Design, Synthesis, and Biological Evaluation of Substituted 4,6-Dihydrospiro[[1,2,3]triazolo[4,5-b]pyridine-7,3'-indoline]-2',5(3H)-dione Analogues as Potent NS4B Inhibitors for the Treatment of Dengue Virus Infection

Antineoplastic indole-containing compounds with potential VEGFR inhibitory properties

Cancer is one of the most significant health challenges worldwide. Various techniques, tools and therapeutics/materials have been developed in the last few decades for the treatment of cancer, together with great interest, funding and efforts from the scientific society. However, all the reported studies and efforts seem insufficient to combat the various types of cancer, especially the advanced ones. The overexpression of tyrosine kinases is associated with cancer proliferation and/or metastasis. VEGF, an important category of tyrosine kinases, and its receptors (VEGFR) are hyper-activated in different cancers. Accordingly, they are known as important factors in the angiogenesis of different tumors and are considered in the development of effective therapeutic approaches for controlling many types of cancer. In this case, targeted therapeutic approaches are preferable to the traditional non-selective approaches to minimize the side effects and drawbacks associated with treatment. Several indole-containing compounds have been identified as effective agents against VEGFR. Herein, we present a summary of the recent indolyl analogs reported within the last decade (2012-2023) with potential antineoplastic and VEGFR inhibitory properties. The most important drugs, natural products, synthesized potent compounds and promising hits/leads are highlighted. Indoles functionalized and conjugated with various heterocycles beside spiroindoles are also considered.

C3-Spirooxindoles: Divergent chemical synthesis and bioactivities (2018-2023)

This scientific review documents the recent progress of C3-spirooxindoles chemistry (synthesis and reaction mechanism) and their bioactivities, focusing on the promising results as well as highlighting the biological mechanism via the reported molecular docking findings of the most bioactive derivatives. C3-Spirooxindoles are attractive bioactive agents and have been found in a variety of natural compounds, including alkaloids. They are widely investigated in the field of medicinal chemistry and play a key role in medication development, such as antivirals, anticancer agents, antimicrobials, etc. Regarding organic synthesis, several traditional and advanced strategies have been reported, particularly those that started with isatin derivatives.

Therapeutic potential of salicylamide derivatives for combating viral infections

Since time immemorial human beings have constantly been fighting against viral infections. The ongoing and devastating coronavirus disease 2019 pandemic represents one of the most severe and most significant public health emergencies in human history, highlighting an urgent need to develop broad-spectrum antiviral agents. Salicylamide (2-hydroxybenzamide) derivatives, represented by niclosamide and nitazoxanide, inhibit the replication of a broad range of RNA and DNA viruses such as flavivirus, influenza A virus, and coronavirus. Moreover, nitazoxanide was effective in clinical trials against different viral infections including diarrhea caused by rotavirus and norovirus, uncomplicated influenza A and B, hepatitis B, and hepatitis C. In this review, we summarize the broad antiviral activities of salicylamide derivatives, the clinical progress, and the potential targets or mechanisms against different viral infections and highlight their therapeutic potential in combating the circulating and emerging viral infections in the future.

3-[N,N-Bis(sulfonyl)amino]isoxazolines with Spiro-Annulated or 1,2-Annulated Cyclooctane Rings Inhibit Reproduction of Tick-Borne Encephalitis, Yellow Fever, and West Nile Viruses

Spirocyclic compounds containing heterocyclic moieties represent promising 3D scaffolds for modern drug design. In the search for novel anti-flaviviral agents, we have obtained a series of 3-[N,N-bis(sulfonyl)amino]isoxazolines containing spiro-annulated cyclooctane rings and assessed their antiviral activity against tick-borne encephalitis (TBEV), yellow fever (YFV), and West Nile (WNV) viruses. The structural analogs of spirocyclic compounds with a single sulfonyl group or 1,2-annulated cyclooctane ring were also investigated. Almost all the studied 3-[N,N-bis(sulfonyl)amino]isoxazolines revealed antiviral activity against TBEV and WNV. The most active against TBEV was spiro-isoxazoline derivative containing p-nitrophenyl groups in the sulfonyl part (EC₅₀ 2.0 ± 0.5 μM), while the highest potency against WNV was found for the compounds with lipophilic substituents in sulfonyl moiety, naphtyl being the most favorable one (EC₅₀ 1.3 ± 0.5 μM). In summary, two novel scaffolds of anti-flaviviral agents based on N,N-bis(sulfonyl)amino]isoxazoline were proposed, and the compounds of this type demonstrated activity against TBEV and WNV.

