5‐(Piperidin‐4‐yl)‐3‐Hydroxypyrazole: A Novel Scaffold for Probing the Orthosteric γ‐Aminobutyric Acid Type A Receptor Binding Site

A series of bioisosteric N₁‐ and N₂‐substituted 5‐(piperidin‐4‐yl)‐3‐hydroxypyrazole analogues of the partial GABA_AR agonists 4‐PIOL and 4‐PHP have been designed, synthesized, and characterized pharmacologically. The unsubstituted 3‐hydroxypyrazole analogue of 4‐PIOL ( 2 a ; IC₅₀～300 μM ) is a weak antagonist at the α₁β₂γ₂ GABA_AR, whereas substituting the N₁‐ or N₂‐position with alkyl or aryl substituents resulted in antagonists with binding affinities in the high nanomolar to low micromolar range at native rat GABA_ARs. Docking studies using a α₁β₂γ₂ GABA_AR homology model along with the obtained SAR indicate that the N₁‐substituted analogues of 4‐PIOL and 4‐PHP, 2 a – k , and previously reported 3‐substituted 4‐PHP analogues share a common binding mode to the orthosteric binding site in the receptor. Interestingly, the core scaffold of the N₂‐substituted analogues of 4‐PIOL and 4‐PHP, 3 b – k , are suggested to flip 180° thereby adapting to the binding pocket and addressing a cavity situated above the core scaffold.     

Lipase‐catalyzed dynamic hydrolytic resolution of (R,S)‐2,2,2‐trifluoroethyl α‐chlorophenyl acetate in water‐saturated isooctane

The hydrolytic resolution of (R,S)‐2,2,2‐trifluoroethyl α‐chlorophenylacetate in water‐saturated isooctane containing Lipase MY(I) at 35 °C is selected as the best reaction condition for producing (R)‐α‐chlorophenyl acetic acid. The kinetic constants, and hence an enantiomeric ratio of 33.6, are estimated and employed for the modeling of time‐course conversions of both substrates by considering product inhibition and enzyme deactivation effects. A successful dynamic kinetic resolution is also achieved, giving the desired (R)‐α‐chlorophenylacetic acid of 93.0% yield and ee_P = 89.5% when 80 mmol dm^?3 trioctylamine acting as the racemization catalyst and enzyme activator is initially added. Copyright © 2006 Society of Chemical Industry     

Maximum volumetric production of β‐galactosidase by Kluyveromyces fragilis in fed‐batch culture with automatic control

The production of β‐galactosidase by Kluyveromyces fragilis was studied in different culture systems, with dissolved oxygen concentration control and using defined media. An operating strategy of fed‐batch culture with automatic control of substrate addition regulated by dissolved oxygen concentration, consisting of the replacement of variable volumes of broth by fresh medium (once the fed‐batch culture has finished), was designed. The volumetric enzyme productivity (Q_p, 13 600 UI dm^?3 h^?1) obtained was 38% higher than that reached in continuous culture of K fragilis with dissolved oxygen concentration control and far higher than that obtained by batch culture of K fragilis under the same aeration conditions. © 2002 Society of Chemical Industry     

Aryl Biphenyl‐3‐ylmethylpiperazines as 5‐HT7 Receptor Antagonists

The 5‐HT₇ receptor (5‐HT₇R) is a promising therapeutic target for the treatment of depression and neuropathic pain. The 5‐HT₇R antagonist SB‐269970 exhibited antidepressant‐like activity, whereas systemic administration of the 5‐HT₇R agonist AS‐19 significantly inhibited mechanical hypersensitivity and thermal hyperalgesia. In our efforts to discover selective 5‐HT₇R antagonists or agonists, aryl biphenyl‐3‐ylmethylpiperazines were designed, synthesized, and biologically evaluated against the 5‐HT₇R. Among the synthesized compounds, 1‐([2′‐methoxy‐(1,1′‐biphenyl)‐3‐yl]methyl)‐4‐(2‐methoxyphenyl)piperazine ( 28 ) was the best binder to the 5‐HT₇R (pK_i=7.83), and its antagonistic property was confirmed by functional assays. The selectivity profile of compound 28 was also recorded for the 5‐HT₇R over other serotonin receptor subtypes, such as 5‐HT₁R, 5‐HT₂R, 5‐HT₃R, and 5‐HT₆R. In a molecular modeling study, the 2‐methoxyphenyl moiety attached to the piperazine ring of compound 28 was proposed to be essential for the antagonistic function.     

