Discovery of potent isoxazoline glycoprotein IIb/IIIa receptor antagonists

Manganese-Catalyzed 5-Endo-trig Oxygenative Cyclization of α,β-Unsaturated Oximes under Air and Ambient Conditions for the Synthesis of 4,5-Dihydroisoxazoles

The stereoselective 5-endo-trig oxygenative cyclization of α,β-unsaturated oximes was achieved using molecular oxygen (O2) and a manganese catalyst. Several 4-hydroxy-4,5-dihydroisoxazoles were obtained in high yields by directly incorporating O2 from the atmosphere (eliminating the necessity for a pure oxygen environment) and using an unprecedentedly low loading of Mn(acac)3 (as little as 0.020 mol %) without additional additives. Because of its desirable features, such as operational simplicity, inexpensive catalyst, mild reaction conditions (open flask conditions at room temperature), and broad substrate compatibility, this novel reaction provides an attractive synthetic approach to producing 4-hydroxy-4,5-dihydroisoxazoles.

Enantioselective 1,3-Dipolar Cycloadditions of α-Methylene Lactams to Construct Spirocycles

Spirocyclic scaffolds are important motifs due to their potential to bestow favorable effects on pharmaceutical compounds. However, there is a need for efficient methods for their enantioselective construction. We report a method for the asymmetric 1,3-dipolar cycloaddition of diazoacetates or nitrile oxides with α-methylene lactams to prepare chiral spirocyclic heterocycles. The methodology is high yielding (up to 91% yield) and enantioselective (up to 89% ee) for a wide range of N-substituents and 6- and 7-membered ring lactam substrates.

From α-keto acids to nitrile oxides enabled by copper nitrate: a facile access to fused isoxazolines

An unprecedented generation of nitrile oxides was developed from α-keto acids and copper nitrate through a novel carbon–carbon bond cleavage mode, affording pharmacologically interesting fused isoxazolines via 1,3-dipolar cycloadditions.

Room temperature iron(ii)-catalyzed radical cyclization of unsaturated oximes with hypervalent iodine reagents

An iron(ii)-catalyzed radical cyclization of oximes with hypervalent iodine reagents was developed, which enabled the construction of the isoxazoline backbone.

A Facile Synthesis of 2,5-Dihydroisoxazoles via an Organoselenium-Induced Stereoselective Cyclisation and Deselenylation Reaction

The organoselenium-induced ring-closure reactions of O-allyl oximes give cyclic iminium salts that can be reduced in situ with NaBH4 to produce N-alkyl-4–phenylselenoisoxazolidines; selenoxide syn-elimination follows to form 2, 5-dihydroisoxazoles in good yields.

Catalytic enantioselective synthesis of carboxy-substituted 2-isoxazolines by cascade oxa-Michael-cyclization

An efficient quinidine-based phase-transfer-catalyzed enantioselective cascade oxa-Michael-cyclization reaction of hydroxylamine with various β-carboxy-substituted α,β-unsaturated ketones has been achieved for the preparation of chiral carboxy-substituted 2-isoxazolines. This cascade reaction provided the desired products in good yields (up to 98%) with excellent enantioselectivities (91-96% ee). In addition, the cascade reaction was effectively applied to the first catalytic asymmetric synthesis of the herbicide (S)-methiozolin.

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.

Palladium-Catalyzed Synthesis of Δ(2)-Isoxazoline from Toluene Derivatives Enabled by the Triple Role of Silver Nitrate

A palladium-catalyzed direct synthesis of Δ(2)-isoxazoline from toluene derivatives has been established. The present reaction proceeds through nondirected Csp(3)-H activation, benzylic nitration, dehydration, and cycloaddition. This protocol also features the unusual triple role of silver nitrate in a one-pot reaction.

