Structure-activity relationship studies on 1-[2-(4-Phenylphenoxy)ethyl]pyrrolidine (SC-22716), a potent inhibitor of leukotriene A(4) (LTA(4)) hydrolase

C-C Coupling through Nitrogen Deletion: Application to Library Synthesis

A protocol for parallel C(sp³ )-C(sp³ ) coupling of (hetero)aromatic aldehydes and (hetero)arylmethyl amines based on a reductive amination - "nitrogen deletion" reaction sequence has been developed. After preliminary validation experiments, an illustrative compound library of 25 members was prepared with 76 % synthetic efficiency. The estimated chemical space accessible by the proposed approach covers almost 600 000 representatives that are scarcely represented in current compound databases.

Palladium-Catalyzed Aryldifluoromethylation of Aryl Halides with Aryldifluoromethyl Trimethylsilanes

Diaryl difluoromethanes are valuable targets for medicinal chemistry because they are bioisosteres of diaryl ethers and can function as replacements for diaryl methane, ketone, and sulfone groups. However, methods to prepare diaryl difluoromethanes are scarce, especially methods starting from abundant aryl halides. We report the Pd-catalyzed aryldifluoromethylation of aryl halides with aryldifluoromethyl trimethylsilanes (TMSCF2 Ar). The reaction occurs when the catalyst contains a simple, but unusual, dialkylaryl phosphine ligand that promotes transmetallation of the silane. Computational studies show that reductive elimination following transmetallation occurs with a low barrier, despite the fluorine atoms on the α-carbon, due to coordination of the difluorobenzyl π-system to palladium. The co-development of a cobalt-catalyzed synthesis of the silanes broadened the scope of the process including several applications to the synthesis biologically relevant diaryl difluoromethanes.

Early diagnostic imaging of pneumonia with an ultra-sensitive two-photon near-infrared fluorescent probe

The mortality rate of pneumonia increases significantly with the prolongation of illness. In the pursuit of a tool to accurately diagnose pneumonia in its early stages, we designed and synthesized a two-photon near-infrared fluorescent probe (DCQN) to identify increased concentrations of the inflammation marker SO₂. The probe was found to specifically react with SO₂ by undergoing a 1,4-addition reaction to generate near-infrared fluorescence with good sensitivity (6 s), a large Stokes shift (110 nm) and low detection limit (1.49 nM). DCQN has near-infrared emission as well as good two-photon performance, which can image exogenous and endogenous SO₂ in cells and avoid interference from background fluorescence from cells. Furthermore, this study achieved accurate imaging of a pneumonia lesion site in deep tissues to provide a tool for the fluorescence diagnostic imaging of pneumonia in situ.

Drug discovery strategies for novel leukotriene A4 hydrolase inhibitors

IntroductionLeukotriene A4 hydrolase (LTA4H) is the final and rate limiting enzyme regulating the biosynthesis of leukotriene B4 (LTB4), a pro-inflammatory lipid mediator implicated in a large number of inflammatory pathologies. Inhibition of LTA4H not only prevents LTB4 biosynthesis but also induces a lipid mediator class-switch within the 5-lipoxygenase pathway, elevating biosynthesis of the anti-inflammatory lipid mediator Lipoxin A4. Ample preclinical evidence advocates LTA4H as attractive drug target for the treatment of chronic inflammatory diseases.Areas coveredThis review covers details about the biochemistry of LTA4H and describes its role in regulating pro- and anti-inflammatory mediator generation. It summarizes recent efforts in medicinal chemistry toward novel LTA4H inhibitors, recent clinical trials testing LTA4H inhibitors in pulmonary inflammatory diseases, and potential reasons for the discontinuation of former development programs.Expert opinionGiven the prominent role of LTB4 in initiating and perpetuating inflammation, LTA4H remains an appealing drug target. The reason former attempts targeting this enzyme have not met with success in the clinic can be attributed to compound-specific liabilities of first-generation inhibitors and/or choice of target indications to test this mode of action. A new generation of highly potent and selective LTA4H inhibitors is currently undergoing clinical testing in indications with a strong link to LTB4 biology.

