The reaction of B-alkyl-9-borabicyclo[3.3.1]nonanes with aldehydes and ketones. A facile elimination of the alkyl group by aldehydes

Certain B-alkyl-9-borabicyclo[3.3.1]nonanes (9-BBN) reduce benzaldehyde to benzyl alcohol under exceptionally mild conditions. Factors which contribute to a high rate of reaction include: an increase in the degree of substitution at the position β to the boron (isobutyl > 1-butyl >> ethyl), the ability of the alkyl group to form a syn-planar B—C—C—H conformation (cyclopentyl ? norbornyl > sec-butyl >> cyclohexyl), and the presence of an electron-withdrawing para-substituent on the benzaldehyde (p-Cl > p-H > p-CH₃O). The B-alkyl group is transformed into an olefin as the benzaldehyde is reduced. Elimination takes place predominantly if not exclusively towards the more highly substituted β hydrogen. The reaction obeys second order kinetics. The observations are consistent with a cyclic mechanism rather than a dehydroboration-reduction pathway.     

Efficient double bond migration of allylbenzenes catalyzed by Pd(OAc)2-HFIP system with unique substituent effect

A novel catalyst system of Pd(OAc)₂-HFIP induces double-bond migration of allylbenzenes under mild conditions with low catalytic loading to afford 1-propenylbenzenes. The reaction shows a unique substituent effect that is highly dependent on the distance of substituents from the allylic moiety. Thus, the reactivity of substrates bearing a methyl group is ordered in para > meta > ortho, whereas it is entirely reversed as ortho > meta > para for methoxy and chloro substituents.     

Synthesis and properties of organosoluble polyimides based on novel perfluorinated monomer hexafluoro-2,4-toluenediamine

New highly fluorinated aromatic polyimides based on hexafluoro-2,4-toluenediamine and commercially available dianhydrides (6FDA and ODPA) were synthesized by one-pot high temperature polycondensation in benzoic acid melt. Owing to the CF₃ group and fluorine atoms in the meta-linked phenylenediamine fragment, these polyimides combine good solubility in organic solvents including such a low boiling point solvent as chloroform with high glass transition temperatures (330-345 °C), thermal and thermooxidative stability (T₅ is >500 °C). The highly fluorinated polyimide films (hydrogen content is ≤1%) exhibit good dielectric properties and low water absorption as well as excellent optical transparency in the UV-vis region (cut-off wavelength is 311 nm for 6FDA-based and 357 nm for ODPA-based polyimides), which is very important for optoelectronic materials.     

Pseudo-template molecularly imprinted polymer for selective screening of trace β-lactam antibiotics in river and tap water

To assess the potential risks associated with the environmental exposure of β-lactam antibiotics (BLAs), the monitoring of the occurrence, distribution, and fate of these emerging contaminants in the environment is required. Herein, we demonstrate a molecularly imprinted solid-phase extraction (MISPE) method for selective and reliable screening of trace BLAs in river and tap water. By developing a low-temperature photopolymerization, highly selective molecularly imprinted polymers (MIPs) for five BLAs (penicillin G, amoxicillin, ampicillin, nafcillin and mezlocillin) were synthesized. Nafcillin was chosen as a pseudo template to make the MIP sorbent (Nafc-MIP), which was used in pseudo-template MISPE for preconcentration of the other four BLAs from river and tap water. The application of pseudo-template MISPE overcomes the template bleeding, which significantly elevates the sample background and restricts the application of MIP for detection of the target BLA below 2 μg/L. The average recoveries of BLAs are in the range of 60–90% when Nafc-MIP was adopted as the selective MISPE sorbent. The developed method was validated, and applied to the screening of trace β-lactam antibiotics in river and tap water. The linearity of the calibration curve for each BLA was observed over the range of 0.1–20 μg/L (r > 0.998). The β-lactam antibiotics were found within the range of 0–9.56 μg/L in river water at the downstream of antibiotics manufacturers, and none were detected in the tap water.     

An efficient preparative scale resolution of 3-phenylbutyric acid by lipase from Burkholderia cepacia (Chirazyme L1)

Lipase from Burkholderia cepacia (Chirazyme L1) catalysed the highly enantioselective hydrolysis of racemic methyl 3-phenylbutyrate to afford (R)-(−)-methyl 3-phenylbutyrate of >98% ee (E>50). The resolution was performed at 150 g scale yielding 68.7 g of (R)-(−)-methyl 3-phenylbutyrate (>98% ee, 92% yield on enantiomer) and (S)-(+)-3-phenylbutyric acid of 89% ee.     

