Crude peroxidase from onion solid waste as a tool for organic synthesis. Part II: oxidative dimerization-cyclization of methyl p-coumarate, methyl caffeate and methyl ferulate

The ability of a crude onion peroxidase preparation to act as a biocatalyst for the oxidative dimerization-cyclization of methyl p-coumarate, methyl caffeate and methyl ferulate is presented. The products of the reaction have been fully characterized and were found to possess potent antioxidant activity in a ferric reducing antioxidant power (FRAP) assay.     

A convenient synthesis of substituted 2,2′:6′,2″-terpyridines

The 2,2′:6′,2″-terpyridines 8a and 8b were prepared in good yield by reacting α-acetoxy-α-chloro-β-keto-esters 1 (R¹ = ⁿPr and Ph) with the bis-amidrazone 7 and 2,5-norbornadiene 5 in ethanol at reflux.     

Asymmetric synthesis of 6-(2′,3′,4′,5′,6′-pentafluorophenyl)-δ-lactones via “allyl”boranes: application for the synthesis of fluorinated analog of key pharmacophore of statin drugs

Asymmetric “allyl”boration of pentafluorobenzaldehyde with various α-pinene based “allyl”boranes provides homoallylic alcohols in high de and ee; the alcohols have been converted into δ-lactones via acryloylation, ring-closing metathesis and hydrogenation. Pentafluorophenyl analog of key pharmacophore of statin drugs has been synthesized using diastereoselective epoxidation and regioselective reduction as key steps.     

Study on disulfur-backboned nucleic acids: Part IV.Efficient synthesis of 3′,5′-dithio-2′-deoxyguanosine

An efficient and novel method for synthesizing 3′,5′-dithio-2′-deoxyguanosine was described. In this method normal guanosine was used as the strating materials. A very efficient procedure was used to synthesize 2´-O-tosylguanosine 1, which used 0.1eq DBTO instead of 2eq. 1 was treated with LTBH to give 9-(2-deoxy-β-D-threo-pentofuranosyl)guanine 2. 2 could be easily truned to the target compound.     

Hydrogen-bonded rotamers of 2′,4′,6′-trihydroxy-3′-formyldihydrochalcone, an intermediate in the synthesis of a dihydrochalcone from Leptospermum recurvum

Synthesis of 2′,4′,6′-trihydroxy-3′-methyldihydrochalcone, isolated as a natural product for the first time (ex Leptospermum recurvum), proceeds through 2′,4′,6′-trihydroxy-3′-formyldihydrochalcone. Two stable rotamers of this formyl derivative have been identified and the problems associated with NMR assignments of this type of compound have been attributed to conformational exchange. Rotamer ratios from molecular modelling and ab initio calculations agree well with those obtained from low temperature NMR studies. There is also excellent correlation between experimental NMR chemical shifts for the hydrogen-bonded hydroxyl protons with those derived from ab initio calculations. This formyl dihydrochalcone showed promising bioactivity in antiviral and antimicrobial assays.     

Highly efficient synthesis of 2′,3′-didehydro-2′,3′-dideoxy-β-nucleosides through a sulfur-mediated reductive 2′,3′-trans-elimination. From iodomethylcyclopropanes to thiirane analogs

Taking into account the thiophilic properties of iodine, a very simple methodology to achieve 2′,3′-didehydro-2′,3′-dideoxy-β-nucleosides in high yield was performed, using mild, and inexpensive conditions, by means of the treatment of 2′-deoxy-3′,5′-dibenzoyl-2′-iodo-β-nucleoside derivatives with NaHS. The process has shown to be highly dependent of the relative geometry between the iodine atom and the adjacent leaving group. In this way, different essays carried out with pyranose derivatives have concluded in no reaction when the vicinal groups to eliminate do not adopt a trans-diaxial disposition. In addition, the treatment of 2-iodomethyl-cyclopropane-1,1-dicarboxylic acid diethyl ester under the same conditions softly and readily leads to the obtention of a mixture of the expected 2-allyl-malonic acid diethyl ester (as the minor product) and the thiirane derivative 2-thiiranylmethyl-malonic acid diethyl ester (as the major product). In this case, the responsible of the reaction progress are the nucleophilic properties of the sulfur atom rather than the thiophilic character of the iodine atom.     