Therapeutics for flaviviral infections

Flaviviruses are vector-borne pathogens capable of causing devastating human diseases. The re-emergence of Zika in 2016 notoriously led to a widescale epidemic in the Americas. New daunting evidence suggests that a single mutation in Zika virus genome may increase transmission and pathogenesis, further highlighting the need to be prepared for flavivirus outbreaks. Dengue, in particular infects about 400 million people each year, leading to reoccurring local outbreaks. Public health efforts to mitigate flavivirus transmission is largely dependent on vector control strategies, as only a limited number of flavivirus vaccines have been developed thus far. There are currently no commercially available antivirals for flaviviruses, leaving supportive care as the primary treatment option. In this review, we will briefly paint a broad picture of the flavivirus landscape in terms of therapeutics, with particular focus on viral targets, promising novel compounds entering the drug discovery pipeline, as well as model systems for evaluating drug efficacy.

Spirooxindole: A Versatile Biologically Active Heterocyclic Scaffold

Spirooxindoles occupy an important place in heterocyclic chemistry. Many natural spirooxindole-containing compounds have been identified as bio-promising agents. Synthetic analogs have also been synthesized utilizing different pathways. The present article summarizes the recent development of both natural and synthetic spirooxindole-containing compounds prepared from isatin or its derivatives reported in the last five years. The spirooxindoles are categorized based on their mentioned biological properties.

Efficient construction of diverse spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] via [3 + 3] cycloaddition of MBH carbonates of isatins with β-enamino maleimides

An efficient method to construct unique spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] was successfully developed via a DABCO promoted formal [3 + 3] cycloaddition reaction of MBH carbonates of isatins with β-enamino maleimides in acetonitrile at room temperature. This reaction afforded multifunctionalized spiro[indoline-3,4'-pyrrolo[3,4-b]pyridines] and spiro[dipyrrolo[3,4-b:3',4'-e]pyridine-8,3'-indolines] in good yields and with lower diastereoselectivity. The relative configuration of the two diasteromers of the spiro compounds was clearly elucidated by the determination of eight single crystal structures.

Dengue virus NS4B protein as a target for developing antivirals

Dengue virus is an important pathogen affecting global population while no specific treatment is available against this virus. Effort has been made to develop inhibitors through targeting viral nonstructural proteins such as NS3 and NS5 with enzymatic activities. No potent inhibitors entering clinical studies have been developed so far due to many challenges. The genome of dengue virus encodes four membrane-bound nonstructural proteins which do not possess any enzymatic activities. Studies have shown that the membrane protein-NS4B is a validated target for drug discovery and several NS4B inhibitors exhibited antiviral activities in various assays and entered preclinical studies.. Here, we summarize the recent studies on dengue NS4B protein. The structure and membrane topology of dengue NS4B derived from biochemical and biophysical studies are described. Function of NS4B through protein-protein interactions and some available NS4B inhibitors are summarized. Accumulated studies demonstrated that cell-based assays play important roles in developing NS4B inhibitors. Although the atomic structure of NS4B is not obtained, target-based drug discovery approach become feasible to develop NS4B inhibitors as recombinant NS4B protein is available.

Recent in vivo advances of spirocyclic scaffolds for drug discovery

INTRODUCTION

Spirocyclic scaffolds are an exceptional tool in drug design, allowing fine-tuning of a molecule's conformational and physicochemical properties. As it expands and diversifies, so does the number of therapeutics that contain this core. Several spirocyclic drugs are already marketed, and considerably more have shown promising results.

AREAS COVERED

This review addresses recent in vivo studies (2017-2021) on applying spirocyclic compounds to treat various diseases, mainly grouped within neurological, infectious, and metabolic diseases and cancer. An emphasis is given on the influence of the spiro-structure on activity and consequent structure-activity study. In vivo results and their significance in the future progression towards clinical trials are also presented.

EXPERT OPINION

Spirocyclic compounds present an exciting opportunity as an unexplored chemical space in medicinal chemistry. However, their development is hindered by their complexity and synthesis challenges. Furthermore, a clear preference is still seen for readily available spirocyclic compounds involving amine or amide bonds. Nevertheless, these are temporary as high-throughput synthesis, and computational techniques allow fast optimization studies. In our opinion, the field of spirocyclic chemistry will continue to thrive and contribute to drug development, improving activity and selectivity on emergent ailments, such as cancer, metabolic, infectious, and neurological diseases.

