Discovery of an orally active series of isoxazoline glycoprotein IIb/IIIa antagonists

O-H bond activation of β,γ-unsaturated oximes via hydrogen atom transfer (HAT) and photoredox dual catalysis

Hydrogen atom transfer (HAT) and photoredox dual catalysis provides a unique opportunity in organic synthesis, enabling the direct activation of C/Si/S-H bonds. However, the activation of O-H bonds of β,γ-unsaturated oximes poses a challenge due to their relatively high redox potential, which exceeds the oxidizing capacity of most currently developed photocatalysts. We here demonstrate that the combination of HAT and photoredox catalysis allows the activation of O-H bond of β,γ-unsaturated oximes. The strategy effectively addresses the oxime's high redox potential and offers a universal pathway for iminoxyl radical formation. Leveraging the versatility of this approach, a diverse array of valuable heterocycles have been synthesized with the use of different radical acceptors. Mechanistic studies confirm a HAT process for the O-H bond activation.

Enantio- and Chemoselective Intramolecular Iridium-Catalyzed O-Allylation of Oximes

A method for the enantio- and chemoselective iridium-catalyzed O-allylation of oximes is described. Kinetic resolution in an intramolecular setting provides enantioenriched oxime ethers and aliphatic allylic alcohols. The synthetic potential of the products generated with this method is showcased by their elaboration into a series of heterocyclic compounds and the formal synthesis of glycoprotein GP IIb-IIIa receptor antagonist (-)-roxifiban. Preliminary mechanistic experiments and computational data shed light on the remarkable chemoselectivity of the reaction.

2-Isoxazolines: A Synthetic and Medicinal Overview

Isoxazolines are nitrogen- and oxygen-containing five-membered heterocyclic scaffolds with extensive biological activities. This framework can be readily obtained in good to excellent yields through 1,3-dipolar cycloaddition between nitrones with alkynes or allenes, aryl/alkyl halides, alkynes, and oxaziridines under mild conditions. This scaffold has been an emerging area of interest for many researchers given their wide range of bioactivities. Herein we review synthetic strategies toward isoxazolines and the role these efforts have had in enhancing the biological activity of natural products and synthetic compounds such as antitubercular agents, COX-1 inhibitors, COX-2 inhibitors (e. g., valdecoxib), nicotinic receptor modulators, and MIF inhibitors. With a focus on efforts from 2010 onward, this review provides in-depth coverage of the design and biological evaluation of isoxazoline systems and their impact on various pathologies.

5-(4H)-Oxazolones and Their Benzamides as Potential Bioactive Small Molecules

The five membered heterocyclic oxazole group plays an important role in drug discovery. Oxazolones present a wide range of biological activities. In this article the synthesis of 4-substituted-2-phenyloxazol-5(4H)-ones from the appropriate substituted aldehydes via an Erlenmeyer–Plochl reaction is reported. Subsequently, the corresponding benzamides were produced via a nucleophilic attack of a secondary amine on the oxazolone ring applying microwave irradiation. The compounds are obtained in good yields up to 94% and their structures were confirmed using IR, ¹H-NMR, ¹³C-NMR and LC/MS data. The in vitro anti-lipid peroxidation activity and inhibitory activity against lipoxygenase and trypsin induced proteolysis of the novel derivatives were studied. Inhibition of carrageenin-induced paw edema (CPE) and nociception was also determined for compounds 4a and 4c. Oxazolones 2a and 2c strongly inhibit lipid peroxidation, followed by oxazolones 2b and 2d with an average inhibition of 86.5%. The most potent lipoxygenase inhibitor was the bisbenzamide derivative 4c, with IC₅₀ 41 μM. The benzamides 3c, 4a–4e and 5c were strong inhibitors of proteolysis. The replacement of the thienyl moiety by a phenyl group does not favor the protection. Compound 4c inhibited nociception higher than 4a. The replacement of thienyl groups by phenyl ring led to reduced biological activity. Docking studies of the most potent LOX inhibitor highlight interactions through allosteric mechanism. All the potent derivatives present good oral bioavailability.

Key role of MIF-related neuroinflammation in neurodegeneration and cognitive impairment in Alzheimer's disease

Background

Macrophage Migration Inhibitory Factor (MIF) is a potent proinflammatory cytokine that promotes the production of other immune mediators. MIF is produced by most cell types in the brain including microglia, astrocytes and neurons. Enhanced expression of MIF might contribute to the persistent activation of glial, chronic neuroinflammation and neurodegeneration. Here, we investigated the effect of MIF on inflammatory markers and spatial learning in a mouse model of sporadic AD and on tau pathology in AD patients.

