Structure-activity relationship (SAR) optimization of 6-(indol-2-yl)pyridine-3-sulfonamides: identification of potent, selective, and orally bioavailable small molecules targeting hepatitis C (HCV) NS4B

Design, synthesis, and biological evaluation of 5-(1H-indol-5-yl)isoxazole-3-carboxylic acids as novel xanthine oxidase inhibitors

Xanthine oxidase (XO) is a key enzyme for the production of uric acid in the human body. XO inhibitors (XOIs) are clinically used for the treatment of hyperuricemia and gout, as they can effectively inhibit the production of uric acid. Previous studies indicated that both indole and isoxazole derivatives have good inhibitory effects against XO. Here, we designed and synthesized a novel series of N-5-(1H-indol-5-yl)isoxazole-3-carboxylic acids according to bioisosteric replacement and hybridization strategies. Among the obtained target compounds, compound 6c showed the best inhibitory activity against XO with an IC50 value of 0.13 μM, which was 22-fold higher than that of the classical antigout drug allopurinol (IC50 = 2.93 μM). Structure-activity relationship analysis indicated that the hydrophobic group on the nitrogen atom of the indole ring is essential for the inhibitory potencies of target compounds against XO. Enzyme kinetic studies proved that compound 6c acted as a mixed-type XOI. Molecular docking studies showed that the target compound 6c could not only retain the key interactions similar to febuxostat at the XO binding site but also generate some new interactions, such as two hydrogen bonds between the oxygen atom of the isoxazole ring and the amino acid residues Ser876 and Thr1010. These results indicated that 5-(1H-indol-5-yl)isoxazole-3-carboxylic acid might be an efficacious scaffold for designing novel XOIs and compound 6c has the potential to be used as a lead for further the development of novel anti-gout candidates.

SNAr or Sulfonylation? Chemoselective Amination of Halo(het)arene Sulfonyl Halides for Synthetic Applications and Ultralarge Compound Library Design

The chemoselectivity of halo(het)arene sulfonyl halide aminations is studied thoroughly under parallel synthesis conditions, and the scope and limitations of the method are established. It is shown that SNAr-reactive sulfonyl halides typically undergo sulfonamide synthesis during the first step; the second amination is also possible provided that the SNAr-active center is sufficiently reactive. On the contrary, sulfonyl fluorides bearing an arylating moiety undergo selective transformation at the latter reactive center under proper control. Further sulfur-fluoride exchange (SuFEx) is also possible, which can be especially valuable for some sulfonyl halide classes. The developed two-step parallel double amination protocol provides access to a 6.67-billion compound synthetically tractable REAL-type chemical space (76% expected synthesis success rate).

Development of Azaindole-Based Frameworks as Potential Antiviral Agents and Their Future Perspectives

The azaindole (AI) framework continues to play a significant role in the design of new antiviral agents. Modulating the position and isosteric replacement of the nitrogen atom of AI analogs notably influences the intrinsic physicochemical properties of lead compounds. The intra- and intermolecular interactions of AI derivatives with host receptors or viral proteins can also be fine tuned by carefully placing the nitrogen atom in the heterocyclic core. This wide-ranging perspective article focuses on AIs that have considerable utility in drug discovery programs against RNA viruses. The inhibition of influenza A, human immunodeficiency, respiratory syncytial, neurotropic alpha, dengue, ebola, and hepatitis C viruses by AI analogs is extensively reviewed to assess their plausible future potential in antiviral drug discovery. The binding interaction of AIs with the target protein is examined to derive a structural basis for designing new antiviral agents.

