A new type of catalytic tandem 1,4-addition-aldol reaction which proceeds through an (oxa-pi-allyl)rhodium intermediate

The reaction of 9-aryl-9-borabicyclo[3.3.1]nonanes (B-Ar-9BBN) with alpha,beta-unsaturated ketones and aldehydes in the presence of 3 mol % [Rh(OMe)(cod)](2) in toluene at 20 degrees C for 2 h gave high yields of the tandem 1,4-addition-aldol reaction products with high syn selectivity. The reaction proceeds through the catalytic cycle consisting of 1,4-addition of an organorhodium species to an alpha,beta-unsaturated ketone and the aldol addition of the resulting (oxa-pi-allyl)rhodium intermediate to an aldehyde.     

Asymmetric conjugate 1,4-addition of arylboronic acids to alpha, beta-unsaturated esters catalyzed by Rhodium(I)/(S)-binap

Arylboronic acids underwent the conjugate 1,4-addition to alpha, beta-unsaturated esters to give beta-aryl esters in high yields in the presence of a rhodium(I) catalyst. The addition of arylboronic acids to isopropyl crotonate resulted in high yields and high enantioselectivity exceeding 90% ee in the presence of 3 mol % of Rh(acac)(C(2)H(4))(2) and (S)-binap at 100 degrees C. The rhodium/(S)-binap complex provided (R)-3-phenylbutanoate in the addition of phenylboronic acid to benzyl crotonate. The effects on the enantioselectivity of chiral phosphine ligands, rhodium precursors, and substituents on alpha,beta-unsaturated esters are discussed, as well as the mechanistic aspect of the catalytic cycle.     

Isomerization reaction of olefin using RuClH(CO)(PPh(3))(3)

When methyl 5-(tert-butyldiphenylsilyl)oxy-2-pentenoate was refluxed in toluene in the presence of RuClH(CO)(PPh(3))(3) (5 mol %), double-bond migration took place to afford methyl 5-(tert-butyldiphenylsilyl)oxy-4-pentenoate in high yield. This means that the double bond conjugated with the ester moiety migrates to a deconjugated position by a ruthenium catalyst. We planned to prepare an enol ether from alpha,beta-unsaturated compounds having an ether moiety in a tether using ruthenium-catalyzed isomerization of the double bond. As a result, silyl or benzyl enol ether was obtained from the alpha,beta-unsaturated ester having alcohol protected by the silyl or benzyl group in a tether in high yield. In this reaction, double bond migration of alpha,beta-unsaturated ketone and alpha,beta-unsaturated amide took place to produce deconjugated compounds. Moreover, the double bond of alpha, beta-unsaturated ester having a triple or double bond in a molecule migrated to produce conjugated enyne and diene. On the other hand, treatment of a bis-metalated compound having an alpha, beta-unsaturated ester moiety or the double bond in a tether with RuClH(CO)(PPh(3))(3) gave allyl bis-metalated compound in good yield. These compounds are useful units in synthetic organic chemistry.     

Ruthenium-catalyzed reaction of alpha,beta-unsaturated imines with carbon monoxide and alkenes leading to beta,gamma-unsaturated gamma-butyrolactams: involvement of direct carbonylation at olefinic C[bond]H Bonds as a key step

The reaction of alpha,beta-unsaturated imines with CO and alkenes in the presence of Ru(3)(CO)(12) as a catalyst results in a three-component coupling reaction that gives alpha,alpha-disubstituted beta,gamma-unsaturated gamma-butyrolactams. The reaction proceeds via a two-step sequence involving the initial formation of ketone derivatives by catalytic carbonylation at the beta-olefinic C-H bonds of alpha,beta-unsaturated imines, followed by the (uncatalyzed) intramolecular nucleophilic attack of the imine nitrogen on the ketonic carbon to generate a tetrahedral intermediate, which then undergoes a 1,2-ethyl migration. The reaction of a cyclic unsaturated imine, derived from the reaction of (1R)-(-)-myrtenal with tert-butylamine, gives a beta-aminocyclopentene derivative, which is formed by an aldol-type condensation of the initially formed ketone, indicating the initial formation of ethyl ketone.     