Methods

We examined the effects of MIF deficiency and pharmacological MIF inhibition in vitro and in vivo. In vitro, quantitative PCR and ELISA were used to assess cytokine production of STZ-treated glial cells. In vivo, C57BL/6 mice were subjected to intracerebroventricular streptozotocin injection (3 mg/kg, ICV-STZ). Neuroinflammation and contextual learning performance were assessed using quantitative PCR and fear conditioning, respectively. Pharmacological MIF inhibition was achieved with intraperitoneal injections of ISO-1 (daily, IP, 20 mg/kg in 5% DMSO in 0.9% NaCl) for 4 weeks following ICV-STZ injection. The findings from ISO-1 treated mice were confirmed in MIF knockout C57BL/6. To assess the role of MIF in human AD, cerebrospinal fluid levels of MIF and hyperphosphorylated tau were measured using ELISA.

Results

Administration ICV-STZ resulted in hippocampal dependent cognitive impairment. MIF inhibition with ISO-1 significantly improved the STZ-induced impairment in contextual memory performance, indicating MIF-related inflammation as a major contributor to ICV-STZ-induced memory deficits. Furthermore, inhibition of the MIF resulted in reduced cytokine production in vitro and in vivo.

In human subjects with AD at early clinical stages, cerebrospinal fluid levels of MIF were increased in comparison with age-matched controls, and correlated with biomarkers of tau hyper-phosphorylation and neuronal injury hinting at MIF levels as a potential biomarker for early-stage AD.

Conclusions

The present study indicates the key role of MIF in controlling the chronic cytokine release in neuroinflammation related to tau hyperphosphorylation, neurodegeneration, and clinical manifestations of AD, suggesting the potential of MIF inhibition as therapeutic strategy to slow down neurodegeneration and clinical disease progression.

Copper nitrate-mediated synthesis of 3-aryl isoxazolines and isoxazoles from olefinic azlactones

A copper nitrate-mediated [2 + 2 + 1] cycloaddition reaction was developed for the expedient synthesis of isoxazolines and isoxazoles from olefinic azlactones.

Hypervalent iodine-mediated Ritter-type amidation of terminal alkenes: The synthesis of isoxazoline and pyrazoline cores

Hypervalent iodine-mediated olefin functionalization provides a rapid gateway towards accessing both various heterocyclic cores and functional groups. In this regard, we have developed a Ritter-type alkene functionalization utilizing a PhI(OAc)₂ ((diacetoxyiodo)benzene, PIDA)/Lewis acid combination in order to access isoxazoline and pyrazoline cores. Based on allyl ketone oximes and allyl ketone tosylhydrazones, we have developed an alkene oxyamidation and amido-amidation protocol en route to accessing both isoxazoline and pyrazoline cores. Additionally, acetonitrile serves as both the solvent and an amine source in the presence of this PIDA/Lewis acid combination. This operationally straightforward and metal-free protocol provides an easy access to isoxazoline and pyrazoline derivatives.

Review of the synthesis of acyclic and cyclic oxime ethers

Oxime ethers have attracted much attention due to their potential biological activities and wide variety of synthetic applications.

Organic carbamates in drug design and medicinal chemistry

The carbamate group is a key structural motif in many approved drugs and prodrugs. There is an increasing use of carbamates in medicinal chemistry and many derivatives are specifically designed to make drug-target interactions through their carbamate moiety. In this Perspective, we present properties and stabilities of carbamates, reagents and chemical methodologies for the synthesis of carbamates, and recent applications of carbamates in drug design and medicinal chemistry.

A novel allosteric inhibitor of macrophage migration inhibitory factor (MIF)

Macrophage migration inhibitory factor (MIF) is a catalytic cytokine and an upstream mediator of the inflammatory pathway. MIF has broad regulatory properties, dysregulation of which has been implicated in the pathology of multiple immunological diseases. Inhibition of MIF activity with small molecules has proven beneficial in a number of disease models. Known small molecule MIF inhibitors typically bind in the tautomerase site of the MIF trimer, often covalently modifying the catalytic proline. Allosteric MIF inhibitors, particularly those that associate with the protein by noncovalent interactions, could reveal novel ways to block MIF activity for therapeutic benefit and serve as chemical probes to elucidate the structural basis for the diverse regulatory properties of MIF. In this study, we report the identification and functional characterization of a novel allosteric MIF inhibitor. Identified from a high throughput screening effort, this sulfonated azo compound termed p425 strongly inhibited the ability of MIF to tautomerize 4-hydroxyphenyl pyruvate. Furthermore, p425 blocked the interaction of MIF with its receptor, CD74, and interfered with the pro-inflammatory activities of the cytokine. Structural studies revealed a unique mode of binding for p425, with a single molecule of the inhibitor occupying the interface of two MIF trimers. The inhibitor binds MIF mainly on the protein surface through hydrophobic interactions that are stabilized by hydrogen bonding with four highly specific residues from three different monomers. The mode of p425 binding reveals a unique way to block the activity of the cytokine for potential therapeutic benefit in MIF-associated diseases.