Straightforward synthesis of 3′-deoxy-3′,4′-didehydronucleoside-5′-aldehydes via 2′,3′-O-orthoester group elimination: a simple route to 3′,4′-didehydronucleosides

Straightforward, high-yielding syntheses of 3′-deoxy-3′,4′-didehydronucleoside-5′-aldehydes and 3′-deoxy-3′,4′-didehydronucleosides starting from 2′,3′-O-orthoester derivatives of ribonucleosides are described.     

Preparation of a series of novel fluorophores, N-substituted 6-amino and 6,6″-diamino-2,2′:6′,2″-terpyridine by palladium-catalyzed amination

A new series of N-substituted 6-amino- and 6,6″-diamino-2,2′:6′,2″-terpyridine (6-amino- and 6,6″-diamino-tpy) was conveniently synthesized in one-step by Pd-catalyzed amination of bromo-substituted tpys with various amines. For highly coordinating tpy substrates, use of appropriate chelating phosphine ligand was critical to achieve moderate to satisfactory yield. The prepared N-substituted 6-amino- and 6,6″-diamino-tpys exhibited moderate to intense fluorescence in dichloromethane with fine-tuned fluorescence maxima ranging from 385 to 455 nm.     

2,2′:6′,2″-Terpyridine[hydroxypropyl-β-cyclodextrin] 1:3 complex used as chelating agent for the determination of iron with a sensitive, selective and fast liquid chromatographic method

In the present work, 2,2′:6′,2″-Terpyridine (terpy), a substance with very poor aqueous solubility, was dissolved in water, after formation of its inclusion complex with hydroxypropyl-β-cyclodextrin (HPβCD), in a 1:3 stoichiometry. The obtained [terpy:(HPβCD)₃] supramolecule, with enhanced aqueous solubility, enables its usage as a reagent at RP-LC methods. It was found that, terpy after inclusion complexation retains unaffected the ability of binding to Fe²⁺. It was also observed that, the stable, reddish-purple [Fe(terpy)]²⁺ complex was formed quantitatively in a wide pH range (2-9). Subsequently, iron as active substance or impurity in a drug product, can be determined through UV-vis measurements of [Fe(terpy)₂]²⁺. Speed, sensitivity and selectivity are the most important features of the isocratic RP-LC method, developed to determine iron in pharmaceutical formulations. The duration of the chromatographic separation was less than 4.0 min. The method was linear, precise and accurate from 0.17 to 2.2 mg l⁻¹ of iron and the detection limit was found to be 5 μg l⁻¹. The absorbance at 318 and 552 nm allowed the quantitation of Fe (II) and Fe (III) after reduction, as well as of total Fe (II + III). Moreover, there were no interferences from Fe³⁺, Ni²⁺, Co²⁺ or Cu²⁺.     

A practical one-pot procedure for the synthesis of pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidinones by a tandem aza-Wittig/heterocumulene-mediated annulation strategy

A simple one-pot and efficient method is described for the synthesis of pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidinone derivatives 6 via a tandem aza-Wittig/heterocumulene-mediated annulation process. The iminophosphorane 3 reacted with aryl isocyanates, followed by heterocyclization on addition of secondary amines to give the corresponding guanidine intermediates 5, which were cyclized in the presence of a catalytic amount of potassium carbonate to tricyclic compounds 6. Similarly, iminophosphorane 3 reacts with phenols, thiophenol, or ROH to give 2-aryl(alkyl)oxy(thio)pyrazino[2′,3′:4,5]thieno[3,2-d]pyrimidinone derivatives 7 in good yields. The corresponding carbodiimide 4c and guanidine-type intermediate compounds 5 could be isolated and characterized, thus confirming the suggested reaction pathway. However, two isomeric pyrazinothienopyrimidinones 8 and 9 may be produced in the reaction of iminophosphorane 3 with aromatic isocyanates and subsequent reaction with primary amines in the presence of a catalytic amount of potassium carbonate. The effects of the nucleophiles and isocyanates on the regioselectivity of the cyclization have been investigated.     