N‐Benzyl Substitution of Polyhydroxypyrrolidines: The Way to Selective Inhibitors of Golgi α‐Mannosidase II

Inhibition of the biosynthesis of complex N‐glycans in the Golgi apparatus influences progress of tumor growth and metastasis. Golgi α‐mannosidase II (GMII) has become a therapeutic target for drugs with anticancer activities. One critical task for successful application of GMII drugs in medical treatments is to decrease their unwanted co‐inhibition of lysosomal α‐mannosidase (LMan), a weakness of all known potent GMII inhibitors. A series of novel N‐substituted polyhydroxypyrrolidines was synthesized and tested with modeled GH38 α‐mannosidases from Drosophila melanogaster (GMIIb and LManII). The most potent structures inhibited GMIIb (K_i=50–76 μm , as determined by enzyme assays) with a significant selectivity index of IC₅₀(LManII)/IC₅₀(GMIIb) >100. These compounds also showed inhibitory activities in in vitro assays with cancer cell lines (leukemia, IC₅₀=92–200 μm ) and low cytotoxic activities in normal fibroblast cell lines (IC₅₀>200 μm ). In addition, they did not show any significant inhibitory activity toward GH47 Aspergillus saitoiα1,2‐mannosidase. An appropriate stereo configuration of hydroxymethyl and benzyl functional groups on the pyrrolidine ring of the inhibitor may lead to an inhibitor with the required selectivity for the active site of a target α‐mannosidase.     

siRNA Modified with 2′‐Deoxy‐2′‐C‐methylpyrimidine Nucleosides

(2′S)‐2′‐Deoxy‐2′‐C‐methyluridine and (2′R)‐2′‐deoxy‐2′‐C‐methyluridine were incorporated in the 3′‐overhang region of the sense and antisense strands and in positions 2 and 5 of the seed region of siRNA duplexes directed against Renilla luciferase, whereas (2′S)‐2′‐deoxy‐2′‐C‐methylcytidine was incorporated in the 6‐position of the seed region of the same constructions. A dual luciferase reporter assay in transfected HeLa cells was used as a model system to measure the IC₅₀ values of 24 different modified duplexes. The best results were obtained by the substitution of one thymidine unit in the antisense 3′‐overhang region by (2′S)‐ or (2′R)‐2′‐deoxy‐2′‐C‐methyluridine, reducing IC₅₀ to half of the value observed for the natural control. The selectivity of the modified siRNA was measured, it being found that modifications in positions 5 and 6 of the seed region had a positive effect on the ON/OFF activity.     

Development of 3‐Phenyl‐N‐(2‐(3‐phenylureido)ethyl)‐thiophene‐2‐sulfonamide Compounds as Inhibitors of Antiapoptotic Bcl‐2 Family Proteins

Antiapoptotic Bcl‐2 family proteins, such as Bcl‐x_L, Bcl‐2, and Mcl‐1, are often overexpressed in tumor cells, which contributes to tumor cell resistance to chemotherapies and radiotherapies. Inhibitors of these proteins thus have potential applications in cancer treatment. We discovered, through structure‐based virtual screening, a lead compound with micromolar binding affinity to Mcl‐1 (inhibition constant (K_i)=3 μM ). It contains a phenyltetrazole and a hydrazinecarbothioamide moiety, and it represents a structural scaffold not observed among known Bcl‐2 inhibitors. This work presents the structural optimization of this lead compound. By following the scaffold‐hopping strategy, we have designed and synthesized a total of 82 compounds in three sets. All of the compounds were evaluated in a fluorescence‐polarization binding assay to measure their binding affinities to Bcl‐x_L, Bcl‐2, and Mcl‐1. Some of the compounds with a 3‐phenylthiophene‐2‐sulfonamide core moiety showed sub‐micromolar binding affinities to Mcl‐1 (K_i=0.3–0.4 μM ) or Bcl‐2 (K_i≈1 μM ). They also showed obvious cytotoxicity on tumor cells (IC₅₀<10 μM ). Two‐dimensional heteronuclear single quantum coherence NMR spectra of three selected compounds, that is, YCW‐E5, YCW‐E10, and YCW‐E11, indicated that they bind to the BH3‐binding groove on Bcl‐x_L in a similar mode to ABT‐737. Several apoptotic assays conducted on HL‐60 cells demonstrated that these compounds are able to induce cell apoptosis through the mitochondrial pathway. We propose that the compounds with the 3‐phenylthiophene‐2‐sulfonamide core moiety are worth further optimization as effective apoptosis inducers with an interesting selectivity towards Mcl‐1 and Bcl‐2.     