Facile Synthesis of 3-Aryl-5-(2-Oxopyrrolidin-1-yl)- and 5-(Pyridin-4-yl)-4,5-Dihydroisoxazoles via 1,3-Dipolar Cycloaddition under Mild Conditions

A convenient and efficient synthetic approach for the synthesis of 5-substituted 3-aryl-4,5-dihydroisoxazoles is reported. In the presence of triethylamine, a series of hydroximoyl chlorides were transformed into nitrile oxides, followed by reaction with N-vinyl-2-pyrrolidinone (or 4-vinylpyridine) by a 1,3-dipolar cycloaddition to give novel 4,5-dihydroisoxazole derivatives.

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.

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.

Critical modifications of the ISO-1 scaffold improve its potent inhibition of macrophage migration inhibitory factor (MIF) tautomerase activity

Based on the scaffold of (S,R)-3-(4-hydroxyphenyl)-4,5-dihydro-5-isoxazole acetic acid methyl ester (ISO-1), an inhibitor of the proinflammatory cytokine MIF, two critical modifications and chiral resolution have significantly improved the potency of the inhibition. Compound (R)-17 is 20-fold more potent than ISO-1 and inhibits MIF tautomerase activity with an IC(50) of 550 nM.

Design, synthesis, and biological activity of non-basic compounds as factor Xa inhibitors: SAR study of S1 and aryl binding sites

Compound 7 was identified as the active metabolite of 6 by HPLC and mass spectral analysis. Modification of lead compound 7 by transformation of its N-oxide 6-6 biaryl ring system and fused aromatics produced a series of non-basic fXa inhibitors with excellent potency in anti-fXa and anticoagulant assays. The optimized compounds 73b and 75b showed sub to one digit micromolar anticoagulant activity (PTCT2). Particularly, anti-fXa activity was detected in plasma of rats orally administered with 1mg/kg of compound 75b.

Novel RGD-like molecules based on the tyrosine template: design, synthesis, and biological evaluation on isolated integrins αVβ3/αIIbβ3 and in cellular adhesion tests

RGD (Arg-Gly-Asp) peptidomimetics have been designed for covalent anchorage on biomaterials. The tyrosine template was thus equipped with (i) a basic side chain of various flexibility, (ii) an acidic side chain, which incorporated the XPS fluorine tag, and (iii) a spacer-arm terminated by a primary amine for surface grafting. The most active compounds showed IC50 values in the nanomolar range versus isolated human integrins alphaVbeta3 and alphaIIbbeta3. Preincubation of CaCo2 cells with soluble peptidomimetics (2 and 19a) prevented cellular adhesion on culture plates coated with vitronectin. On the other hand, peptidomimetics (19a and 19b) immobilized on a poly(ethylene)terephthalate membrane (PET) promoted CaCo2 cells adhesion. A modeling study at the ab initio level in MINI-1' basis allowed to compare the various synthetic ligands of integrins and to propose novel pharmacophore structures.

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.

Enantioselective enzymatic aminolysis of a racemic 2-isoxazolylacetate alkyl ester

Pseudomonas cepacia lipase or Candida antartica lipase B catalyzes the enantioselective aminolysis of a racemic 2-isoxazolylacetate alkyl ester, isobutyl 2-[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetate, by 3-amino-N-(butoxycarbonyl)-L-alanine methyl ester, mono(4-methylbenzenesulfonate) to produce the corresponding amide, (R)-methyl-3-[[[3-(4-cyanophenyl)-4,5-dihydro-5-isoxazolyl]acetyl]amino]-N-(butoxycarbonyl)-L-alanine, which is an intermediate in the preparation of an isoxazoline-based platelet glycoprotein IIb/IIIa antagonist. Key words: enantioselective aminolysis, Pseudomonas cepacia lipase, Candida antartica lipase B.

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 1: design of potent and specific 3,9-diazaspiro[5.5]undecanes

The synthesis and biological activity of novel glycoprotein IIb-IIla antagonists containing the 3,9-diazaspiro[5.5]undecane nucleus are described. The potent activity of these compounds as platelet aggregation inhibitors demonstrates the utility of the spirocyclic structures as a central template for nonpeptide RGD mimics.