Potential of Marine Terpenoids against SARS-CoV-2: An In Silico Drug Development Approach

In an emergency, drug repurposing is the best alternative option against newly emerged severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection. However, several bioactive natural products have shown potential against SARS-CoV-2 in recent studies. The present study selected sixty-eight broad-spectrum antiviral marine terpenoids and performed molecular docking against two novel SARS-CoV-2 enzymes (main protease or M^pro or 3CL^pro) and RNA-dependent RNA polymerase (RdRp). In addition, the present study analysed the physiochemical-toxicity-pharmacokinetic profile, structural activity relationship, and phylogenetic tree with various computational tools to select the 'lead' candidate. The genomic diversity study with multiple sequence analyses and phylogenetic tree confirmed that the newly emerged SARS-CoV-2 strain was up to 96% structurally similar to existing CoV-strains. Furthermore, the anti-SARS-CoV-2 potency based on a protein-ligand docking score (kcal/mol) exposed that the marine terpenoid brevione F (-8.4) and stachyflin (-8.4) exhibited similar activity with the reference antiviral drugs lopinavir (-8.4) and darunavir (-7.5) against the target SARS-CoV-M^pro. Similarly, marine terpenoids such as xiamycin (-9.3), thyrsiferol (-9.2), liouvilloside B (-8.9), liouvilloside A (-8.8), and stachyflin (-8.7) exhibited comparatively higher docking scores than the referral drug remdesivir (-7.4), and favipiravir (-5.7) against the target SARS-CoV-2-RdRp. The above in silico investigations concluded that stachyflin is the most 'lead' candidate with the most potential against SARS-CoV-2. Previously, stachyflin also exhibited potential activity against HSV-1 and CoV-A59 within IC₅₀, 0.16-0.82 µM. Therefore, some additional pharmacological studies are needed to develop 'stachyflin' as a drug against SARS-CoV-2.

Modulating Twisted Amide Geometry and Reactivity Through Remote Substituent Effects

The unusual reactivity of twisted amides has long been associated with the degree of amide distortion, though classical bridged bicyclic amides offer limited methods to further modify these parameters. Here, we report that the geometry and reactivity of a single twisted amide scaffold can be significantly modulated through remote substituent effects. Guided by calculated ground state geometries, a library of twisted amide derivatives was efficiently prepared through a divergent synthetic strategy. Kinetic and mechanistic investigations of these amides in the alkylation/halide-rebound ring-opening reaction with alkyl halides show a strong positive correlation between the electron donating ability of the substituent and distortion of the amide bond, leading to rates of nucleophilic substitution spanning nearly 2 orders of magnitude. The rate limiting step of the cascade sequence is found to be dependent on the nature of the substituent, and additional studies highlight the role of solvent polarity and halide ion on reaction pathway and efficiency.

Mn(III)-Mediated Radical Cyclization of o-Alkenyl Aromatic Isocyanides with Boronic Acids: Access to N-Unprotected 2-Aryl-3-cyanoindoles

The synthesis of N-unprotected 2-aryl-3-cyanoindoles was realized via the Mn(III)-mediated radical cascade cyclization of o-alkenyl aromatic isocyanides with boronic acids. A possible mechanism involving a sequential intermolecular radical addition, intramolecular cyclization, and cleavage of the C-C bond under mild reaction conditions is proposed. Mechanism studies show that H₂O or O₂ might provide the oxygen source for the elimination of benzaldehyde.

Discovery of potent Covid-19 main protease inhibitors using integrated drug-repurposing strategy

The emergence and rapid spreading of novel SARS-CoV-2 across the globe represent an imminent threat to public health. Novel antiviral therapies are urgently needed to overcome this pandemic. Given the significant role of the main protease of Covid-19 for virus replication, we performed a drug-repurposing study using the recently deposited main protease structure, 6LU7. For instance, pharmacophore- and e-pharmacophore-based hypotheses such as AARRH and AARR, respectively, were developed using available small molecule inhibitors and utilized in the screening of the DrugBank repository. Further, a hierarchical docking protocol was implemented with the support of the Glide algorithm. The resultant compounds were then examined for their binding free energy against the main protease of Covid-19 by means of the Prime-MM/GBSA algorithm. Most importantly, the machine learning-based AutoQSAR algorithm was used to predict the antiviral activities of resultant compounds. The hit molecules were also examined for their drug-likeness and toxicity parameters through the QikProp algorithm. Finally, the hit compounds activity against the main protease was validated using molecular dynamics simulation studies. Overall, the present analysis yielded two potential inhibitors (DB02986 and DB08573) that are predicted to bind with the main protease of Covid-19 better than currently used drug molecules such as N3 (cocrystallized native ligand), lopinavir, and ritonavir.