Separation of human,bovine, and porcine insulins,three very closely related proteins,by micellar electrokinetic chromatography

Human, bovine, and porcine insulins are small proteins with very closely related amino acid sequences, which makes their separation challenging. In this study, we took advantage of the high‐resolution power of CE, and more particularly of micellar electrokinetic chromatography, to separate those biomolecules. Among several surfactants, perfluorooctanoic acid ammonium salt was selected. Then, using a design of experiments approach, the optimal BGE composition was found to consist of 50 mM ammonium acetate pH 9.0, 65 mM perfluorooctanoic acid ammonium salt, and 4% MeOH. The three insulins could be separated within 12 min with a satisfactory resolution. This method could be useful to detect possible counterfeit pharmaceutical formulations. Indeed, it would be easy to determine if human insulin was replaced by bovine or porcine insulin.     

EPR and magnetic properties of heteronuclear Mn(n)Mg(6-)(n)(O(2)CNEt(2))(12): impact of structural distortions on Mn(II) in weak ligand fields

The reaction between Mn(6)L(12) and Mg(6)L(12) (L = N,N-diethylcarbamate) results in isolation of heteronuclear complexes Mn(n)Mg(6)(-)(n)L(12). A series was prepared with different doping factors n by varying the Mn/Mg ratio in the crystallization solutions. Single-crystal X-ray diffraction shows that MnMg(5)L(12) is isostructural with Mn(6)L(12) and Mg(6)L(12). Magnetic susceptibility data on the series Mn(n)Mg(6)(-)(n)L(12) (n = 1-6) are consistent with antiferromagnetic Mn.Mn interactions. At low n, the magnetic data demonstrate the formation of magnetically isolated Mn(2+) centers. This was confirmed by measurement of the EPR spectrum at a doping factor n = 0.06 in solution, as a powder, and as single crystals. These show hyperfine interactions consistent with isolated Mn(2+). The EPR spectrum of Mn(0.06)Mg(5.94)L(12) exhibits a dominant signal at g(eff) = 4, and a wide series of less intense signals spanning 200-6000 G in the X-band regime. This unusual behavior in a weak-field Mn(2+) complex is attributed to the substantial distortions from cubic ligand field geometry in this system. The g(eff) = 4 signals are attributed to a C(2)-symmetric hexacoordinate Mn(2+) ion with D > 0.3 cm(-)(1) and E/D = 0.33. The wide series is assigned to an axial C(4)(v) pentacoordinate Mn(2+) site with D = 0.05 cm(-)(1). Comparison of the g(eff) = 4 signals to the g = 4.1 signals exhibited by the tetramanganese complex in photosystem II belies the fact that they almost certainly arise from different spin systems. In addition, the similarity of the spectrum of Mn(n)Mg(6)(-)(n)L(12) to mononuclear Mn(4+) complexes suggests that considerable care must be exercised in the use of EPR as a fingerprint for the manganese oxidation state, particularly in manganese proteins where molecular composition may not be precisely established.     

Determination of melengestrol acetate in bovine tissues by automated coupled-column normal-phase high-performance liquid chromatography

A method has been developed for the determination of melengestrol acetate in bovine tissues at lower levels than previously reported. Liquid-liquid extraction of tissue homogenates provided crude clean-up while final isolation, screening, and quantification was done on-line with an automated, normal-phase, coupled-column high-performance liquid chromatographic system. The chromatographic system included phenyl and silica analytical columns for the purposes of isolation and final separation, respectively. These columns provided a large difference in selectivity when operated under normal-phase conditions which allowed for the efficient isolation of melengestrol acetate from the complex tissue extracts. Mobile phases were composed of hexane and dichloromethane modified with methanol and water. Transfer and enrichment of the analyte from the primary phenyl column to the silica column was via a short (12 mm x 4 mm I.D.) silica column. Regeneration and equilibration of the phenyl column was performed after the injection of each tissue extract and was accomplished simultaneously while analytical separation occurred on the final silica column. Routing of the mobile phases and regeneration solvent was performed with automated switching valves. The total time required for each analysis was 12 min. Quantification is demonstrated using external standards with UV detection at 287 nm. The overall recovery of the method was 86% with a coefficient of variation of 9.84% at the 10 ppb [the American billion (10(9] is used in this article] level in bovine liver extracts.     

