Intramolecular Charge Interactions as a Tool to Control the Coiled‐Coil‐to‐Amyloid Transformation

Under the influence of a changed environment, amyloid‐forming proteins partially unfold and assemble into insoluble β‐sheet rich fibrils. Molecular‐level characterization of these assembly processes has been proven to be very challenging, and for this reason several simplified model systems have been developed over recent years. Herein, we present a series of three de novo designed model peptides that adopt different conformations and aggregate morphologies depending on concentration, pH value, and ionic strength. The design strictly follows the characteristic heptad repeat of the α‐helical coiled‐coil structural motif. In all peptides, three valine residues, known to prefer the β‐sheet conformation, have been incorporated at the solvent‐exposed b, c, and f positions to make the system prone to amyloid formation. Additionally, pH‐controllable intramolecular electrostatic repulsions between equally charged lysine (peptide A) or glutamate (peptide B) residues were introduced along one side of the helical cylinder. The conformational behavior was monitored by circular dichroism spectroscopic analysis and thioflavin T fluorescence, and the resulting aggregates were further characterized by transmission electron microscopy. Whereas uninterrupted α‐helical aggregates are found at neutral pH, Coulomb repulsions between lysine residues in peptide A destabilize the helical conformation at acidic pH values and trigger an assembly into amyloid‐like fibrils. Peptide B features a glutamate‐based switch functionality and exhibits opposite pH‐dependent folding behavior. In this case, α‐helical aggregates are found under acidic conditions, whereas amyloids are formed at neutral pH. To further validate the pH switch concept, peptide C was designed by including serine residues, thus resulting in an equal distribution of charged residues. Surprisingly, amyloid formation is observed at all pH values investigated for peptide C. The results of further investigations into the effect of different salts, however, strongly support the crucial role of intramolecular charge repulsions in the model system presented herein.     

Synthesis of new optically active α,α′,β‐trisubstituted‐β‐lactones as monomers for stereoregular biopolyesters

Various optically active (4R)‐alkyloxycarbonyl‐3,3‐dialkyl‐2‐oxetanones as monomers were synthesized from L‐(S)‐malic acid in six steps to prepare a new family of stereopolyesters for biomedical applications. The synthesis began with an esterification followed of a dialkylation in the aim to introduce hydrophobic groups as methyl or reactive group as allyl. Then, a saponification has permitted to obtain the corresponding diacids that reacted with appropriate alcohols to furnish different monoesters. The last and most important step was activation of hydroxyl group of monoesters with the asymmetric carbon configuration inversion according to the Mitsunobu reaction. Thus, this reaction has provided lactones from monoesters with 100% enantiomeric excess which was confirmed by ¹H NMR and by the synthesis of corresponding isotactic and semicrystalline homopolyesters. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2586–2597     

Immobilized endoproteinase Glu‐C to magnetic bead cellulose as a tool in proteomic analysis

Magnetic bead cellulose activated with divinyl sulfone was used for the immobilization of Staphylococcus aureus endoproteinase Glu‐C (EC 3.4.21.19). The immobilized proteinase was characterized by increased thermostability, by decreased self‐cleavage activity, and a possibility of repeated use. The prepared immobilized enzyme was applied for the proteolytic cleavage of α‐casein and BSA under different conditions (different composition of buffers, different pH, and different time of digestion). The possibilities of the direct use of enzyme reaction products for MALDI TOF MS analysis were shown.     

ZrCl4 as an Efficient Catalyst for Crossed‐Aldol Condensation of Cyclic Ketones with Aromatic Aldehydes in Refluxing Ethanol

The aldol condensation reaction of cyclic ketones with aromatic aldehydes in ethanol under reflux conditions using ZrCl₄ as a catalyst to afford the corresponding α,α′‐bis(substituted benzylidene and cinnamylidene)cycloalkanones in excellent yields has been described. No self‐condensation product was produced.     

