Design, synthesis and biological evaluation of indolizine derivatives as HIV-1 VIF-ElonginC interaction inhibitors

Pyrrole-Based Enaminones as Building Blocks for the Synthesis of Indolizines and Pyrrolo[1,2-a]pyrazines Showing Potent Antifungal Activity

As a new approach, pyrrolo[1,2-a]pyrazines were synthesized through the cyclization of 2-formylpyrrole-based enaminones in the presence of ammonium acetate. The enaminones were prepared with a straightforward method, reacting the corresponding alkyl 2-(2-formyl-1H-pyrrol-1-yl)acetates, 2-(2-formyl-1H-pyrrol-1-yl)acetonitrile, and 2-(2-formyl-1H-pyrrol-1-yl)acetophenones with DMFDMA. Analogous enaminones elaborated from alkyl (E)-3-(1H-pyrrol-2-yl)acrylates were treated with a Lewis acid to afford indolizines. The antifungal activity of the series of substituted pyrroles, pyrrole-based enaminones, pyrrolo[1,2-a]pyrazines, and indolizines was evaluated on six Candida spp., including two multidrug-resistant ones. Compared to the reference drugs, most test compounds produced a more robust antifungal effect. Docking analysis suggests that the inhibition of yeast growth was probably mediated by the interaction of the compounds with the catalytic site of HMGR of the Candida species.

Synthesis of Indolizines via Tf2O-Mediated Cascade Reaction of Pyridyl-enaminones with Thiophenols/Thioalcohols

A cost-effective, highly regioselective and metal-free version for the synthesis of indolizine derivatives by means of Tf₂O-mediated cascade reaction of pyridyl-enaminones and thiophenols/thioalcohols under mild reaction conditions has been reported. Diverse electron-rich indolizine derivatives could be obtained in up to 94% yield via the selective 1,4-addition of vinyl iminium triflate tandem cyclization/aromatization, which allowed the simultaneous construction of C-N and C-S/and one example of C-Se bonds.

Tetrahydroxydiboron and Nickel Chloride Cocatalyzed Rapid Radical Cyclization toward Pyrrolizidine and Indolizidine Alkaloids

A novel tetrahydroxydiboron and nickel chloride cocatalyzed radical cyclization cascade with a broad substrate scope and an ultrashort reaction time was developed. The mechanistic investigation indicated that the reaction might involve a homocleavage of tetrahydroxydiboron and nickel hydride intermediates. This approach enables the simple and efficient synthesis of a series of heteropolycycles.

Electro-Oxidative sp3 C-H Bond Functionalization and Annulation Cascade: Synthesis of Novel Heterocyclic Substituted Indolizines

Indolizine derivatives are prevalent in many synthetic intermediates, pharmaceuticals, and organic materials. Herein, we report a novel electro-oxidative cascade cyclization reaction that uses electricity as the primary energy input to promote the reaction, leading to a series of heterocyclic substituted indolizine derivatives under exogenous-oxidant-free conditions. It is noteworthy that this electrochemical method provides a novel strategy for generating heterocyclic diversity of quinazolinones and quinolines on indolizines. In addition, the sole byproduct in the reaction was molecular hydrogen.

Cascade synthesis of indolizines and pyrrolo[1,2-a]pyrazines from 2-formyl-1-propargylpyrroles

A straightforward synthesis of indolizines and pyrrolo[1,2-a]pyrazines was performed through a cascade condensation/cyclization/aromatization reaction of substituted 2-formyl-N-propargylpyrroles with active methylene compounds such as nitromethane, alkyl malonates, methyl cyanoacetate and malononitrile. Under basic conditions, the reaction proceeded satisfactorily to provide the corresponding 6,7-disubstituted indolizines. The condensation of the pyrrolic analogues with ammonium acetate gave rise to pyrrolo[1,2-a]pyrazines in high yields. N-Allenyl-2-formylpyrroles behaved as more reactive substrates than 2-formyl-N-propargylpyrroles, furnishing the expected indolizines in higher yields. Hence, an allenyl-containing intermediate was probably generated as the reactive species in the reaction mechanism of some N-propargyl pyrroles prior to the cyclization reaction.

Access to 6-hydroxy indolizines and related imidazo[1,5-a]pyridines through the SN2 substitution/condensation/tautomerization cascade process

A simple and efficient cascade reaction was developed for the construction of hydroxy substituted indolizines from pyrrole-2-carbaldehydes and commercially available 4-halogenated acetoacetic esters.

