A convenient synthesis of new enantiomerically pure trihydroxypyrrolizidines using l-erythrose glycosylhydroxylamine as a masked acyclic chiral nitrone

A route has been developed for the synthesis of enantiomerically pure trihydroxylated pyrrolizidines starting from l-erythrose glycosylhydroxylamine. The latter acts as a masked acyclic nitrone and reacts diastereoselectively from its Re-face with methyl acrylate to give the corresponding isoxazolidines, which after reductive N-O cleavage are recyclized to trihydroxypyrrolizidines via a Mitsunobu condensation.     

3-Carboxylate-Substituted Isoindolinones in K2CO3-Catalyzed Michael Reactions

Activated 3-substituted isoindolinones have proved to be efficient nucleophiles in K₂CO₃-catalyzed Michael reactions of several types of electron-deficient olefins. Moreover, tricyclic pyrrolizidines have been conveniently synthesized via a modification of the described general protocol as a consequence of a cascade Michael/cyclization reaction of unsaturated aldehydes.     

A flexible stereospecific synthesis of polyhydroxylated pyrrolizidines from commercially available pyranosides

Nitrogen-containing sugar analogues, known as azasugars or iminosugars, such as polyhydroxylated piperdines, pyrrolidines, pyrrolizidines, and indolizidines, have the potential to become important therapeutic agents due to their ability to inhibit glycosidases. Synthetic pathways that are able to systematically produce a variety of these azasugars are eagerly sought after, since even minute structural or stereochemical changes often significantly alter the degree of inhibition. The synthesis of tetrahydroxylated pyrrolizidines 40 and 41 starting from methyl alpha-d-glucopyranoside is described and will be used as a template to develop syntheses of all the stereoisomers of polyhydroxylated pyrrolizidine 9 as well as other analogous bicyclic polyhydroxylated iminosugars. The key steps in this synthesis involve a one-pot conversion of a halopyranoside to a divinylamine by employing a simultaneous Zn reduction and reductive amination of the resulting aldehyde. After protection of the amine, a ring-closing metathesis results in a multifunctional eight-membered ring that then undergoes an internal S(N)2 cyclization to form an alkene-containing pyrrolizidine 33. Dihydroxylation of the alkene followed by hydrogenolysis of the benzyl protecting groups results in tetrahydroxylated pyrrolizidines 40 and 41.     

Highly Enantioselective Intramolecular 1,3‐Dipolar Cycloaddition: A Route to Piperidino‐Pyrrolizidines

Enantioselective catalytic intermolecular 1,3‐dipolar cycloadditions are powerful methods for the synthesis of heterocycles. In contrast, intramolecular enantioselective 1,3‐dipolar cycloadditions are virtually unexplored. A highly enantioselective synthesis of natural‐product‐inspired pyrrolidino‐piperidines by means of an intramolecular 1,3‐dipolar cycloaddition with azomethine ylides is now reported. The method has a wide scope and yields the desired cycloadducts with four tertiary stereogenic centers with up to 99 % ee. Combining the enantioselective catalytic intramolecular 1,3‐dipolar cycloaddition with a subsequent diastereoselective intermolecular 1,3‐dipolar cycloaddition yielded complex piperidino‐pyrrolizidines with very high stereoselectivity in a one‐pot tandem reaction.     

Synthesis of Pyrrolidines and Pyrrolizidines with α‐Pseudoquaternary Centers by Copper‐Catalyzed Condensation of α‐Diazodicarbonyl Compounds and Aryl γ‐Lactams

N‐aryl γ‐lactams react intermolecularly with acceptor–acceptor diazo reagents, usually dicarbonyl compounds, in a copper‐catalyzed process to yield functionalized pyrrolidines with α‐pseudoquaternary centers. As 1,2‐acyl or ‐phosphoryl migration is preferred, single regioisomers are obtained. Furthermore, in the presence of a Lewis acid, subsequent Friedel–Crafts reactions yield tricyclic pyrrolizidines in excellent yields (90–96 %) and diastereoselectivities (up to >20:1).     

On the inverse miniemulsion copolymerization and terpolymerization of acrylamide, <Emphasis Type="Italic">N,N′</Emphasis>-methylenebis(acrylamide) and methacrylic acid

The kinetics of free-radical copolymerization and terpolymerization of acrylamide (AAm), N, N′-methylenebis(acrylamide) (MBA) and methacrylic acid (MA) in the inverse water/monomer/cyclohexane/Tween 85 miniemulsion was investigated. Polymerizable sterically-stable miniemulsions were formulated in cyclohexane as a continuous medium. Polymerizations are very fast and reach the final conversion within several minutes. The dependence of the polymerization rate vs. conversion is described by a curve with two nonstationary rate intervals. The maximum rate of polymerization slightly increases with increasing concentration of crosslinking monomer (MBA) and strongly decreases by the addition of MA. The rate of polymerization is inversely proportional to the 0.9 ^th and 1.8 ^th power of the particle concentration without and with MA, respectively. The number of polymer particles is inversely proportional to the 0.18 ^th and 0.13 ^th power of MBA concentration. The kinetic and colloidal parameters of the miniemulsion polymerization are discussed in terms of microemulsion polymerization model.     

