1,3,4-Trisubstituted pyrrolidine CCR5 receptor antagonists. Part 2: lead optimization affording selective, orally bioavailable compounds with potent anti-HIV activity

Identification of novel Ebola virus inhibitors using biologically contained virus

Despite recent advancements in the development of vaccines and monoclonal antibody therapies for Ebola virus disease, treatment options remain limited. Moreover, management and containment of Ebola virus outbreaks is often hindered by the remote nature of the locations in which the outbreaks originate. Small-molecule compounds offer the advantage of being relatively cheap and easy to produce, transport and store, making them an interesting modality for the development of novel therapeutics against Ebola virus disease. Furthermore, the repurposing of small-molecule compounds, previously developed for alternative applications, can aid in reducing the time needed to bring potential therapeutics from bench to bedside. For this purpose, the Medicines for Malaria Venture provides collections of previously developed small-molecule compounds for screening against other infectious diseases. In this study, we used biologically contained Ebola virus to screen over 4,200 small-molecule drugs and drug-like compounds provided by the Medicines for Malaria Venture (i.e., the Pandemic Response Box and the COVID Box) and the Centre for Drug Design and Discovery (CD3, KU Leuven, Belgium). In addition to confirming known Ebola virus inhibitors, illustrating the validity of our screening assays, we identified eight novel selective Ebola virus inhibitors. Although the inhibitory potential of these compounds remains to be validated in vivo, they represent interesting compounds for the study of potential interventions against Ebola virus disease and might serve as a basis for the development of new therapeutics.

Discovery of Novel CCR5 Ligands as Anticolorectal Cancer Agents by Sequential Virtual Screening

C-C chemokine receptor type 5 (CCR5) is a member of the G protein-coupled receptor. CCR5 and its interaction with chemokine ligands have been crucial for understanding and tackling human immunodeficiency virus (HIV)-1 entry into target cells. In recent years, the change in CCR5 expression has been related to the progression of different cancer types. Patients treated with the CCR5 ligand, maraviroc (MVC), showed a deceleration in tumor development especially for metastatic colorectal cancer. Based on the crystal structure of CCR5, we herein describe a multistage virtual screening protocol including pharmacophore screening, molecular docking, and protein-ligand interaction fingerprint (PLIF) postdocking filtration for discovery of novel CCR5 ligands. The applied virtual screening protocol led to the identification of four hits with binding modes showing access to the major and minor pockets of the MVC binding site. Compounds 2-4 showed a decrease in cellular proliferation upon testing on the metastatic colorectal cancer cell line, SW620, displaying 12, 16, and 4 times higher potency compared to MVC, respectively. Compound 3 induced apoptosis by arresting cells in the G0/G1 phase of the cell cycle similar to MVC. Further in vitro assays showed compound 3 drastically decreasing the CCR5 expression and cellular migration 48 h post treatment, indicating its ability to inhibit metastatic activity in SW620 cells. The discovered hits represent potential leads for the development of novel classes of anticolorectal cancer agents targeting CCR5.

Synthetic routes and structure-activity relationships (SAR) of anti-HIV agents: A key review

The worldwide increase of AIDS, an epidemic infection in constant development has an essential and still requires potent antiretroviral chemotherapeutic agents for reducing the integer of deaths caused by HIV. Thus, there is an urgent need for new anti-HIV drug candidates with increased strength, new targets, superior pharmacokinetic properties, and compact side effects. From this viewpoint, we first review present strategies of anti-HIV drug innovation and the synthesis of heterocyclic or natural compound as anti-HIV agents for facilitating the development of more influential and successful anti-HIV agents.

Recent updates for designing CCR5 antagonists as anti-retroviral agents

The healthcare system faces various challenges in human immunodeficiency virus (HIV) therapy due to resistance to Anti-Retroviral Therapy (ART) as a consequence of the evolutionary process. Despite the success of antiretroviral drugs like Zidovudine, Zalcitabine, Raltegravir WHO ranks HIV as one of the deadliest diseases with a mortality of one million lives in 2016. Thus, there emerges an urgency of developing a novel anti-retroviral agent that combat resistant HIV strains. The clinical development of ART from a single drug regimen to current triple drug combination is very slow. The progression in the structural biology of the viral envelope prompted the discovery of novel targets, which can be demonstrated a proficient approach for drug design of anti-retroviral agents. The current review enlightens the recent updates in the structural biology of the viral envelope and focuses on CCR5 as a validated target as well as ways to overcome CCR5 resistance. The article also throws light on the SAR studies and most prevalent mutations in the receptor for designing CCR5 antagonists that can combat HIV-1 infection. To conclude, the paper lists diversified scaffolds that are in pipeline by various pharmaceutical companies that could provide an aid for developing novel CCR5 antagonists.

