highly druggable pocket that is the most intracellular allosteric site observed in class A G-protein-coupled receptors so far; this site spatially overlaps the G-protein-binding site in homologous receptors. CCR2-RA-[R] inhibits CCR2 non-competitively by blocking activation-associated conformational changes and formation of the G-protein-binding interface. The conformational signature of the conserved microswitch residues observed in double-antagonist-bound CCR2 resembles the most inactive G-protein-coupled receptor structures solved so far. Like other protein-protein interactions, receptor-chemokine complexes are considered challenging therapeutic targets for small molecules, and the present structure suggests diverse pocket epitopes that can be exploited to overcome obstacles in drug design.

New 3-Acyl Tetramic Acid Derivatives from the Deep-Sea-Derived Fungus Lecanicillium fusisporum.

Seven rare C3-C6 reduced 3-acyl tetramic acid derivatives, lecanicilliumins A-G (1-7), along with the known analogue cladosporiumin D (8), were obtained from the extract of the deep-sea-derived fungus Lecanicillium fusisporum GXIMD00542 within the family Clavipitacae. Their structures were elucidated by extensive spectroscopic data analysis, quantum chemistry calculations and chemical reaction. Compounds 1, 2, 5-7 exhibited moderate anti-inflammatory activity against NF-κB production using lipopolysaccharide (LPS) induced RAW264.7 cells with EC50 values range of 18.49-30.19 µM.

Nitrogen-Containing Secondary Metabolites from a Deep-Sea Fungus Aspergillus unguis and Their Anti-Inflammatory Activity.

Aspergillus is well-known as the second-largest contributor of fungal natural products. Based on NMR guided isolation, three nitrogen-containing secondary metabolites, including two new compounds, variotin B (1) and coniosulfide E (2), together with a known compound, unguisin A (3), were isolated from the ethyl acetate (EtOAc) extract of the deep-sea fungus Aspergillus unguis IV17-109. The planar structures of 1 and 2 were elucidated by an extensive analysis of their spectroscopic data (HRESIMS, 1D and 2D NMR). The absolute configuration of 2 was determined by comparison of its optical rotation value with those of the synthesized analogs. Compound 2 is a rare, naturally occurring substance with an unusual cysteinol moiety. Furthermore, 1 showed moderate anti-inflammatory activity with an IC50 value of 20.0 µM. These results revealed that Aspergillus unguis could produce structurally diverse nitrogenous secondary metabolites, which can be used for further studies to find anti-inflammatory leads.

Bursatella leachii Purple Ink Secretion Concentrate Exerts Cytotoxic Properties against Human Hepatocarcinoma Cell Line (HepG2): In Vitro and In Silico Studies.

Liver cancer is a leading cause of cancer death globally. Marine mollusc-derived drugs have gained attention as potential natural-based anti-cancer agents to overcome the side effects caused by conventional chemotherapeutic drugs during cancer therapy. Using liquid chromatography-mass spectrometry, the main biomolecules in the purple ink secretion released by the sea hare, named Bursatella leachii (B. leachii), were identified as hectochlorin, malyngamide X, malyngolide S, bursatellin and lyngbyatoxin A. The cytotoxic effects of B. leachii ink concentrate against human hepatocarcinoma (HepG2) cells were determined to be dose- and time-dependent, and further exploration of the underlying mechanisms causing the programmed cell death (apoptosis) were performed. The expression of cleaved-caspase-8 and cleaved-caspase-3, key cysteine-aspartic proteases involved in the initiation and completion of the apoptosis process, appeared after HepG2 cell exposure to the B. leachii ink concentrate. The gene expression levels of pro-apoptotic BAX, TP53 and Cyclin D1 were increased after treatment with the B. leachii ink concentrate. Applying in silico approaches, the high scores predicted that bioactivities for the five compounds were protease and kinase inhibitors. The ADME and cytochrome profiles for the compounds were also predicted. Altogether, the B. leachii ink concentrate has high pro-apoptotic potentials, suggesting it as a promising safe natural product-based drug for the treatment of liver cancer.

Total Synthesis of Kibdelomycin.

A modular total synthesis of kibdelomycin is disclosed that should enable structure-activity relationship (SAR) studies of this interesting class of antibiotics. The route uses simple building blocks and addresses lingering questions about its structural assignment and relationship to amycolamicin, a recently described natural product reported to have a similar structure. Initial antibacterial assays reveal that both C-22 epimers (the N-glycosidic linkage) of the natural product have similar activity while structurally truncated analogs lose activity.

Pan-3C Protease Inhibitor Rupintrivir Binds SARS-CoV-2 Main Protease in a Unique Binding Mode.