Evaluation of bis-alkylamidoxime O-alkylsulfonates as orally available antimalarials

The main threat to controlling malaria is the emerging multidrug resistance of Plasmodium sp. parasites. Bis-alkylamidines were developed as a potential new chemotherapy that targets plasmodial phospholipid metabolism. Unfortunately, these compounds are not orally available. To solve this absorption issue, we investigated a prodrug strategy based on sulfonate derivatives of alkylamidoximes. A total of 25 sulfonates were synthesized as prodrug candidates of one bis-N-alkylamidine and of six N-substituted bis-C-alkylamidines. Their antimalarial activities were evaluated in vitro against P. falciparum and in vivo against P. vinckei in mice to define structure-activity relationships. Small alkyl substituents on the sulfonate group of both C-alkyl- and N-alkylamidines led to the best oral antimalarial activities; alkylsulfonate derivatives are chemically transformed into the corresponding alkylamidines.

Macrophage migration inhibitory factor deficiency protects pancreatic islets from palmitic acid-induced apoptosis

As a result of chronic exposure to high levels of free fatty acids, glucose and inflammatory mediators β-cell apoptosis occurs at the end stage of obesity-associated type 2 diabetes (T2D). One potentially deleterious molecule for β-cell function associated with T2D and obesity in humans is macrophage migration inhibitory factor (MIF). Therefore, the aim of this study was to explore MIF expression in vivo during development of obesity and insulin resistance in high-fat diet (HFD)-fed C57BL/6 mice and whether MIF inhibition could affect β-cell apoptosis and dysfunction induced by palmitic acid (PA) in vitro. Indeed, increase in systemic and locally produced MIF correlated well with the weight gain, triglyceride upregulation, glucose intolerance and insulin resistance, which developed in HFD-fed mice. In in vitro settings PA dose-dependently induced MIF secretion before apoptosis development in islets. Further, mif gene deletion, mRNA silencing or protein inhibition rescued β-cells from PA-induced apoptosis as measured by MTT assay and histone-DNA enzyme linked immuno sorbent assay. Protection from induced apoptosis was mediated by altered activation of caspase pathway and correlated with changes in the level of Bcl-2 family members. Further, MIF inhibition conveyed a significant resistance to PA-induced downregulation of insulin and PDX-1 expression and ATP content. However, β-cell function was not entirely preserved in the absence of MIF judging by low glucose oxidation and depolarized mitochondrial membrane. In conclusion, the observed considerable preservation of β-cells from nutrient-induced apoptosis might implicate MIF as a potential therapeutic target in the later stage of obesity-associated T2D.

Synthesis and bio-evaluation of human macrophage migration inhibitory factor inhibitor to develop anti-inflammatory agent

Macrophage migration inhibitory factor (MIF), a pro-inflammatory cytokine, is involved in the development of an array of inflammatory disorders including rheumatoid arthritis, inflammatory bowel disease, psoriasis, multiple sclerosis and sepsis. The synthesis of MIF-inhibitor is a rationale approach to develop novel anti-inflammatory agent to treat multitude of inflammatory diseases. In this work, we have synthesized and evaluated MIF-inhibitory activity of a series of small molecules containing isoxazoline skeleton. Mode of binding of this inhibitor to human MIF (huMIF) was determined by docking studies. The synthesized molecules inhibit tautomerase activity of huMIF. The anti-inflammatory activity of the most active inhibitor, 4-((3-(4-hydroxy-3-methoxyphenyl)-4, 5-dihydroisoxazol-5-yl) methoxy) benzaldehyde (4b) was evaluated against huMIF-induced inflammation in a cellular model (RAW 264.7 cell). Compound 4b significantly inhibits huMIF-mediated NF-κB translocation to the nucleus, up-regulation of inducible nitric oxide synthase and nitric oxide production in RAW 264.7 cell which are the markers for inflammation. The compound 4b is not cytotoxic as evident from cell viability assay. Hence, the compound 4b has potential to be a novel anti-inflammatory agent.