Structural Analysis of Chemokine Receptor-Ligand Interactions

This review focuses on the construction and application of structural chemokine receptor models for the elucidation of molecular determinants of chemokine receptor modulation and the structure-based discovery and design of chemokine receptor ligands. A comparative analysis of ligand binding pockets in chemokine receptors is presented, including a detailed description of the CXCR4, CCR2, CCR5, CCR9, and US28 X-ray structures, and their implication for modeling molecular interactions of chemokine receptors with small-molecule ligands, peptide ligands, and large antibodies and chemokines. These studies demonstrate how the integration of new structural information on chemokine receptors with extensive structure–activity relationship and site-directed mutagenesis data facilitates the prediction of the structure of chemokine receptor–ligand complexes that have not been crystallized. Finally, a review of structure-based ligand discovery and design studies based on chemokine receptor crystal structures and homology models illustrates the possibilities and challenges to find novel ligands for chemokine receptors.

The next generation of HIV/AIDS drugs: novel and developmental antiHIV drugs and targets

There are presently 42 million people worldwide living with HIV/AIDS, the majority of which have limited access to antiretrovirals. Even if worldwide penetration was possible, our current chemotherapeutic strategies still suffer from issues of cost, patient compliance, deleterious acute and chronic side effects, emerging single and multidrug resistance, and generalized treatment and economic issues. Even our best antiretroviral therapeutic strategy, highly active antiretroviral therapy (HAART), falls short of completely suppressing HIV replication. Therefore, expansion of current therapeutic options by discovering new antiretrovirals and targets will be critical in the coming years. This review addresses the current status of reverse transcriptase and protease inhibitor development, and summarizes the progress in emerging classes of HIV inhibitors, including entry (T-20, T-1249), coreceptor (SCH-C, SCH-D), integrase (beta-Diketos) and p7 nucleocapsid Zn finger inhibitors (thioesters and PATEs). In addition, the processes of virus entry, PIC transport to the nucleus, HIV interaction with nuclear pores, Tat function, Rev function and virus budding (Tsg101 and ubiquitination) are examined, and proof of concept inhibitors and potential antiviral targets discussed.

Novel CCR5 antagonists for the treatment of HIV infection: a review of compounds patented in 2006 - 2008

IMPORTANCE OF THE FIELD

The HIV/AIDS epidemic and the resultant therapeutic efforts have continued to evolve over the last several years. The continued challenges in vaccine development, the growing longevity of the patient population and the emergence of resistant strains to current highly active antiretroviral therapy necessitate the development of new, effective therapeutics which target novel mechanism of actions. CCR5, a member of the GPCR superfamily, plays a key role as a co-receptor during the HIV viral entry process. The utility of CCR5 antagonists in the clinical setting has been validated, culminating in the launch of maraviroc (Selzentry by Pfizer (New York, NY, USA) in 2007.

AREAS COVERED IN THIS REVIEW

This review covers patent applications for small-molecule CCR5 selective antagonists published between 2006 and 2008 and related literature, with a focus on the treatment of HIV infection.

WHAT THE READER WILL GAIN

The reader will gain information on patent literature from 2006 to 2008 on CCR5 antagonists for the treatment of HIV infection.

TAKE HOME MESSAGE

A variety of new chemotypes have emerged over this period. These efforts support the potential to develop the next generation of CCR5 antagonists for the treatment of HIV with improved potency, tolerability and convenience.