In silico design and analysis of NS4B inhibitors against hepatitis C virus

The hepatitis C virus is a communicable disease that gradually harms the liver leading to cirrhosis and hepatocellular carcinoma. Important therapeutic interventions have been reached since the discovery of the disease. However, its resurgence urges the need for new approaches against this malady. The NS4B receptor is one of the important proteins for Hepatitis C Virus RNA replication that acts by mediating different viral properties. In this work, we opt to explore the relationships between the molecular structures of biologically tested NS4B inhibitors and their corresponding inhibitory activities to assist the design of novel and potent NS4B inhibitors. For that, a set of 115 indol-2-ylpyridine-3-sulfonamides (IPSA) compounds with inhibitory activity against NS4B is used. A hybrid genetic algorithm combined with multiple linear regressions (GA-MLR) was implemented to construct a predictive model. This model was further used and applied to a set of compounds that were generated based on a pharmacophore modeling study combined with virtual screening to identify structurally similar lead compounds. Multiple filtrations were implemented for selecting potent hits. The selected hits exhibited advantageous molecular features, allowing for favorable inhibitory activity against HCV. The results showed that 7 out of 1285 screened compounds, were selected as potent candidate hits where Zinc14822482 exhibits the best predicted potency and pharmacophore features. The predictive pharmacokinetic analysis further justified the compounds as potential hit molecules, prompting their recommendation for a confirmatory biological evaluation. We believe that our strategy could help in the design and screening of potential inhibitors in drug discovery.Communicated by Ramaswamy H. Sarma.

Efficient construction of diverse 3-cyanoindoles under novel tandem catalysis

A novel and rapid construction of 3-cyanoindoles by palladium-catalyzed tandem reactions has been developed. "N-H" free unprotected, N-alkyl and N-aryl 3-cyanoindoles are obtained with good to excellent yields. The usefulness of this synthetic approach is further demonstrated by the successful synthesis of practical compounds such as the therapeutic estrogen receptor ligand A precursor. Mechanism study shows that the tandem catalysis exploits a Suzuki cross-coupling with subsequent base-induced isoxazole fragmentation, followed by the aldimine condensation.

Metabolic and Pharmaceutical Aspects of Fluorinated Compounds

The applications of fluorine in drug design continue to expand, facilitated by an improved understanding of its effects on physicochemical properties and the development of synthetic methodologies that are providing access to new fluorinated motifs. In turn, studies of fluorinated molecules are providing deeper insights into the effects of fluorine on metabolic pathways, distribution, and disposition. Despite the high strength of the C-F bond, the departure of fluoride from metabolic intermediates can be facile. This reactivity has been leveraged in the design of mechanism-based enzyme inhibitors and has influenced the metabolic fate of fluorinated compounds. In this Perspective, we summarize the literature associated with the metabolism of fluorinated molecules, focusing on examples where the presence of fluorine influences the metabolic profile. These studies have revealed potentially problematic outcomes with some fluorinated motifs and are enhancing our understanding of how fluorine should be deployed.

Efficient Synthesis and Docking Studies of Novel Benzothiazole-Based Pyrimidinesulfonamide Scaffolds as New Antiviral Agents and Hsp90α Inhibitors

A series of novel substituted 2-pyrimidylbenzothiazoles incorporating either sulfonamide moieties or the amino group at C2 of the pyrimidine ring were synthesized and evaluated for its antiviral potency. The novel synthesis of the ring system was carried out by reacting guanidine or N-arylsulfonated guanidine with different derivatives of ylidene benzothiazole based on Michael addition pathways. The antiviral activity of the newly synthesized compounds was examined by a plaque reduction assay against HSV-1, CBV4, HAV HM 175, HCVcc genotype 4 viruses, and HAdV7. In the case of HSV-1, it was determined that 5 out of the 21 synthesized compounds exhibited superior viral reduction in the range of 70-90% with significant IC₅₀, CC₅₀, and SI values as compared with acyclovir. In the case of CBV4, nine compounds have shown more than 50% reduction. Comparable results were obtained for seven of these synthesized compounds when evaluated against HAV with only a couple of them showing 50% reduction or more against HCVcc genotype 4. Remarkably, one compound, 9a, has shown broad action against all five examined viruses, rendering it as potentially an effective antiviral agent. The five potent compounds 9a, 9b, 14b, 14g, and 14h against HSV-1 have also presented inhibitory activity against the Hsp90α protein with IC₅₀ in the range of 4.87-10.47 μg/mL. Interestingly, a combination of the potent synthesized compounds with acyclovir led to IC₅₀ values lower than that of acyclovir alone. The potent compounds 9a, 9b, 14b, 14g, and 14h were also docked inside the active site of Hsp90α to assess the interaction pattern between the tested compounds and the active site of the protein.

