Cyclic HIV protease inhibitors capable of displacing the active site structural water molecule

Indazole as a Privileged Scaffold: The Derivatives and their Therapeutic Applications

BACKGROUND

Heterocyclic compounds, also called heterocycles, are a major class of organic chemical compound that plays a vital role in the metabolism of all living cells. The heterocyclic compound, indazole, has attracted more attention in recent years and is widely present in numerous commercially available drugs. Indazole-containing derivatives, representing one of the most important heterocycles in drug molecules, are endowed with a broad range of biological properties.

METHODS

A literature search was conducted in PubMed, Google Scholar and Web of Science regarding articles related to indazole and its therapeutic application.

RESULTS

The mechanism and structure-activity relationship of indazole and its derivatives were described. Based on their versatile biological activities, the compounds were divided into six groups: anti-inflammatory, antibacterial, anti-HIV, antiarrhythmic, antifungal and antitumour. At least 43 indazole-based therapeutic agents were found to be used in clinical application or clinical trials.

CONCLUSION

This review is a guide for pharmacologists who are in search of valid preclinical/clinical drug compounds where the progress of approved marketed drugs containing indazole scaffold is examined from 1966 to the present day. Future direction involves more diverse bioactive moieties with indazole scaffold and greater insights into its mechanism.

Strategies for Antiviral Drug Discovery

The need for antiviral drugs is growing rapidly as more viral diseases are recognized. The methods used to discover these drugs have evolved considerably over the past 40 years and the overall process of discovery can be broken down into sub-processes which include lead generation, lead optimization and lead development. Various methods are now employed to ensure these processes are carried out efficiently. For lead generation, screening methodologies have developed to the extent where hundreds of thousands of compounds can be screened against a particular target. An alternative approach is to use the structures of enzyme substrates as a starting point for drug discovery. Much use is now made of X-ray crystallographic data of target–inhibitor complexes for the optimization of lead structures, and methods for preparing libraries of compounds to assist both generation and optimization of leads are welldeveloped. The methods used to predict and improve the pharmacokinetic properties of compounds are also changing rapidly. Finally, novel approaches to antiviral therapy using oligonucleotide-based compounds or modulating the host immune response are also being explored. This review discusses these approaches, provides examples of where their application has been successful and sets them against a historical background.

Perturbation of fluid dynamics properties of water molecules during G protein-coupled receptor-ligand recognition: the human A2A adenosine receptor as a key study

Recent advances in structural biology revealed that water molecules play a crucial structural role in the protein architecture and ligand binding of G protein-coupled receptors. In this work, we present an alternative approach to monitor the time-dependent organization of water molecules during the final stage of the ligand-receptor recognition process by means of membrane molecular dynamics simulations. We inspect the variation of fluid dynamics properties of water molecules upon ligand binding with the aim to correlate the results with the binding affinities. The outcomes of this analysis are transferred into a bidimensional graph called water fluid dynamics maps, that allow a fast graphical identification of protein "hot-spots" characterized by peculiar shape and electrostatic properties that can play a critical role in ligand binding. We hopefully believe that the proposed approach might represent a valuable tool for structure-based drug discovery that can be extended to cases where crystal structures are not yet available, or have not been solved at high resolution.

Strategies to calculate water binding free energies in protein-ligand complexes

Water molecules are commonplace in protein binding pockets, where they can typically form a complex between the protein and a ligand or become displaced upon ligand binding. As a result, it is often of great interest to establish both the binding free energy and location of such molecules. Several approaches to predicting the location and affinity of water molecules to proteins have been proposed and utilized in the literature, although it is often unclear which method should be used under what circumstances. We report here a comparison between three such methodologies, Just Add Water Molecules (JAWS), Grand Canonical Monte Carlo (GCMC), and double-decoupling, in the hope of understanding the advantages and limitations of each method when applied to enclosed binding sites. As a result, we have adapted the JAWS scoring procedure, allowing the binding free energies of strongly bound water molecules to be calculated to a high degree of accuracy, requiring significantly less computational effort than more rigorous approaches. The combination of JAWS and GCMC offers a route to a rapid scheme capable of both locating and scoring water molecules for rational drug design.

The Influence of Bioisosteres in Drug Design: Tactical Applications to Address Developability Problems

The application of bioisosteres in drug discovery is a well-established design concept that has demonstrated utility as an approach to solving a range of problems that affect candidate optimization, progression, and durability. In this chapter, the application of isosteric substitution is explored in a fashion that focuses on the development of practical solutions to problems that are encountered in typical optimization campaigns. The role of bioisosteres to affect intrinsic potency and selectivity, influence conformation, solve problems associated with drug developability, including P-glycoprotein recognition, modulating basicity, solubility, and lipophilicity, and to address issues associated with metabolism and toxicity is used as the underlying theme to capture a spectrum of creative applications of structural emulation in the design of drug candidates.