Soluble CD4 and CD4-mimetic compounds inhibit HIV-1 infection by induction of a short-lived activated state

Binding to the CD4 receptor induces conformational changes in the human immunodeficiency virus (HIV-1) gp120 exterior envelope glycoprotein. These changes allow gp120 to bind the coreceptor, either CCR5 or CXCR4, and prime the gp41 transmembrane envelope glycoprotein to mediate virus-cell membrane fusion and virus entry. Soluble forms of CD4 (sCD4) and small-molecule CD4 mimics (here exemplified by JRC-II-191) also induce these conformational changes in the HIV-1 envelope glycoproteins, but typically inhibit HIV-1 entry into CD4-expressing cells. To investigate the mechanism of inhibition, we monitored at high temporal resolution inhibitor-induced changes in the conformation and functional competence of the HIV-1 envelope glycoproteins that immediately follow engagement of the soluble CD4 mimics. Both sCD4 and JRC-II-191 efficiently activated the envelope glycoproteins to mediate infection of cells lacking CD4, in a manner dependent on coreceptor affinity and density. This activated state, however, was transient and was followed by spontaneous and apparently irreversible changes of conformation and by loss of functional competence. The longevity of the activated intermediate depended on temperature and the particular HIV-1 strain, but was indistinguishable for sCD4 and JRC-II-191; by contrast, the activated intermediate induced by cell-surface CD4 was relatively long-lived. The inactivating effects of these activation-based inhibitors predominantly affected cell-free virus, whereas virus that was prebound to the target cell surface was mainly activated, infecting the cells even at high concentrations of the CD4 analogue. These results demonstrate the ability of soluble CD4 mimics to inactivate HIV-1 by prematurely triggering active but transient intermediate states of the envelope glycoproteins. This novel strategy for inhibition may be generally applicable to high-potential-energy viral entry machines that are normally activated by receptor binding.

HIV entry inhibitors and their potential in HIV therapy

This review discusses recent progress in the development of anti-HIV agents targeting the viral entry process. The three main classes (attachment inhibitors, co-receptor binding inhibitors, and fusion inhibitors) are further broken down by specific mechanism of action and structure. Many of these inhibitors are in advanced clinical trials, including the HIV maturation inhibitor bevirimat, from the authors' laboratories. In addition, the CCR5 inhibitor maraviroc has recently been FDA-approved. Possible roles for these agents in anti-HIV therapy, including treatment of virus resistant to current drugs, are also discussed.

Update on the development of HIV entry inhibitors

HIV fusion and entry are two steps in the viral lifecycle that can be targeted by several classes of antiviral drugs. The discovery of chemokines focused the attention on cellular co-receptors used by the virus for entering cells, and on the various steps of such processes that are subject to interactions with small molecules. Intense research has led to a wide range of effective compounds that are able to inhibit these initial steps of viral replication. All steps in the process of HIV entry into the cell may be targeted by specific compounds, grouped into three main classes (attachment inhibitors, co-receptor binding inhibitors and fusion inhibitors), which may be developed as novel antiretrovirals. Thus, several inhibitors of the gp120–CD4 interaction have been discovered (e.g., zintevir and BMS-378806). Small molecule chemokine receptor antagonists acting as HIV entry inhibitors have also been described recently, including those which interact with both the CXCR4 co-receptor (e.g., AMD3100, AMD3465, ALX40-4C, T22, T134 and T140) and CCR5 co-receptor antagonists (TAK-779, TAK-220, E913, AK-602 and NSC 651016 in clinical trials). Recently, a third family of antivirals started to be used clinically (in addition to reverse transcriptase and protease inhibitors), with the advent of enfuvirtide (T20), the first fusion inhibitor to be approved as an anti-HIV agent. Some of these compounds demonstrated in vitro synergism with other classes of antivirals, thus offering the rationale for their combination in therapies for HIV-infected individuals. Many HIV entry and fusion inhibitors are currently being investigated in controlled clinical trials, and a number of them are bioavailable as oral formulations. In 2007, the US FDA approved maraviroc as an anti-HIV agent. Maraviroc is the product of a medicinal chemistry effort initiated following identification of an imidazopyridine CCR5 ligand from a high-throughput screen of the Pfizer compound file. Maraviroc demonstrated potent antiviral activity against all CCR5-tropic HIV-1 viruses tested, including 43 primary isolates from various clades and diverse geographic origin. Maraviroc was active against 200 clinically derived HIV-1 envelope-recombinant pseudoviruses, 100 of which were derived from viruses resistant to existing drug classes. Furthermore, in October 2007, the FDA announced the approval of raltegravir for the treatment of HIV-1 infection as part of combination antiretroviral therapy in treatment-experienced patients with evidence of HIV-1 replication despite optimized background antiretroviral therapy. At present, raltegravir is the only drug in the integrase inhibitor class approved for clinical use. With the approval of raltegravir, oral agents targeting all three constitutive viral enzymes, reverse transcriptase, protease and integrase, are now represented in FDA-approved therapies.