Classification and QSAR models of leukotriene A4 hydrolase (LTA4H) inhibitors by machine learning methods

Leukotriene A4 hydrolase (LTA4H) is an important anti-inflammatory target which can convert leukotriene A4 (LTA4) into pro-inflammatory substance leukotriene B4 (LTB4). In this paper, we built 18 classification models for 463 LTA4H inhibitors by using support vector machine (SVM), random forest (RF) and K-Nearest Neighbour (KNN). The best classification model (Model 2A) was built from RF and MACCS fingerprints. The prediction accuracy of 88.96% and the Matthews correlation coefficient (MCC) of 0.74 had been achieved on the test set. We also divided the 463 LTA4H inhibitors into six subsets using K-Means. We found that the highly active LTA4H inhibitors mostly contained diphenylmethane or diphenyl ether as the scaffold and pyridine or piperidine as the side chain. In addition, six quantitative structure-activity relationship (QSAR) models for 172 LTA4H inhibitors were built by multiple linear regression (MLR) and SVM. The best QSAR model (Model 6A) was built by using SVM and CORINA Symphony descriptors. The coefficients of determination of the training set and the test set were equal to 0.81 and 0.79, respectively. Classification and QSAR models could be used for subsequent virtual screening, and the obtained fragments that were important for highly active inhibitors would be helpful for designing new LTA4H inhibitors.

Recent advances in the catalytic cyclopropanation of unsaturated compounds with diazomethane

The main achievements and development trends of the past 10–15 years related to the catalytic cyclopropanation of unsaturated compounds with diazomethane are integrated and analyzed. The attention is focused on the most efficient catalysts based on palladium compounds. Data on the effects of substrate structure and nature of catalyst components on the regio- and stereoselectivity of these reactions are systematized. Characteristic features of safe methods for diazomethane generation are considered, including the use of membrane technologies and continuous-flow and in situ preparation methods, which have prospects for industrial application.

The bibliography includes 281 references.

Sobetirome prodrug esters with enhanced blood-brain barrier permeability

There is currently great interest in developing drugs that stimulate myelin repair for use in demyelinating diseases such as multiple sclerosis. Thyroid hormone plays a key role in stimulating myelination during development and also controls the expression of important genes involved in myelin repair in adults. Because endogenous thyroid hormone in excess lacks a generally useful therapeutic index, it is not used clinically for indications other than hormone replacement; however, selective thyromimetics such as sobetirome offer a therapeutic alternative. Sobetirome is the only clinical-stage thyromimetic that is known to cross the blood-brain-barrier (BBB) and we endeavored to increase the BBB permeability of sobetirome using a prodrug strategy. Ester prodrugs of sobetirome were prepared based on literature reports of improved BBB permeability with other carboxylic acid containing drugs and BBB permeability was assessed in vivo. One sobetirome prodrug, ethanolamine ester 11, was found to distribute more sobetirome to the brain compared to an equimolar peripheral dose of unmodified sobetirome. In addition to enhanced brain levels, prodrug 11 displayed lower sobetirome blood levels and a brain/serum ratio that was larger than that of unmodified sobetirome. Thus, these data indicate that an ester prodrug strategy applied to sobetirome can deliver increased concentrations of the active drug to the central nervous system (CNS), which may prove useful in the treatment of CNS disorders.

Diverse ways of perturbing the human arachidonic acid metabolic network to control inflammation