Pharmaceutical and medicinal significance of sulfur (SVI)-Containing motifs for drug discovery: A critical review

Sulfur (S^VI) based moieties, especially, the sulfonyl or sulfonamide based analogues have showed a variety of pharmacological properties, and its derivatives propose a high degree of structural diversity that has established useful for the finding of new therapeutic agents. The developments of new less toxic, low cost and highly active sulfonamides containing analogues are hot research topics in medicinal chemistry. Currently, more than 150 FDA approved Sulfur (S^VI)-based drugs are available in the market, and they are widely used to treat various types of diseases with therapeutic power. This comprehensive review highlights the recent developments of sulfonyl or sulfonamides based compounds in huge range of therapeutic applications such as antimicrobial, anti-inflammatory, antiviral, anticonvulsant, antitubercular, antidiabetic, antileishmanial, carbonic anhydrase, antimalarial, anticancer and other medicinal agents. We believe that, this review article is useful to inspire new ideas for structural design and developments of less toxic and powerful Sulfur (S^VI) based drugs against the numerous death-causing diseases.

Synthesis and Biological Evaluation of Novel Indole-Derived Thioureas

A series of 2-(1H-indol-3-yl)ethylthiourea derivatives were prepared by condensation of 2-(1H-indol-3-yl)ethanamine with appropriate aryl/alkylisothiocyanates in anhydrous media. The structures of the newly synthesized compounds were confirmed by spectroscopic analysis and the molecular structures of 8 and 28 were confirmed by X-ray crystallography. All obtained compounds were tested for antimicrobial activity against Gram-positive cocci, Gram-negative rods and for antifungal activity. Microbiological evaluation was carried out over 20 standard strains and 30 hospital strains. Compound 6 showed significant inhibition against Gram-positive cocci and had inhibitory effect on the S. aureus topoisomerase IV decatenation activity and S. aureus DNA gyrase supercoiling activity. Compounds were tested for cytotoxicity and antiviral activity against a large panel of DNA and RNA viruses, including HIV-1 and other several important human pathogens. Interestingly, derivative 8 showed potent activity against HIV-1 wild type and variants bearing clinically relevant mutations. Newly synthesized tryptamine derivatives showed also a wide spectrum activity, proving to be active against positive- and negative-sense RNA viruses.

Sustainable Syntheses of (-)-Jerantinines A & E and Structural Characterisation of the Jerantinine-Tubulin Complex at the Colchicine Binding Site

The jerantinine family of Aspidosperma indole alkaloids from Tabernaemontana corymbosa are potent microtubule-targeting agents with broad spectrum anticancer activity. The natural supply of these precious metabolites has been significantly disrupted due to the inclusion of T. corymbosa on the endangered list of threatened species by the International Union for Conservation of Nature. This report describes the asymmetric syntheses of (-)-jerantinines A and E from sustainably sourced (-)-tabersonine, using a straight-forward and robust biomimetic approach. Biological investigations of synthetic (-)-jerantinine A, along with molecular modelling and X-ray crystallography studies of the tubulin-(-)-jerantinine B acetate complex, advocate an anticancer mode of action of the jerantinines operating via microtubule disruption resulting from binding at the colchicine site. This work lays the foundation for accessing useful quantities of enantiomerically pure jerantinine alkaloids for future development.