Synthesis and biological evaluation of 1,3,3,4-tetrasubstituted pyrrolidine CCR5 receptor antagonists. Discovery of a potent and orally bioavailable anti-HIV agent

A series of 1,3,3,4-tetrasubstituted pyrrolidine containing CCR5 receptor antagonists were designed, which were elaborated either by condensation of a lithium salt of 3-(N,N-dibenzyl)aminopropionic acid methyl ester with ethyl benzoformate or by Baylis-Hillman reaction of ethyl acrylate with ethyl benzoformate and subsequent 1,4-addition of benzylamine, in the key steps. These compounds bearing 4-(N,N-disubstituted)amino piperidine units showed low nanomolar potency against the CCR5 receptor, whereas molecules with a 4-phenylpiperidine moiety displayed poor activity. Asymmetric synthesis of the most potent compound 23 a gave rise to the (3R,4S)-enantiomer 30 and the (3S,4R)-enantiomer 31, which showed IC(50) values of 2.9 and 385.9 nM, respectively. These results indicated that (3R,4S)-configuration in the series of compounds is favored for their interaction with the CCR5 receptor. The possible binding mode of these antagonists with the CCR5 receptor was discussed using a computer-modeling method. Compound 30 displayed excellent replication inhibition of seven genetically diverse R5 HIV-1 strains in the PBMC model, in a concentration-dependent manner with EC(50) values ranging from 0.3 nM to 30 nM. This molecule showed oral bioavailabilities of 41.2 % and 21.6 % in rats and dogs, respectively. Thus, compound 30 is a promising candidate for the treatment of HIV-1 infection.

CCR5 Blockade Modulates Inflammation and Alloimmunity in Primates

Pharmacologic antagonism of CCR5, a chemokine receptor expressed on macrophages and activated T cells, is an effective antiviral therapy in patients with macrophage-tropic HIV infection, but its efficacy in modulating inflammation and immunity is only just beginning to be investigated. In this regard, the recruitment of CCR5-bearing cells into clinical allografts is a hallmark of acute rejection and may anticipate chronic rejection, whereas conventionally immunosuppressed renal transplant patients homozygous for a nonfunctional Delta32 CCR5 receptor rarely exhibit late graft loss. Therefore, we explored the effects of a potent, highly selective CCR5 antagonist, Merck's compound 167 (CMPD 167), in an established cynomolgus monkey cardiac allograft model. Although perioperative stress responses (fever, diminished activity) and the recruitment of CCR5-bearing leukocytes into the graft were markedly attenuated, anti-CCR5 monotherapy only marginally prolonged allograft survival. In contrast, relative to cyclosporine A monotherapy, CMPD 167 with cyclosporine A delayed alloantibody production, suppressed cardiac allograft vasculopathy, and tended to further prolong graft survival. CCR5 therefore represents an attractive therapeutic target for attenuating postsurgical stress responses and favorably modulating pathogenic alloimmunity in primates, including man.

Antibody binding in proximity to the receptor/glycoprotein complex leads to a basal level of virus neutralization

Hypothetically, antibodies may neutralize enveloped viruses by diverse mechanisms, such as disruption of receptor binding, interference with conformational changes required for virus entry, steric hindrance, or virus aggregation. Here, we demonstrate that retroviral infection mediated by the avian sarcoma-leukosis virus (ASLV-A) envelope glycoproteins can be neutralized by an antibody directed against a functionally unimportant component of a chimeric receptor protein. Thus, the binding of an antibody in proximity to the retroviral envelope glycoprotein-receptor complex, without binding to the entry machinery itself, results in neutralization. This finding provides additional support for the hypothesis that steric hindrance is sufficient for antibody-mediated neutralization of retroviruses.