A small-molecule macrophage migration inhibitory factor antagonist protects against glomerulonephritis in lupus-prone NZB/NZW F1 and MRL/lpr mice

Autoimmunity leads to the activation of innate effector pathways, proinflammatory cytokine production, and end-organ injury. Macrophage migration inhibitory factor (MIF) is an upstream activator of the innate response that mediates the recruitment and retention of monocytes via CD74 and associated chemokine receptors, and it has a role in the maintenance of B lymphocytes. High-expression MIF alleles also are associated with end-organ damage in different autoimmune diseases. We assessed the therapeutic efficacy of (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1), an orally bioavailable MIF antagonist, in two distinct models of systemic lupus erythematosus: the NZB/NZW F1 and the MRL/lpr mouse strains. ISO-1, like anti-MIF, inhibited the interaction between MIF and its receptor, CD74, and in each model of disease, it reduced functional and histological indices of glomerulonephritis, CD74(+) and CXCR4(+) leukocyte recruitment, and proinflammatory cytokine and chemokine expression. Neither autoantibody production nor T and B cell activation were significantly affected, pointing to the specificity of MIF antagonism in reducing excessive proinflammatory responses. These data highlight the feasibility of targeting the MIF-MIF receptor interaction by small-molecule antagonism and support the therapeutic value of downregulating MIF-dependent pathways of tissue damage in systemic lupus erythematosus.

Photoresponsive Organogel Based on Supramolecular Assembly of Tris(phenylisoxazolyl)benzene

Azobenzene-substituted tris(phenylisoxazolyl)benzene 1 was developed as a photoresponsive gelator. A detailed study of the self-assembly of the trans- and cis-isomers in solution revealed that the planar trans-isomer assembled to form molecular stacks along its C 3 axis, whereas the cis-isomer did not owing to steric requirements. Based on diffusion ordered spectroscopy experiments, the size of the aggregates formed from the trans-isomer were roughly four times as large as those of the cis-isomer. The photoinduced gel-to-sol transition was achieved by irradiation with UV light at 360 nm. Solid-state morphologies of the trans- and cis-isomers were quite contrastive; the trans-isomer created fibrous supramolecular networks with a lot of voids in which solvent molecules could be immobilized, whereas the cis-isomer never created such fibrous morphologies. The trans–cis structural change of the azobenzene moieties obviously regulates the gelation ability of 1.

Small-molecule inhibitors of integrin alpha2beta1 that prevent pathological thrombus formation via an allosteric mechanism

There is a grave need for safer antiplatelet therapeutics to prevent heart attack and stroke. Agents targeting the interaction of platelets with the diseased vessel wall could impact vascular disease with minimal effects on normal hemostasis. We targeted integrin alpha(2)beta(1), a collagen receptor, because its overexpression is associated with pathological clot formation whereas its absence does not cause severe bleeding. Structure-activity studies led to highly potent and selective small-molecule inhibitors. Responses of integrin alpha(2)beta(1) mutants to these compounds are consistent with a computational model of their mode of inhibition and shed light on the activation mechanism of I-domain-containing integrins. A potent compound was proven efficacious in an animal model of arterial thrombosis, which demonstrates in vivo efficacy for inhibition of this platelet receptor. These results suggest that targeting integrin alpha(2)beta(1) could be a potentially safe, effective approach to long-term therapy for cardiovascular disease.

Pd-catalyzed carboetherification of beta,gamma-unsaturated oximes: a novel approach to Delta2-isoxazolines

A novel route to the synthesis of Delta2-isoxazoline derivatives is described. Reaction of beta,gamma-unsaturated oximes with aryl bromides via palladium-catalyzed carboetherification affords 3,5-disubstituted Delta2-isoxazolines in good yields. The use of Xantphos as ligand is crucial for the transformation. The carboetherification products can be further converted to beta-hydroxy ketones in the presence of Fe powder and NH4Cl.

Small molecule inhibitors of integrin alpha2beta1

Interactions between the integrin, alpha2beta1, and extracellular matrix (ECM), particularly collagen, play a pivotal role in platelet adhesion and thrombus formation. Platelets interact with collagen in the subendothelial matrix that is exposed by vascular damage. To evaluate the potential of alpha2beta1 inhibitors for anticancer and antithrombotic applications, we have developed a series of small molecule inhibitors of this integrin based on a prolyl-2,3-diaminopropionic acid (DAP) scaffold using solid-phase parallel synthesis. A benzenesulfonamide substituent at the N-terminus of the dipepetide and a benzyl urea at the DAP side chain resulted in tight and highly selective inhibition of alpha2beta1-mediated adhesion of human platelets and other cells to collagen.