Iodobenzene‐Catalyzed Synthesis of α‐Azidoketones and α‐Thiocyanatoketones from Aryl Ketones with MCPBA as a Cooxidant

Iodobenzene‐catalyzed synthesis of α‐azidoketones and α‐thiocyanatoketones from aryl ketones with MCPBA as a cooxidant is described. The method is simple, rapid and practical, generating α‐azidoketones and α‐thiocyanatoketones from the aryl ketone without isolation of α‐tosyloxyketones in good to excellent yields.     

Titanyl Acetylacetonate as an Efficient Catalyst for Regioselective 1,2‐Reduction of α,β‐Unsaturated Carbonyl Compounds and Conversion of α‐Diketones & Acyloins to Vicinal Diols with Sodium Borohydride

α,β‐Unsaturated aldehydes and ketones were reduced readily and exclusively to their corresponding allylic alcohols with NaBH₄ and catalytic amounts of titanyl acetylacetonate at room temperature. Reduction reactions were carried out in CH₃CN or THF. This reducing system was also efficient for the reduction of α‐diketones and acyloins to their corresponding vicinal diols in CH₃CN.     

Methylene Blue as a Photosensitizer and Redox Agent: Synthesis of 5‐Hydroxy‐1H‐pyrrol‐2(5H)‐ones from Furans

A highly efficient and general singlet‐oxygen‐initiated one‐pot transformation of readily accessible furans into 5‐hydroxy‐1H‐pyrrol‐2(5H)‐ones has been developed. The methodology was extended to the synthesis of other high‐value α,β‐unsaturated γ‐lactams. This useful set of transformations relies not only on the photosensitizing ability of methylene blue, but also on its redox properties: properties that have until now been virtually ignored in a synthetic context.     

Magnetic nanoparticle γ‐Fe2O3‐immobilized 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene as a highly recyclable and efficient nanocatalyst for the synthesis of α′‐oxindole‐α‐hydroxyphosphonates

Magnetic nanoparticle γ‐Fe₂O₃‐immobilized 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene as a novel magnetic nanocatalyst was synthesized and characterized. The nanoparticle reagent catalyzed efficiently the synthesis of α′‐oxindole‐α‐hydroxyphosphonates from isatins and dimethyl phosphate under solvent‐free conditions at 60 °C. More importantly, the catalyst could be easily recovered by an external magnet and reused six times without significant loss of activity. Copyright © 2014 John Wiley & Sons, Ltd.     

Analogues of α‐Campholenal (= (1R)‐2,2,3‐Trimethylcyclopent‐3‐ene‐1‐acetaldehyde) as Building Blocks for (+)‐β‐Necrodol (= (1S,3S)‐2,2,3‐Trimethyl‐4‐methylenecyclopentanemethanol) and Sandalwood‐like Alcohols