Inhibition of human immunodeficiency virus envelope glycoprotein- mediated single cell lysis by low-molecular-weight antagonists of viral entry

The coexpression of human immunodeficiency virus type 1 (HIV-1) envelope glycoproteins and receptors leads to the lysis of single cells by a process that is dependent upon membrane fusion. This cell lysis was inhibited by low-molecular-weight compounds that interfere with receptor binding or with receptor-induced conformational transitions in the envelope glycoproteins. A peptide, T20, potently inhibited cell-cell fusion but had no effect on single cell lysis mediated by the HIV-1 envelope glycoproteins. Thus, critical events in the lysis of single cells by the HIV-1 envelope glycoproteins occur in intracellular compartments accessible only to small inhibitory compounds.

The clinical potential of chemokine receptor antagonists

Chemokines belong to a family of chemotactic cytokines that direct the migration of immune cells towards sites of inflammation. They mediate their biological effects by binding to cell surface receptors, which belong to the G protein-coupled receptor superfamily. Since chemokines and their receptors have been implicated in the pathophysiology of a number of autoinflammatory diseases, chemokine receptor antagonists could prove to be useful therapeutics to target these diseases. Here, we review the role of chemokines in autoimmunity, concentrating mainly on the chemokine receptors CCR1 and CCR5, and discuss the potential utility of antagonists that target these 2 receptors as they progress through the clinic.

Synthesis and evaluation of CCR5 antagonists containing modified 4-piperidinyl-2-phenyl-1-(phenylsulfonylamino)-butane

Synthesis of analogs containing more rigid bicyclic piperidine replacements for the 4-benzyloxycarbonyl-(ethyl)amino-piperidine moiety of the CCR5 antagonist structure, 1, is described. Although similar binding affinity to the lead was achieved with some analogs they were overall less potent anti-HIV agents suggesting that other features besides CCR5 binding are required for good anti-viral activity.

Stereoselective synthesis of an anti-HIV drug candidate

The asymmetric synthesis of a Merck anti-HIV drug candidate is described. The target molecule contains four stereogenic centers, three of which are located in a highly functionalized cyclopentane unit. The convergent synthesis involves the preparation of two key advanced intermediates: the cyclopentane unit and a substituted pyrazole unit. The cyclopentane unit was prepared via two different procedures; a highly diastereoselective Diels-Alder reaction with a chiral oxazolidinone auxiliary and a sequence that incorporated a molybdenum-catalyzed asymmetric allylic alkylation reaction to set the stereocenters. The other key step was a highly diastereoselective hydroxyl-directed reductive amination. The overall yield for the 16-step synthesis was 10%.

Molecular docking and 3D QSAR studies on 1-amino-2-phenyl-4-(piperidin-1-yl)-butanes based on the structural modeling of human CCR5 receptor

In the present study, we have used an approach combining protein structure modeling, molecular dynamics (MD) simulation, automated docking, and 3D QSAR analyses to investigate the detailed interactions of CCR5 with their antagonists. Homology modeling and MD simulation were used to build the 3D model of CCR5 receptor based on the high-resolution X-ray structure of bovine rhodopsin. A series of 64 CCR5 antagonists, 1-amino-2-phenyl-4-(piperidin-1-yl)-butanes, were docked into the putative binding site of the 3D model of CCR5 using the docking method, and the probable interaction model between CCR5 and the antagonists were obtained. The predicted binding affinities of the antagonists to CCR5 correlate well with the antagonist activities, and the interaction model could be used to explain many mutagenesis results. All these indicate that the 3D model of antagonist-CCR5 interaction is reliable. Based on the binding conformations and their alignment inside the binding pocket of CCR5, three-dimensional structure-activity relationship (3D QSAR) analyses were performed on these antagonists using comparative molecular field analysis (CoMFA) and comparative molecular similarity analysis (CoMSIA) methods. Both CoMFA and CoMSIA provide statistically valid models with good correlation and predictive power. The q(2)(r(cross)(2)) values are 0.568 and 0.587 for CoMFA and CoMSIA, respectively. The predictive ability of these models was validated by six compounds that were not included in the training set. Mapping these models back to the topology of the active site of CCR5 leads to a better understanding of antagonist-CCR5 interaction. These results suggest that the 3D model of CCR5 can be used in structure-based drug design and the 3D QSAR models provide clear guidelines and accurate activity predictions for novel antagonist design.