Alternative chemical modifications reverse the binding orientation of a pharmacophore scaffold in the active site of macrophage migration inhibitory factor

Pharmacophores are chemical scaffolds upon which changes in chemical moieties (R-groups) at specific sites are made to identify a combination of R-groups that increases the therapeutic potency of a small molecule inhibitor while minimizing adverse effects. We developed a pharmacophore based on a carbonyloxime (OXIM) scaffold for macrophage migration inhibitory factor (MIF), a protein involved in the pathology of sepsis, to validate that inhibition of a catalytic site could produce therapeutic benefits. We studied the crystal structures of MIF.OXIM-based inhibitors and found two opposite orientations for binding to the active site that were dependent on the chemical structures of an R-group. One orientation was completely unexpected based on previous studies with hydroxyphenylpyruvate and (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1). We further confirmed that the unexpected binding mode targets MIF in cellular studies by showing that one compound, OXIM-11, abolished the counter-regulatory activity of MIF on anti-inflammatory glucocorticoid action. OXIM-11 treatment of mice, initiated 24 h after the onset of cecal ligation and puncture-induced sepsis, significantly improved survival when compared with vehicle-treated controls, confirming that inhibition of the MIF catalytic site could produce therapeutic effects. The crystal structures of the MIF inhibitor complexes provide insight for further structure-based drug design efforts.

ISO-1 Binding to the Tautomerase Active Site of MIF Inhibits Its Pro-inflammatory Activity and Increases Survival in Severe Sepsis

MIF is a proinflammatory cytokine that has been implicated in the pathogenesis of sepsis, arthritis, and other inflammatory diseases. Antibodies against MIF are effective in experimental models of inflammation, and there is interest in strategies to inhibit its deleterious cytokine activities. Here we identify a mechanism of inhibiting MIF pro-inflammatory activities by targeting MIF tautomerase activity. We designed small molecules to inhibit this tautomerase activity; a lead molecule, "ISO-1 ((S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester)," significantly inhibits the cytokine activity in vitro. Moreover, ISO-1 inhibits tumor necrosis factor release from macrophages isolated from LPStreated wild type mice but has no effect on cytokine release from MIFdeficient macrophages. The therapeutic importance of the MIF inhibition by ISO-1 is demonstrated by the significant protection from sepsis, induced by cecal ligation and puncture in a clinically relevant time frame. These results identify ISO-1 as the first small molecule inhibitor of MIF proinflammatory activities with therapeutic implications and indicate the potential of the MIF active site as a novel target for therapeutic interventions in human sepsis.

Toward the Selection of Ribozymes for 1,3-Dipolar Cycloaddition Reactions

In vitro selection from combinatorial RNA libraries has repeatedly been used to study the catalytic and binding potential of nucleic acids. These selections not only led to RNA sequences catalyzing transformations known from metabolic pathways but also generated novel ribozymes for typical organic reactions. We were interested in 1,3-dipolar cycloaddition reactions, which are important tools for the formation of heterocyclic systems in organic chemistry and might also be found in the hypothetic RNA world. Here we describe our strategy and experiments to isolate RNA molecules catalyzing a 1,3-dipolar cycloaddition between nitrile oxides and an acrylate conjugated to RNA. We used direct selection with linker-coupled reactants, which has previously allowed the generation of true trans-acting catalysts for bimolecular reactions. A photocleavable linker was introduced to provide for a more stringent selection criterion. The 1,3-dipolar cycloaddition reaction was established in aqueous solution using a modified dinucleotide that was tethered to the dipolarophilic substrate. Two selection protocols were established, namely, a low-stringency affinity-based selection protocol, and a high-stringency procedure using the photocleavable moiety. In neither case was an increased activity toward the desired reaction obtained after 15 and 11 selection rounds, respectively. The resulting pools of RNA from several rounds were investigated both in cis and in trans. The limitations of this selection methodology are discussed in comparison with other catalysts for dipolar cycloadditions and, also, with respect to the unconventional substrates used.