Free radical reactions for heterocycle synthesis. Part 6: 2-Bromobenzoic acids as building blocks in the construction of nitrogen heterocycles

A general method to construct a variety of nitrogen heterocycles is introduced. 2-Bromobenzoic acids or acid chlorides are used as the common building blocks to couple with appropriate nitrogen-containing compounds. Sequential aryl radical cyclizations including conjugate additions, spirocyclizations, homolytic and ipso aromatic substitutions, and 1,5-hydrogen atom transfers are employed to prepare tri- and tetracyclic isoindolinones, benzolactams, isoquinolinones, azabenzoisocoumarins, and bridged-azabicyclic compounds.     

Self-assembled multilayer films of poor water-soluble copper(II) complexes constructed from dipyrido[3,2-d:2′,3′-f]quinoxaline (Dpq) ligand as well as their fluorescent properties

New multilayer films were prepared by alternating adsorption of poly(sodium 4-styrenesulfonate) (PSS) and a new complex of [Cu₂(Dpq)₂(Ac)₂(H₂O)₂] (ClO₄)₂·H₂O (1) (Dpq=dipyrido[3,2-d:2′,3′-f]quinoxaline, Ac=acetate) or a related complex [Cu(Dpq)₂(H₂O)] (ClO₄)₂·H₂O (1a) by electrostatic layer-by-layer self-assembly technique, respectively. Compounds 1 and 1a have been synthesized and structurally characterized by elemental analyses, IR spectroscopy, and single-crystal X-ray diffraction analyses. Single-crystal X-ray analyses show that complexes 1 and 1a possess a dinuclear and a mononuclear structure, respectively, which are further extended into layered frameworks by π-π stacking and hydrogen-bonding interactions. The multilayer films were characterized by UV-vis spectroscopy, fluorescence spectroscopy, small-angle X-ray reflectivity measurements, and atomic force microscopy (AFM) imaging. UV spectroscopy shows that the deposition process is regular and highly reproducible from layer to layer. AFM image indicates that the film surface is uniform and smooth. The fluorescent properties of the films were studied and the results showed that the forming condition of the films had great influence on their properties.     

Structure transfer from a polymeric melt to the solid state. Part I: The influence of chain entanglements in linear polyethylene

Melt-spinning experiments were carried out at high quenching rates. Mechanical properties (elongation at break, natural draw ratio, and elastic recovery) have been measured. Significant variations of these quantities were observed when extrusion conditions were changed. This has been attributed to different states of the entanglements within the melt, which are directly transferred into the solid state. This intercorrelation between melt and solid-state properties has been substantiated in the case of rapidly cooled samples, where a poor crystallization on one side and a simultaneous good conservation of melt history on the other side are provoked.     

Cross-condensation of derivatives of cyanoacetic acid and carbonyl compounds. Part 1: Single-stage synthesis of 1′-substituted 6-amino-spiro-4-(piperidine-4′)-2H,4H-pyrano[2,3-c]pyrazole-5-carbonitriles

To develop a method of synthesis of the potentially physiologically active compounds, 1′-substituted 6-amino-spiro-4-(piperidine-4′)-2H,4H-pyrano[2,3-c]pyrazoles, we studied the three-component condensation of substituted piperidin-4-ones, malononitrile and pyrazolin-5-ones. It was found that the electrochemical method of synthesis is more regioselective, the products of the reaction are analytically pure and do not require further recrystallization.     

Plasticized open-cell polyurethane foam as a universal matrix for organic reagents in trace element preconcentration: Part I. Collection of silver traces on dithizone foam

The preparation of plasticized foam containing dithizone or zinc dithizonate is described. The foam was used successfully for the rapid and quantitative collection of trace amounts of silver in batch and column experiments. The preconcentration of small amounts of silver from dilute aqueous solutions was found to be possible. The effects of different plasticizers, pH of the aqueous phase, and dithizone concentration in the foam, on the collection rate of silver were critically investigated.     