A novel assay to identify entry inhibitors that block binding of HIV-1 gp120 to CCR5

HIV-1 infection is initiated by the interaction of the envelope glycoprotein gp120 with the cellular receptor CD4 that triggers conformational changes in gp120 necessary for subsequent interaction with a coreceptor CCR5 (or CXCR4). The CD4-induced (CD4i) conformation of gp120 can be mimicked by a full-length single chain (FLSC) protein consisting of gp120 linked with the D1D2 domains of CD4 by a 20-amino-acid linker. We have used this protein to establish a flow cytometry-based assay and an ELISA-based assay to identify inhibitors that block the binding of gp120 to CCR5. Both assays are specific for detecting the known CCR5 antagonist TAK-779, but the ELISA-based assay was more sensitive, simple, inexpensive, and rapid; thus, it can be adapted to high throughput screening (HTS). The ELISA-based method was validated with a diverse set of known antagonists, for example, TAK-779, AOP-RANTES, PSC-RANTES, and several mAbs.

Syntheses and SAR studies of 4-(heteroarylpiperdin-1-yl-methyl)-pyrrolidin-1-yl-acetic acid antagonists of the human CCR5 chemokine receptor

Efforts toward the exploration of the title compounds as CCR5 antagonists are disclosed. The basis for such work stems from the fact that cellular proliferation of HIV-1 requires the cooperative assistance of both CCR5 and CD4 receptors. The synthesis and SAR of pyrrolidineacetic acid derivatives as CCR5 antagonists displaying potent binding and antiviral properties in a HeLa cell-based HIV-1 infectivity assay are discussed.

Syntheses and biological evaluation of 5-(piperidin-1-yl)-3-phenyl-pentylsulfones as CCR5 antagonists

Cellular proliferation of HIV-1 requires the cooperative assistance of both the CCR5 and CD4 receptors. Our medicinal chemistry efforts in this area have resulted in the identification of N-alkyl piperidine sulfones as CCR5 antagonists. These compounds display potent binding and show antiviral properties in HIV-1 spread cell-based assays.

Antagonists of human CCR5 receptor containing 4-(pyrazolyl)piperidine side chains. Part 2: Discovery of potent, selective, and orally bioavailable compounds

Modifications of the alkyl acetic acid portion and the phenyl on pyrrolidine in our lead pyrazole compound 1 afforded the isopropyl compound 9. This compound is a potent CCR5 antagonist showing good in vitro antiviral activity against HIV-1, an excellent selectivity profile, and good oral bioavailability in three animal species. During this investigation, a new method for the preparation of alpha-(pyrrolidin-1-yl)-alpha,alpha-dialkyl acetic acid from a pyrrolidine and alpha-bromo-alpha,alpha-dialkyl acetic acid using silver triflate was discovered. This allowed us to prepare compounds such as 24 and 25 for the first time. A novel Pd-mediated N-dealkylation of alpha-(pyrrolidin-1-yl)acetic acid was also uncovered.

Antagonists of human CCR5 receptor containing 4-(pyrazolyl)piperidine side chains. Part 3: SAR studies on the benzylpyrazole segment

Extensive SAR studies in our benzylpyrazole series of CCR5 antagonists have shown that both lipophilic and hydrophilic substituents on the phenyl of the benzyl group increase antiviral potency. However, improvements in pharmacokinetic profiles were generally only observed with more lipophilic substitutions. 4-Biphenyl (51) performed the best in this regard. Highly lipophilic substituents impart undesirable ion channel activity to these CCR5 antagonists. Alkoxy substituents provide a good balance of antiviral activity, pharmacokinetic parameters, and selectivity. Compounds 42b and 42d, containing a 3,4-dimethoxy substituent, are considered the most promising improvements over parent compounds 9. They demonstrate improved antiviral activity while retaining good pharmacokinetic profile and selectivity.

Recent progress in discovery of small-molecule CCR5 chemokine receptor ligands as HIV-1 inhibitors

This review addresses key pharmacology and virology issues relevant in discovery and development of CCR5 antagonists as anti-HIV drugs, such as target validation, receptor internalization, allosterism, viral resistance and tropism. Recent progress in the discovery and development of CCR5 antagonists, SAR and clinical status are reviewed. Finally, modeling-based structure of CCR5 is discussed in the context of a small-molecule antagonism of the CCR5 receptor.