A fluorine scan of the phenylamidinium needle of tricyclic thrombin inhibitors: effects of fluorine substitution on pKa and binding affinity and evidence for intermolecular C-F...CN interactions

The H-atoms of the phenylamidinium needle of tricyclic thrombin inhibitors, which interacts with Asp189 at the bottom of the selectivity pocket S1 of the enzyme, were systematically exchanged with F-atoms in an attempt to improve the pharmacokinetic properties by lowering the pK(a) value. Both the pK(a) values and the inhibitory constants K(i) against thrombin and trypsin were decreased upon F-substitution. Interestingly, linear free energy relationships (LFERs) revealed that binding affinity against thrombin is much more affected by a decrease in pK(a) than the affinity against trypsin. Surprising effects of F-substitutions in the phenylamidinium needle on the pK(a) value of the tertiary amine centre in the tricyclic scaffold of the inhibitors were observed and subsequently rationalised by X-ray crystallographic analysis and ab initio calculations. Evidence for highly directional intermolecular C-F...CN interactions was obtained by analysis of small-molecule X-ray crystal structures and investigations in the Cambridge Structural Database (CSD).

Polymorphism of roxifiban

Roxifiban was found to exist in two polymorphic forms. The polymorphs were detected by X-ray powder diffraction and solid-state carbon nuclear magnetic resonance. A slight difference between the two polymorphs was also detected by isothermal microcalorimetry. However, no differences were observed by differential scanning calorimetry, infrared, or Raman spectroscopy. Solubility studies as a function of temperature in a discriminating solvent system permitted characterization of the thermodynamics of the polymorphs. The enthalpy of solution at 25 degrees C was 8.1 kcal/mol and 8.9 kcal/mol for Form I and Form II, respectively, and the thermodynamic transition point was 132 degrees C. The data confirm that the polymorphs are enantiotropic. Form II is the thermodynamically stable crystal form over the practical range of drug substance storage and handling and dosage form processing and storage. However, Form I has been kinetically stable after storage for more than 36 months at 25 degrees C/60% relative humidity with no conversion to Form II occurring.

Combinatorial synthesis and biological evaluation of isoxazole-based libraries as antithrombotic agents

The 3-substituted phenyl-5-isoxazolecarboxaldehydes have been identified as activated aldehydes for the generation of isoxazole-based combinatorial libraries on solid phase through automation. Three highly functionalized isoxazole-based libraries comprising of 32, 96 and 45 compounds each have been synthesized in parallel format using Baylis Hillman reaction, Michael addition, reductive amination and alkylation reactions. With an objective of lead generation all the three libraries were evaluated for their antithrombin activity in vivo.

The tautomerase active site of macrophage migration inhibitory factor is a potential target for discovery of novel anti-inflammatory agents

Macrophage migration inhibitory factor (MIF) is an immunoregulatory protein that is a potential therapeutic target for a number of inflammatory diseases. Evidence exists that an unexpected catalytic active site of MIF may have a biological function. To gain further insight into the role of the catalytic active site, a series of mutational, structural, and biological activity studies were performed. The insertion of an alanine between Pro-1 and Met-2 (PAM) abolishes a non-physiological catalytic activity, and this mutant is defective in the in vitro glucocorticoid counter-regulatory activity of MIF. The crystal structure of MIF complexed to (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1), an inhibitor of MIF d-dopachrome tautomerase activity, reveals that ISO-1 binds to the same position of the active site as p-hydroxyphenylpyruvic acid, a substrate of MIF. ISO-1 inhibits several MIF biological activities, further establishing a role for the catalytic active site of MIF.

Homologs of 1,2,5-hexahydro-3-one-1H-1,4-diazepine (DAP) as novel dipeptidomimetics and molecular scaffolds: efficient preparation of synthons

Structurally constraint dipeptidomimetics represent an important class of conformationally rigid dipeptide surrogates and molecular scaffolds, which are frequently employed in peptide-based structure-activity relationships (SAR) and construction of combinatorial libraries. We report on the design of an improved and general synthetic procedure to prepare synthons related to the trisubstituted 1,2,5-hexahydro-3-one-1H-1,4-diazepines [DAP(Xxx)(alpha7)] (DAP: 1,2,5-hexahydro-3-one-1H-1,4-diazepine; DAP(Xxx)(alpha7): the homologous series of DAP in which alpha refers to the location of the chiral carbon in the i(th) amino acid, Xxx represents the three letter notation for the i-1 amino acids, and 7 denotes the number of atoms in the ring) and their higher homologs [DAP(Xxx)(alphaN)] [Xxx = Phe, Asp(beta-OcHex) (cHex: cyclohexyl), and Arg(N(G)-Tos] (Tos: p-toluenesulfonyl); N = 8-10]. These dipetidomimetic structures are generated by reductive alkylation-mediated Calpha(i)-to-N(i-1) bridging between a Calpha (i)-(CH(2))(i-1)(n)-COSEt (n = 1-4) and H(2)N-C(i-1)HR-CO(2)Fm (Fm: 9-fluorenylmethyl) followed by H(2)N(i)-to-C(i-1)-CO(2)H lactam formation. We also describe the preparation of blocked N-Ac-[DAP(Phe)(alphaN)]-CONMe(2) (N = 8-10), which serve as model systems for detailed conformational analysis reported in the accompanying article.