Isatin derivatives as broad-spectrum antiviral agents: the current landscape

In recent decades, several viruses have resulted in large outbreaks with serious health, economic and social consequences. The current unprecedented outbreak of the new coronavirus, SARS-COV-2, necessitates intensive efforts for delivering effective therapies to eradicate such a deadly virus. Isatin is an opulent heterocycle that has been proven to provide tremendous opportunities in the area of drug discovery. Over the last fifty years, suitably functionalized isatin has shown remarkable and broad-spectrum antiviral properties. The review herein is an attempt to compile all of the reported information about the antiviral activity of isatin derivatives with an emphasis on their structure-activity relationships (SARs) along with mechanistic and molecular modeling studies. In this regard, we are confident that the review will afford the scientific community a valuable platform to generate more potent and cost-effective antiviral therapies based on isatin templates.

Determinants in non-structural protein 4A of dengue virus required for RNA replication and replication organelle biogenesis

Dengue virus (DENV) constitutes one of the most important arboviral pathogens affecting humans. The high prevalence of DENV infections, which cause more than twenty thousand deaths annually, and the lack of effective vaccines or direct-acting antiviral drugs make it a global health concern. DENV genome replication occurs in close association with the host endomembrane system, which is remodeled to form the viral replication organelle that originates from ER membranes. To date, the viral and cellular determinants responsible for the biogenesis of DENV replication organelles are still poorly defined. The viral nonstructural protein (NS) 4A can remodel membranes and has been shown to associate with numerous host factors in DENV replicating cells. In the present study we used reverse and forward genetic screens and identified sites within NS4A required for DENV replication. We also mapped the determinants in NS4A required for interactions with other viral proteins. Moreover, taking advantage of our recently developed polyprotein expression system, we evaluated the role of NS4A in the formation of DENV replication organelles. Together, we report a detailed map of determinants within NS4A required for RNA replication, interaction with other viral proteins and replication organelle formation. Our results suggest that NS4A might be an attractive target for antiviral therapy. Importance DENV is the most prevalent mosquito-borne virus, causing around 390 million infections each year. There are no approved therapies to treat DENV infection and the only available vaccine shows limited efficacy. The viral non-structural proteins have emerged as attractive drug targets, due to their pivotal role in RNA replication and establishment of virus-induced membranous compartments, designated replication organelles (ROs). The transmembrane protein NS4A, generated by cleavage of the NS4A-2K-4B precursor, contributes to DENV replication by unknown mechanisms. Here, we report a detailed genetic interaction map of NS4A and identify residues required for RNA replication and interaction between NS4A-2K-4B and NS2B-3 as well as NS1. Importantly, by means of an expression-based system we demonstrate the essential role of NS4A in ROs biogenesis and identify determinants in NS4A required for this process. Our data suggest that NS4A is an attractive target for antiviral therapy.

Recent studies of nitrogen containing heterocyclic compounds as novel antiviral agents: A review

N-heterocycles are important, not only because of their abundance, but above all because of their chemical, biological and technical significance. They play an important role in biological investigation such as anticancer, antiinflammatory, antibacterial, antiviral, anti-tumor, antidiabetic, etc. In this study, we focused on examining synthesized some 5- or 6-ring N-heterocyclic compounds that showed the antiviral activity in last 5 years, and investigation of these compounds structure-activity relationship studies. This review will be useful to scientists in research fields of organic synthesis, medicinal chemistry, and pharmacology.

The impact of structural bioinformatics tools and resources on SARS-CoV-2 research and therapeutic strategies

SARS-CoV-2 is the causative agent of COVID-19, the ongoing global pandemic. It has posed a worldwide challenge to human health as no effective treatment is currently available to combat the disease. Its severity has led to unprecedented collaborative initiatives for therapeutic solutions against COVID-19. Studies resorting to structure-based drug design for COVID-19 are plethoric and show good promise. Structural biology provides key insights into 3D structures, critical residues/mutations in SARS-CoV-2 proteins, implicated in infectivity, molecular recognition and susceptibility to a broad range of host species. The detailed understanding of viral proteins and their complexes with host receptors and candidate epitope/lead compounds is the key to developing a structure-guided therapeutic design. Since the discovery of SARS-CoV-2, several structures of its proteins have been determined experimentally at an unprecedented speed and deposited in the Protein Data Bank. Further, specialized structural bioinformatics tools and resources have been developed for theoretical models, data on protein dynamics from computer simulations, impact of variants/mutations and molecular therapeutics. Here, we provide an overview of ongoing efforts on developing structural bioinformatics tools and resources for COVID-19 research. We also discuss the impact of these resources and structure-based studies, to understand various aspects of SARS-CoV-2 infection and therapeutic development. These include (i) understanding differences between SARS-CoV-2 and SARS-CoV, leading to increased infectivity of SARS-CoV-2, (ii) deciphering key residues in the SARS-CoV-2 involved in receptor-antibody recognition, (iii) analysis of variants in host proteins that affect host susceptibility to infection and (iv) analyses facilitating structure-based drug and vaccine design against SARS-CoV-2.