Iron Carbonyl-Promoted Isomerization of Olefin Esters to Their alpha,beta-Unsaturated Esters: Methyl Oleate and Other Examples

Ultraviolet photolysis of stoichiometric amounts of methyl oleate and Fe(CO)(5) in hexanes solvent at 0 degrees C gives Fe(CO)(3)(eta(4)-alpha,beta-ester) in which the alpha,beta-unsaturated ester isomer of methyl oleate is stabilized by eta(4)-oxadiene pi coordination of the olefin and ester carbonyl groups to the Fe(CO)(3) unit. Treatment of the Fe(CO)(3)(eta(4)-alpha,beta-ester) with pyridine or CO liberates the free alpha,beta-ester, methyl octadec-trans-2-enoate, in 70% yield. The Fe(CO)(3) unit both catalyzes the olefin isomerization and stabilizes the alpha,beta-unsaturated ester, which results in the formation of the alpha,beta-ester in a yield far above that (3.5%) observed for simple catalyzed methyl oleate isomerization. The much smaller olefin esters, methyl 3-butenoate and ethyl 4-methyl-4-pentenoate, are isomerized under the same conditions to their alpha,beta-unsaturated esters in 94 and 90% yields, respectively. The effects of reaction conditions on the yield, the use of Fe(CO)(3)(cis-cyclooctene)(2) as a nonphotolytic catalyst, and the mechanism of this useful synthetic process are discussed.     

[Cu(Phen)(5-Fu)2](NO3)2配合物与牛血清白蛋白相互作用的荧光光谱研究

以Cu(Ⅱ)作为中心离子,5-氟脲嘧啶(5-Fu)和邻菲咯啉(Phen)作为配体,合成了[Cu(Phen)(5-Fu)2](NO3)2配合物;利用元素分析和红外光谱分析了配合物的组成和化学结构;利用荧光光谱考察了其与牛血清白蛋白(BSA)的相互作用.结果表明.配合物与BSA作用可导致BSA内源荧光猝灭;其猝灭机理为静态...     

The application of (199)Hg NMR and (199m)Hg perturbed angular correlation (PAC) spectroscopy to define the biological chemistry of Hg(II): a case study with designed two- and three-stranded coiled coils

The use of de novo designed peptides is a powerful strategy to elucidate Hg(II)-protein interactions and to gain insight into the chemistry of Hg(II) in biological systems. Cysteine derivatives of the designed alpha-helical peptides of the TRI family [Ac-G-(L(a)K(b)A(c)L(d)E(e)E(f)K(g))(4)-G-NH(2)] bind Hg(II) at high pH values and at peptide/Hg(II) ratios of 3:1 with an unusual trigonal thiolate coordination mode. The resulting Hg(II) complexes are good water-soluble models for Hg(II) binding to the protein MerR. We have carried out a parallel study using (199)Hg NMR and (199m)Hg perturbed angular correlation (PAC) spectroscopy to characterize the distinct species that are generated under different pH conditions and peptide TRI L9C/Hg(II) ratios. These studies prove for the first time the formation of [Hg{(TRI L9C)(2)-(TRI L9C-H)}], a dithiolate-Hg(II) complex in the hydrophobic interior of the three-stranded coiled coil (TRI L9C)(3). (199)Hg NMR and (199m)Hg PAC data demonstrate that this dithiolate-Hg(II) complex is different from the dithiolate [Hg(TRI L9C)(2)], and that the presence of third alpha-helix, containing a protonated cysteine, breaks the symmetry of the coordination environment present in the complex [Hg(TRI L9C)(2)]. As the pH is raised, the deprotonation of this third cysteine generates the trigonal thiolate-Hg(II) complex Hg(TRI L9C)(3)(-) on a timescale that is slower than the NMR timescale (0.01-10 ms). The formation of the species [Hg{(TRI L9C)(2)(TRI L9C-H)}] is the result of a compromise between the high affinity of Hg(II) to form dithiolate complexes and the preference of the peptide to form a three-stranded coiled coil.     