Synthesis and Pharmacological Evaluation of α4β2 Nicotinic Ligands with a 3‐Fluoropyrrolidine Nucleus

Nicotinic acetylcholine receptors (nAChRs) play an important role in many central nervous system disorders such as Alzheimer’s and Parkinson’s diseases, schizophrenia, and mood disorders. The α₄β₂ subtype has emerged as an important target for the early diagnosis and amelioration of Alzheimer’s disease symptoms. Herein we report a new class of α₄β₂ receptor ligands characterized by a basic pyrrolidine nucleus, the basicity of which was properly decreased through the insertion of a fluorine atom at the 3‐position, and a pyridine ring carrying at the 3‐position substituents known to positively affect affinity and selectivity toward the α₄β₂ subtype. Derivatives 3‐(((2S,4R)‐4‐fluoropyrrolidin‐2‐yl)methoxy)‐5‐(phenylethynyl)pyridine ( 11 ) and 3‐((4‐fluorophenyl)ethynyl)‐5‐(((2S,4R)‐4‐fluoropyrrolidin‐2‐yl)methoxy)pyridine ( 12 ) were found to be the most promising ligands identified in this study, showing good affinity and selectivity for the α₄β₂ subtype and physicochemical properties predictive of a relevant central nervous system penetration.     

Fabrication of BaZr0.1Ce0.7Y0.2O3 – δ ‐Based Proton‐Conducting Solid Oxide Fuel Cells Co‐Fired at 1,150 °C

Dense proton‐conducting BaZr_0.1Ce_0.7Y_0.2O_{3 – δ} (BZCY) electrolyte membranes were successfully fabricated on NiO–BZCY anode substrates at a low temperature of 1,150 °C via a combined co‐press and co‐firing process. To fabricate full cells, the LaSr₃Co_1.5Fe_1.5O_{10 – δ}–BZCY composite cathode layer was fixed to the electrolyte membrane by two means of one‐step co‐firing and two‐step co‐firing, respectively. The SEM results revealed that the cathode layer bonded more closely to the electrolyte membrane via the one‐step co‐firing process. Correspondingly, determined from the electrochemical impedance spectroscopy measured under open current conditions, the electrode polarisation and Ohmic resistances of the one‐step co‐fired cell were dramatically lower than the other one for its excellent interface adhesion. With humidified hydrogen (2% H₂O) as the fuel and static air as the oxidant, the maximum power density of the one‐step co‐fired single cell achieved 328 mW cm^–2 at 700 °C, showing a much better performance than that of the two‐step co‐fired single cell, which was 264 mW cm^–2 at 700 °C.     

Synthesis and properties of poly(amide–imide)s based on N,N′‐bis(4‐carboxyphenyl)‐4,4′‐oxydiphthalimide,p‐aminobenzoic acid and various aromatic diamines

A new diimide–diacid monomer, N,N′‐bis(4‐carboxyphenyl)‐4,4′‐oxydiphthalimide (I), was prepared by azeotropic condensation of 4,4′‐oxydiphthalic anhydride (ODPA) and p‐aminobenzoic acid (p‐ABA) at a 1:2 molar ratio in a polar solvent mixed with toluene. A series of poly(amide–imide)s (PAI, III_a–m) was synthesized from the diimide–diacid I (or I′, diacid chloride of I) and various aromatic diamines by direct polycondensation (or low temperature polycondensation) using triphenyl phosphite and pyridine as condensing agents. It was found that only III_k–m having a meta‐structure at two terminals of the diamine could afford good quality, creasable films by solution‐casting; other PAIs III using diamine with para‐linkage at terminals were insoluble and crystalline; though III_g–i contained the soluble group of the diamine moieties, their solvent‐cast films were brittle. In order to improve their to solubility and film quality, copoly(amide–imide)s (Co‐PAIs) based on I and mixtures of p‐ABA and aromatic diamines were synthesized. When on equimolar of p‐ABA (m = 1) was mixed, most of Co‐PAIs IV had improved solubility and high inherent viscosities in the range 0.9–1.5 dl g^?1; however, their films were still brittle. With m = 3, series V was obtained, and all members exhibited high toughness. The solubility, film‐forming ability, crystallinity, and thermal properties of the resultant poly(amide–imide)s were investigated. © 2002 Society of Chemical Industry     