Modular construction of quaternary hemiaminal-based inhibitor candidates and their in cellulo assessment with HIV-1 protease

Non-peptidomimetic drug-like protease inhibitors have potential for circumventing drug resistance. We developed a much-improved synthetic route to our previously reported inhibitor candidate displaying an unusual quaternized hemi-aminal. This functional group forms from a linear precursor upon passage into physiological media. Seven variants were prepared and tested in cellulo with our HIV-1 fusion-protein technology that result in an eGFP-based fluorescent readout. Three candidates showed inhibition potency above 20μM and toxicity at higher concentrations, making them attractive targets for further refinement. Importantly, our class of original inhibitor candidates is not recognized by two major multidrug resistance pumps, quite in contrast to most clinically applied HIV-1 protease inhibitors.

2-Pyrone natural products and mimetics: isolation, characterisation and biological activity

The review summarises natural products containing the 2-pyrone moiety. An emphasis has been placed upon the biological activity associated with 2-pyrones, particularly with respect to potential therapeutic or anti-microbial agents. Where appropriate, non-natural 2-pyrone analogues are discussed, particularly those derived from natural product lead compounds.

Topological models for the prediction of HIV-protease inhibitory activity of tetrahydropyrimidin-2-ones

Relationship between the topological indices and HIV-protease inhibitory activity of tetrahydropyrimidine-2-ones has been investigated. Three topological indices, Wiener's index--a distance based topological descriptor, Zagreb group parameter--an adjacency based topological descriptor and eccentric connectivity index--an adjacency-cum-distance based topological descriptor were used for the present investigations. A dataset comprising of 80 substituted tetrahydropyrimidine-2-one analogues was selected for the present studies. The values of the Wiener's index, Zagreb group parameter and eccentric connectivity index for each of the 80 compounds comprising the dataset were computed using an in-house computer program. The dataset was divided randomly into training and test sets. Resultant data was analyzed and suitable models were developed after identifying the active ranges in the training set. Subsequently, a biological activity was assigned to each of the compound involved in the test set using these models, which was then compared with the reported HIV-protease inhibitory activity. Accuracy of prediction using these models was found to vary from a minimum of approximately 86% to a maximum of approximately 88%.

Scaffold Hopping in De Novo Design. Ligand Generation in the Absence of Receptor Information

We report here the de novo generation of chemotypes and scaffolds for the estrogen receptor, without use of the receptor structure in the assembly phase. Through use of ligand superpositions or a single bound conformation of a known active, a pseudoreceptor can be generated as a design envelope, within which novel structures are readily assembled. Many of these structures have high similarity to known chemotypes. Scaffold hopping is readily achieved within this pseudoreceptor, indicating the advantages of such an approach in discovery research.

Synthesis of heterocyclic and carbocyclic fluoro-olefins by ring-closing metathesis

[reaction: see text] Ring-closing metathesis (RCM) of vinyl fluoride-containing dienes in the presence of ruthenium alkylidene carbene complex 11 proceeded efficiently to give six- and seven-membered cyclic vinyl fluorides. The RCM reaction was used to prepare amine- and sulfamide-linked cyclo-olefins, as well as carbocyclic systems, from a simple commercial fluoro-olefin.

Design and synthesis of broad-based mono- and bi- cyclic inhibitors of FIV and HIV proteases

Based on the substrate transition state and our strategy to tackle the problem of drug resistance, a series of HIV/FIV protease (HIV /FIV PR) monocyclic inhibitors incorporating a 15- or 17-membered macrocycle with an equivalent P3 or P3' group and a unique unnatural amino acid, (2R, 3S)-3-amino-2-hydroxy-4-phenylbutyric acid, have been designed and synthesized. In addition, based on the structure of TL3 with small P3/P3' group, we have synthesized two conformationally restricted bicyclic inhibitors containing the macrocycle, which mimic the P1/P1'-P3/P3' tripeptide [Phe-Val-Ala] of TL3. We have found that the contribution of the macrocycle in our monocyclic inhibitors is important to the overall activity, but the ring size does not affect the activity to a significant extent. Several inhibitors that were developed in this work, exhibit low nanomolar inhibitory activity against the wild-type HIV/FIV PR and found to be highly effective against some drug-resistant as well as TL3-resistant mutants of HIV PRs. Compound 15, in particular, is the most effective cyclic inhibitor in hand to inhibit FIV replication in tissue culture at a concentration of 1.0 micro g/mL (1.2 microM).

Targeting the HIV-protease in AIDS therapy: a current clinical perspective

This review deals with clinical applications of compounds that inhibit the action of the protease encoded within the genome of human immunodeficiency virus (HIV). The HIV-protease is essential for viral maturation and represents an important therapeutic target in the fight against AIDS. Following a brief overview of the enzyme structure and function, the article focuses on a number of peptide and non-peptide based HIV-protease inhibitors that are in current clinical use. These drugs are discussed both with respect to their efficacy in treatment of AIDS, and to problems related to insurgence of viral resistance and side effects seen to date in patient populations.