Structure‐Guided Minimalist Redesign of the L‐Fuculose‐1‐Phosphate Aldolase Active Site: Expedient Synthesis of Novel Polyhydroxylated Pyrrolizidines and their Inhibitory Properties Against Glycosidases and Intestinal Disaccharidases

A minimalist active site redesign of the L ‐fuculose‐1‐phosphate aldolase from E. coli FucA was envisaged, to extend its tolerance towards bulky and conformationally restricted N‐Cbz‐amino aldehyde acceptor substrates (Cbz=benzyloxycarbonyl). Various mutants at the active site of the FucA wild type were obtained and screened with seven sterically demanding N‐Cbz‐amino aldehydes including N‐Cbz‐prolinal derivatives. FucA F131A showed an aldol activity of 62 μmol h^?1 mg^?1 with (R)‐N‐Cbz‐prolinal, whereas no detectable activity was observed with the FucA wild type. For the other substrates, the F131A mutant gave aldol activities from 4 to about 25 times higher than those observed with the FucA wild type. With regard to the stereochemistry of the reactions, the (R)‐amino aldehydes gave exclusively the anti configured aldol adducts whereas their S counterparts gave variable ratios of anti/syn diastereoisomers. Interestingly, the F131A mutant was highly stereoselective both with (R)‐ and with (S)‐N‐Cbz‐prolinal, exclusively producing the anti and syn aldol adducts, respectively. Molecular models suggest that this improved activity towards bulky and more rigid substrates, such as N‐Cbz‐prolinal, could arise from a better fit of the substrate into the hydrophobic pocket created by the F131A mutation, due to an additional π–cation interaction with the residue K205′ and to efficient contact between the substrate and the mechanistically important Y113′ and Y209′ residues. An expedient synthesis of novel polyhydroxylated pyrrolizidines related to the hyacinthacine and alexine types was accomplished through aldol additions of dihydroxyacetone phosphate (DHAP) to hydroxyprolinal derivatives with the hyperactive FucA F131A as catalyst. The iminocyclitols obtained were fully characterised and found to be moderate to weak inhibitors (relative to 1,4‐dideoxy‐1,4‐imino‐L ‐arabinitol (LAB) and 1,4‐dideoxy‐1,4‐imino‐D ‐arabinitol (DAB)) against glycosidases and rat intestinal saccharidases.     

Modeling and simulation of free radical polymerization of styrene under semibatch reactor conditions

The first part of this approach is concerned with the elaboration of a radical polymerization model of styrenne, based on a kinetic diagram that includes chemical and thermal initiation, propagation, termination by recombination and chain transfer to the monomer. Furthermore, volume contraction during polymerization is considered, as well as the gel and glass effects. The mathematical formalism that describes the model in terms of moments is explored in detail. The model was then used to predict the changes in monomer conversion and molecular weight after intermediate addition of initiator and monomer. The results of this operation are dependent on the conditions of the reaction mass, quantity, and moment of substance addition. Therefore, the simulations were performed at different times with respect to the gel effect; before, during and after this phenomenon, and also with respect to different temperatures and initiators. Increasing the initiator concentration before the gel effect leads to an earlier appearance of the phenomenon and to a decrease in molecular weight. The ratio reveals a polydispersity index smaller for the intermediate addition of initiator. No significant changes take place during or after the gel effect. If along with the initiator, unreacted monomver (used to dissolve the initiator) enters the reactor, a small dip in conversion is observed. The general conclusion of this paper reveals the intermediate addition of initiator as a method to control polymer properties and to prevent the “dead-end” polymerization of styrene.     

Epicatechin-copper 9II) complexes: Damage of small intestinal epithelium

Four epicatechins [(−)-epicatechin (EC), (−)-epicatechin gallate (ECg), (−)-epigallocatechin (EGC), (−)-epigallocatechin gallate (EGCg)] and their corresponding copper complexes were compared with regard to their effect on the viability of Caco-2 colon cancer cells in vitro, measured by 3-(4,5-dimethylthyazol-2-yl) 2,5-diphenyltetrazolium bromide (MTT) assay. The viability of Caco-2 cells exposed to EC (1 mM), ECg (1 mM) or EGC (1mM) respectively, for 30 min, was comparable to that of the saline control group, while EGCg (1 mM) apparently enhanced cellular activity. in contrast, the cells treated with epicatechin-copper complexes were killed. Bivalent copper 91 mM), in similar conditions, did not affect the cells. No cell leakage or other histological differences were observed, implying a rapid cell death. The suggested mechanism of killing is by OH radical attack, produced in the presence of epicatechin-copper complexes, but not in the presence of either of the epicatechins or copper alone. The reaction sites are discussed.     