Antibody Epitope of Human α‐Galactosidase A Revealed by Affinity Mass Spectrometry: A Basis for Reversing Immunoreactivity in Enzyme Replacement Therapy of Fabry Disease

α‐Galactosidase (αGal) is a lysosomal enzyme that hydrolyses the terminal α‐galactosyl moiety from glycosphingolipids. Mutations in the encoding genes for αGal lead to defective or misfolded enzyme, which results in substrate accumulation and subsequent organ dysfunction. The metabolic disease caused by a deficiency of human α‐galactosidase A is known as Fabry disease or Fabry–Anderson disease, and it belongs to a larger group known as lysosomal storage diseases. An effective treatment for Fabry disease has been developed by enzyme replacement therapy (ERT), which involves infusions of purified recombinant enzyme in order to increase enzyme levels and decrease the amounts of accumulated substrate. However, immunoreactivity and IgG antibody formation are major, therapy‐limiting, and eventually life‐threatening complications of ERT. The present study focused on the epitope determination of human α‐galactosidase A against its antibody formed. Here we report the identification of the epitope of human αGal(309–332) recognized by a human monoclonal anti‐αGal antibody, using a combination of proteolytic excision of the immobilized immune complex and surface plasmon resonance biosensing mass spectrometry. The epitope peptide, αGal(309–332), was synthesized by solid‐phase peptide synthesis. Determination of its affinity by surface plasmon resonance analysis revealed a high binding affinity for the antibody (K_D=39×10^?9 m ), which is nearly identical to that of the full‐length enzyme (K_D=16×10^?9 m ). The proteolytic excision affinity mass spectrometry method is shown here to be an efficient tool for epitope identification of an immunogenic lysosomal enzyme. Because the full‐length αGal and the antibody epitope showed similar binding affinities, this provides a basis for reversing immunogenicity upon ERT by: 1) treatment of patients with the epitope peptide to neutralize antibodies, or 2) removal of antibodies by apheresis, and thus significantly improving the response to ERT.     

N,N′‐Dioxide‐Magnesium Ditriflate Complex‐Catalyzed Asymmetric α‐Hydroxylation of β‐Keto Esters and β‐Keto Amides

The highly catalytic asymmetric α‐hydroxylation of 1‐tetralone‐derived β‐keto esters and β‐keto amides using tert‐butyl hydroperoxide (TBHP) as the oxidant was realized by a chiral N,N′‐dioxide‐magnesium ditriflate [Mg(OTf)₂] complex. A series of corresponding chiral α‐hydroxy dicarbonyl compounds was obtained in excellent yields (up to 99%) with excellent enantioselectivities (up to 98% ee). The products were easily transformed into useful building blocks and the precursor of daunomycin was achieved in an asymmetric catalytic way for the first time.     

Potent,Metabolically Stable 2‐Alkyl‐8‐(2H‐1,2,3‐triazol‐2‐yl)‐9H‐adenines as Adenosine A2A Receptor Ligands