Inflammation and other common disorders including diabetes, cardiovascular disease, and cancer are often the result of several molecular abnormalities and are not likely to be resolved by a traditional single-target drug discovery approach. Though inflammation is a normal bodily reaction, uncontrolled and misdirected inflammation can cause inflammatory diseases such as rheumatoid arthritis and asthma. Nonsteroidal anti-inflammatory drugs including aspirin, ibuprofen, naproxen, or celecoxib are commonly used to relieve aches and pains, but often these drugs have undesirable and sometimes even fatal side effects. To facilitate safer and more effective anti-inflammatory drug discovery, a balanced treatment strategy should be developed at the biological network level. In this Account, we focus on our recent progress in modeling the inflammation-related arachidonic acid (AA) metabolic network and subsequent multiple drug design. We first constructed a mathematical model of inflammation based on experimental data and then applied the model to simulate the effects of commonly used anti-inflammatory drugs. Our results indicated that the model correctly reproduced the established bleeding and cardiovascular side effects. Multitarget optimal intervention (MTOI), a Monte Carlo simulated annealing based computational scheme, was then developed to identify key targets and optimal solutions for controlling inflammation. A number of optimal multitarget strategies were discovered that were both effective and safe and had minimal associated side effects. Experimental studies were performed to evaluate these multitarget control solutions further using different combinations of inhibitors to perturb the network. Consequently, simultaneous control of cyclooxygenase-1 and -2 and leukotriene A4 hydrolase, as well as 5-lipoxygenase and prostaglandin E2 synthase were found to be among the best solutions. A single compound that can bind multiple targets presents advantages including low risk of drug-drug interactions and robustness regarding concentration fluctuations. Thus, we developed strategies for multiple-target drug design and successfully discovered several series of multiple-target inhibitors. Optimal solutions for a disease network often involve mild but simultaneous interventions of multiple targets, which is in accord with the philosophy of traditional Chinese medicine (TCM). To this end, our AA network model can aptly explain TCM anti-inflammatory herbs and formulas at the molecular level. We also aimed to identify activators for several enzymes that appeared to have increased activity based on MTOI outcomes. Strategies were then developed to predict potential allosteric sites and to discover enzyme activators based on our hypothesis that combined treatment with the projected activators and inhibitors could balance different AA network pathways, control inflammation, and reduce associated adverse effects. Our work demonstrates that the integration of network modeling and drug discovery can provide novel solutions for disease control, which also calls for new developments in drug design concepts and methodologies. With the rapid accumulation of quantitative data and knowledge of the molecular networks of disease, we can expect an increase in the development and use of quantitative disease models to facilitate efficient and safe drug discovery.

An efficient and metal free synthesis of benzylpyridines using HI through the deoxygenation reaction

An efficient and practical method for the synthesis of benzylpyridines has been developed using aqueous hydroiodic acid in acetic acid.

A novel tamoxifen derivative, ridaifen-F, is a nonpeptidic small-molecule proteasome inhibitor

In a survey of nonpeptide noncovalent inhibitors of the human 20S proteasome, we found that a novel tamoxifen derivative, RID-F (compound 6), inhibits all three protease activities of the proteasome at submicromolar levels. Structure-activity relationship studies revealed that a RID-F analog (RID-F-S*4, compound 25) is the smallest derivative compound capable of inhibiting proteasome activity, with a potency similar to that of RID-F. Kinetic analyses of the inhibition mode and competition experiments involving biotin-belactosin A (a proteasome inhibitor) binding indicated that the RID-F derivatives interact with the protease subunits in a different manner. Culturing of human cells with these compounds resulted in accumulation of ubiquitinated proteins and induction of apoptosis. Thus, the RID-F derivatives may be useful lead chemicals for the generation of a new class of proteasome inhibitors.

Synthesis and SAR study of novel 3,3-diphenyl-1,3-dihydroindol-2-one derivatives as potent eIF2·GTP·Met-tRNAiMet ternary complex inhibitors

The growing recognition of inhibition of translation initiation as a new and promising paradigm for mechanism-based anti-cancer therapeutics is driving the development of potent, specific, and druggable inhibitors. The 3,3-diaryloxindoles were recently reported as potential inhibitors of the eIF2·GTP·Met-tRNAi(Met) ternary complex assembly and 3-{5-tert-butyl-2-hydroxyphenyl}-3-phenyl-1,3-dihydro-2H-indol-2-one #1181 was identified as the prototypic agent of this chemotype. Herein, we report our continuous effort to further develop this chemotype by exploring the structural latitude toward different polar and hydrophobic substitutions. Many of the novel compounds are more potent than the parent compound in the dual luciferase ternary complex reporter assay, activate downstream effectors of reduced ternary complex abundance, and inhibit cancer cell proliferation in the low μM range. Moreover, some of these compounds are decorated with substituents that are known to endow favorable physicochemical properties and as such are good candidates for evaluation in animal models of human cancer.