Fluorine and Fluorinated Motifs in the Design and Application of Bioisosteres for Drug Design

The electronic properties and relatively small size of fluorine endow it with considerable versatility as a bioisostere and it has found application as a substitute for lone pairs of electrons, the hydrogen atom, and the methyl group while also acting as a functional mimetic of the carbonyl, carbinol, and nitrile moieties. In this context, fluorine substitution can influence the potency, conformation, metabolism, membrane permeability, and P-gp recognition of a molecule and temper inhibition of the hERG channel by basic amines. However, as a consequence of the unique properties of fluorine, it features prominently in the design of higher order structural metaphors that are more esoteric in their conception and which reflect a more sophisticated molecular construction that broadens biological mimesis. In this Perspective, applications of fluorine in the construction of bioisosteric elements designed to enhance the in vitro and in vivo properties of a molecule are summarized.

From machine learning to deep learning: progress in machine intelligence for rational drug discovery

Machine intelligence, which is normally presented as artificial intelligence, refers to the intelligence exhibited by computers. In the history of rational drug discovery, various machine intelligence approaches have been applied to guide traditional experiments, which are expensive and time-consuming. Over the past several decades, machine-learning tools, such as quantitative structure-activity relationship (QSAR) modeling, were developed that can identify potential biological active molecules from millions of candidate compounds quickly and cheaply. However, when drug discovery moved into the era of 'big' data, machine learning approaches evolved into deep learning approaches, which are a more powerful and efficient way to deal with the massive amounts of data generated from modern drug discovery approaches. Here, we summarize the history of machine learning and provide insight into recently developed deep learning approaches and their applications in rational drug discovery. We suggest that this evolution of machine intelligence now provides a guide for early-stage drug design and discovery in the current big data era.

Chemical genetics-based development of small molecules targeting hepatitis C virus

Hepatitis C virus (HCV) infection is a major worldwide problem that has emerged as one of the most significant diseases affecting humans. There are currently no vaccines or efficient therapies without side effects, despite today's advanced medical technology. Currently, the common therapy for most patients (i.e. genotype 1) is combination of HCV-specific direct-acting antivirals (DAAs). Up to 2011, the standard of care (SOC) was a combination of peg-IFNα with ribavirin (RBV). After approval of NS3/4A protease inhibitor, SOC was peg-IFNα and RBV with either the first-generation DAAs boceprevir or telaprevir. In the past several years, various novel small molecules have been discovered and some of them (i.e., HCV polymerase, protease, helicase and entry inhibitors) have undergone clinical trials. Between 2013 and 2016, the second-generation DAA drugs simeprevir, asunaprevir, daclatasvir, dasabuvir, sofosbuvir, and elbasvir were approved, as well as the combinational drugs Harvoni^®, Zepatier^®, Technivie^®, and Epclusa^®. A number of reviews have been recently published describing the structure-activity relationship (SAR) in the development of HCV inhibitors and outlining current therapeutic approaches to hepatitis C infection. Target identification involves studying a drug's mechanism of action (MOA), and a variety of target identification methods have been developed in the past few years. Chemical biology has emerged as a powerful tool for studying biological processes using small molecules. The use of chemical genetic methods is a valuable strategy for studying the molecular mechanisms of the viral lifecycle and screening for anti-viral agents. Two general screening approaches have been employed: forward and reverse chemical genetics. This review reveals information on the small molecules in HCV drug discovery by using chemical genetics for targeting the HCV protein and describes successful examples of targets identified with these methods.

Current therapy for chronic hepatitis C: The role of direct-acting antivirals

One of the most exciting developments in antiviral research has been the discovery of the direct-acting antivirals (DAAs) that effectively cure chronic hepatitis C virus (HCV) infections. Based on more than 100 clinical trials and real-world studies, we provide a comprehensive overview of FDA-approved therapies and newly discovered anti-HCV agents with a special focus on drug efficacy, mechanisms of action, and safety. We show that HCV drug development has advanced in multiple aspects: (i) interferon-based regimens were replaced by interferon-free regimens; (ii) genotype-specific drugs evolved to drugs for all HCV genotypes; (iii) therapies based upon multiple pills per day were simplified to a single pill per day; (iv) drug potency increased from moderate (∼60%) to high (>90%) levels of sustained virologic responses; (v) treatment durations were shortened from 48 to 12 or 8 weeks; and (vi) therapies could be administered orally regardless of prior treatment history and cirrhotic status. However, despite these remarkable achievements made in HCV drug discovery, challenges remain in the management of difficult-to-treat patients.