ECE mechanism as a tool for the investigation of unstable metal complexes: Part I. Electrochemical reduction of trans-[CoBr2(N)4]+-type complexes on the mercury electrode

A polarographic investigation of trans-[CoBr₂(N)₄]⁺-type complexe where (N)₄ represents (NH₃)₄, (ethylenediamine)₂ and (propylenediamine)₂, has been carried out in acetate buffer solutions. These complexes gave two polarographic waves; the first wave corresponds to the reduction of Co(III) to Co(II) and the second to the reduction of Co(II) to Co(0). The relation between current and time of the first wave in a positive potential is dependent on the dissolution wave due to bromide ions produced by acid hydrolysis and parallel ECE mechanism. Overall reaction is as follows: at the electrode surface, [Co(III)Br₂(N)₄]⁺+e^-→[Co(II)Br₂(N)₄] [Co(II)Br₂(N)₄]+6H₂O→[Co(II)(H₂O₆]²⁺+2Br^-+(N)₄ 2Br^-+2Hg→Hg₂Br₂+2e and in the solution, [Co(III)Br₂(N)₄]⁺+2H₂O→[Co(III)(H₂O₂(N)₄]³⁺+2Br^-The effects of the acid hydrolysis of a tervalent cobalt complex on the current—potential curve were simulated.     

The Structural Systematics of Protonation of Some Important Nitrogen‐base Ligands. I Some Univalent Anion Salts of Doubly Protonated 2, 2′:6′, 2″‐Terpyridyl

A number of salts of 2,2′:6′,2″ ‐terpyridyl (‘tpy’) with univalent anions (halides : X = Cl, Br, I; oxyanions of increasing basicity: ClO₄, NO₃, ‘tfa’ = trifluoroacetate, ‘tca’ = trichloroacetate), variously solvated, have been structurally characterized by single crystal X‐ray studies. In all cases the tpy moieties are found to be doubly protonated [tpyH₂]²⁺, the hydrogen atoms being associated with the nitrogen atoms of the peripheral rings, these together with the central nitrogen atom being directed towards a common focus, in most cases ‘chelating’ one of the counter‐ion components in diverse ways. Thus the chloride and bromide compounds are isomorphous [(tpyH₂)X]⁺X⁻·H₂O arrays; a second dihydrate phase is also described for the chloride, the two forms having the unchelated anion and water molecules engaged in hydrogen‐bonded networks essentially independent of [(tpyH₂)X]⁺. The iodide is anhydrous, and of a different structural type, the anions, presumably too large for chelation, lying out of plane to either side, and linking different cations into a one‐dimensional polymer; in the perchlorate, the unsolvated aggregate is now discrete [(tpyH₂)X₂], a pair of perchlorate ions disposed to either side of the tpy plane, lying each with one oxygen atom interacting with both of the two protonating hydrogen atoms. In the anhydrous X = NO₃, tfa, tca arrays, the lattices are solvated by the parent acids; one oxygen atom of each anion is chelated by the [tpyH₂]²⁺ as in the chlorides, the other anion, with the acid, forming an independent ‘acid salt’ counterion [XHX]⁻ in each case, retaining the additional protonic hydrogen rather than further protonating the central ring, all being of the form [(tpyH₂)X]X·HX = [(tpyH₂)X][X(HX)].     

The reciprocal CuInS2+2CdSe⇔CuInSe2+2CdS system. Part I. The quasi-binary CuInSe2-CdSe system: Phase diagram and crystal structure of solid solutions

The type of interaction in quasi-binary system CuInSe₂ (CIS)-CdSe was investigated using differential thermal and X-ray phase analysis methods. The limits of existence of solid solutions based on low-temperature (α) and high-temperature (γ) CIS modifications and CdSe (β) with chalcopyrite, sphalerite and wurtzite structures, respectively, were established in sub-solidus region at 620 K and 870 K. For certain compositions of solid solutions, the structure was refined using powder X-ray diffraction. A phase diagram of the CIS-CdSe system was constructed. A peritectic process L+β⇔γ takes place in the system at 1260 K.     

Technical Procedures for the Syntheses of Carotenoids and Related Compounds from 6-Oxo-isophorone: Syntheses of (3R,3′R)-Zeaxanthin. Part I

Starting from the readily available, optically active (4R)-4-hydroxy-2,2,6-trimethylcyclohexanone ( 1 ), a new technical synthesis of (3R,3′R)-zeaxanthin is described. According to a 2(C₉ + C₆) + C₁₀ = C₄₀ construction scheme, the ketone 1 was first transformed with (E)-3-methylpent-2-en-4-yn-1-ol ( 5 ) into a C₁₅-intermediate which, by a three-step sequence, could be converted into the known olefinic C₁₅-Wittig salt 4 . Optimized conditions for the final Wittig reaction of 4 with the C₁₀-dialdehyde 3 are discussed. Based on 1 , the overall yield of the entire technical process is ca. 40%.