Rupintrivir targets the 3C cysteine proteases of the picornaviridae family, which includes rhinoviruses and enteroviruses that cause a range of human diseases. Despite being a pan-3C protease inhibitor, rupintrivir activity is extremely weak against the homologous 3C-like protease of SARS-CoV-2. In this study, the crystal structures of rupintrivir were determined bound to enterovirus 68 (EV68) 3C protease and the 3C-like main protease (Mpro) from SARS-CoV-2. While the EV68 3C protease-rupintrivir structure was similar to previously determined complexes with other picornavirus 3C proteases, rupintrivir bound in a unique conformation to the active site of SARS-CoV-2 Mpro splitting the catalytic cysteine and histidine residues. This bifurcation of the catalytic dyad may provide a novel approach for inhibiting cysteine proteases.

Characterization of Chalkophomycin, a Copper(II) Metallophore with an Unprecedented Molecular Architecture.

Metals play essential roles in life by coordination with small molecules, proteins, and nucleic acids. Although the coordination of copper ions in many proteins and methanobactins is known, the coordination chemistry of Cu(II) in natural products and their biological functions remain underexplored. Herein, we report the discovery of a Cu(II)-binding natural product, chalkophomycin (CHM, 1), from Streptomyces sp. CB00271, featuring an asymmetric square-coordination system of a bidentate diazeniumdiolate and a conjugated 1H-pyrrole 1-oxide-oxazoline. The structure of 1 may inspire the synthesis of Cu(II) chelators against neurodegenerative diseases or Cu(II)-based antitumor therapeutics.

Total Synthesis of the Potent and Broad-Spectrum Antibiotics Amycolamicin and Kibdelomycin.

The complex and intriguing structures of the antibiotics amycolamicin and kibdelomycin are herein confirmed through total synthesis. Careful titration of the synthetic products reveals that kibdelomycin is the salt form of amycolamicin. This synthesis employs a highly convergent strategy, which provides a modular approach for further SAR studies of this class of antibiotics.

Biosynthesis of para-Cyclophane-Containing Hirsutellone Family of Fungal Natural Products.

Hirsutellones are fungal natural products containing a macrocyclic para-cyclophane connected to a decahydrofluorene ring system. We have elucidated the biosynthetic pathway for pyrrocidine B (3) and GKK1032 A2 (4). Two small hypothetical proteins, an oxidoreductase and a lipocalin-like protein, function cooperatively in the oxidative cyclization of the cyclophane, while an additional hypothetical protein in the pyrrocidine pathway catalyzes the exo-specific cycloaddition to form the cis-fused decahydrofluorene.

Discovery of a novel class of heteroaryl-pyrrolidinones as positive allosteric modulators of the muscarinic acetylcholine receptor M1.

This Letter describes the synthesis and optimization of a series of heteroaryl-pyrrolidinone positive allosteric modulators (PAMs) of the muscarinic acetylcholine receptor M1 (mAChR M1). Through the continued optimization of M1 PAM tool compound VU0453595, with a focus on replacement of the 6,7-dihydro-5H-pyrrolo[3,4-b]pyridin-5-one with a wide variety of alternative 4,5-dihydropyrrolo-fused heteroaromatics, the generation of M1 PAMs with structurally novel chemotypes is disclosed. Two compounds from these subseries, 8b (VU6005610) and 20a (VU6005852), show robust selectivity for the M1 mAChR, and no M1 agonism. Both compounds have favorable preliminary PK profiles in vitro;8b additionally demonstrates high brain exposure in a rodent IV cassette model.

Structure-Activity Relationships for the Marine Natural Product Sintokamides: Androgen Receptor N-Terminus Antagonists of Interest for Treatment of Metastatic Castration-Resistant Prostate Cancer.

Synthetic analogues of the marine natural product sintokamides have been prepared in order to investigate the structure-activity relationships for the androgen receptor N-terminal domain (AR NTD) antagonist activity of the sintokamide scaffold. An in vitro LNCaP cell-based transcriptional activity assay with an androgen-driven luciferase (Luc) reporter was used to monitor the potency of analogues. The data have shown that the chlorine atoms on the leucine side chains are essential for potent activity. Analogues missing the nonchlorinated methyl groups of the leucine side chains (C-1 and C-17) are just as active and in some cases more active than the natural products. Analogues with the natural R configuration at C-10 and the unnatural R configuration at C-4 are most potent. Replacing the natural propionamide N-terminus cap with the more sterically hindered pivaloylamide N-terminus cap leads to enhanced potency. The tetramic acid fragment and the methyl ether on the tetramic acid fragment are essential for activity. The SAR optimized analogue 76 is more selective, easier to synthesize, more potent, and presumed to be more resistant to proteolysis than the natural sintokamides.

Design, synthesis and biological evaluation of novel pyrrolidone-based derivatives as potent p53-MDM2 inhibitors.