Enantioselective Synthesis of 3-Allylindolizines via Sequential Rh-Catalyzed Asymmetric Allylation and Tschitschibabin Reaction

The first highly regio- and enantioselective synthesis of 3-allylindolizines has been developed by the sequential Rh-catalyzed asymmetric allylation and Tschitschibabin reaction. Above the 20:1 branch/linear ratio, up to a 96% yield and 99% ee could be obtained with the help of tert-butyl-substituted chiral bisoxazolinephosphine ligand. In situ generated highly nucleophilic 2-alkylpyridinium ylides are utilized to undergo the asymmetric alkylation reaction before cyclization.

Inhibitory activities of indolizine derivatives: a patent review

INTRODUCTION

Indolizines are structural isomers with indoles. Although several indole-based commercial drugs are available in the market, none of the indolizine-based drugs are available up-to-date. Natural and synthetic indolizines have a wide-range of pharmaceutical importance such as antitumor, antimycobacterial, antagonist, and antiproliferative activities. This prompted us to search and collect all possible data about the pharmacological importance of indolizine to open an avenue to the researchers in exploring more medicinal applications of such biologically important compounds.

AREAS COVERED

The current review article covers the advancements in the biological and pharmacological activities of indolizine-based compounds during the last decade. The covered areas of this work involved anticancer, anti-HIV-1, anti-inflammatory, antimicrobial, anti-tubercular, larvicidal, anti-schizophrenia, CRTh2 antagonist's activities in addition to enzymatic inhibitory activity.

EXPERT OPINION

The discovery of indolizine drugs will be a major breakthrough as compared with their widely available drug-containing indole isosteres. Major work collected here was focused on anticancer, anti-tubercular, anti-inflammatory, and enzymatic inhibitory activities. The SAR study of the reported biologically active indolizines is summarized throughout the review whenever highlighted to the rationale the behavior of inhibitory action. Several indolizines with certain functions provided great enhancement in the therapeutic activities comparing with reference drugs.

Discovery of fused heterocyclic carboxamide derivatives as novel α7-nAChR agonists: Synthesis, preliminary SAR and biological evaluation

The α7 nicotinic acetylcholine receptor (α7 nAChR) has emerged as a promising therapeutic target for schizophrenia. In our previous work, a novel series of α7-nAChR agonists bearing scaffold of indolizine were discovered. To explore the effect of aromaticity on the activity and find more active agents, herein, fused heterocyclic carboxamide derivatives were designed and synthesized in this study. Based on the evaluation by two-electrode voltage clamp in Xenopus oocytes, 27 of the synthesized compounds showed obvious agonism of α7 nAChR. Particularly, compounds 10a and 10e showed significantly higher E_max than EVP-6124. The result illustrated the importance of aromaticity to the activity of agonism. Compound 10a, which showed EC₅₀ of 1.88 μM and E_max of 72.4%, was further characterized comprehensively, including co-application with type II positive allosteric modulator PNU-120596, selectivity with other closely related ligand-gated ion channel, etc. The results showed that 10a showed moderate selectivity over other subtypes such as α4β2 and α3β4 nAChR. 10a evoked α7-like currents that were inhibited by MLA and enhanced in the presence of the α7 PAM PNU-120596. The analysis of binding mode and understanding of structure-activity relationship provided insights to develop more potent novel α7-nAChR agonists.

HIV-1 Escape from Small-Molecule Antagonism of Vif

Although antiretroviral therapy can suppress HIV-1 replication effectively, virus reservoirs persist in infected individuals and virus replication rapidly rebounds if therapy is interrupted. Currently, there is a need for therapeutic approaches that eliminate, reduce, or control persistent viral reservoirs if a cure is to be realized. This work focuses on the preclinical development of novel, small-molecule inhibitors of the HIV-1 Vif protein. Vif inhibitors represent a new class of antiretroviral drugs that may expand treatment options to more effectively suppress virus replication or to drive HIV-1 reservoirs to a nonfunctional state by harnessing the activity of the DNA-editing cytidine deaminase A3G, a potent, intrinsic restriction factor expressed in macrophage and CD4⁺ T cells. In this study, we derived inhibitor escape variants to characterize the mechanism by which these novel agents inhibit virus replication and to provide evidence for target validation.