To complete our panorama in structure–activity relationships (SARs) of sandalwood‐like alcohols derived from analogues of α‐campholenal (= (1R)‐2,2,3‐trimethylcyclopent‐3‐ene‐1‐acetaldehyde), we isomerized the epoxy‐isopropyl‐apopinene (?)‐ 2d to the corresponding unreported α‐campholenal analogue (+)‐ 4d (Scheme 1). Derived from the known 3‐demethyl‐α‐campholenal (+)‐ 4a , we prepared the saturated analogue (+)‐ 5a by hydrogenation, while the heterocyclic aldehyde (+)‐ 5b was obtained via a Bayer‐Villiger reaction from the known methyl ketone (+)‐ 6 . Oxidative hydroboration of the known α‐campholenal acetal (?)‐ 8b allowed, after subsequent oxidation of alcohol (+)‐ 9b to ketone (+)‐ 10 , and appropriate alkyl Grignard reaction, access to the 3,4‐disubstituted analogues (+)‐ 4f,g following dehydration and deprotection. (Scheme 2). Epoxidation of either (+)‐ 4b or its methyl ketone (+)‐ 4h , afforded stereoselectively the trans‐epoxy derivatives 11a,b , while the minor cis‐stereoisomer (+)‐ 12a was isolated by chromatography (trans/cis of the epoxy moiety relative to the C₂ or C₃ side chain). Alternatively, the corresponding trans‐epoxy alcohol or acetate 13a,b was obtained either by reduction/esterification from trans‐epoxy aldehyde (+)‐ 11a or by stereoselective epoxidation of the α‐campholenol (+)‐ 15a or of its acetate (?)‐ 15b , respectively. Their cis‐analogues were prepared starting from (+)‐ 12a . Either (+)‐ 4h or (?)‐ 11b , was submitted to a Bayer‐Villiger oxidation to afford acetate (?)‐ 16a . Since isomerizations of (?)‐ 16 lead preferentially to β‐campholene isomers, we followed a known procedure for the isomerization of (?)‐epoxyverbenone (?)‐ 2e to the norcampholenal analogue (+)‐ 19a . Reduction and subsequent protection afforded the silyl ether (?)‐ 19c , which was stereoselectively hydroborated under oxidative condition to afford the secondary alcohol (+)‐ 20c . Further oxidation and epimerization furnished the trans‐ketone (?)‐ 17a , a known intermediate of either (+)‐β‐necrodol (= (+)‐(1S,3S)‐2,2,3‐trimethyl‐4‐methylenecyclopentanemethanol; 17c ) or (+)‐(Z)‐lancifolol (= (1S,3R,4Z)‐2,2,3‐trimethyl‐4‐(4‐methylpent‐3‐enylidene)cyclopentanemethanol). Finally, hydrogenation of (+)‐ 4b gave the saturated cis‐aldehyde (+)‐ 21 , readily reduced to its corresponding alcohol (+)‐ 22a . Similarly, hydrogenation of β‐campholenol (= 2,3,3‐trimethylcyclopent‐1‐ene‐1‐ethanol) gave access via the cis‐alcohol rac‐ 23a , to the cis‐aldehyde rac‐ 24 .     

The kinetics of polycondensation of α,α′‐dichloro‐p‐xylene with 4,4′‐isopropylidenediphenol using benzyltriethylammonium chloride as a phase‐transfer catalyst

The phase‐transfer catalyzed polycondensation of α,α′‐dichloro‐p‐xylene with 4,4′‐isopropylidenediphenol was carried out using benzylethylammonium chloride in a two‐phase system of an aqueous alkaline solution and benzene at 60 °C under nitrogen atmosphere. The rate of polycondensation was expressed as the combined terms of quaternary onium cation and 4,4′‐isopropylidenediphenolate anion rather than the feed concentration of catalyst and 4,4′‐isopropylidenediphenol. The measured concentrations of hydroxide and chloride anion in the aqueous solution and α,α′‐dichloro‐p‐xylene in the organic phase were used to obtain the reaction rate constant with the integral method, and to analyze the polycondensation mechanism with a cyclic phase‐transfer initiation step in the heterogeneous liquid–liquid system. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3059–3066, 2000     

Metal‐Free and Efficient Epoxidation of α,β‐Unsaturated Ketones with 1,1,2,2‐Tetrahydroperoxy‐1,2‐Diphenylethane as a Powerful Solid Oxidant

1,1,2,2‐Tetrahydroperoxy‐1,2‐diphenylethane was used for the efficient and metal‐free epoxidation of various α,β‐unsaturated ketones, carried out under mild alkaline conditions at room temperature.     

Polycondensation of α‐amino acid esters in the presence of yttrium triflate as a Lewis acid

To develop polycondensation methods for poly(α‐amino acid)s, we describe a first examination to use yttrium triflate as a Lewis acid for polycondensation of α‐amino acid esters. In the absence of Lewis acid, no polycondensation of 2‐methoxyphenyl glycinate ( 1b ) at room temperature proceeded. While the polycondensation of 1b was carried out with 5 mol % yttrium triflate, a condensation product of glycine was obtained in 16% yield. Although polycondensation of 4‐nitrophenyl L ‐leucinate ( 1c ) and 4‐nitrophenyl L ‐valinate ( 1d ) were also promoted with 5 mol % yttrium triflate, the condensation products of both α‐amino acid esters were obtained in only a few percent yield. When 1d was polymerized in the presence of 100 mol % yttrium triflate, high molecular weight poly(L ‐valine) was obtained in 91% yield. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 4731–4735, 2006     