A targeted contrast agent for magnetic resonance imaging of thrombus: implications of spatial resolution

A preparation of ultra-small superparamagnetic iron oxide (USPIO) particles coupled to an RGD peptide (RGD-USPIO) was investigated as an MR contrast agent, targeted to activated platelets, in both ex vivo and in vivo thrombus models. Thrombus visualization ex vivo was compared using RGD-USPIO and a non-targeted UPSIO. The influence of thrombus visualization on thrombus exposure time to RGD-USPIO (ex vivo) and on the spatial resolution of the MR image (ex vivo and in vivo) was assessed. RGD-USPIO resulted in better thrombus visualization than non-targeted USPIO ex vivo, and maximum enhancement was achieved after approximately one hour exposure time of the thrombus to RGD-USPIO. The ability to visualize the clots was highly dependent on the spatial resolution of the image. In vivo, an in-plane resolution of less than 0.2 x 0.2 mm(2) was required for good clot visualization after contrast enhancement. It is concluded that the achievable resolution and sensitivity is a potential limitation to the usefulness of active vascular targeting in MRI.

Mass spectrometric and NMR characterization of metabolites of roxifiban, a potent and selective antagonist of the platelet glycoprotein IIb/IIIa receptor

1. The methyl ester prodrug roxifiban is an orally active, potent and selective antagonist of the platelet glycoprotein GPIIb/IIIa receptor and is being developed for the prevention and treatment of arterial thrombosis. 2. Roxifiban was rapidly hydrolyzed to the zwitterion XV459 in vivo and by liver slices from the rat, mouse and human and by intestinal cores from dog. XV459 was metabolized to only a small extent in vitro and in vivo. 3. Studies with rat and dog given radiolabelled roxifiban showed limited oral absorption with the majority of the radiolabel being excreted in faeces. After i.v. doses of 14C-roxifiban, most of the radioactivity was recovered in the urine of rat whereas the dog excreted significant amounts of radioactivity in bile and urine. 4. XV459 could be metabolized extrahepatically by dog gut flora to produce an isoxazoline ring-opened metabolite. In vitro hepatic metabolism of XV459 was mainly by hydroxylation at the prochiral and chiral centres of the isoxazoline ring. These hydroxylated metabolites were not detected in the urine and plasma of human volunteers administered roxifiban. 5. Initial LC/MS identification of metabolites was achieved by dosing the rat with an equimolar mixture of d0:d4 roxifiban and detecting isotopic clusters of pseudomolecular ions. Unequivocal characterization of these metabolites was achieved by LC/MS, LC/NMR and high-field NMR techniques using synthetic standards of the metabolites. 6. The synthesis of one hydroxylated metabolite enabled the assignment of the correct stereochemistry of the substituted hydroxyl group on the isoxazoline ring.

Diastereoselective synthesis of hydantoin- and isoxazoline-substituted dispirocyclobutanoids

Synthetic strategies for constructing novel achiral cyclobutanoid isoxazolidinoimidazolidinedione heterocycles, with a generalized structure of II, have been developed via 1,3-dipolar cycloaddition and carbanilide cyclization transformations from methylenecyclobutane 13. The exo methylene cyclobutane system has made the realization of some diasteroselectivity possible, such that the H-bond (Boc-NH) directed product (i.e., 14) was obtained with 3:1 selectivity relative to the non-H-bond directed product (i.e., 15).

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.

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.

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.

Synthesis and evaluation of RGD peptidomimetics aimed at surface bioderivatization of polymer substrates

Several RGD peptidomimetics have been prepared, in a convergent way, from the common ortho-aminotyrosine template (O-substituted with an anchorage-arm or a methyl group, and alpha N-substituted with a fluorine tag for XPS analysis), and various omega-aminoacid derivatives. The most flexible compounds have shown a biological activity similar to that of the peptide reference (RGDS) in the platelet aggregation test. The compound 16a could be fitted (by modelisation) with DMP 728 and c(RGDfV), two cyclic peptides that are good ligands of integrins. The compound 16b has been covalently fixed on the surface of a poly(ethylene terephthalate) membrane used as support for mammalian cell cultivation.