Design and fast synthesis of C-terminal duplicated potent C(2)-symmetric P1/P1'-modified HIV-1 protease inhibitors

An analysis of the X-ray structure of a complex of HIV-1 protease with a linear C(2)-symmetric C-terminal duplicated inhibitor guided the selection of a series of diverse target compounds. These were synthesized with the objective to identify suitable P1/P1' substituents to provide inhibitors with improved antiviral activity. Groups with various physical properties were attached to the para-positions of the P1/P1' benzyloxy groups in the parent inhibitor. A p-bromobenzyloxy compound, prepared in only three steps from commercially available starting materials, was utilized as a common precursor in all reactions. The subsequent coupling reactions were completed within a few minutes and relied on palladium catalysis and flash heating with microwave irradiation. All of the compounds synthesized exhibited good inhibitory potency in the protease assay, with K(i) values ranging from 0.09 to 3.8 nM. A 30-fold improvement of the antiviral effect in cell culture, compared to the parent compound, was achieved with four of the inhibitors. The differences in K(i) values were not correlated to the differences in antiviral effect, efficiency against mutant virus, or reduced potency in the presence of human serum. The poorest enzyme inhibitors in fact belong to the group with the best antiviral effect. The binding features of two structurally related inhibitors, cocrystallized with HIV-1 protease, are discussed with special emphasis on the interaction at the enzyme/water phase.

Counteracting HIV-1 protease drug resistance: structural analysis of mutant proteases complexed with XV638 and SD146, cyclic urea amides with broad specificities

The long-term therapeutic benefit of HIV antiretroviral therapy is still threatened by drug-resistant variants. Mutations in the S1 subsite of the protease are the primary cause for the loss of sensitivity toward many HIV protease inhibitors, including our first-generation cyclic urea-based inhibitors DMP323 and DMP450. We now report the structures of the three active-site mutant proteases V82F, I84V, and V82F/I84V in complex with XV638 and SD146, two P2 analogues of DMP323 that are 8-fold more potent against the wild type and are able to inhibit a broad panel of drug-resistant variants [Jadhav, P. K., et al. (1997) J. Med. Chem. 40, 181-191]. The increased efficacy of XV638 and SD146 is due primarily to an increase in P2-S2 interactions: 30-40% more van der Waals contacts and two to four additional hydrogen bonds. Furthermore, because these new interactions do not perturb other subsites in the protease, it appears that the large complementary surface areas of their P2 substituents compensate for the loss of P1-S1 interactions and reduce the probability of selecting for drug-resistant variants.

Design and selection of DMP 850 and DMP 851: the next generation of cyclic urea HIV protease inhibitors

BACKGROUND

Recent clinical trials have demonstrated that HIV protease inhibitors are useful in the treatment of AIDS. It is necessary, however, to use HIV protease inhibitors in combination with other antiviral agents to inhibit the development of resistance. The daunting ability of the virus to rapidly generate resistant mutants suggests that there is an ongoing need for new HIV protease inhibitors with superior pharmacokinetic and efficacy profiles. In our attempts to design and select improved cyclic urea HIV protease inhibitors, we have simultaneously optimized potency, resistance profile, protein binding and oral bioavailability.

RESULTS

We have discovered that nonsymmetrical cyclic ureas containing a 3-aminoindazole P2 group are potent inhibitors of HIV protease with excellent oral bioavailability. Furthermore, the 3-aminoindazole group forms four hydrogen bonds with the enzyme and imparts a good resistance profile. The nonsymmetrical 3-aminoindazoles DMP 850 and DMP 851 were selected as our next generation of cyclic urea HIV protease inhibitors because they achieve 8 h trough blood levels in dog, with a 10 mg/kg dose, at or above the protein-binding-adjusted IC90 value for the worst single mutant--that containing the Ile84-->Val mutation.

CONCLUSIONS

In selecting our next generation of cyclic urea HIV protease inhibitors, we established a rigorous set of criteria designed to maximize chances for a sustained antiviral effect in HIV-infected individuals. As DMP 850 and DMP 851 provide plasma levels of free drug that are sufficient to inhibit wild-type HIV and several mutant forms of HIV, they could show improved ability to decrease viral load for clinically significant time periods. The ultimate success of DMP 850 and DMP 851 in clinical trials might depend on achieving or exceeding the oral bioavailability seen in dog.