The HIV-1 accessory protein Vif, which counteracts the antiviral action of the DNA-editing cytidine deaminase APOBEC3G (A3G), is an attractive and yet unexploited therapeutic target. Vif reduces the virion incorporation of A3G by targeting the restriction factor for proteasomal degradation in the virus-producing cell. Compounds that inhibit Vif-mediated degradation of A3G in cells targeted by HIV-1 would represent a novel antiviral therapeutic. We previously described small molecules with activity consistent with Vif antagonism. In this study, we derived inhibitor escape HIV-1 variants to characterize the mechanism by which these novel agents inhibit virus replication. Here we show that resistance to these agents is dependent on an amino acid substitution in Vif (V142I) and on a point mutation that likely upregulates transcription by modifying the lymphocyte enhancing factor 1 (LEF-1) binding site. Molecular modeling demonstrated a docking site in the Vif-Elongin C complex that is disrupted by these inhibitors. This docking site is lost when Vif acquires the V142I mutation that leads to inhibitor resistance. Competitive fitness experiments indicated that the V142I Vif and LEF-1 binding site mutations created a virus that is better adapted to growing in the presence of A3G than the wild-type virus.

Convenient construction of tetrahydrochromeno[4',3':2,3]indolizino[8,7-b]indoles and tetrahydroindolizino[8,7-b]indoles via one-pot domino reaction

The functionalized tetrahydrochromeno[4',3':2,3]indolizino[8,7-b]indoles were conveniently synthesized in high yields by one-pot domino reaction of tryptamines, alkyl propiolates and 2-aryl-3-nitro-2H-chromenes. Under similar conditions, the one-pot reaction of tryptamines, alkyl propiolates and β-nitroalkenes resulted in functionalized tetrahydroindolizino[8,7-b]indoles. The reaction mechanism involved sequential generation of β-enamino ester, Michael addition, Pictet-Spengler reaction and annulation process. The reaction showed high atomic economy and met the goals of sustainable chemistry.

Viral subversion of APOBEC3s: Lessons for anti-tumor immunity and tumor immunotherapy

APOBEC3s (A3) are endogenous DNA-editing enzymes that are expressed in immune cells including T lymphocytes. A3s target and mutate the genomes of retroviruses that infect immune tissues such as the human immunodeficiency virus (HIV). Therefore, A3s were classically defined as host anti-viral innate immune factors. In contrast, we and others showed that A3s can also benefit the virus by mediating escape from adaptive immune recognition and drugs. Crucially, whether A3-mediated mutations help or hinder HIV, is not up to chance. Rather, the virus has evolved multiple mechanisms to actively and maximally subvert A3 activity. More recently, extensive A3 mutational footprints in tumor genomes have been observed in many different cancers. This suggests a role for A3s in cancer initiation and progression. On the other hand, multiple anti-tumor activities of A3s have also come to light, including impact on immune checkpoint molecules and possible generation of tumor neo-antigens. Here, we review the studies that reshaped the view of A3s from anti-viral innate immune agents to host factors exploited by HIV to escape from immune recognition. Viruses and tumors share many attributes, including rapid evolution and adeptness at exploiting mutations. Given this parallel, we then discuss the pro- and anti-tumor roles of A3s, and suggest that lessons learned from studying A3s in the context of anti-viral immunity can be applied to tumor immunotherapy.

Synthesis of spiro[indoline-3,3'-pyrrolizines] by 1,3-dipolar reactions between isatins, L-proline and electron-deficient alkenes

Two spiro[indoline-3,3'-pyrrolizine] derivatives have been synthesized in good yield with high regio- and stereospecificity using one-pot reactions between readily available starting materials, namely L-proline, substituted 1H-indole-2,3-diones and electron-deficient alkenes. The products have been fully characterized by elemental analysis, IR and NMR spectroscopy, mass spectrometry and crystal structure analysis. In (1'RS,2'RS,3SR,7a'SR)-2'-benzoyl-1-hexyl-2-oxo-1',2',5',6',7',7a'-hexahydrospiro[indoline-3,3'-pyrrolizine]-1'-carboxylic acid, C₂₈H₃₂N₂O₄, (I), the unsubstituted pyrrole ring and the reduced spiro-fused pyrrole ring adopt half-chair and envelope conformations, respectively, while in (1'RS,2'RS,3SR,7a'SR)-1',2'-bis(4-chlorobenzoyl)-5,7-dichloro-2-oxo-1',2',5',6',7',7a'-hexahydrospiro[indoline-3,3'-pyrrolizine], which crystallizes as a partial dichloromethane solvate, C₂₈H₂₀Cl₄N₂O₃·0.981CH₂Cl₂, (II), where the solvent component is disordered over three sets of atomic sites, these two rings adopt envelope and half-chair conformations, respectively. Molecules of (I) are linked by an O-H...·O hydrogen bond to form cyclic R₆⁶(48) hexamers of \overline{3} (S₆) symmetry, which are further linked by two C-H...O hydrogen bonds to form a three-dimensional framework structure. In compound (II), inversion-related pairs of N-H...O hydrogen bonds link the spiro[indoline-3,3'-pyrrolizine] molecules into simple R₂²(8) dimers.