Development of predictive quantitative structure–activity relationship model and its application in the discovery of human leukotriene A4 hydrolase inhibitors

Background: Human LTA4H catalyzes the conversion of LTA4 to LTB4 and plays a key role in innate immune responses. Inhibition of this enzyme can be a valid method in the treatment of inflammatory response exhibited through LTB4. Results & discussion: The quantitative structure–activity relationship (QSAR) models were developed using genetic function approximation and validated. A training set of 26 diverse compounds and their molecular descriptors were used to develop highly correlating QSAR models. A six-descriptor model explaining the biological activity of the training and test sets with correlation values of 0.846 and 0.502, respectively, was selected as the best model and used in a database screening of drug-like Maybridge database followed by molecular docking. Conclusion: Based on the predicted potent inhibitory activities, expected binding mode and molecular interactions at the active site of hLTA4H final leads were selected as to be utilized in designing future hLTA4H inhibitors.

Leukotriene A4 Hydrolase: Biology, Inhibitors and Clinical Applications

Leukotriene A4 hydrolase is a zinc-containing cytosolic enzyme with both hydrolase and aminopeptidase activity. LTA4H stereospecifically catalyzes the transformation of the unstable epoxide LTA4 to the potent pro-inflammatory mediator LTB4. Variations in the lta4h gene have been linked to susceptibility to multiple diseases including myocardial infarction, stroke and asthma. Pre-clinical animal models and human biomarker data have implicated LTB4 in inflammatory diseases. Several groups have now identified selective inhibitors of LTA4H, many of which were influenced by the disclosure of a protein crystal structure a decade ago. Clinical validation of LTA4H remains elusive despite the progression of inhibitors into pre-clinical and clinical development.

In vitro inhibition of translation initiation by N,N'-diarylureas--potential anti-cancer agents

Symmetrical N,N'-diarylureas: 1,3-bis(3,4-dichlorophenyl)-, 1,3-bis[4-chloro-3-(trifluoromethyl)phenyl]- and 1,3-bis[3,5-bis(trifluoromethyl)phenyl]urea, were identified as potent activators of the eIF2α kinase heme regulated inhibitor. They reduce the abundance of the eIF2·GTP·tRNA(i)(Met) ternary complex and inhibit cancer cell proliferation. An optimization process was undertaken to improve their solubility while preserving their biological activity. Non-symmetrical hybrid ureas were generated by combining one of the hydrophobic phenyl moieties present in the symmetrical ureas with the polar 3-hydroxy-tolyl moiety. O-alkylation of the later added potentially solubilizing charge bearing groups. The new non-symmetrical N,N'-diarylureas were characterized by ternary complex reporter gene and cell proliferation assays, demonstrating good bioactivities. A representative sample of these compounds potently induced phosphorylation of eIF2α and expression of CHOP at the protein and mRNA levels. These inhibitors of translation initiation may become leads for the development of potent, non-toxic, and target specific anti-cancer agents.

Effect of the leukotriene A4 hydrolase aminopeptidase augmentor 4-methoxydiphenylmethane in a pre-clinical model of pulmonary emphysema

The leukotriene A(4) hydrolase enzyme is a dual functioning enzyme with the following two catalytic activities: an epoxide hydrolase function that transforms the lipid metabolite leukotriene A(4) to leukotriene B(4) and an aminopeptidase function that hydrolyzes short peptides. To date, all drug discovery efforts have focused on the epoxide hydrolase activity of the enzyme, because of extensive biological characterization of the pro-inflammatory properties of its metabolite, leukotriene B(4). Herein, we have designed a small molecule, 4-methoxydiphenylmethane, as a pharmacological agent that is bioavailable and augments the aminopeptidase activity of the leukotriene A(4) hydrolase enzyme. Pre-clinical evaluation of our drug showed protection against intranasal elastase-induced pulmonary emphysema in murine models.

High-throughput screening assay for sphingosine kinase inhibitors in whole blood using RapidFire® mass spectrometry

To facilitate discovery of compounds modulating sphingosine-1-phosphate (S1P) signaling, the authors used high-throughput mass spectrometry technology to measure S1P formation in human whole blood. Since blood contains endogenous sphingosine (SPH) and S1P, mass spectrometry was chosen to detect the conversion of an exogenously added 17-carbon-long variant of sphingosine, C17SPH, into C17S1P. The authors developed procedures to achieve homogeneous mixing of whole blood in 384-well plates and for a method requiring minimal manipulations to extract S1P from blood in 96- and 384-well plates prior to analyses using the RapidFire(®) mass spectrometry system.