Spirocyclic nonpeptide glycoprotein IIb-IIIa antagonists. Part 3: synthesis and SAR of potent and specific 2,8-diazaspiro[4.5]decanes

The synthesis and biological activity of analogues containing spiro piperidinylpyridine and pyrrolidinylpyridine templates are described. The potent activity of these compounds as platelet aggregation inhibitors demonstrates the utility of the spiro structures as central template for nonpeptide RGD mimics.

Synthesis and in vitro antifungal activities of novel triazole antifungal agent CS-758

Synthesis and in vitro antifungal activities of a novel triazole antifungal agent CS-758 (former name, R-120758) are described. The minimum inhibitory concentrations (MICs) of a series of dioxane-triazole compounds related to R-102557 were examined. Variation of the length of the chain between the dioxane ring and the phenyl ring revealed that the linkage with two double bonds is the most preferable. When a cyano group was introduced to the C4 position on the benzene ring, MICs improved further. A fluorine atom was introduced to obtain CS-758. The MICs of CS-758 surpassed those of fluconazole and itraconazole against Candida, Aspergillus and Cryptococcus species. The precursor (E,E)-aldehyde was synthesized stereoselectively from 3-fluoro-4-methylbenzonitrile using the Horner-Wadsworth-Emmons reaction.

Platelet GPIIb/IIIa binding characteristics of small molecule RGD mimetic: distinct binding profile for Roxifiban

A number of non-peptide orally active RGD mimetic prodrug such as Orbofiban, Sibrafiban, SR121566, Roxifiban and others entered into the clinical evaluation stage. Some of these agents were terminated and some are still in clinical trials. The present study examined the platelet GPIIb/IIIa binding profiles for the active form of Roxifiban, Sibrafiban, SR121566 and Orbofiban using 3H-Roxifiban active form (XV459), 3H-DMP728, 125I-Echistatin, and 125I-Fibrinogen. Either DMP728, Orbofiban, Sibrafiban, SR121566 or Roxifiban active form as well as other RGD mimetic bind to the same binding site(s) on human platelets as evident from the competitive inhibition of binding of each other to human platelet. Additionally, Roxifiban active form competed with FITC labeled GPIIb/IIIa antagonist cyclic RGD peptidomimetic (XL086) as demonstrated using confocal microscopy technique. Roxifiban active form (XV459) demonstrated the highest potency in inhibiting 3H-XV459, 3H-DMP728, 125I-Echistatin, and 125I-Fibrinogen binding to human platelets as compared to the others. Structure activity relationship within the isoxazoline Roxifiban series showed that substituent at the alpha-carbon next to the carboxy terminal represents an exosite for the affinity binding to human platelets leading to slow platelet dissociation rate. These data indicated a distinct binding profile for Roxifiban (high affinity to both activated and resting platelets associated with a relatively slow K(off)) as compared to others. These differences might determine the pharmacodynamics and pharmackokinetics of the different GPIIb/IIIa antagonists.

Synthesis and pharmacology of modified amidine isoxazoline glycoprotein IIb/IIIa receptor antagonists

Selective antagonism of the platelet GPIIb/IIIa receptor represents an attractive mechanism for the prevention and treatment of a number of thrombotic disease states. The antiplatelet activity of the oral GPIIb/IIIa receptor antagonists DMP 754 and DMP 802 have been disclosed. In this paper, the synthesis and biological evaluation of a series of potent N-substituted benzamidine isoxazolines are explored. The effect of benzamidine substitution on the duration of antiplatelet efficacy in dog is presented.

Spirocyclic nonpeptide glycoprotein IIb-IIIa antagonists. Part 2: design of potent antagonists containing the 3-azaspiro[5.5]undecanes

The synthesis and biological activity of novel glycoprotein IIb-IlIa anatagonists containing 3-azaspiro[5.5]undec-9-yl nucleus are described. The potent activity of these compounds as platelet aggregation inhibitors demonstrates the utility of the monoazaspirocyclic structure as central template for nonpeptide RGD mimics.