Peptidomimetic design

Major discoveries have been made of new type-I and type-III peptidomimetic inhibitors of peptide-derived systems. Innovative reversible inhibitors of cysteine proteases and renin, and additional examples of peptidomimetic inhibitors of interleukin-1 beta-converting enzyme, neutral endopeptidase, herpes simplex virus protease, thrombin, HIV protease, Ras farnesyltransferase, the RGD motif, Factor Xa and various aspartic proteases have been discovered.

Cyclic HIV protease inhibitors: design and synthesis of orally bioavailable, pyrazole P2/P2' cyclic ureas with improved potency

Highly potent HIV-1 protease (HIVPR) inhibitors have been designed and synthesized by introducing bidentate hydrogen-bonding oxime and pyrazole groups at the meta-position of the phenyl ring on the P2/P2' substituents of cyclic ureas. Nonsymmetrical cyclic ureas incorporating 3(1H)-pyrazolylbenzyl as P2 and hydrophilic functionalities as P2' show potent protease inhibition and antiviral activities against HIV and have good oral bioavailabilities. The X-ray structure of HIVPR.10A complex confirms that the two pyrazole rings of 10A form bidentate hydrogen bonds with the side-chain oxygen (C=O) and backbone nitrogen (N-H) of Asp30/30' of HIVPR.

Molecular recognition of cyclic urea HIV-1 protease inhibitors

As long as the threat of human immunodeficiency virus (HIV) protease drug resistance still exists, there will be a need for more potent antiretroviral agents. We have therefore determined the crystal structures of HIV-1 protease in complex with six cyclic urea inhibitors: XK216, XK263, DMP323, DMP450, XV638, and SD146, in an attempt to identify 1) the key interactions responsible for their high potency and 2) new interactions that might improve their therapeutic benefit. The structures reveal that the preorganized, C2 symmetric scaffolds of the inhibitors are anchored in the active site of the protease by six hydrogen bonds and that their P1 and P2 substituents participate in extensive van der Waals interactions and hydrogen bonds. Because all of our inhibitors possess benzyl groups at P1 and P1', their relative binding affinities are modulated by the extent of their P2 interactions, e.g. XK216, the least potent inhibitor (Ki (inhibition constant) = 4.70 nM), possesses the smallest P2 and the lowest number of P2-S2 interactions; whereas SD146, the most potent inhibitor (Ki = 0.02 nM), contains a benzimidazolylbenzamide at P2 and participates in fourteen hydrogen bonds and approximately 200 van der Waals interactions. This analysis identifies the strongest interactions between the protease and the inhibitors, suggests ways to improve potency by building into the S2 subsite, and reveals how conformational changes and unique features of the viral protease increase the binding affinity of HIV protease inhibitors.

Potent cyclic urea HIV protease inhibitors with 3-aminoindazole P2/P2' groups

Cyclic ureas containing 3-aminoindazole P2/P2' groups are extremely potent inhibitors of HIV protease. The parent 3-aminoindazole 6 showed a Ki < 0.01 nM but poor translation of enzyme activity to antiviral activity was observed. A series of 3-alkylaminoindazoles revealed that translation improved with increasing lipophilicity. An X-ray crystal structure of 6 bound to HIV protease was obtained.

Analysis of the S3 and S3' subsite specificities of feline immunodeficiency virus (FIV) protease: development of a broad-based protease inhibitor efficacious against FIV, SIV, and HIV in vitro and ex vivo

The S3 and S3' subsite binding specificities of HIV and feline immunodeficiency virus proteases (FIV) proteases (PRs) have been explored by using C2-symmetric competitive inhibitors. The inhibitors evaluated contained (1S, 2R, 3R, 4S)-1,4-diamino-1, 4-dibenzyl-2,3-diol as P1 and P1' units, Val as P2 and P2' residues, and a variety of amino acids at the P3 and P3' positions. All inhibitors showed very high potency against HIV PR in vitro, and their Ki values ranged between 1.1 and 2.6 nM. In contrast to the low restriction of P3 and P3' residues observed in HIV PR, FIV PR exhibited strong preference for small hydrophobic groups at the S3 and S3' subsites. Within this series, the most effective inhibitor against FIV PR contained Ala at P3 and P3'. Its Ki of 41 nM was 415- and 170-fold lower than those of the inhibitors without the P3 and P3' moieties or with the Phe at these positions, respectively. In addition, these compounds were tested against mutant FIV PRs, which contain amino acid substitutions corresponding to those in native HIV PR at homologous sites, and their efficacy of inhibition progressively increased up to 5-fold. The most potent FIV PR inhibitor was selected for examination of its effectiveness in tissue culture, and it was able to block nearly 100% of virus production in an acute infection at 1 microg/ml (1.1 microM) against HIV, FIV, and simian immunodeficiency virus. Furthermore, it was not toxic to cells, and even after 2 months of culture there was no sign of resistance development by virus. The findings suggest that inhibitors with small P3 residue may be efficacious against a broad range of HIV variants as well as interspecies PRs.