Hydroxamic Acids Block Replication of Hepatitis C Virus

Base-mediated [3 + 2]-cycloannulation strategy for the synthesis of pyrazolo[1,5-a]pyridine derivatives using (E)-β-iodovinyl sulfones

Pyrazolo[1,5-a]pyridines continue to occupy a special place in medicinal chemistry, but the direct construction of 3-sulfonyl analogues remains unexplored. Under basic conditions, pyridinium-N-amine and the corresponding dipolar aminide played a vibrant role in [3 + 2]-cycloaddition using (E)-β-iodovinyl sulfones. K₂CO₃-mediated tandem cycloannulative-desulfonylation of (E)-β-iodovinyl sulfones with 1-aminopyridinium iodide is realized to access 2-substituted pyrazolo[1,5-a]pyridines in good to high yields. An essential modification of the dipolar N-tosylpyridinium imide allows the first preparative synthesis of 3-sulfonyl-pyrazolo[1,5-a]pyridines in moderate to high yields. Of note, the metal-free protocol features a broad substrate scope with good functional group tolerance and compatibility. The efficacy of the process was proved with gram-scale reactions, and a plausible mechanism is also presented based on concrete results.

Palladium-catalyzed radical cascade cyanoalkylsulfonylation/cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with cyclobutanone oxime esters and DABSO

A palladium-catalyzed radical cascade cyanoalkylsulfonylation/cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with DABCO·(SO₂)₂ and cyclobutanone oxime esters via cleavage of a C-C single bond and insertion of SO₂ was described. A series of cyanoalkylsulfone-containing cyclopenta[gh]phenanthridines were obtained in moderate-to-good yields, thus featuring mild reaction conditions, a broad substrate scope, and a high functional group tolerance.

Mild Copper-Catalyzed, l-Proline-Promoted Cross-Coupling of Methyl 3-Amino-1-benzothiophene-2-carboxylate

Cu-catalyzed N-arylation is a useful tool for the chemical modification of aromatic heterocycles. Herein, an efficient carbon–nitrogen cross-coupling of methyl 3-amino-1-benzothiophene-2-carboxylate with a range of (hetero)aryl iodides using CuI, l-proline and Cs₂CO₃ in dioxane at moderate temperature is described. The procedure is an extremely general, relatively cheap, and experimentally simple way to afford the N-substituted products in moderate to high yields. The structures of the new heterocyclic compounds were confirmed by NMR spectroscopy and HRMS investigation.

Strategies To Design Selective Histone Deacetylase Inhibitors

This review classifies drug-design strategies successfully implemented in the development of histone deacetylase (HDAC) inhibitors, which have many applications including cancer treatment. Our focus is on especially demanded selective HDAC inhibitors and their structure-activity relationships in relation to corresponding protein structures. The main part of the paper is divided into six subsections each narrating how optimization of one of six structural features can influence inhibitor selectivity. It starts with the impact of the zinc binding group on selectivity, continues with the optimization of the linker placed in the substrate binding tunnel as well as the adjustment of the cap group interacting with the surface of the protein, and ends with the addition of groups targeting class-specific sub-pockets: the side-pocket-, lower-pocket- and foot-pocket-targeting groups. The review is rounded off with a conclusion and an outlook on the future of HDAC inhibitor design.

Copper(II)-Catalyzed Direct C-H (Hetero)arylation at the C3 Position of Indoles Assisted by a Removable N,N-Bidentate Auxiliary Moiety

The regioselective arylation of inert C3-H bonds in indoles reacting with arylboronates via effective copper-mediated catalysis with the aid of a facile and removable 2-pyridinylisopropyl (PIP) group without ligand participation is reported. This newly established method features high compatibility with diverse functional groups between coupling partners, including both indole substrates and arylboron reagents, consequentially leading to operational simplicity and providing access to generate the desired arylated products in good to excellent yields of up to 97%. Synthetically, the PIP-derived amide moiety could subsequently be readily removed under mild reaction conditions to produce useful indole carboxylic acids for further transformation.