Sulfamic Acid as a Cost‐Effective and Recyclable Catalyst for β‐Amino Carbonyl Compounds Synthesis

Sulfamic acid was used as a catalyst in the synthesis of β‐amino carbonyl compounds from amines, acetophenone and aldehyde. The reaction was carried out at room temperature. High selectivity, mild reaction temperature, cost‐effective catalyst, simple product separation and catalyst recycle were notable achievements in the reaction. Another feature was that the reaction could be performed on a relatively larger scale to the model reaction (50 times), which also gave good yields. In particular, the first preparation of β, β'‐diamino diketone derivatives via the direct coupling of amines, acetophenone and isophthalic aldehyde promoted by sulfamic acid has been developed.     

NH2SO3H–SiO2 as a new water‐compatible,recyclable heterogeneous catalyst for the synthesis of novel (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction

NH₂SO₃H–SiO₂/water as a novel catalytic system was used for the synthesis of (α,β‐unsaturated) β‐amino ketones via aza‐Michael reaction at reflux conditions. The methodology was of general applicability and the catalyst exhibited activity up to five cycles. The catalyst was characterized for the first time using FT‐IR, X‐ray diffraction and scanning electron microscopic–energy dispersion analytical X‐ray. The stability of the catalyst was evaluated by differential scanning calorimetry and TGA/differential thermal analysis. High efficiency of the catalyst along with its recycling ability and the rather low loading demonstrated in reactions are the merits of the presented protocol. Copyright © 2013 John Wiley & Sons, Ltd.     

A unique combination of KI/ZnFe2O4 as a catalyst for oxidative Strecker reaction

α‐Aminonitriles as key intermediates for the preparation of α‐amino acid derivatives, amides, diamines, peptides, proteins and heterocycles were synthesized through methylarene oxidation in the Strecker reaction using a unique combination of KI/ZnFe₂O₄ as the best catalyst and aqueous tert‐butyl hydroperoxide as oxidant. A wide range of amines and methylarenes were converted to the corresponding products. Operational simplicity, short reaction time and recyclability of the catalyst are advantages of this protocol.     

Transition Metal Free Chemoselective Reduction of α,β‐Unsaturated Ketones to Saturated Ketones Using Tosyl Hydrazide as a Hydrogen Donor

An efficient, inexpensive and simple method for the reduction of various α,β‐unsaturated ketones to corresponding saturated ketones using tosyl hydrazide as a hydrogen donor in DMF using calcium oxide powder has been reported. A variety of enones underwent reduction without forming undesirable side products. High chemoselectivity, broad functional group tolerance and good yields are the noteworthy features of this protocol.     

An analytical method for measuring α‐amylase activity in starch‐containing foods

The quality of starch‐containing foods may be significantly impaired by contamination with very small amounts of α‐amylase, which can enzymatically hydrolyze the starch and cause viscosity loss. Thus, for quality control, it is necessary to have an analytical method that can measure low amylase activity. We developed a sensitive analytical method for measuring the activity of α‐amylase (from Bacillus subtilis) in starch‐containing foods. The method consists of six steps: (1) crude extraction of α‐amylase by centrifugation and filtration; (2) α‐amylase purification by desalting and anion‐exchange chromatography; (3) reaction of the purified amylase with boron‐dipyrromethene (BODIPY)‐labeled substrate, which releases a fluorescent fragment upon digestion of the substrate, thus avoiding interference from starch derivatives in the sample; (4) stopping the reaction with acetonitrile; (5) reversed‐phase solid‐phase extraction of the fluorescent substrate to remove contaminating dye and impurities; and (6) separation and measurement of BODIPY fluorescence by HPLC. The proposed method could quantify α‐amylase activities as low as 10 mU/mL, which is enough to reduce the viscosity of starch‐containing foods. Copyright © 2012 John Wiley & Sons, Ltd.     