Aerogel nanoscale magnesium oxides as a destructive sorbent for toxic chemical agents

An autoclave hypercritical drying procedure has been used to prepare precursors of MgO from Mg(OCH₃)₂. This material was prepared with a specific surface area of 1200 m² g ¹. The dehydrated materials consisted of much smaller crystallites than conventionally prepared MgO and were free of OCH₃ groups. The precursors and samples of magnesium oxide were taken for experimental evaluation of their reactivity with mustard. The largest percentage of the conversion mustard into non-toxic products after the elapse of the reaction was 77%.     

Novel Biotreatment Process for Glycol Waters

Propylene oxide (PO), propylene glycol (PG), and polyols are produced from propylene via propylene chlorohydrin. Effluents from these plants contain biological oxygen demand/chemical oxygen demand (BOD/COD) loads besides high chloride concentrations. The high salinity poses severe problem to adopt conventional methods like activated sludge processes. Presently, a simple, economically viable and versatile microbiological process has been developed to get more than 90% biodegradation in terms of BOD/COD, utilizing specially developedPseudomonas andAerobacter. The process can tolerate high salinity up to 10 wt% NaCl or 5 wt% CaCl₂ and can withstand wide variations in_pH (5.5–11.0) and temperature (15–45°C). The biodegradation of glycols involves two steps. The enzymatic conversion of glycols to carboxylic and hydroxycarboxylic acids is aided byPseudo- omonas. Further degradation to CO₂ and H₂O by carboxylic acid utilizingAerobacter, and possible metabolic degradative pathway of glycols are discussed. Various process parameters obtained in the lab scale (50 L bioreactor) and pilot scale (20 m³ bioreactor), and unique features of our process are also discussed.     

Convenient synthesis and NMR spectral studies of variously substituted <Emphasis Type="Italic">N</Emphasis>-methylpiperidin-4-one-<Emphasis Type="Italic">O</Emphasis>-benzyloximes

Abstract  A series of variously substituted N-methylpiperidin-4-one-O-benzyloximes were synthesized by three different methods. Among them, the direct conversion of 2,6-diarylpiperidin-4-ones into the corresponding oxime ethers (method A) was proved to be better than the other two methods in the sense of good yield, convenience, easy work-up and quick reaction time. All the synthesized compounds are characterized by IR, Mass and NMR (¹H NMR, ¹³C NMR, ¹H-¹H COSY, ¹H-¹³C COSY and HMBC) spectral studies. The conformational preference of the synthesized oxime ethers with/without alkyl and aryl substituents at C-3/C-5 and C-2/C-6 is discussed using the spectral data. The observed chemical shifts and coupling constants suggest that the synthesized oxime ethers adopt chair conformation with equatorial orientation of all the substituents, whereas 1-methyl-3-isopropyl-2,6-diphenylpiperidin-4-one-O-benzyloxime also exists in boat conformation. Based on the NMR data, the effects of oximination on ring carbons and their associated protons and alkyl substituents are discussed. In addition, the effect of NMe group on the 2,6-diarylpiperidin-4-one-O-benzyloximes was also studied. Graphical abstract        

Response ofClostridium Acetobutylicum to the presence of mixed extractants

The volumetric productivity of many fermentations is productlimited.In situ removal of these products with liquid organic extractants is limited by either a low product distribution coefficient or toxicity of the extractant. This paper presents results from studies using mixed extractants, namely mixtures of toxic extractants that have high distribution coefficients for the product and nontoxic extractants that have low distribution coefficients. The production of butanol byClostridium acetobutylicum was chosen as a model system for these studies. The mechanisms of toxicity of mixed extractants and the observed responses to their presence are discussed.     

Potentiometric studies on the complex formation of lanthanides with proline and hydroxyproline

The formation of the lanthanide (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu) complexes with proline and hydroxyproline has been investigated by potentiometric methods as well as by a turbidimetric one which has provided some additional conclusions. It has been found that 11 and a slight amount of 21 complexes are formed. The deviation from the typical course of the formation function is discussed. It is suggested that the perturbations of complex formation in the systems are caused by hydrolysis. The stability constants of the complexes are reported.

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Potentiometrische Untersuchungen an Lanthanid-Komplexen von Prolin und Hydroxyprolin

Zusammenfassung Die Bildung von Lanthanid-Komplexen (La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Lu) mit Prolin und Hydroxyprolin wurde potentiometrisch und mit Hilfe von Trübungsmessungen untersucht. Es wurde festgestellt, daß sich Komplexe der Zusammensetzung 11 und in kleiner Menge auch 21 bilden. Die Abweichung von typischem Verlauf der Bildungskurven wurde untersucht. Es wurde dabei festgestellt, daß für die Störungen in der Komplexbildung die Hydrolyse verantwortlich ist. Die Stabilitätskonstanten wurden bestimmt.