Pharmacoinformatic Investigation of Medicinal Plants from East Africa

Medicinal plants have widely been used in the traditional treatment of ailments and have been proven effective. Their contribution still holds an important place in modern drug discovery due to their chemical, and biological diversities. However, the poor documentation of traditional medicine, in developing African countries for instance, can lead to the loss of knowledge related to such practices. In this study, we present the Eastern Africa Natural Products Database (EANPDB) containing the structural and bioactivity information of 1870 unique molecules isolated from about 300 source species from the Eastern African region. This represents the largest collection of natural products (NPs) from this geographical region, covering literature data of the period from 1962 to 2019. The computed physicochemical properties and toxicity profiles of each compound have been included. A comparative analysis of some physico-chemical properties like molecular weight, H-bond donor/acceptor, logPo/w , etc. as well scaffold diversity analysis has been carried out with other published NP databases. EANPDB was combined with the previously published Northern African Natural Products Database (NANPDB), to form a merger African Natural Products Database (ANPDB), containing ∼6500 unique molecules isolated from about 1000 source species (freely available at http://african-compounds.org). As a case study, latrunculins A and B isolated from the sponge Negombata magnifica (Podospongiidae) with previously reported antitumour activities, were identified via substructure searching as molecules to be explored as putative binders of histone deacetylases (HDACs).

Diisobutylaluminum Hydride Promoted Selectivity-Switchable Synthesis of Benzothiophene Oxides and Benzothiophenes via an Al-Li-Dimetalated Intermediate

We developed an efficient and direct method for synthesis of benzothiophene oxides from 1-bromo-2-[2-(trimethylsilyl)ethynyl]benzenes and thionyl chloride as an easily accessible source of the sulfinyl group. Benzothiophenes were also synthesized selectively by simply increasing the amount of thionyl chloride. These methods achieved efficient syntheses of various benzothiophene oxides and benzothiophenes. The further modification of the benzothiophene oxides obtained was also demonstrated.

TBPB-initiated cascade cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with sulfinic acids: access to sulfone-containing cyclopenta[gh]phenanthridines

A novel TBPB-initiated cascade cyclization of 3-arylethynyl-[1,1'-biphenyl]-2-carbonitriles with sulfinic acids via C-S, C-C and C-N bond formation for the synthesis of 3-sulfonated cyclopenta[gh]phenanthridines under metal-free conditions has been developed. This protocol features mild conditions, good functional group tolerance and a broad substrate scope. By using this protocol, a variety of potentially bioactive 3-sulfonated cyclopenta[gh]phenanthridines were facilely synthesized via direct annulation.

Targeting histone epigenetics to control viral infections

During the past decades, many studies have significantly broadened our understanding of complex virus-host interactions to control chromatin structure and dynamics.1, 2 However, the role and impact of such modifications during viral infections is not fully revealed. Indeed, this type of regulation is bidirectional between the virus and the host. While viral replication and gene expression are significantly impacted by histone modifications on the viral chromatin,³ studies have shown that some viral pathogens dynamically manipulate cellular epigenetic factors to enhance their own survival and pathogenesis, as well as escape the immune system defense lines.⁴ In this dynamic, histone posttranslational modifications (PTMs) appear to play fundamental roles in the regulation of chromatin structure and recruitment of other factors.⁵ Genuinely, those PTMs play a vital role in lytic infection, latency reinforcement, or, conversely, viral reactivation.⁶ In this chapter, we will examine and review the involvement of histone modifications as well as their potential manipulation to control infections during various viral life cycle stages, highlighting their prospective implications in the clinical management of human immunodeficiency virus (HIV), herpes simplex virus (HSV), human cytomegalovirus (HCMV), hepatitis B and C viruses (HBV and HCV, respectively), Epstein–Barr virus (EBV), and other viral diseases. Targeting histone modifications is critical in setting the treatment of chronic viral infections with both lytic and latent stages (HIV, HCMV, HSV, RSV), virus-induced cancers (HBV, HCV, EBV, KSHV, HPV), and epidemic/emerging viruses (e.g. influenza virus, arboviruses).

Chiral Bicyclic NHC/Cu Complexes for Catalytic Asymmetric Borylation of α,β-Unsaturated Esters

The potential of using chiral bicyclic NHC ligands that exhibit modularity was investigated in the Cu-catalyzed asymmetric borylation reaction of α,β-unsaturated esters. After screening for ligands and optimization of the reaction conditions, the corresponding products were afforded with good enantioselectivities (up to 85% ee).