Rhodium-catalyzed 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyl compounds: large accelerating effects of bases and ligands

The effects of ligands and bases in the rhodium(I)-catalyzed 1,4-addition of arylboronic acids to alpha,beta-unsaturated carbonyl compounds were reinvestigated to carry out the reaction under mild conditions. Rhodium(I) complexes possessing a 1,5-cyclooctadiene (cod) and a hydroxo ligand such as [RhOH(cod)](2) exhibited excellent catalyst activities compared to those of the corresponding rhodium-acac or -chloro complexes and their phosphine derivatives. The reaction was further accelerated in the presence of KOH, thus allowing the 1,4-addition even at 0 degrees C. A cationic rhodium(I)-(R)-binap complex, [Rh(R-binap)(nbd)]BF(4), catalyzed the reaction at 25-50 degrees C in the presence of Et(3)N with high enantioselectivities of up to 99% ee for alpha,beta-unsaturated ketones, 92% for aldehydes, 94% for esters, and 92% for amides.     

Mechanistic analysis of reductive nitrosylation on water-soluble cobalt(III)-porphyrins

The reactions of NO and/or NO2- with three water-soluble cobalt porphyrins [Co(III)(P)(H2O)2]n, where P = TPPS, TCPP, and TMPyP, were studied in detail. At pH < 3, the reaction with NO proceeds through a single reaction step. From the kinetic data and activation parameters, the [Co(III)(P)(NO)(H2O)]n complex is proposed to be the primary product of the reaction with NO. This complex reacts further with a second NO molecule through an inner-sphere electron-transfer reaction to generate the final product, [Co(III)(P)(NO-)](n-1). At pH > 3, although a single reaction step is also observed, a systematic study as a function of the NO and NO2- concentrations revealed that two reaction steps are operative. In the first, NO2- and NO compete to substitute coordinated water in [Co(III)(P)(H2O)2]n to yield [Co(III)(P)(NO)(H2O)]n and [Co(III)(P)(NO2-)(H2O)](n-1) as the primary reaction products. Only the nitrite complex could be detected and no final product formation was observed during the reaction. It is proposed that [Co(III)(P)(NO)(H2O)]n rapidly reacts with NO2- to form the nitrite complex, which in the second reaction step reacts with another NO molecule to generate the final product through an inner-sphere electron-transfer reaction. The reported results are relevant for the interaction of vitamin B(12a) with NO and NO2-.     

The electrochemical behavior of N-n-undecyl-N''-(sodium-p-amino-benzenesulfonate)thiourea and its interaction with bovine serum albumin

In pH 5.5 phosphate buffer solution,N-n-undecyl-N'-(sodium-p-amino-benzenesulfonate)thiourea(UPT)produced a pair of redox peaks on the bare glassy carbon electrode.At the multi-walled carbon nanotube(MWNT)modified electrode,the electrochemical behavior of UPT enhanced greatly.In the presence of bovine serum albumin (BSA),the peak currents of UPT decreased linearly due to the formation of a super-molecular complex.This method was successfully applied to the determination of BSA in a bovine serum sample.     