Cycloheptyl‐fused NNO‐ligands as electronically modifiable supports for M(II) (M = Co,Fe) chloride precatalysts; probing performance in ethylene oligo‐/polymerization

The N,N,O‐cobalt(II), [2,3‐{C₄H₈C(NAr)}:5,6‐{C₄H₈C(O)}C₅HN]CoCl₂ (Ar = 2,6‐(CHPh₂)₂‐4‐MeC₆H₂ Co1 , 2,6‐(CHPh₂)₂‐4‐EtC₆H₂ Co2 , 2,6‐(CHPh₂)₂‐4‐ClC₆H₂ Co3 , 2,6‐(CHPh₂)₂‐4‐FC₆H₂ Co4 ) and N,N,O‐iron(II) complexes, [2,3‐{C₄H₈C(NAr)}:5,6‐{C₄H₈C(O)}C₅HN]FeCl₂ (Ar = 2,6‐(CHPh₂)₂‐4‐MeC₆H₂ Fe1 , 2,6‐(CHPh₂)₂‐4‐EtC₆H₂ Fe2 , 2,6‐(CHPh₂)₂‐4‐ClC₆H₂ Fe3 , 2,6‐(CHPh₂)₂‐4‐FC₆H₂ Fe4 ), each containing one sterically enhanced but electronically modifiable N‐2,6‐dibenzhydryl‐4‐R²‐phenyl group, have been prepared by a one‐pot template approach using α,α′‐dioxo‐2,3:5,6‐bis(pentamethylene)pyridine, the corresponding aniline along with the respective cobalt or iron salt in acetic acid. Distorted square pyramidal geometries are a feature of the molecular structures of Co1 – Co4 . Upon activation with MAO or MMAO, Co1 – Co4 show good activities (up to 2.2 × 10⁵ g mol^?1(Co) h^?1) affording short chain oligomers (C₄–C₃₀) with good α‐olefin selectivity. By contrast, Fe1 – Fe4 , in the presence of MMAO, displayed moderate activities (up 10.9 × 10⁴ g(PE) mol^?1(Fe) h^?1) for ethylene polymerization forming low‐molecular‐weight linear polymers (up to 13.0 kg mol^?1) incorporating saturated n‐propyl and i‐butyl chain ends. For both cobalt and iron, the precatalysts incorporating the more electron withdrawing 4‐R²‐substituents [Cl ( Co3 / Fe3 ), F ( Co4 / Fe4 )] deliver the best catalytic activities, while with cobalt, these types of substituents additionally broaden the oligomeric distribution. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55 , 3980–3989     

A Novel Method for the Asymmetric Synthesis of α,β‐Diamino Acids by a Glucose‐Mediated Stereoselective Strecker Reaction

A novel method for the asymmetric synthesis of α,β‐diamino acids by using the 2,3,4,6‐tetra‐O‐pivaloyl‐β‐D ‐glucopyranosyl group (Piv₄Glc) as chiral auxiliary was developed (Table and Scheme). The reaction was promoted by CuBr?Me₂S as Lewis acid, and high yields and good diastereoselectivities were achieved.     

Capillary electrophoresis analysis of different variants of the amyloidogenic protein β2‐microglobulin as a simple tool for misfolding and stability studies

Free solution capillary electrophoresis with UV detection is here used to retrieve information on the conformational changes of wild‐type β₂‐microglobulin and a series of naturally and artificially created variants known to have different stability and amyloidogenic potential. Under nondenaturing conditions, the resolution of at least two folding conformers at equilibrium is obtained and a third species is detected for the less stable isoforms. Partial denaturation by using chaotropic agents such as acetonitrile or trifluoroethanol reveals that the separated peaks are at equilibrium, as the presence of less structured species is either enhanced or induced at the expenses of the native form. Reproducible CE data allow to obtain an interesting semiquantitative correlation between the peak areas observed and the protein stability. Thermal unfolding over the range 25–42°C is induced inside the capillary for the two pathogenic proteins (wtβ₂‐microglobulin and D76N variant): the large differences observed upon small temperature variation draw attention on the robustness of analytical methods when dealing with proteins prone to misfolding and aggregation.