Aminolytic kinetic resolution of trans epoxides for the simultaneous production of chiral trans β-amino alcohols in the presence of chiral Cr(III) salen complex using an ionic liquid as a green reaction media

Chiral Cr(III) salen complex 1 having t-Bu substituents at 3,3′ and 5,5′-positions was used as a catalyst for the highly enantioselective aminolytic kinetic resolution (AKR) of racemic trans epoxides with different anilines as nucleophile in the presence of different ionic liquids at rt. Excellent yields (>98%) of anti β-aminoalcohols with high enantioselectivity (ee >99%) was achieved in 4 h when [bmim]PF₆ was used as the ionic liquid. The present ionic liquid mediated AKR process is recyclable (up to six cycles with no loss in performance) and is five times quicker than the homogeneous process utilizing conventional organic solvents.     

Water vapour adsorption and contrast-modified SAXS in microporous polymer-based carbons of different surface chemistry

The adsorption of water vapour on highly microporous activated carbons with different surface chemistry is investigated by small angle X-ray scattering (SAXS) as well as by adsorption isotherms. The water changes the intensity of the SAXS in a way that depends on how the pores are filled. With wetting liquids such as hexane, a pseudo binary model can be assumed in which pore-filling in reciprocal space q is described by a density function p(q). For water, clusters develop, even in the most oxidized carbon, creating a fully ternary system. In the Porod scattering region, however, the final slope is insensitive to the liquid-vapour interfaces. In this region, for the less oxidized samples, p(q) shows reasonable agreement with the adsorption isotherms. At low relative pressure P/P ₀, however, the SAXS results indicate a small degree of filling (about 10%) that is not reflected in the isotherms. The highly oxidized sample attains a degree of filling of about 70% that, unlike the corresponding isotherm, is constant for P/P ₀>0. These differences may be due to kinetic effects and/or ageing, involving either redistribution of the water molecules or modifications of the surface groups.     

Solubility of (+)-Usnic Acid in Water, Ethanol, Acetone, Ethyl Acetate and n-Hexane

Using ultraviolet spectrophotometry, the solubility of (+)-usnic acid in water, ethanol, acetone, ethyl acetate and n-hexane were measured at temperatures from (278.15 to 338.15) K at atmospheric pressure. The results obtained led to the solubility order: ethyl acetate > acetone > n-hexane > ethanol > water. The solubility values were correlated with the Apelblat equation, the λh equation and the ideal model. The results showed that these three models agreed well with the experimental data.     

Synthesis of enantiopure β-amino alcohols via AKR/ARO of epoxides using recyclable macrocyclic Cr(III) salen complexes

A series of chiral macrocyclic Cr(III) salen complexes 1-8 were synthesized and characterized. These complexes were found to be highly active, regio-, diastereo-, and enantioselective catalysts in aminolytic kinetic resolution (AKR) of racemic trans-epoxides as well as asymmetric ring opening (ARO) of prochiral meso-epoxides with various anilines as nucleophiles at room temperature in 18-24 h. Excellent yields (>99% with respect to the nucleophile) with high enantioselectivity (ee, >99%) of chiral anti-β-amino alcohols was achieved with concomitant recovery of corresponding epoxides in high ee (up to >99%). The complex 1 also catalyzed the ARO of meso-epoxides to provide corresponding syn-β-amino alcohols in high yield (99%) and ee (up to 91%). Due to built-in basic sites in the catalyst, no external base (as an additive) was required to promote AKR and ARO reactions. The catalyst 1 was conveniently recycled several times with retention of its performance. The AKR of trans-stilbene oxide with aniline was successfully demonstrated at relatively higher scale (10 mmol) using the catalyst 1.     

Synthesis of diastereo- and enantiomerically pure anti-3-methyl-1,4-pentanediol via lipase catalysed acylation

Racemic trans-4,5-dimethylhydrofuran-2(3H)-one was synthesised from 5-methyl-furan-2(3H)-one, (α-angelica lactone). The key reaction in the synthesis was the 1,4-conjugate addition of an organocuprate to 5-methylfuran-2(5H)-one (β-angelica lactone). Different types of organocuprates were tested with the highest anti:syn ratio of 99.4:0.6 being obtained by the use of a Gilman organocuprate reagent. The enantioselective acylation of racemic 3-methyl-pentan-1,4-diol, catalysed by a variety of lipases in organic media, was investigated. The highest enantioselectivity (E > 400) was obtained when Novozyme 435 was used as the catalyst at a water activity of a_w ∼ 0. Thus, both enantiomers, (3S,4R)- and (3R,4S)-3-methyl-pentan-1,4-diol, were obtained in very high diastereomeric (>99% de) and enantiomeric purities (>99.8% and >97.4% ee, respectively).     