Inhibition of the interactions of the tumor suppressor protein p53 with its negative regulators MDM2 in vitro and in vivo, representing a valuable therapeutic strategy for cancer treatment. The natural product chalcone exhibited moderate inhibitory activity against MDM2, thus based on the binding mode between chalcone and MDM2, a hit unsaturated pyrrolidone scaffold was obtained through virtual screening. Several unsaturated pyrrolidone derivatives were synthesized and biological evaluated. As a result, because the three critical hydrophobic pockets of MDM2 were occupied by the substituted-phenyl linked at the pyrrolidone fragment, compound 4 h demonstrated good binding affinity with the MDM2. Additionally, compound 4 h also showed excellent antitumor activity and selectivity, and no cytotoxicity against normal cells in vitro. The further antitumor mechanism studies were indicated that compound 4 h could successfully induce the activation of p53 and corresponding downstream p21 proteins, thus successfully causing HCT116 cell cycle arrest in the G1/M phase and apoptosis. Thus, the novel unsaturated pyrrolidone p53-MDM2 inhibitors could be developed as novel antitumor agents.

Synthesis and Bioactivity of Ancorinoside B, a Marine Diglycosyl Tetramic Acid.

The sponge metabolite ancorinoside B was prepared for the first time in 16 steps and 4% yield. It features a ß-d-galactopyranosyl-(1→4)-ß-d-glucuronic acid tethered to a d-aspartic acid-derived tetramic acid. Key steps were the synthesis of a fully protected d-lactose derived thioglycoside, its attachment to a C20-aldehyde spacer, functionalization of the latter with a terminal N-(ß-ketoacyl)-d-aspartate, and a basic Dieckmann cyclization to close the pyrrolidin-2,4-dione ring with concomitant global deprotection. Ancorinoside B exhibited multiple biological effects of medicinal interest. It inhibited the secretion of the cancer metastasis-relevant matrix metalloproteinases MMP-2 and MMP-9, and also the growth of Staphylococcus aureus biofilms by ca 87% when applied at concentrations as low as 0.5 µg/mL. This concentration is far below its MIC of ca 67 µg/mL and thus unlikely to induce bacterial resistance. It also led to a 67% dispersion of preformed S. aureus biofilms when applied at a concentration of ca 2 µg/mL. Ancorinoside B might thus be an interesting candidate for the control of the general hospital, catheter, or joint protheses infections.

Synthesis and preliminary biological evaluation of antibacterial and antifungal 5-arylidene tetramic acid-cadmium(II) complexes.

The synthesis and biological evaluation of 5-arylidene-N-acetyl-tetramic acids cadmium(II) complexes are reported. Eleven novel compounds were prepared, characterized by nuclear magnetic resonance experiments and screened for their antimicrobial activity against five bacterial species (Escherichia coli, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and methicillin-resistant Staphylococcus aureus [MRSA]) and two fungi (Candida albicans and Cryptococcus neoformans). The complexes showed similar or enhanced activities against MRSA in comparison to the corresponding ligands and, additionally, promising antifungal activities against C. neoformans. The most active compounds 3c and 3h showed remarkable activities against MRSA (minimum inhibitory activity [MIC] values of 32 and 4 µg/ml, respectively) and C. neoformans (MIC values of 8 and 16 µg/ml, respectively), accompanied by no human cell toxicity and hemolytic activity within the tested concentration range. The results demonstrate that appropriately functionalized tetramic acids attached with lipophilic alkanoyl chain and after complexation with cadmium(II) ions may act as valuable lead compounds for further investigations toward the development of novel antibacterial and/or antifungal agents.

Effect of N-Vinyl-2-Pyrrolidone (NVP), a Bromodomain-Binding Small Chemical, on Osteoblast and Osteoclast Differentiation and Its Potential Application for Bone Regeneration.

The human skeleton is a dynamic and remarkably organized organ system that provides mechanical support and performs a variety of additional functions. Bone tissue undergoes constant remodeling; an essential process to adapt architecture/resistance to growth and mechanical needs, but also to repair fractures and micro-damages. Despite bone's ability to heal spontaneously, certain situations require an additional stimulation of bone regeneration, such as non-union fractures or after tumor resection. Among the growth factors used to increase bone regeneration, bone morphogenetic protein-2 (BMP2) is certainly the best described and studied. If clinically used in high quantities, BMP2 is associated with various adverse events, including fibrosis, overshooting bone formation, induction of inflammation and swelling. In previous studies, we have shown that it was possible to reduce BMP2 doses significantly, by increasing the response and sensitivity to it with small molecules called "BMP2 enhancers". In the present study, we investigated the effect of N-Vinyl-2-pyrrolidone (NVP) on osteoblast and osteoclast differentiation in vitro and guided bone regeneration in vivo. We showed that NVP increases BMP2-induced osteoblast differentiation and decreases RANKL-induced osteoclast differentiation in a dose-dependent manner. Moreover, in a rabbit calvarial defect model, the histomorphometric analysis revealed that bony bridging and bony regenerated area achieved with NVP-loaded poly (lactic-co-glycolic acid (PLGA) membranes were significantly higher compared to unloaded membranes. Taken together, our results suggest that NVP sensitizes BMP2-dependent pathways, enhances BMP2 effect, and inhibits osteoclast differentiation. Thus, NVP could prove useful as "osteopromotive substance" in situations where a high rate of bone regeneration is required, and in the management of bone diseases associated with excessive bone resorption, like osteoporosis.