Structural isomers of cinnamic hydroxamic acids block HCV replication via different mechanisms

A set of ortho-, meta- and para-substituted cinnamic hydroxamic acids (CHAs) was synthesized. In each series of structural isomers, a phenyl substituent was linked to an aromatic ring of the parent cinnamic acid via a linker of one to four atoms in length. Using a cell test system with the full-length replicon of hepatitis C virus (HCV), we established a relationship between the suppression of HCV replicon propagation and the inhibition of class I/IIb histone deacetylases (HDACs). Anti-HCV activity correlated with the inhibition of HDAC8 in the case of ortho-CHAs, while in the case of meta-CHAs it correlated with the inhibition of HDAC1/2/3 and HDAC6. The antiviral activity of para-CHAs was many times stronger than that of meta-CHAs with about the same efficiency of HDAC1/2/3/6 inhibition, which indicated the existence of an additional cell target that does not belong to the studied group of HDACs.

Synthesis of N'-propylhydrazide analogs of hydroxamic inhibitors of histone deacetylases (HDACs) and evaluation of their impact on activities of HDACs and replication of hepatitis C virus (HCV)

N'-Propylhydrazide analogs of hydroxamic inhibitors of histone deacetylases (HDACs), including tubastatin A, vorinostat and belinostat, were synthesized. All prepared compounds inhibited HDAC1/2/3, but not HDAC6, except for one hydrazide analog of HDAC4/5/7 inhibitor that was completely inactive. A novel 4-substituted derivative of N'-propylbenzohydrazide with extremely high anti-HCV activity was discovered.

Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Suppresses Human Adenovirus Gene Expression and Replication

Human adenovirus (HAdV) causes minor illnesses in most patients but can lead to severe disease and death in pediatric, geriatric, and immunocompromised individuals. No approved antiviral therapy currently exists for the treatment of these severe HAdV-induced diseases. In this study, we show that the pan-histone deacetylase (HDAC) inhibitor SAHA reduces HAdV-5 gene expression and DNA replication in tissue culture, ultimately decreasing virus yield from infected cells. Importantly, SAHA also reduced gene expression from more virulent and clinically relevant serotypes, including HAdV-4 and HAdV-7. In addition to SAHA, several other HDAC inhibitors (e.g., trichostatin A, apicidin, and panobinostat) also affected HAdV gene expression. We determined that loss of class I HDAC activity, mainly HDAC2, impairs efficient expression of viral genes, and that E1A physically interacts with HDAC2. Our results suggest that HDAC activity is necessary for HAdV replication, which may represent a novel pharmacological target in HAdV-induced disease.IMPORTANCE Although human adenovirus (HAdV) can cause severe diseases that can be fatal in some populations, there are no effective treatments to combat HAdV infection. In this study, we determined that the pan-histone deacetylase (HDAC) inhibitor SAHA has inhibitory activity against several clinically relevant serotypes of HAdV. This U.S. Food and Drug Administration-approved compound affects various stages of the virus lifecycle and reduces virus yield even at low concentrations. We further report that class I HDAC activity, particularly HDAC2, is required for efficient expression of viral genes during lytic infection. Investigation of the mechanism underlying SAHA-mediated suppression of HAdV gene expression and replication will enhance current knowledge of virus-cell interaction and may aid in the development of more effective antivirals with lower toxicity for the treatment of HAdV infections.

Histone Deacetylase 3 Inhibitor Suppresses Hepatitis C Virus Replication by Regulating Apo-A1 and LEAP-1 Expression

Histone deacetylase (HDAC) inhibitors show clinical promise for the treatment of cancers, including hepatocellular carcinoma (HCC). In this study, we investigated the effect of HDAC inhibitor treatment on hepatitis C virus (HCV) replication in Huh7 human liver cells and in a mouse model of HCV infection. Viral replication was markedly suppressed by the HDAC3 inhibitor at concentrations below 1 mmol/L, with no cellular toxicity. This was accompanied by upregulation of liver-expressed antimicrobial peptide 1(LEAP-1) and downregulation of apolipoprotein-A1 (Apo-A1), as determined by microarray and quantitative RT-PCR analyses. Moreover, HDAC3 was found to modulate the binding of CCAAT-enhancer-binding protein α (C/EBPα), hypoxia-inducible factor 1α (HIF1α), and signal transducer and activator of transcription 3 (STAT3) to the LEAP-1 promoter. HDAC3 inhibitor treatment also blocked HCV replication in a mouse model of HCV infection. These results indicate that epigenetic therapy with HDAC3 inhibitor may be a potential treatment for diseases associated with HCV infection such as HCC.