Introduction to fragment-based drug discovery

Fragment-based drug discovery (FBDD) has emerged in the past decade as a powerful tool for discovering drug leads. The approach first identifies starting points: very small molecules (fragments) that are about half the size of typical drugs. These fragments are then expanded or linked together to generate drug leads. Although the origins of the technique date back some 30 years, it was only in the mid-1990s that experimental techniques became sufficiently sensitive and rapid for the concept to be become practical. Since that time, the field has exploded: FBDD has played a role in discovery of at least 18 drugs that have entered the clinic, and practitioners of FBDD can be found throughout the world in both academia and industry. Literally dozens of reviews have been published on various aspects of FBDD or on the field as a whole, as have three books (Jahnke and Erlanson, Fragment-based approaches in drug discovery, 2006; Zartler and Shapiro, Fragment-based drug discovery: a practical approach, 2008; Kuo, Fragment based drug design: tools, practical approaches, and examples, 2011). However, this chapter will assume that the reader is approaching the field with little prior knowledge. It will introduce some of the key concepts, set the stage for the chapters to follow, and demonstrate how X-ray crystallography plays a central role in fragment identification and advancement.

Discovery of 4-[(2S)-2-{[4-(4-chlorophenoxy)phenoxy]methyl}-1-pyrrolidinyl]butanoic acid (DG-051) as a novel leukotriene A4 hydrolase inhibitor of leukotriene B4 biosynthesis

Both in-house human genetic and literature data have converged on the identification of leukotriene 4 hydrolase (LTA(4)H) as a key target for the treatment of cardiovascular disease. We combined fragment-based crystallography screening with an iterative medicinal chemistry effort to optimize inhibitors of LTA(4)H. Ligand efficiency was followed throughout our structure-activity studies. As applied within the context of LTA(4)H inhibitor design, the chemistry team was able to design a potent compound 20 (DG-051) (K(d) = 26 nM) with high aqueous solubility (>30 mg/mL) and high oral bioavailability (>80% across species) that is currently undergoing clinical evaluation for the treatment of myocardial infarction and stroke. The structural biology-chemistry interaction described in this paper provides a sound alternative to conventional screening techniques. This is the first example of a gene-to-clinic paradigm enabled by a fragment-based drug discovery effort.

Discovery of leukotriene A4 hydrolase inhibitors using metabolomics biased fragment crystallography

We describe a novel fragment library termed fragments of life (FOL) for structure-based drug discovery. The FOL library includes natural small molecules of life, derivatives thereof, and biaryl protein architecture mimetics. The choice of fragments facilitates the interrogation of protein active sites, allosteric binding sites, and protein−protein interaction surfaces for fragment binding. We screened the FOL library against leukotriene A4 hydrolase (LTA4H) by X-ray crystallography. A diverse set of fragments including derivatives of resveratrol, nicotinamide, and indole were identified as efficient ligands for LTA4H. These fragments were elaborated in a small number of synthetic cycles into potent inhibitors of LTA4H representing multiple novel chemotypes for modulating leukotriene biosynthesis. Analysis of the fragment-bound structures also showed that the fragments comprehensively recapitulated key chemical features and binding modes of several reported LTA4H inhibitors.

Identification of a potent, selective, and orally active leukotriene a4 hydrolase inhibitor with anti-inflammatory activity

LTA 4H is a ubiquitously distributed 69 kDa zinc-containing cytosolic enzyme with both hydrolase and aminopeptidase activity. As a hydrolase, LTA 4H stereospecifically catalyzes the transformation of the unstable epoxide LTA 4 to the diol LTB 4, a potent chemoattractant and activator of neutrophils and a chemoattractant of eosinophils, macrophages, mast cells, and T cells. Inhibiting the formation of LTB 4 is expected to be beneficial in the treatment of inflammatory diseases such as inflammatory bowel disease (IBD), asthma, and atherosclerosis. We developed a pharmacophore model using a known inhibitor manually docked into the active site of LTA 4H to identify a subset of compounds for screening. From this work we identified a series of benzoxazole, benzthiazole, and benzimidazole inhibitors. SAR studies resulted in the identification of several potent inhibitors with an appropriate cross-reactivity profile and excellent PK/PD properties. Our efforts focused on further profiling JNJ 27265732, which showed encouraging efficacy in a disease model relevant to IBD.

