1,3,4-Trisubstituted pyrrolidine CCR5 receptor antagonists. Part 1: discovery of the pyrrolidine scaffold and determination of its stereochemical requirements

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.

Production and use of HIV-1 luciferase reporter viruses

This unit describes the production and use of HIV-1 luciferase reporter viruses. These viruses are used to rapidly and accurately quantify HIV-1 in cell culture. Protocols are also presented for screening and characterization of small molecule inhibitors of HIV-1 entry into cells.

7-Benzyl-2,7-diaza-spiro-[4.4]nonan-1-one

In the title compound, C(14)H(18)N(2)O, both the spiro-linked five-membered rings adopt envelope conformations, with a C atom as the flap in one ring and an N atom in the other. The dihedral angle between the two four-atom planes is 80.46 (8)°. In the crystal, the mol-ecules are linked by N-H⋯O hydrogen bonds to generate C(4) chains propagating in [010].

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.

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.

Pyrrolidine-carboxamides and oxadiazoles as potent hNK1 antagonists

The preparation and structure-activity-relationships of novel pyrrolidine-carboxamides and oxadiazoles are described. Compounds in this series were found to be potent hNK(1) antagonists in vitro and efficacious in vivo with minimal interactions with P(450) liver enzymes. Oxadiazole analog 22 was determined to have excellent hNK(1) binding affinity, functional activity, and a good PD response in vivo.

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.

The design and synthesis of a tricyclic single-nitrogen scaffold that serves as a 5-HT2C receptor agonist

5-HT2C agonists have shown efficacy in limiting food consumption and thus may serve as an important drug class in combating obesity. We describe the design and synthesis of a novel tricyclic single-nitrogen scaffold that was used to produce 5-HT2C agonists. SAR was developed around this chemotype and compounds were identified that were potent (Ki<15 nM) and selective relative to other 5-HT2 receptors. The most promising compound displayed a good pharmacokinetic profile in multiple animal species, and was efficacious in an acute feeding study in rats.

I want a new drug: G-protein-coupled receptors in drug development

Huey Lewis and the News summed it up nicely in their 1980s hit record: 'I want a new drug, one that won't make me sick, one that won't make me crash my car, or make me feel three feet thick'. The song could be an anthem for drug discovery in the pharmaceutical industry. We all want new and better drugs with fewer side effects, which are effective for combating the major diseases of our time: cancer, heart disease, obesity and autoimmune diseases. How do we get these new drugs? There are currently some new ideas in drug discovery, centered on that staple diet of the pharmaceutical industry, the G-protein-coupled receptor (GPCR) superfamily. In silico methods, employing receptor-based modeling, offer a more rational approach in the design of drugs targeting GPCRs. These approaches can be used to understand receptor selectivity and species specificity of drugs that interact with GPCRs. In addition, there are various novel approaches, such as the design and potential utility of drugs that target more than one GPCR ('dual specificity' drugs).

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.

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 1: Discovery and SAR study of 4-pyrazolylpiperidine side chains

Replacement of the flexible connecting chains between the piperidine moiety and an aromatic group in previous CCR5 antagonists with heterocycles, such as pyrazole and isoxazole, provided potent CCR5 antagonists with excellent anti-HIV-1 activity in vitro. SAR studies revealed optimal placement of an unsubstituted nitrogen atom in the heterocycle to be meta to the bond connected to the 4-position of piperidine. Truncation of a benzyl group to a phenyl group afforded compounds with dramatically improved oral bioavailability, albeit with reduced activity.

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.

CCR5 antagonists: 3-(pyrrolidin-1-yl)propionic acid analogues with potent anti-HIV activity

[reaction: see text] A novel approach to alpha,alpha-disubstituted-beta-amino acids (beta(2,2)-amino acids) was employed in the synthesis of a series of 3-(pyrrolidin-1-yl)propionic acids possessing high affinity for the CCR5 receptor and potent anti-HIV activity. The rat pharmacokinetics for these new analogues featured higher bioavailabilities and lower rates of clearance as compared to cyclopentane 1.

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.

Development and evaluation of pharmacological agents targeting chemokine receptors

Chemokine receptors belong to one of the most pharmacologically exploited proteins, the G-protein-coupled receptors. Drugs that target these receptors make up greater than 45% of all known marketed medicines. Several excellent reviews published recently have concentrated on the biology, pathophysiology, and molecular mechanisms of action of the chemokines [C. Gerard, B.J. Rollins, Nat. Immunol. 2 (2001) 108; C.R. Mackay, Nat. Immunol. 2 (2001) 95; M. Thelen, Nat. Immunol. 2 (2001) 129] and the reader is directed toward them to gain a thorough understanding of the importance of this growing family of proteins. Although some background will be given here to aid in an understanding of the medical importance of chemokines, this review will focus on the rapid advances that have been made in identifying and characterizing chemokine receptor antagonists, by discussing their efficacy in animal models of disease as well as detailing their progression through human clinical trials. This approach is exemplified by specific reference to CCR1 and CCR5, which are the most advanced chemokine receptor programs.

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. 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.

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.

Potential new therapies for the treatment of HIV-1 infection

The development and clinical use of chemotherapeutic agents for the treatment of persistent HIV-1 infection over the past decade has profoundly and favorably affected the course of HIV-1 disease for many infected individuals. Unfortunately, the long-term use of these therapies is complicated by unwanted metabolic side effects, by issues of adherence, and by the selection of viral variants with reduced susceptibility. These complications have spurred the search for new anti-HIV-1 agents having improved pharmacological properties and expressing activity against viral variants resistant to the currently available agents. This brief review describes the current state of this search as well as potentially novel viral targets for chemotherapeutic intervention.

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.

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

Investigations of the structure-activity relationships of 1,3,4-trisubstituted pyrrolidine human CCR5 receptor antagonists afforded orally bioavailable compounds with the ability to inhibit HIV replication in vitro.