Inhibition of adenosine A_2A receptors has been shown to elicit a therapeutic response in preclinical animal models of Parkinson’s disease (PD). We previously identified the triazolo‐9H‐purine, ST1535, as a potent A_2AR antagonist. Studies revealed that ST1535 is extensively hydroxylated at the ω‐1 position of the butyl side chain. Here, we describe the synthesis and evaluation of derivatives in which the ω‐1 position has been substituted (F, Me, OH) in order to block metabolism. The stability of the compounds was evaluated in human liver microsomes (HLM), and the affinity for A_2AR was determined. Two compounds, (2‐(3,3‐dimethylbutyl)‐9‐methyl‐8‐(2H‐1,2,3‐triazol‐2‐yl)‐9H‐purin‐6‐amine ( 3 b ) and 4‐(6‐amino‐9‐methyl‐8‐(2H‐1,2,3‐triazol‐2‐yl)‐9H‐purin‐2‐yl)‐2‐methylbutan‐2‐ol ( 3 c ), exhibited good affinity against A_2AR (K_i=0.4 nM and 2 nM , respectively) and high in vitro metabolic stability (89.5 % and 95.3 % recovery, respectively, after incubation with HLM for two hours).     

Synthesis of ω‐amino‐α‐phenylcarbonate alkanes and their polymerization to [n]‐polyurethanes

Aliphatic [n]‐polyurethanes have recently been synthesized from ω‐isocyanato‐α‐alkanols or, more traditionally, by cationic ring‐opening polymerization of cyclourethanes or by the Bu₂Sn(OMe)₂‐promoted polycondensation of ω‐hydroxy‐α‐O‐phenylurethane alkanes. For the latter procedures, the conditions employed do not seem to be suitable for highly functionalized monomers. In contrast, the polymerization of ω‐amino‐α‐phenylcarbonate alkanes is expected to occur under milder conditions. ω‐Amino‐α‐phenylcarbonate alkanes have been synthesized from 6‐aminohexanol (1) and 3‐aminopropanol (6). The procedure involves the N‐Boc protection of the amino group, followed by activation of the alcohol. Removal of the N‐Boc affords the corresponding ω‐amino‐1‐O‐phenyloxycarbonyloxyalkane hydrochlorides. Other oligomeric comonomers between 1 and 6 have been prepared. The polymerization of these precursors takes place in the absence of metal catalysts to afford the corresponding linear and regioregular [n]‐polyurethanes. The procedure described is useful for the preparation of stable ω‐amino‐α‐phenylcarbonate alkane derivatives, which possess varied chain lengths between the terminal functions. These monomers yield [n]‐polyurethanes having various structures starting from just two aminoalkanols. The polyurethanes were obtained in high yields, with reasonable molecular weight and polydispersity values, and they were characterized spectroscopically and thermally. These studies reveal constitutionally uniform structures that are free of carbonate or urea linkages. Copyright © 2010 Society of Chemical Industry     

The Tertiary Amine Nitrogen Atom of Piperazine Sulfonamides as a Novel Determinant of Potent and Selective β3‐Adrenoceptor Agonists

Novel compounds were prepared in fair to good yields as human β₃‐adrenoceptor (β₃‐AR) agonists. In particular, aryloxypropanolamines 7 a – d (EC₅₀=0.57–2.1 nM ) and arylethanolamines 12 a , b , e (EC₅₀=6.38–19.4 nM ) were designed to explore the effects of modifications at the right‐hand side of these molecules on their activity as β₃‐AR agonists. Piperidine sulfonamides 15 a – c , e – g (EC₅₀=6.1–36.2 nM ) and piperazine sulfonamide derivatives 20 – 29 (EC₅₀=1.79–49.3 nM ) were examined as compounds bearing a non‐aromatic linker on the right‐ and left‐hand sides of the molecules. Some piperazine sulfonamides were found to be potent and selective β₃‐AR agonists, even if the amine nitrogen atom is tertiary and not secondary, as is the case for all β₃‐AR agonists reported so far. (S)‐3‐{4‐{N‐{4‐{2‐[2‐Hydroxy‐3‐(4‐hydroxyphenoxy)propylamino]ethyl}phenyl}sulfamoyl}phenoxy}propanoic acid ( 7 d ; EC₅₀=0.57 nM ), (R)‐N‐{4‐[2‐(2‐hydroxy‐2‐phenylethylamino)ethyl]phenyl}‐4‐(3‐octylureido)benzenesulfonamide ( 12 e ; EC₅₀=6.38 nM ), (R)‐2‐[1‐(4‐methoxyphenylsulfonyl)piperidin‐4‐ylamino]‐1‐phenylethanol ( 15 f ; EC₅₀=6.1 nM ), and (S)‐4‐{2‐hydroxy‐3‐[4‐(4‐methoxyphenylsulfonyl)piperazin‐1‐yl]propoxy}phenol ( 25 ; EC₅₀=1.79 nM ) were found to be the most potent β₃‐AR agonists of the aryloxypropanolamine, arylethanolamine, piperidine sulfonamide, and piperazine sulfonamide classes, respectively. The two most potent compounds were identified as possible candidates for further development of β₃‐AR agonists useful in the treatment of β₃‐AR‐mediated pathological conditions.     