Crystalline versus amorphous content of lumaxistrade mark analog XP280 using X-ray and electron diffraction methods

In the course of the development of Lumaxistrade mark (roxifiban), the physical state of XP280 (the besylate salt of the active metabolites of roxifiban) and SC887 (the mesylate salt of the free base of roxifiban) were characterized. Powder X-ray diffraction patterns of XP280 were ambiguous in that a high degree of background signal was present and potentially indicative of the existence of an amorphous phase. Herein the results of combined synchrotron X-ray diffraction and electron microscopy (diffraction and imaging) studies on XP280 and SC887 are reported. The combination of these two techniques allowed an unambiguous assessment of the crystallinity, as well as determination of four of the unit cell parameters of XP280 and complete determination of the unit cell parameters for SC887.

Ring constrained analogues of beta-alanine-containing GPIIb/IIIa receptor antagonists

A series of ring constrained analogues of the GPIIb/IIIa receptor antagonist XR299 (1) was investigated as potential inhibitors of glycoprotein IIb/IIIa, a platelet receptor that plays a key role in platelet aggregation and platelet adhesion. Ring size was found to have a large effect on in vitro potency. Selected compounds showed good in vitro activity, a preference for binding to activated platelets, and modest duration of action when dosed i.v. as a racemate in a canine model.

The twists and turns of beta-peptides

Recently, it has been discovered that peptides composed of beta-amino acids are capable of adopting novel secondary structures demonstrating that peptides composed of alpha-amino acids are not unique in their ability to fold into well-defined structures. Cyclic as well as acyclic peptides composed of beta-amino acid residues adopt turn, helical, and sheet-like conformations. Here, we discuss the synthesis and conformational preferences of individual, substituted beta-amino acids as well as the structures that peptides composed of these residues, beta-peptides, may adopt.

Optimization and validation of chiral high-performance liquid chromatographic method for analysis of a fibrinogen (gpIIb/IIIa) receptor antagonist

A chiral HPLC separation on an alpha 1-acid glycoprotein (AGP) column was developed for the separation of roxifiban, a fibrinogen receptor antagonist, from its related chiral impurities. The proposed method was optimized for mobile phase buffer concentration, organic modifier, and temperature using experimental design. The method was then validated for use in release testing of the roxifiban drug substance.

Rapid synthesis of RGD mimetics with isoxazoline scaffolds on solid phase: identification of alphavbeta3 antagonists lead compounds

Isoxazoline containing RGD mimetics were rapidly synthesized on a solid phase to optimize linkers, regioisomers of isoxazoline scaffolds, and exosite binding groups to yield lead alphavbeta3 antagonists.

Polymorph determination for the GP IIb/IIIa antagonist, roxifiban, using a combination of electron diffraction and synchrotron X-ray powder diffraction techniques

Unit cell parameters of two polymorphs of roxifiban have been determined by a combination of transmission electron microscopy (TEM) single-crystal and synchrotron X-ray powder diffraction techniques. While it was difficult to differentiate the two forms by their standard X-ray diffraction patterns, the high-resolution synchrotron patterns clearly showed striking differences. Unit cells for the two forms required the use of cell parameters derived from TEM diffraction patterns. The two unit cells are, not surprisingly, very similar except for a doubling of one of the axes for form II. The combined use of TEM and synchrotron patterns appears to be a good general approach for characterizing complex (low-symmetry, large unit cell) polymorphs.

Isoxazoline GPIIb/IIIa antagonists bearing a phosphoramidate

Isoxazolinylacetamides bearing a phosphoramidate group alpha- to the carboxylate moiety (3) were prepared and evaluated for in vitro antiplatelet efficacy. They were found to bind GPIIb/IIIa with high affinity and were potent antagonists of ADP mediated platelet aggregation.

Platelet glycoprotein IIb/IIIa receptor antagonists derived from isoxazolidines

A series of isoxazolidines has been synthesized as mimetics of the RGD sequence and was evaluated as antagonists of the platelet glycoprotein IIb/IIIa receptor. These compounds were shown to be highly potent GPIIb/IIIa antagonists, exhibiting submicromolar potencies.

Synthesis and antiplatelet effects of an isoxazole series of glycoprotein IIb/IIIa antagonists

Despite the excellent in vitro potency of a series of benzamide glycoprotein IIb/IIIa antagonists, which have been reported previously, poor in vivo potency in the inhibition of platelet aggregation was observed when the most potent inhibitor XU057 was dosed intravenously to dogs. In this communication, we report that replacement of the benzamide in XU057 with an isoxazolecarboxamide resulted in significant improvement in in vivo potency. More importantly, the analogue XU065 showed an excellent oral antiplatelet effect in dogs.