Synthesis of glutamic acid analogs as potent inhibitors of leukotriene A4 hydrolase

Leukotriene B(4) (LTB(4)) is a potent pro-inflammatory mediator that has been implicated in the pathogenesis of multiple diseases, including psoriasis, inflammatory bowel disease, multiple sclerosis and asthma. As a method to decrease the level of LTB(4) and possibly identify novel treatments, inhibitors of the LTB(4) biosynthetic enzyme, leukotriene A(4) hydrolase (LTA(4)-h), have been explored. Here we describe the discovery of a potent inhibitor of LTA(4)-h, arylamide of glutamic acid 4f, starting from the corresponding glycinamide 2. Analogs of 4f are then described, focusing on compounds that are both active and stable in whole blood. This effort culminated in the identification of amino alcohol 12a and amino ester 6b which meet these criteria.

Lipoxygenase inhibitors: a comparative QSAR study review and evaluation of new QSARs

This paper contains a quantitative structure activity relationship (QSAR) study for lipoxygenase (LO) inhibitors. It reveals that in almost all cases, the clog P parameter plays an important part in the QSARs (linear or bilinear model). In some cases the steric factors such as the overall molar refractivity (CMR) or the substituents molar refractivity (MR) (linear or parabola) are important. Electronic effects are comparatively unimportant. The study shows that log P as calculated from the Clog P program is suitable for this form of QSAR study.

Development of a Homogeneous Time-Resolved Fluorescence Leukotriene B4Assay for Determining the Activity of Leukotriene A4Hydrolase

Leukotriene A4(LTA4) hydrolase catalyzes a rate-limiting final biosynthetic step of leukotriene B4(LTB4), a potent lipid chemotatic agent and proinflammatory mediator. LTB4has been implicated in the pathogenesis of various acute and chronic inflammatory diseases, and thus LTA4hydrolase is regarded as an attractive therapeutic target for anti-inflammation. To facilitate identification and optimization of LTA4hydrolase inhibitors, a specific and efficient assay to quantify LTB4is essential. This article describes the development of a novel 384-well homogeneous time-resolved fluorescence assay for LTB4(LTB4HTRF®assay) and its application to establish an HTRF-based LTA4hydrolase assay for lead optimization. This LTB4HTRF assay is based on competitive inhibition and was established by optimizing the reagent concentration, buffer composition, incubation time, and assay miniaturization. The optimized assay is sensitive, selective, and robust, with a Z' factor of 0.89 and a subnanomolar detection limit for LTB4. By coupling this LTB4HTRF assay to the LTA4hydrolase reaction, an HTRF-based LTA4hydrolase assay was established and validated. Using a test set of 16 LTA4hydrolase inhibitors, a good correlation was found between the IC50values obtained using LTB4HTRF with those determined using the LTB enzyme-linked immunoassay ( R = 0.84). The HTRF-based LTA4hydrolase assay was shown to be an efficient and suitable4assay for determining compound potency and library screening to guide the development of potent inhibitors of LTA4hydrolase. ( Journal of Biomolecular Screening 2007:536-545)

Synthesis and structure activity relationships of novel non-peptidic metallo-aminopeptidase inhibitors

Racemic derivatives of 3-amino-2-tetralone were synthesised and evaluated for their ability to inhibit metallo-aminopeptidase activities. New compounds substituted in position 2 by methyl ketone, substituted oximes or hydroxamic acids as well as heterocyclic derivatives were evaluated against representative members of zinc-dependent aminopeptidases: leucine aminopeptidase (E.C. 3.4.11.1), aminopeptidase-N (E.C. 3.4.11.2), Aeromonas proteolytica aminopeptidase (E.C. 3.4.11.10), and the aminopeptidase activity of leukotriene A(4) hydrolase (E.C. 3.3.2.6). Several compounds showed K(i) values in the low micromolar range against the 'one-zinc' aminopeptidases, while most of them were rather poor inhibitors of the 'two-zinc' enzymes. This interesting selectivity profile may guide the design of new, specific inhibitors of target mammalian aminopeptidases with one active site zinc.