Defective Y2O3−x–driven anomalous photocatalytic enhancement using Y2O3−x–TiO2−x nanorod composite composition spreads

Synergistic photocatalysis is reported, using the optimal amounts of oxygen vacancies of high‐k materials and nanoarchitecture maneuvering by employing a combinatorial sputtering approach. The highlights include (i) the successful fabrication of samples using combinatorial sputtering; (ii) a systematic investigation of the coupling effect between Y₂O_3?x and TiO_2?x; (iii) elucidating charge carrier transport through current‐voltage (I‐V) and capacitance‐voltage (C‐V) characterizations; and (iv) providing an alternative application for high‐dielectric constant (high‐k) materials in photocatalysis. The simple yet effective composition spread technique rapidly determined that Sample 6 (4 at% Y₂O_3?x‐96 at% TiO_2?x, TiO_2?x‐rich on the Y₂O_3?x–TiO_2?x nanorod composite composition spread) exhibited the highest photocatalytic efficiency (i.e., approximately 3.4 times and 1.4 times higher than that of P25 and pure TiO_2?x nanorods, respectively). The predominant factor was determined to be electron migration along defective Y₂O_3?x nanorods to the sample surface. The extracted mobility was discovered to be an order of magnitude greater than that of pure TiO_2?x. The photoelectrochemical stability and reusability were also demonstrated.     

Synthesis and Biological Evaluation of 1‐Methyl‐1H‐indole–Pyrazoline Hybrids as Potential Tubulin Polymerization Inhibitors

A series of 1‐methyl‐1H‐indole–pyrazoline hybrids were designed, synthesized, and biologically evaluated as potential tubulin polymerization inhibitors. Among them, compound e19 [5‐(5‐bromo‐1‐methyl‐1H‐indol‐3‐yl)‐3‐(3,4,5‐trimethoxyphenyl)‐4,5‐dihydro‐1H‐pyrazole‐1‐carboxamide] showed the most potent inhibitory effect on tubulin assembly (IC₅₀=2.12 μm ) and in vitro growth inhibitory activity against a panel of four human cancer cell lines (IC₅₀ values of 0.21–0.31 μm ). Further studies confirmed that compound e19 can induce HeLa cell apoptosis, cause cell‐cycle arrest in G₂/M phase, and disrupt the cellular microtubule network. These studies, along with molecular docking and 3D‐QSAR modeling, provide an important basis for further optimization of compound e19 as a potential anticancer agent.     

Targeting an Aromatic Hotspot in Plasmodium falciparum 1‐Deoxy‐d‐xylulose‐5‐phosphate Reductoisomerase with β‐Arylpropyl Analogues of Fosmidomycin

Blocking the 2‐C‐methyl‐d ‐erythrithol‐4‐phosphate pathway for isoprenoid biosynthesis offers new ways to inhibit the growth of Plasmodium spp. Fosmidomycin [(3‐(N‐hydroxyformamido)propyl)phosphonic acid, 1 ] and its acetyl homologue FR‐900098 [(3‐(N‐hydroxyacetamido)propyl)phosphonic acid, 2 ] potently inhibit 1‐deoxy‐d ‐xylulose‐5‐phosphate reductoisomerase (Dxr), a key enzyme in this biosynthetic pathway. Arylpropyl substituents were introduced at the β‐position of the hydroxamate analogue of 2 to study changes in lipophilicity, as well as electronic and steric properties. The potency of several new compounds on the P. falciparum enzyme approaches that of 1 and 2 . Activities against the enzyme and parasite correlate well, supporting the mode of action. Seven X‐ray structures show that all of the new arylpropyl substituents displace a key tryptophan residue of the active‐site flap, which had made favorable interactions with 1 and 2 . Plasticity of the flap allows substituents to be accommodated in many ways; in most cases, the flap is largely disordered. Compounds can be separated into two classes based on whether the substituent on the aromatic ring is at the meta or para position. Generally, meta‐substituted compounds are better inhibitors, and in both classes, smaller size is linked to better potency.     