Palladium-Catalyzed Intramolecular Oxidative Arylations for the Synthesis of Fused Biaryl Sulfones

This study unveils palladium-catalyzed intramolecular oxidative cyclizations in biaryl and heterobiaryl sulfones providing direct access to fused biaryl sulfones (dibenzothiophene-5,5-dioxides). Variously substituted dibenzothiophene-5,5-dioxides could be readily prepared in good to excellent yields under optimized conditions. In addition, bromination afforded dibromo derivative of dibenzothiophene-5,5-dioxides, providing platform for late-stage diversification. The translational applications of this current protocol have successfully been demonstrated in the synthesis of 2,8-diamino derivative of dibenzothiophene-5,5-dioxides, a α₇-nicotinic acetylcholine receptor agonist analogue, and novel single fluorene-tethered dibenzothiophene-5,5-dioxide, an organic emitter.

Metal-free C-H thioarylation of arenes using sulfoxides: a direct, general diaryl sulfide synthesis

Metal-free C-H thioarylation of arenes and heteroarenes using methyl sulfoxides constitutes a general protocol for the synthesis of high value diaryl sulfides. The coupling of arenes and heteroarenes with in situ activated sulfoxides is regioselective, uses readily available starting materials, is operationally simple, and tolerates a wide range of functional groups.

Cellular defence or viral assist: the dilemma of HDAC6

Histone deacetylase 6 (HDAC6) is a unique cytoplasmic deacetylase that regulates various important biological processes by preventing protein aggregation and deacetylating different non-histone substrates including tubulin, heat shock protein 90, cortactin, retinoic acid inducible gene I and β-catenin. Growing evidence has indicated a dual role for HDAC6 in viral infection and pathogenesis: HDAC6 may represent a host defence mechanism against viral infection by modulating microtubule acetylation, triggering antiviral immune response and stimulating protective autophagy, or it may be hijacked by the virus to enhance proinflammatory response. In this review, we will highlight current data illustrating the complexity and importance of HDAC6 in viral pathogenesis. We will summarize the structure and functional specificity of HDAC6, and its deacetylase- and ubiquitin-dependent activity in key cellular events in response to virus infection. We will also discuss how HDAC6 exerts its direct or indirect histone modification ability in viral lytic-latency switch.

Palladium-Catalyzed Synthesis of 2,3-Disubstituted Benzothiophenes via the Annulation of Aryl Sulfides with Alkynes

A new method has been developed for the synthesis of 2,3-disubstituted benzothiophenes involving the palladium-catalyzed annulation of aryl sulfides with alkynes. This convergent approach exhibited good functional group tolerance, providing rapid access to a diverse array of derivatives from simple, readily available starting materials. This protocol can also be used to synthesize 2-silyl-substituted benzothiophenes, which can be used as versatile platforms for the synthesis of 2,3-unsymmetrically substituted benzothiophenes.

Design and synthesis of an activity-based protein profiling probe derived from cinnamic hydroxamic acid

In our continued effort to discover new anti-hepatitis C virus (HCV) agents, we validated the anti-replicon activity of compound 1, a potent and selective anti-HCV hydroxamic acid recently reported by us. Generally favorable physicochemical and in vitro absorption, distribution, metabolism, and excretion (ADME) properties exhibited by 1 made it an ideal parent compound from which activity-based protein profiling (ABPP) probe 3 was designed and synthesized. Evaluation of probe 3 revealed that it possessed necessary anti-HCV activity and selectivity. Therefore, we have successfully obtained compound 3 as a suitable ABPP probe to identify potential molecular targets of compound 1. Probe 3 and its improved analogs are expected to join a growing list of ABPP probes that have made important contributions to not only the studies of biochemical and cellular functions but also discovery of selective inhibitors of protein targets.

Synthesis and Biological Investigation of Oxazole Hydroxamates as Highly Selective Histone Deacetylase 6 (HDAC6) Inhibitors

Histone deacetylase 6 (HDAC6) catalyzes the removal of an acetyl group from lysine residues of several non-histone proteins. Here we report the preparation of thiazole-, oxazole-, and oxadiazole-containing biarylhydroxamic acids by a short synthetic procedure. We identified them as selective HDAC6 inhibitors by investigating the inhibition of recombinant HDAC enzymes and the protein acetylation in cells by Western blotting (tubulin vs histone acetylation). The most active compounds exhibited nanomolar potency and high selectivity for HDAC6. For example, an oxazole hydroxamate inhibits HDAC6 with an IC50 of 59 nM and has a selectivity index of >200 against HDAC1 and HDAC8. This is the first report showing that the nature of a heterocycle directly connected to a zinc binding group (ZBG) can be used to modulate subtype selectivity and potency for HDAC6 inhibitors to such an extent. We rationalize the high potency and selectivity of the oxazoles by molecular modeling and docking.