     

On the three-phase mass transfer with solid particles adhered to the gas-liquid interface

A heterogeneous, multi-layer mass transfer model is proposed for prediction of the effect of multi-layer packing of catalyst particles adhered to the gas-liquid interface. The behavior of the mass transfer rate with respect to the multi-layer packing, to the particle size and mass transfer coefficient without particles is discussed. It is shown that enhancement can be considerably increased by multi-layer packing compared to that of mono-layer packing, depending on the values of particle size and mass transfer coefficient. The predicted mass transfer rates using the proposed model was verified with experimental data taken from the literature. The model presented should be superior to that of published in the literature.     

Competitive conversion of methylcyclohexane andn-octane. Variation of hydrogen partial pressure

The presence of added hydrogen does not significantly alter the relative conversion of methylcyclohexane andn-octane. The results for conversion at a total pressure of 0.1 mPa are consistent with a mechanism where chemisorption is irreversible and rate limiting even where the hydrogen partial pressure is 0.094 mPa. Dedicated to Professor Pál Tétényi on the occasion of his 70th birthday     

An ab initio study of the ground and excited states of p-benzoquinone

The results of anab initio SCF calculation for the ground state and CI calculations for the excited states of p-benzoquinone are presented and discussed. A minimum basis set of Slater type orbitals was employed and the CI calculations were performed by considering single excitations from valence to virtual SCF molecular orbitals. The convergence of the calculated excitation energies is studied as a function of the number of orbitals used in the CI calculations. These calculations explain quite well the experimental results.     

Empirical assessment on the cellulase digestibility of processedEucalyptus wood

Samples ofEucalyptus globulus wood were delignified in HC1-catalyzed acetic acid medium under selected conditions and extracted with alkaline solutions to improve their susceptibility to enzymatic hydrolysis. The effects of three independent variables defining the operational conditions of the alkaline extraction stage on five dependent variables measuring both the chemical composition and the susceptibility of the solid residues to enzymatic hydrolysis were assessed using empirical models deduced from experimental data. The enzymatic conversion depended mainly on the NaOH concentration used in the alkaline extraction. Hydrolysis yields up to 76% were predicted for operational conditions within the range studied for the independent variables.     

Synthesis,spectral characterization,redox and antimicrobial activity of Schiff base transition metal(II) complexes derived from 4-aminoantipyrine and 3-salicylideneacetylacetone

A novel tetradentate N₂O₂ type Schiff base, synthesized from 1-phenyl-2,3-dimethyl-4-aminopyrazol-5-one(4-aminoantipyrine) and 3-salicylidene-acetylacetone, forms stable complexes with transition metal ions such as Cu ^II , Ni ^II , Co ^II and Zn ^II in ethanol. Microanalytical data, magnetic susceptibility, IR, UV-Vis.,¹H-NMR, ESR and Mass spectral techniques were used to confirm the structures. Electronic absorption spectra of the complexes suggest a square-planar geometry around the central metal ion. These complexes show higher conductance values, supporting their electrolytic nature. The monomeric nature of the complexes was confirmed from their magnetic susceptibility values. Cyclic voltammogram of the copper(II) and nickel(II) complexes in DMSO solution at 300 K were recorded and the results are discussed. The X-band ESR spectra of the copper complex were recorded and the molecular orbital coefficient values were calculated from the spectra. The in vitro antimicrobial activities of the investigated compounds were tested against bacteria such as Klebsiella pneumoniae, Staphylococcus aureus, Bacillus subtilis and Escherichia coli and fungi like Aspergillus niger and Rhizoctonia bataicola. Most of the metal chelates show higher antimicrobial activity for the above microorganisms than that of the free ligand.     

Novel Ni−Fe-oxide systems for catalytic oxidation of cyanide in an aqueous phase

Catalytic activity of mixed Ni?Fe oxide systems with respect to air oxidation of aqueous cyanide solution at 308 K was investigated. The catalysts employed were prepared by an oxidation-precipitation method at room temperature and were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, and chemical analysis. The cyanide oxidation rate was found to be dependent on the catalyst's calcination temperature, pH of the medium, and catalyst loading. Results revealed that the catalyst calcined at 120°C is the most active where up to 90% of free cyanide (4 mM) was removed after oxidation for 30 minutes in the presence of 2.5 g/L catalyst at pH 9.5. The cyanide conversion becomes less favorable as the pH of the solution increases (with other constant parameters). The selectivity data showed that carbon dioxide is the main oxidation product, regardless of pH of the solution.