APOBEC Enzymes as Targets for Virus and Cancer Therapy

Human DNA cytosine-to-uracil deaminases catalyze mutations in both pathogen and cellular genomes. APOBEC3D, APOBEC3F, APOBEC3G, and APOBEC3H restrict human immunodeficiency virus 1 (HIV-1) infection in cells deficient in the viral infectivity factor (Vif), and have the potential to catalyze sublethal levels of mutation in viral genomes in Vif-proficient cells. At least two APOBEC3 enzymes, and in particular APOBEC3B, are sources of somatic mutagenesis in cancer cells that drive tumor evolution and may manifest clinically as recurrence, metastasis, and/or therapy resistance. Consequently, APOBEC3 enzymes are tantalizing targets for developing chemical probes and therapeutic molecules to harness mutational processes in human disease. This review highlights recent efforts to chemically manipulate APOBEC3 activities.

CD4-gp120 interaction interface - a gateway for HIV-1 infection in human: molecular network, modeling and docking studies

The major causative agent for Acquired Immune Deficiency Syndrome (AIDS) is Human Immunodeficiency Virus-1 (HIV-1). HIV-1 is a predominant subtype of HIV which counts on human cellular mechanism virtually in every aspect of its life cycle. Binding of viral envelope glycoprotein-gp120 with human cell surface CD4 receptor triggers the early infection stage of HIV-1. This study focuses on the interaction interface between these two proteins that play a crucial role for viral infectivity. The CD4-gp120 interaction interface has been studied through a comprehensive protein-protein interaction network (PPIN) analysis and highlighted as a useful step towards identifying potential therapeutic drug targets against HIV-1 infection. We prioritized gp41, Nef and Tat proteins of HIV-1 as valuable drug targets at early stage of viral infection. Lack of crystal structure has made it difficult to understand the biological implication of these proteins during disease progression. Here, computational protein modeling techniques and molecular dynamics simulations were performed to generate three-dimensional models of these targets. Besides, molecular docking was initiated to determine the desirability of these target proteins for already available HIV-1 specific drugs which indicates the usefulness of these protein structures to identify an effective drug combination therapy against AIDS.

Synthesis and biological activities of indolizine derivatives as alpha-7 nAChR agonists

Human α7 nicotinic acetylcholine receptor (nAChR) is a promising therapeutic target for the treatment of schizophrenia accompanied with cognitive impairment. Herein, we report the synthesis and agonistic activities of a series of indolizine derivatives targeting to α7 nAChR. The results show that all synthesized compounds have affinity to α7 nAChR and some give strong agonistic activity, particularly most active agonists show higher potency than control EVP-6124. The docking and structure-activity relationship studies provide insights to develop more potent novel α7 nAChR agonists.

Recent advances in the synthesis of indolizines and their π-expanded analogues

Synthesis of indolizines developed during the last decade is reviewed, with special emphasis given to densely functionalized architectures, breakthrough strategies, compounds bearing electron-donating and electron-withdrawing substituents and π-expanded systems.

Palladium-catalyzed highly efficient synthesis of functionalized indolizines via cross-coupling/cycloisomerization cascade

Pd-catalyzed cross-coupling/cycloisomerization of 3-(2-pyridyl) propargyl carbonates with organoboronic acids provides a straightforward route for the synthesis of 1,3-disubstituted indolizines.

The APOBEC3 family of retroelement restriction factors

The ability to regulate and even target mutagenesis is an extremely valuable cellular asset. Enzyme-catalyzed DNA cytosine deamination is a molecular strategy employed by vertebrates to promote antibody diversity and defend against foreign nucleic acids. Ten years ago, a family of cellular enzymes was first described with several proving capable of deaminating DNA and inhibiting HIV-1 replication. Ensuing studies on the apolipoprotein B mRNA-editing enzyme catalytic polypeptide-like 3 (APOBEC3) restriction factors have uncovered a broad-spectrum innate defense network that suppresses the replication of numerous endogenous and exogenous DNA-based parasites. Although many viruses possess equally elaborate counter-defense mechanisms, the APOBEC3 enzymes offer a tantalizing possibility of leveraging innate immunity to fend off viral infection. Here, we focus on mechanisms of retroelement restriction by the APOBEC3 family of restriction enzymes, and we consider the therapeutic benefits, as well as the possible pathological consequences, of arming cells with active DNA deaminases.