Studies directed toward the total synthesis of azaspiracid: stereoselective construction of C(1)-C(12), C(13)-C(19), and C(21)-C(25) fragments

[reaction: see text] The efficient entry to the C(1)-C(12), C(13)-C(19), and C(21)-C(25) fragments of azaspiracid is outlined. The C(1)-C(12) portion is constructed using a key asymmetric allenyl borane addition to the corresponding alpha,beta-unsaturated aldehyde. The synthesis of the C(13)-C(19) portion utilizes an Evans asymmetric alkylation followed by Sharpless asymmetric dihydroxylation. In addition, a novel solution to the mismatched effects of a neighboring chiral oxazolidinone during a Sharpless dihydroxylation is detailed.     

Palladium-catalyzed cascade reaction of alpha,beta-unsaturated sulfones with aryl iodides

Unlike traditionally used acyclic 1,2-disubstituted alkenes, the reaction of alpha,beta-unsaturated phenyl sulfones with aryl iodides under Heck reaction conditions (Pd(OAc)(2) as catalyst, Ag(2)CO(3) as base in DMF at 120 (0)C) takes place mainly by a cascade process, involving one unit of the alkene and three units of the aryl iodide, to afford a substituted 9-phenylsulfonyl-9,10-dihydrophenanthrene. The dominant formation of this 3:1 coupling product, instead of the Heck trisubstituted olefin, shows that aromatic C-H bond activation processes can compete with the usually fast syn beta-hydrogen elimination step in the Heck arylation of an acyclic olefin. The structural scope of this palladium-catalyzed cascade arylation of alpha,beta-unsaturated sulfones has proved to be wide with regard to substitution at the beta-position (alkyl, aryl, or alkenyl substitution), substitution at the sulfone unit (alkyl or phenyl sulfones), and configuration at the CdoublebondC bond (trans or cis). Moreover, although less favored than in the case of the arylation of alpha,beta-unsaturated sulfones, similarly substituted 9,10-dihydrophenanthrenes have also been obtained in the case of alpha,beta-unsaturated phosphine oxides and alpha,beta-unsaturated phosphonate esters. A Pd(0)-Pd(II)-Pd(IV) mechanistic pathway involving the successive formation of highly electrophilic sigma-alkylpalladium intermediates and palladacycles is proposed for this multicomponent arylation.     

A sol-gel derived pH-responsive bovine serum albumin molecularly imprinted poly(ionic liquids) on the surface of multiwall carbon nanotubes

A pH-responsive surface molecularly imprinted poly(ionic liquids) (MIPILs) was prepared on the surface of multiwall carbon nanotubes (MWCNTs) by a sol-gel technique. The material was synthesized using a 3-aminopropyl triethoxysilane modified multiwall carbon nanotube (MWCNT-APTES) as the substrate, bovine serum albumin (BSA) as the template molecule, an alkoxy-functionalized IL 1-(3-trimethoxysilyl propyl)-3-methyl imidazolium chloride ([TMSPMIM]Cl) as both the functional monomer and the sol-gel catalyst, and tetraethoxysilane (TEOS) as the crosslinking agent. The molecular interaction between BSA and [TMSPMIM]Cl was quantitatively evaluated by UV–vis spectroscopy prior to polymerization so as to identify an optimal template/monomer ratio and the most suitable pH value for the preparation of the MWCNTs@BSA-MIPILs. This strategy was found to be effective to overcome the problems of trial-and-error protocol in molecular imprinting. The optimum synthesis conditions were as follows: template/monomer ratio 7:20, crosslinking agent content 2.0–2.5 mL, temperature 4 °C and pH 8.9 Tris–HCl buffer. The influence of incubation pH on adsorption was also studied. The result showed that the imprinting effect and selectivity improved significantly with increasing incubation pH from 7.7 to 9.9. This is mainly because the non-specific binding from electrostatic and hydrogen bonding interactions decreased greatly with the increase of pH value, which made the specific binding affinity from shape selectivity strengthened instead. The polymers synthesized under the optimal conditions were then characterized by BET surface area measurement, FTIR, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The adsorption capacity, imprinting effect, selective recognition and reusability were also evaluated. The as-prepared MWCNTs@BSA-MIPILs were also found to have a number of advantages including high surface area (134.2 m² g⁻¹), high adsorption capacity (55.52 mg g⁻¹), excellent imprinting effect (imprinting factor of up to 5.84), strong selectivity (selectivity factor of 2.61 and 5.63 for human serum albumin and bovine hemoglobin, respectively), and good reusability.     