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HCV genotype-specific drugs evolve to pan-genotypic drugs.

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Drug potency increases from moderate (∼60%) to high (>90%) levels of sustained virologic response.

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Treatment durations are shortened from a 48-week to 12-week or 8-week period.

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HCV therapies based upon multiple pills per day are simplified to a single pill per day.

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HCV therapies are administered orally regardless of prior treatment history and cirrhotic status.

Discovery of 2-(4-sulfonamidophenyl)-indole 3-carboxamides as potent and selective inhibitors with broad hepatitis C virus genotype activity targeting HCV NS4B

A novel series of 2-(4-sulfonamidophenyl)-indole 3-carboxamides was identified and optimized for activity against the HCV genotype 1b replicon resulting in compounds with potent and selective activity. Further evaluation of this series demonstrated potent activity across HCV genotypes 1a, 2a and 3a. Compound 4z had reduced activity against HCV genotype 1b replicons containing single mutations in the NS4B coding sequence (F98C and V105M) indicating that NS4B is the target. This novel series of 2-(4-sulfonamidophenyl)-indole 3-carboxamides serves as a promising starting point for a pan-genotype HCV discovery program.

A Journey around the Medicinal Chemistry of Hepatitis C Virus Inhibitors Targeting NS4B: From Target to Preclinical Drug Candidates

Hepatitis C virus (HCV) infection is a global health burden with an estimated 130-170 million chronically infected individuals and is the cause of serious liver diseases such as cirrhosis and hepatocellular carcinoma. HCV NS4B protein represents a validated target for the identification of new drugs to be added to the combination regimen recently approved. During the last years, NS4B has thus been the object of impressive medicinal chemistry efforts, which led to the identification of promising preclinical candidates. In this context, the present review aims to discuss research published on NS4B functional inhibitors focusing the attention on hit identification, hit-to-lead optimization, ADME profile evaluation, and the structure-activity relationship data raised for each compound family taken into account. The information delivered in this review will be a useful and valuable tool for those medicinal chemists dealing with research programs focused on NS4B and aimed at the identification of innovative anti-HCV compounds.

Preclinical Characterization and In Vivo Efficacy of GSK8853, a Small-Molecule Inhibitor of the Hepatitis C Virus NS4B Protein

The hepatitis C virus (HCV) NS4B protein is an antiviral therapeutic target for which small-molecule inhibitors have not been shown to exhibit in vivo efficacy. We describe here the in vitro and in vivo antiviral activity of GSK8853, an imidazo[1,2-a]pyrimidine inhibitor that binds NS4B protein. GSK8853 was active against multiple HCV genotypes and developed in vitro resistance mutations in both genotype 1a and genotype 1b replicons localized to the region of NS4B encoding amino acids 94 to 105. A 20-day in vitro treatment of replicons with GSK8853 resulted in a 2-log drop in replicon RNA levels, with no resistance mutation breakthrough. Chimeric replicons containing NS4B sequences matching known virus isolates showed similar responses to a compound with genotype 1a sequences but altered efficacy with genotype 1b sequences, likely corresponding to the presence of known resistance polymorphs in those isolates. In vivo efficacy was tested in a humanized-mouse model of HCV infection, and the results showed a 3-log drop in viral RNA loads over a 7-day period. Analysis of the virus remaining at the end of in vivo treatment revealed resistance mutations encoding amino acid changes that had not been identified by in vitro studies, including NS4B N56I and N99H. Our findings provide an in vivo proof of concept for HCV inhibitors targeting NS4B and demonstrate both the promise and potential pitfalls of developing NS4B inhibitors.