[Leukotriene-lipoxygenase pathway and drug discovery]

The first drugs affecting the leukotriene-lipoxygenase pathway, which have been introduced in clinical application, inhibit effects of slow reacting substance of anaphylaxis (SRS-A). Although, a 5-lipoxygenase inhibitor was first used in clinical practice as an anti-asthma drug, cysteinyl-leukotriene type 1 receptor (cysLT(1)R) antagonists are preferred as anti-asthma and anti-rhinitis drugs because they are almost as effective as the 5-lipoxygenase inhibitors but have fewer side effects. The cloning of genes related to lipoxygenase-leukotriene metabolism prompted us to try to elucidate the role of leukotrienes in various inflammations. There are at least two types of cysLTRs known: cysLT(1)R and cysLT(2)R. CysLT(1)R plays an important role in the pathophysiology of asthma; however, the role of the cysLT(2)R remains unknown. The abundant distribution of cysLT(2)R in heart and brain tissues suggests that cysLTs play an important role in the pathophysiology of ischemic heart diseases or arrhythmias and through this receptor (cysLT(2)R), psychoneurological disorders. The use of a selective cysLT(2)R antagonist may clarify these questions. Since the 5-lipoxygenase pathway is abundantly expressed in atherosclerotic lesions, and 12/15-lipoxygenase is able to oxygenate polyunsaturated fatty acid esterified in the membranous phospholipids, 5-lipoxygenase or 12/15-lipoxygenase inhibitors may prevent progression of atherosclerosis. In addition, it has been reported that 15-lipoxygenase participates in suppression of prostate cancer. In conclusion, the leukotriene-lipoxygenase metabolism may be involved in the pathophysiology of acute inflammatory to chronic progressive disorders. We think that more drugs modifying leukotriene-lipoxygenase metabolism will be introduced into clinical practice in the future.

Synthesis of imidazopyridines and purines as potent inhibitors of leukotriene A4 hydrolase

The synthesis and biological evaluation of a series of heterocyclic analogues of the previously reported LTA(4) hydrolase inhibitor 1b are described. Imidazopyridine and purine analogues are specifically highlighted with several demonstrating excellent potency in our in vitro assays, as well as good oral activity in a mouse ex vivo assay.

Pyrrolidine and piperidine analogues of SC-57461A as potent, orally active inhibitors of leukotriene A(4) hydrolase

The synthesis and biological evaluation of a series of functionalized pyrrolidine- and piperidine-containing analogues of our lead LTA(4) hydrolase inhibitor, SC-57461A, is described. A number of compounds showed excellent potency in our in vitro screens and several demonstrated good oral activity in a mouse ex vivo assay. These efforts led to the identification of SC-56938 (14) as a potent, orally active inhibitor of LTA(4) hydrolase.

Synthesis of potent leukotriene A(4) hydrolase inhibitors. Identification of 3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid

Leukotriene B(4) (LTB(4)) is a potent, proinflammatory mediator involved in the pathogenesis of a number of diseases including inflammatory bowel disease, psoriasis, rheumatoid arthritis, and asthma. The enzyme LTA(4) hydrolase represents an attractive target for pharmacological intervention in these disease states, since the action of this enzyme is the rate-limiting step in the production of LTB(4). Our previous efforts focused on the exploration of a series of analogues related to screening hit SC-22716 (1, 1-[2-(4-phenylphenoxy)ethyl]pyrrolidine) and resulted in the identification of potent, orally active inhibitors such as 2. Additional structure-activity relationship studies around this structural class resulted in the identification of a series of alpha-, beta-, and gamma-amino acid analogues that are potent inhibitors of the LTA(4) hydrolase enzyme and demonstrated good oral activity in a mouse ex vivo whole blood LTB(4) production assay. The efforts leading to the identification of clinical candidate SC-57461A (8d, 3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid) are described.

Leukotriene A4 hydrolase

The leukotrienes (LTs) are a family of lipid mediators involved in inflammation and allergy. Leukotriene B4 is a classical chemoattractant, which triggers adherence and aggregation of leukocytes to the endothelium at only nanomolar concentrations. In addition, leukotriene B4 modulates immune responses, participates in the host-defense against infections, and is a key mediator of PAF-induced lethal shock. Because of these powerful biological effects, leukotriene B4 is implicated in a variety of acute and chronic inflammatory diseases, e.g. nephritis, arthritis, dermatitis, and chronic obstructive pulmonary disease. The final step in the biosynthesis of leukotriene B4 is catalyzed by leukotriene A4 hydrolase, a unique bi-functional zinc metalloenzyme with an anion-dependent aminopeptidase activity. Here we describe the most recent developments regarding our understanding of the structure, function, and catalytic mechanisms of leukotriene A4 hydrolase.