Lead compounds discovered from libraries: part 2

Many lead compounds with the potential to progress to viable drug candidates have been identified from libraries during the past two years. There are two key strategies most often employed to find leads from libraries: first, high-throughput biological screening of corporate compound collections; and second, synthesis and screening of project-directed libraries (i.e. target-based libraries). Numerous success stories, including the discovery of several clinical candidates, testify to the utility of chemical library collections as proven sources of new leads for drug development.

1,3,4-Trisubstituted pyrrolidine CCR5 receptor antagonists. Part 3: polar functionality and its effect on anti-HIV-1 activity

Incorporation of acidic functional groups into a lead CCR5 antagonist identified from a targeted combinatorial library resulted in compounds with enhanced anti-HIV-1 activity and attenuated L-type calcium channel affinity.

1,3,4 Trisubstituted pyrrolidine CCR5 receptor antagonists bearing 4-aminoheterocycle substituted piperidine side chains

A new class of 4-(aminoheterocycle)piperidine derived 1,3,4 trisubstituted pyrrolidine CCR5 antagonists is reported. Compound 4a is shown to have good binding affinity (1.8 nM) and antiviral activity in PBMC's (IC(95)=50 nM). Compound 4a also has improved PK properties relative to 1.

1,3,4-Trisubstituted pyrrolidine CCR5 receptor antagonists: modifications of the arylpropylpiperidine side chains

The 4-(3-phenylprop-1-yl)piperidine moiety of the 1,3,4-trisubstituted pyrrolidine CCR5 antagonist 1 was modified with electron deficient aromatics as well as replacement of the benzylic methylene with sulfones, gem-difluoromethylenes and alcohols in an effort to balance the antiviral potency with reasonable pharmacokinetics.

1,3,4-Trisubstituted pyrrolidine CCR5 receptor antagonists. Part 4: Synthesis of N-1 acidic functionality affording analogues with enhanced antiviral activity against HIV

A series of alpha-(pyrrolidin-1-yl)acetic acids is presented as selective and potent antivirals against HIV. Several of the pyrrolidine zwitterions demonstrated reasonable in vitro properties, enhanced antiviral activities and improved pharmacokinetic profiles over pyrrolidine 1.

Chemokine receptor antagonism as an approach to anti-inflammatory therapy: 'just right' or plain wrong?

Inflammation plays a pivotal role in exacerbating a wide array of human diseases. The chemokines are a group of proteins that control the movement and activation of the immune cells involved in all aspects of the inflammatory response. Recently, their cognate receptors have attracted considerable interest as therapeutic targets, in part because they are G-protein-coupled receptors, which have been antagonized successfully before by the pharmaceutical industry. Indeed, several companies have now reported the development of selective small-molecule chemokine receptor antagonists, and some of these compounds have even entered human Phase I clinical trials. Preclinical studies of the responsiveness of murine models of inflammation to either pharmacologic or genetic intervention have suggested that antagonism of some chemokine receptors may well prove to be a safe and efficacious approach to anti-inflammatory therapy.

New therapeutics that modulate chemokine networks

Chemokines are small cytokines that control a wide variety of biological and pathological processes, from immunosurveillance to inflammation, and from viral infection to cancer. The numerous known chemokine receptors have given hope that selective receptor antagonism might be possible, which could allow us to control which cells are recruited and activated at any time and in any place. As chemokine receptors are G-protein-coupled receptors, which are classical targets for the pharmaceutical industry, it is hoped that chemokines could be the first cytokines for which small-molecule receptor antagonists could be developed. Recently, reports of chemokine-receptor antagonists, both in vitro and in animal models of disease, have been published. It is anticipated that this field could produce clinically useful therapies in the next few years.

CCR5 antagonists: bicyclic isoxazolidines as conformationally constrained N-1-substituted pyrrolidines

A series of CCR5 antagonists containing bicyclic isoxazolidines was generated through a nitrone mediated cycloaddition with olefins bearing the preferred pharmacophores previously described. Potent antagonists (3 and 16) were generated with enhanced affinity for the CCR5 receptor while maintaining antiviral activity against HIV.

Combinatorial synthesis of CCR5 antagonists

Herein we report the preparation of a combinatorial library of compounds with potent CCR5 binding affinity. The library design was aided by SAR generated in a traditional medicinal chemistry effort. Compounds with novel combinations of subunits were discovered that have high binding affinity for the CCR5 receptor. A potent CCR5 antagonist from the library, compound 11 was found to have moderate anti-HIV-1 activity.