Mesoporous phosphated and sulphated silica as solid acid catalysts for glycerol acetylation

Sulphate- and phosphate-loaded silicas were synthesised using the sol-gel method with different sulphate and phosphate loadings. These catalysts were characterised using Fourier transform infrared spectroscopy (FT-IR), the Brunauer-Emmett-Teller (BET) method and X-ray photoelectron spectroscopy (XPS). Acidity was measured using the temperature-programmed desorption of ammonia (TPD-NH3) method. The results showed that glycerol esterification with acetic acid conversion decreased as follows: α(H₂SO₄) (100 %) > α(H₃PO₄) (99 %) > α(silica loaded with 20 % sulphuric acid) (SS-20; 98 %) > α(silica loaded with 20 % phosphoric acid) (PS-20; 83 %). These studies suggest that the solid acid catalytic activity in the esterification of glycerol is highly dependent on catalyst acidity strength, pore size and surface area.     

A new titanate/(+)-(1R,2S)-cis-1-amino-2-indanol system for the asymmetric synthesis of (S)-tenatoprazole

Tenatoprazole, a substituted imidazopyridinyl derivative, is an irreversible proton pump inhibitor (PPI), which is used for the prevention and treatment of gastric acid-related diseases. A new highly efficient asymmetric oxidation using cumene hydroperoxide (CHP) as the oxidant in the presence of titanium tetraisopropoxide (Ti(OiPr)₄) and (+)-(1R,2S)-cis-1-amino-2-indanol, in a polar aprotic solvent at 0-20 °C, has been developed to prepare tenatoprazole with an enantiomeric excess of >99%, a chemoselectivity of >90% and a chemical yield of >90% from the corresponding sulfide. This procedure was successfully implemented on scales ranging from 100 mg to multiple kilograms. Detailed studies of the parameters controlling purity and yield for this reaction are presented.     

Water-soluble chiral monosulfonamide-cyclohexane-1,2-diamine-RhCp complex and its application in the asymmetric transfer hydrogenation (ATH) of ketones

Monosulfonamide ligands with heteroatom/heterocyclic systems were derived from trans-(1R,2R)-cyclohexane-1,2-diamine and complexed with [Ru(benzene)Cl₂]₂, [Cp^∗RhCl₂]₂ in situ and used in the ATH of aromatic ketones with aqueous sodium formate as the hydrogen source. The chiral secondary alcohols were obtained with >93% enantioselectivity and >89% yield. Reduction in water was faster than in isopropanol/KOH. Addition of surfactants showed little or no effects.     

The thermal properties of cobalt(II), nickel(II) and copper(II) iminodiacetates

The thermal properties of the Cu(II), Ni(II) and Co(II) complexes of iminodiacetic acid (H₂IMDA) were determined using TG, DTG and DSC techniques. The complexes, of general formula, MIMDA-2H₂O evolved water of hydration from 50 to 150°C which was followed by the decomposition of the anhydrous complex in the 250 to 400°C temperature range. The thermal stability, as determined by procedural decomposition temperatures, was: Ni(II) >Co(II) >Cu(II). The thermal stability is discussed in terms of IR spectra, ΔH, and ΔS, as well as thermal data.     

Enzymatic resolution of α-tetralols by CALB-catalyzed acetylation

A series of homochiral α-tetralols, as well as their respective acetates, has been obtained by esterification of racemic tetralols, using Candida antarctica lipase (CALB—Novozym^® 435) as the biocatalyst. This enzyme is shown to be highly efficient for the kinetic resolution of the substrates studied, affording the (+)-tetralols and the (+)-acetates in excellent enantiomeric excess (up to >99%) and very good yields (>40%).     

Reactivity of sugar cane bagasse as a natural solid phase extractor for selective removal of Fe(III) and heavy-metal ions from natural water samples