Pharmacological characterization of SC-57461A (3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl), a potent and selective inhibitor of leukotriene A(4) hydrolase I: in vitro studies

Leukotriene (LT) B(4) is an inflammatory mediator that has been implicated in the pathogenesis of various diseases, including inflammatory bowel disease and psoriasis. As the rate-limiting step for LTB(4) production, LTA(4) hydrolase represents an attractive target for therapeutic agents that interfere with LTB(4) production. In the present study we evaluated a chemically novel compound designated SC-57461A (3-[methyl[3-[4-(phenylmethyl)phenoxy]propyl]amino]propanoic acid HCl) as an inhibitor of LTA(4) hydrolase. Pharmacological comparisons are made to its free acid SC-57461. SC-57461A is a potent competitive inhibitor of recombinant human LTA(4) hydrolase when either LTA(4) (IC(50) = 2.5 nM, K(i) = 23 nM) or peptide substrates (IC(50) = 27 nM) are used. In human whole blood, the IC(50) for calcium ionophore-induced LTB(4) production was 49 nM, indicative of good cell penetration. Whole blood production of the cyclooxygenase metabolite thromboxane B(2) was not affected. SC-57461A was also active in several other species, including mouse, rat, dog, and rhesus monkey. The data indicate that SC-57461A is a potent and selective inhibitor of LTA(4) hydrolase.

Antipsoriatic anthrones with modulated redox properties. 5. Potent inhibition of human keratinocyte growth, induction of keratinocyte differentiation, and reduced membrane damage by novel 10-arylacetyl-1,8-dihydroxy-9(10H)-anthracenones

The synthesis and structure-activity relationships (SARs) of a series of novel 10-arylacetyl-1,8-dihydroxy-9(10H)-anthracenones are described. Acylation of anthralin with either the appropriate arylacetyl chlorides or arylacetic acids in the presence of pyridine or via the coupling agent dicyclohexylcarbodiimide (DCC), respectively, furnished this structural class of antipsoriatic agents. Potential antipsoriatic activity was evaluated in complementary assays specifically addressed to three important aspects of psoriasis. First, several compounds were identified which are equally potent as inhibitors of human keratinocyte growth as the antipsoriatic agent anthralin. Furthermore, improved ratio of antiproliferative activity to cytotoxicity is demonstrated by the reduced potential of the novel analogues to induce membrane damage, which is a benefit of their reduced ability to generate oxygen radicals as documented by deoxyribose degradation. Second, analogue 3o bearing a hydroxamate functional group was also a highly potent inhibitor of LTB(4) biosynthesis in addition to its excellent antiproliferative activity. SARs of these inhibitors of both keratinocyte growth and LTB(4) biosynthesis with respect to the nature of the para-substitution in the 10-phenylacetyl side chain are discussed. Third, the compounds were also evaluated for their ability to induce the formation of cornified envelope protein in keratinocytes. Cross-linking of cellular protein as a marker of terminal differentiation of keratinocytes was observed for many 10-arylacetyl analogues at concentrations required to arrest cell growth. This newly uncovered activity of the novel anthracenones suggests antipsoriatic potential with respect to disturbance of keratinocyte differentiation, in addition to hyperproliferative and inflammatory aspects of psoriasis.

10-Phenylbutyryl-substituted anthracenones as inhibitors of keratinocyte growth and LTB(4) biosynthesis

A recent observation that phenylbutyryl anthracenone 2, an analogue of the antipsoriatic anthralin, is a potent inhibitor of leukotriene B(4) (LTB(4)) biosynthesis has prompted a search of other anthracenones with improved antiproliferative activity. In that direction, a limited number of analogues related to 2 have been prepared and evaluated in the HaCaT keratinocytes proliferation and in the polymorphonuclear leukocyte LTB(4) assay. The 4-methoxy analogue 2a and the side chain methylated 2l retain the full inhibitory activity of 1 against LTB(4) biosynthesis while their antiproliferative activity is markedly enhanced and comparable to that of the antipsoriatic anthralin. In contrast to anthralin, cytotoxic effects against cell membranes are strongly reduced as documented by the LDH activity released from cytoplasm of keratinocytes.