Discovery of a Small Molecule Inhibitor of Human Adenovirus Capable of Preventing Escape from the Endosome

Human adenoviruses (HAdVs) display a wide range of tissue tropism and can cause an array of symptoms from mild respiratory illnesses to disseminated and life-threatening infections in immunocompromised individuals. However, no antiviral drug has been approved specifically for the treatment of HAdV infections. Herein, we report our continued efforts to optimize salicylamide derivatives and discover compound 16 (JMX0493) as a potent inhibitor of HAdV infection. Compound 16 displays submicromolar IC₅₀ values, a higher selectivity index (SI > 100) and 2.5-fold virus yield reduction compared to our hit compound niclosamide. Moreover, unlike niclosamide, our mechanistic studies suggest that the antiviral activity of compound 16 against HAdV is achieved through the inhibition of viral particle escape from the endosome, which bars subsequent uncoating and the presentation of lytic protein VI.

Stereoselective synthesis and applications of spirocyclic oxindoles

This review summaries recent synthetic developments towards spirocyclic oxindoles and applications as valuable medicinal and synthetic targets.

Indole - a promising pharmacophore in recent antiviral drug discovery

The bicyclic molecule indole has been in the limelight because of its numerous pharmacological potencies. It is used as an excellent scaffold in drug discovery of medicinal drugs such as antimicrobials, anticancer agents, antihypertensives, anti-proliferative agents and anti-inflammatory agents. In spite of its diverse therapeutic activity, it is used as a key pharmacophore in synthesizing the most potent biological agents. Besides, viral infections are ubiquitous and their prevention and cure have become a great challenge. In this regard, the design of indole-containing antiviral drugs is accomplished to combat viral infections. A lot of research is being carried out towards antiviral drug discovery by many researchers round the clock. Herein, the antiviral activity of recently discovered indole scaffolds is compiled and critically evaluated to give a meaningful summary. In addition, the structure-activity relationship of remarkable antiviral agents is discussed. Also, the structural motifs attributed to noteworthy antiviral properties are highlighted to guide future antiviral research.

Deciphering the Role of Bovine Viral Diarrhea Virus Non-Structural NS4B Protein in Viral Pathogenesis

Bovine viral diarrhea virus (BVDV) is a (+) ssRNA virus that belongs to the family Flaviviridae. BVDV is a significant animal pathogen causing substantial economic losses to the cattle industry worldwide through respiratory and gastrointestinal infections and abortion or birth of persistently infected calves. While the immunogenic profile of some of the BVDV proteins (i.e., E^rns, E2 and NS3) is well established during viral pathogenesis, very little information is available about most of BVDV's non-structural proteins in this regard. In recent times, the NS4B protein has emerged as an interesting target of diagnostic, vaccination and therapeutic value in viral infections of other members of the family Flaviviridae due to its key scaffold-like contribution in the viral replication complex. Although, BVDV-NS4B has a membrane topology alongside its role in induction of autophagosomes in vitro. However, information on its immunogenicity during BVDV pathogenesis and vaccination is scarce. To characterize the immunogenic profile of the NS4B, five cows were vaccinated with the live attenuated BVDV vaccine Bovela^® and blood samples were taken pre- and post-immunization for serum isolation. Virus neutralization assay (VNA) confirmed the presence of anti-BVDV antibodies in the sera of vaccinated cows. VNA also revealed pre-existing antibodies against BVDV in the pre-immunization sera of two cows. To identify BVDV-NS4B specific antibodies, the NS4B protein was expressed in mammalian cells by using the pCI-neo vector system. The sera from BVDV vaccinated cows were evaluated for the presence of BVDV-NS4B specific antibodies through western blot and indirect ELISA. Interestingly, t sera from cows with pre-existing immunity against BVDV were able to detect NS4B in western blot and ELISA, suggesting the presence of NS4B-specific antibodies. The obtained results provide the first indication of the immunogenic nature of BVDV-NS4B protein in sero-converted animals. These findings are consistent with the observation made for NS4B in other Flaviviridae members and confirm this protein as an interesting target with diagnostic, vaccination and therapeutic value.