Synthesis and Highly Stereoselective Hydrogenation of the Statin Precursor Ethyl (5S)‐5,6‐Isopropylidenedioxy‐3‐oxohexanoate

A search for the large‐scale preparation of (5S)‐5,6‐(isopropylidenedioxy)‐3‐oxohexanoates ( 2 ) – a key intermediate in the synthesis of pharmacologially important statins – starting from (S)‐malic acid is described. The synthesis of the required initial compound methyl (3S)‐3,4‐(isopropylidenedioxy)butanoate ( 1 ) by Moriwake’s reduction of dimethyl (S)‐malate ( 3 ) has been improved. Direct 2‐C chain elongation of ester 1 using the lithium enolate of tert‐butyl acetate has been shown to be successful at a 3‐ to 5‐fold excess of the enolate. Unfortunately, the product, tert‐butyl (5S)‐5,6‐(isopropylidenedioxy)‐3‐oxohexanoate ( 2a ) is unstable during distillation. Ethyl (5S)‐5,6‐(isopropylidenedioxy)‐3‐oxohexanoate ( 2b ) was prepared alternatively on a multigram scale from (3S)‐3,4‐(isopropylidenedioxy)butanoic acid ( 7 ) by activation with N,N′‐carbonyldiimidazole and subsequent reaction with Mg(OOCCH₂COOEt)₂. A convenient pathway for the in situ preparation of the latter is also described. Ethyl ester ( 2b ) can be advantageously purified by distillation. The stereochemistry of the catalytic hydrogenation of β‐keto ester ( 2b ) to ethyl (5S)‐5,6‐(isopropylidenedioxy)‐3‐hydrohyhexanoate (syn‐ 6 and anti‐ 6 ) has been studied using a number of homogeneous achiral and chiral Rh(I) and Ru(II) complexes with phosphine ligands. A comparison of Rh(I) and Ru(II) catalysts with (S)‐ and (R)‐BINAP as chiral ligands revealed opposite activity in dependence on the polarity of the solvent. No influence of the chiral backbone of substrate 2b on the enantioselectivity was noted. A ratio of syn‐ 6 /anti‐ 6 =2.3 was observed with an achiral (Ph₃P)₃RuCl₂ catalyst. Ru[(R)‐Tol‐BINAP]Cl₂ neutralized with one equivalent of AcONa afforded the most efficient catalytic system for the production of optically pure syn‐(5S)‐5,6‐isopropylidenedioxy‐3‐hydroxyhexanoate (syn‐ 6 ) at a preparative substrate/catalyst ratio of 1000:1.     

Evaluation of (4‐Arylpiperidin‐1‐yl)cyclopentanecarboxamides As High‐Affinity and Long‐Residence‐Time Antagonists for the CCR2 Receptor

Animal models suggest that the chemokine ligand 2/CC‐chemokine receptor 2 (CCL2/CCR2) axis plays an important role in the development of inflammatory diseases. However, CCR2 antagonists have failed in clinical trials because of a lack of efficacy. We previously described a new approach for the design of CCR2 antagonists by the use of structure–kinetics relationships (SKRs). Herein we report new findings on the structure–affinity relationships (SARs) and SKRs of the reference compound MK‐0483, its diastereomers, and its structural analogues as CCR2 antagonists. The SARs of the 4‐arylpiperidine group suggest that lipophilic hydrogen‐bond‐accepting substituents at the 3‐position are favorable. However, the SKRs suggest that a lipophilic group with a certain size is desired [e.g., 3‐Br: K_i=2.8 nM , residence time (t_res)=243 min; 3‐iPr: K_i=3.6 nM , t_res=266 min]. Alternatively, additional substituents and further optimization of the molecule, while keeping a carboxylic acid at the 3‐position, can also prolong t_res; this was most prominently observed in MK‐0483 (K_i=1.2 nM , t_res=724 min) and a close analogue (K_i=7.8 nM ) with a short residence time.