Discovery of imidazo[2,1-b]thiazole HCV NS4B inhibitors exhibiting synergistic effect with other direct-acting antiviral agents

The design, synthesis, and SAR studies of novel inhibitors of HCV NS4B based on the imidazo[2,1-b]thiazole scaffold were described. Optimization of potency with respect to genotype 1b resulted in the discovery of two potent leads 26f (EC50 = 16 nM) and 28g (EC50 = 31 nM). The resistance profile studies revealed that 26f and 28g targeted HCV NS4B, more precisely the second amphipathic α helix of NS4B (4BAH2). Cross-resistance between our 4BAH2 inhibitors and other direct-acting antiviral agents targeting NS3/4A, NS5A, and NS5B was not observed. For the first time, the synergism of a series of combinations based on 4BAH2 inhibitors was evaluated. The results demonstrated that our 4BAH2 inhibitor 26f was synergistic with NS3/4A inhibitor simeprevir, NS5A inhibitor daclatasvir, and NS5B inhibitor sofosbuvir, and it could also reduce the dose of these drugs at almost all effect levels. Our study suggested that favorable effects could be achieved by combining 4BAH2 inhibitors such as 26f with these approved drugs and that new all-oral antiviral combinations based on 4BAH2 inhibitors were worth developing to supplement or even replace current treatment regimens for curing HCV infection.

6-(Azaindol-2-yl)pyridine-3-sulfonamides as potent and selective inhibitors targeting hepatitis C virus NS4B

A structure-activity relationship investigation of various 6-(azaindol-2-yl)pyridine-3-sulfonamides using the HCV replicon cell culture assay led to the identification of a potent series of 7-azaindoles that target the hepatitis C virus NS4B. Compound 2ac, identified via further optimization of the series, has excellent potency against the HCV 1b replicon with an EC50 of 2nM and a selectivity index of >5000 with respect to cellular GAPDH RNA. Compound 2ac also has excellent oral plasma exposure levels in rats, dogs and monkeys and has a favorable liver to plasma distribution profile in rats.

Fluorine in medicinal chemistry

Since its first use in the steroid field in the late 1950s, the use of fluorine in medicinal chemistry has become commonplace, with the small electronegative fluorine atom being a key part of the medicinal chemist's repertoire of substitutions used to modulate all aspects of molecular properties including potency, physical chemistry and pharmacokinetics. This review will highlight the special nature of fluorine, drawing from a survey of marketed fluorinated pharmaceuticals and the medicinal chemistry literature, to illustrate key concepts exploited by medicinal chemists in their attempts to optimize drug molecules. Some of the potential pitfalls in the use of fluorine will also be highlighted.

Heterocycle-to-Heterocycle Route to Quinoline-4-amines: Reductive Heterocyclization of 3-(2-Nitrophenyl)isoxazoles

A variety of quinoline-4-amines were synthesized from substituted 3-(2-nitrophenyl)isoxazoles utilizing Zn0 or Fe0 dust and HOAc via a reductive heterocyclization process. The starting isoxazoles were synthesized from readily available starting materials. A brief survey of functional groups tolerated in this reductive heterocyclization was performed and several 10-amino-3,4-dihydrobenzo[b][1,6]naphthyridin-1(2H)-one and 9-amino-3,4-dihydroacridin-1(2H)-one examples were synthesized.

C7-derivatization of C3-alkylindoles including tryptophans and tryptamines

A versatile strategy for C7-selective boronation of tryptophans, tryptamines, and 3-alkylindoles by way of a single-pot C2/C7-diboronation-C2-protodeboronation sequence is described. The combination of a mild iridium-catalyzed C2/C7-diboronation followed by an in situ palladium-catalyzed C2-protodeboronation allows efficient entry to valuable C7-boroindoles that enable further C7-derivatization. The versatility of the chemistry is highlighted by the gram-scale synthesis of C7-boronated N-Boc-L-tryptophan methyl ester and the rapid synthesis of C7-halo, C7-hydroxy, and C7-aryl tryptophan derivatives.

Highly potent HCV NS4B inhibitors with activity against multiple genotypes

The exploration of novel inhibitors of the HCV NS4B protein that are based on a 2-oxadiazoloquinoline scaffold is described. Optimization to incorporate activity across genotypes led to a potent new series with broad activity, of which inhibitor 1 displayed the following EC50 values: 1a, 0.08 nM; 1b, 0.10 nM; 2a, 3 nM; 2b, 0.6 nM, 3a, 3.7 nM; 4a, 0.9 nM; 6a, 3.1 nM.