Discovery of Novel Substituted N-(4-Amino-2-chlorophenyl)-5-chloro-2-hydroxybenzamide Analogues as Potent Human Adenovirus Inhibitors

An effective therapy for human adenovirus (HAdV) infections in immunocompromised patients and healthy individuals with community-acquired pneumonia remains an unmet medical need. We herein reported a series of novel substituted N-(4-amino-2-chlorophenyl)-5-chloro-2-hydroxybenzamide analogues as potent HAdV inhibitors. Compounds 6, 15, 29, 40, 43, 46, 47, and 54 exhibited increased selectivity indexes (SI > 100) compared to the lead compound niclosamide, while maintaining sub-micromolar to low micromolar potency against HAdV. The preliminary mechanistic studies indicated that compounds 6 and 43 possibly target the HAdV DNA replication process, while compounds 46 and 47 suppress later steps of HAdV life cycle. Notably, among these derivatives, compound 15 showed improved anti-HAdV activity (IC₅₀ = 0.27 μM), significantly decreased cytotoxicity (CC₅₀ = 156.8 μM), and low in vivo toxicity (maximum tolerated dose = 150 mg/kg in hamster) as compared with niclosamide, supporting its further in vivo efficacy studies for the treatment of HAdV infections.

Recent progress on phenotype-based discovery of dengue inhibitors

Dengue fever is the world's most prevalent mosquito-borne viral disease caused by the four serotypes of dengue virus, which are widely spread throughout tropical and sub-tropical countries. There has been an urgent need to identify an effective and safe dengue inhibitor as a therapeutic and a prophylactic agent for dengue fever. Most clinically approved antiviral drugs for the treatment of human immunodeficiency syndrome-1 (HIV-1) and hepatitis C virus (HCV) target virally encoded enzymes such as protease or polymerase. Inhibitors of these enzymes were typically identified by target-based screening followed by optimization via structure-based design. However, due to the lack of success to date of research efforts to identify dengue protease and polymerase inhibitors, alternative strategies for anti-dengue drug discovery need to be considered. As a complementary approach to the target-based drug discovery, phenotypic screening is a strategy often used in identification of new chemical starting points with novel mechanisms of action in the area of infectious diseases such as antibiotics, antivirals, and anti-parasitic agents. This article is an overview of recent reports on dengue phenotypic screens and discusses phenotype-based hit-to-lead chemistry optimization. The challenges encountered and the outlook on dengue phenotype-based lead discovery are discussed at the end of this article.

Design, synthesis and biological evaluation of spiropyrazolopyridone derivatives as potent dengue virus inhibitors

The effective treatment for dengue virus infection continues to be a challenge. We herein reported our continued SAR exploration on the spiropyrazolopyridone scaffold. Introducing different substituents at the 3́- or 5́-site of the pyrazolopyridone core or moving the benzyl chain to the adjacent nitrogen led to a significant loss of potency on DENV-2. While a narrow range of substitutions were tolerated at the para-position of the phenyl ring, di-substitution on the phenyl ring is beneficial for DENV-2 potency and has variable influences on DENV-3 potency depending on the exact compound. Among these molecules, compounds 22 (JMX0376) with 4-chloro-3-fluorobenzyl and 24 (JMX0395) with 2,4-bis(trifluoromethyl)benzyl showed the most potent and broadest inhibitory activities against DENV-1 to -3 with nanomolar to low micromolar EC₅₀ values.

Structure-Activity Relationship Studies on Diversified Salicylamide Derivatives as Potent Inhibitors of Human Adenovirus Infection

The effective treatment of adenovirus (HAdV) infections in immunocompromised patients still poses great challenges. Herein, we reported our continued efforts to optimize a series of salicylamide derivatives as potent inhibitors of HAdV infection. Of these, nine compounds (11, 13, 14, 17, 20, 58, 60, 62, and 70) showed significantly improved anti-HAdV activities with nanomolar to submicromolar IC₅₀ values and high selectivity indexes (SI > 100), indicating better safety windows, compared to those of the lead compound niclosamide. Our mechanistic assays suggest that compounds 13, 62, and 70 exert their activities in the HAdV entry pathway, while compounds 14 and 60 likely target the HAdV DNA replication, and 11, 17, 20, and 58 inhibit later steps after DNA replication. Given the broad anti-viral activity profile of niclosamide, these derivatives may also offer therapeutic potential for other viral infections.