This work introduces the feasibility of using sugar cane bagasse (SCB) – a sugar cane industry waste – as a selective solid phase extractor for Fe(III). The order of metal uptake capacities in μmol g^?1 for the extraction of six tested metal ions from aqueous solution using static technique is Fe(III) > Cu(II) > Pb(II) > Zn(II) > Cd(II) > Co(II). Since SCB exhibits remarkable binding characteristics for Fe(III), special interest was devoted for optimizing its uptake and studying its selectivity properties under static and dynamic conditions. In this respect, batch experiments were carried out at the pH range 1.0–4.0, initial concentration of metal ion (10–100 μmol), weight of phase (25, 50, 75, 100, 125 and 150 mg) and shaking time (10, 30, 45, 60, 90, 120 and 150 min). FT-IR spectra of SCB before and after uptake of Fe(III) were recorded to explore the nature of the functional groups responsible for binding of Fe(III) onto the studied natural biosorbent. The equilibrium data were better fitted with Langmuir model (r² = 0.985) than Freundlich model (r² = 0.934). Moreover, Fe(III) sorption was fast and completed within 60 min. The adsorption kinetics data were best fitted with the pseudo-second-order type. As a view to find a suitable application of SCB based on its unique property as a benign sorbent, it was found that, Fe(III) spiked natural water samples such as doubly distilled water (DDW), drinking tap water (DTW), natural drinking water (NDW), ground water (GW) and Nile River water (NRW) was quantitatively recovered (>95.0%) using batch and column experiments, with no matrix interferences.     

A simple procedure for the esterification of alcohols with sodium carboxylate salts using 1-tosylimidazole (TsIm)

An efficient and selective method for esterification of alcohols using N-(p-toluenesulfonyl)imidazole (TsIm) is described. In this method, alcohols are refluxed with a mixture of RCO₂Na (R: alkyl and aryl), TsIm, and triethylamine in the presence of catalytic amounts of tetra-n-butylammonium iodide (TBAI) in DMF to afford the corresponding esters in good yields. This methodology is highly efficient for various structurally diverse alcohols with selectivity for ROH: 1° > 2° > 3°.     

Good linear relationship between logarithms of Eigen’s water exchange constants for several divalent metal ions and activation energies of corresponding metal-catalyzed alkoxysilane hydrolysis in ethylene-propylene copolymer system

Catalytic efficiencies of seven divalent metal acetylacetonate complexes [M(acac)₂; M = Cd(II), Co(II), Cu(II), Fe(II), Ni(II), Pb(II), and Zn(II)] with respect to the water-crosslinking kinetics of vinyltrimethoxysilane-grafted ethylene-propylene copolymer (EPR-g-VTMS) were investigated to examine the effects of progressive changes in metal ion using ATR-FTIR spectroscopy. The hydrolysis activation energies of EPR-g-VTMS follows the order: No catalyst ≈ Ni(acac)₂ > Co(acac)₂ > Fe(acac)₂ ≈ Zn(acac)₂ > Cd(acac)₂ ≈ Cu(acac)₂ > Pb(acac)₂. Interestingly, the kinetics results revealed that the plots of hydrolysis activation energies of EPR-g-VTMS containing M(acac)₂ complexes and Eigen’s water exchange constants for corresponding metal ions showed a excellent linear relationship, suggesting that the reaction pathway for the silane water-crosslinking with hydrous M(acac)₂ complex in EPR-g-VTMS system may be similar to that for water exchange of the metal ion in an aqueous system. Based on the knowledge of traditional kinetics studies by Eigen and Wilkins and hybrid sol-gel chemistry, the plausible catalytic mechanism for M(acac)₂ complexes in EPR-g-VTMS system was proposed.     

Highly diastereoselective chemoenzymatic synthesis of (2′R)- and (2′S)-2′-deoxy[2′-H]guanosines

In an effort to develop an efficient synthetic method of highly diastereoselective (2′R)- and (2′S)-2′-deoxy[2′-²H]guanosines, chemoenzymatic conversion was investigated. The synthesis of (2′R > 98% de)-2′-deoxy[2′-²H]guanosine was achieved by biological transdeoxyribosylation using (2′R > 98% de)-2′-deoxy[2′-²H]uridine, 2,6-diaminopurine, and Enterobacter aerogenes AJ-11125, followed by treatment with adenosine deaminase. (2′S > 98% de)-2′-Deoxy[2′-²H]guanosine was synthesized from (2′S > 98% de)-2′-deoxy[2′-²H]uridine and 2,6-diaminopurine using thymidine phosphorylase and purine nucleoside phosphorylase instead of E. aerogenes AJ-11125.     

Synthesis of enantiomerically pure desmethylzopiclone and determination of its absolute configuration

Two synthetic methods have been established for the preparation of enantiomerically pure desmethylzopiclone, a metabolite of zopiclone. In Method A, (S)-desmethylzopiclone was prepared by demethylation of (S)-zopiclone with 1-chloroethyl chloroformate in high yield. Enantiomerically pure zopiclone (>99% ee) was obtained through a highly efficient resolution process in >36% overall yield. In Method B, racemic desmethylzopiclone was resolved with l-N-benzyloxycarbonyl phenylalanine (l-ZPA) followed by recrystallization in good yield. The absolute stereochemistry of the (+)-enantiomer was first determined to be the (S)-configuration by X-ray crystallography.