Platinum chalcogenido MCM-41 analogues. High hexagonal order in mesostructured semiconductors based on Pt(2+) and [Ge(4)Q(10)](4-) (Q = S, Se) and [Sn(4)Se(10)](4-) adamantane clusters

Highly periodic hexagonal honeycombs of platinum-germanium chalcogenide and platinum-tin selenide frameworks were prepared by linking corresponding [Ge(4)Q(10)](4)(-) (Q = S, Se) and [Sn(4)Se(10)](4)(-) clusters with Pt(2+) ions. The non-oxidic honeycombs designated as C(n)PyPtGeQ and C(n)PyPtSnSe were templated by the lyotropic liquid-crystalline phase of alkylpyridinium surfactant [C(n)H(2)(n)(+1)NC(5)H(5)]Br (C(n)PyBr) with n= 12, 14, 16, 18, 20, and 22. Although the materials are amorphous at the microscale, they have crystalline mesoporosity with well-ordered and aligned surfactant-filled cylindrical pores. In addition to high mesoscopic order, the pore-pore separation is adjustable with the surfactant chain length (i.e., value of n). The quality of these materials, as judged by the degree of hexagonal order, rivals or exceeds that reported for the highest quality MCM-41 silicates. The materials have the lowest band gap reported so far for mesostructured chalcogenides solids, in the range 1.5 < E(g)< 2.3 eV. The C(n)PyPtGeS analogues show intense photoluminescence at 77 K when excited with light above the band gap.     

Electrochemical behavior of Ru(H_2bpp)_2(PF_6)_2 and its interaction with bovine serum albumin(BSA)

In this paper,it was found that Ru（H₂bpp）₂（PF₆）2（H₂bpp = 2,6-bis（pyrazol-3-yl）pyridine） complex had excellent electrochemical activity at the carbon paste electrode in the buffer solution of Tris-HCl（pH 7.0） with a couple reversible redox peaks at 0.296 V and 0.348 V,respectively.Voltammetry was used to investigate the electrochemical behavior of Ru（H₂bpp）₂（PF₆）₂ and the interaction between Ru（H₂bpp）₂（PF₆）₂ and bovine serum albumin（BSA）.In the present of BSA,the oxidation peak current of Ru（H₂bpp）₂（PF₆）₂ complex was decreased linearly and the decrease of oxidation peak current of Ru（H₂bpp）₂（PF₆）₂ is proportional to BSA concentration from 0.1 to 2.5 mg/L with a detection limit 0.02 mg/L.     

Bile acids. LXXVI. Analyses of bile acids and sterols by high-performance liquid chromatography with a microbore column

The mobilities of several free and conjugated 5 beta-bile acids, cholesterol and analogues, and alpha, beta-unsaturated sterols and steroidal acids have been investigated with a microbore reversed-phase high-performance liquid chromatographic column (50 cm X 1 mm I.D., 12% C18) with appropriate solvent mixtures at flow-rates of 50-100 microliter/min and a UV monitor set at 193, 198, 212, or 243 nm. With a solvent mixture of 2-propanol-10 mM phosphate buffer, pH 7.0 (160:340) bile acids or their conjugates were separated in a manner similar to those by microBondapak columns (10% C18). The lower detection limit of the conjugates was 20 pmoles with the UV detector set at 193 nm, whereas the lower limit for alpha, beta-unsaturated keto sterols or steroidal acids was 5 pmoles at 243 nm. The detection limit for cholesterol with the UV monitor at 198 nm was 10 pmoles. Contributions of substituent groups of sterols to their time of elution (capacity factor) were calculated for several substituted 4-cholesten-3-ones.     

Synthesis of luminescent gold(I) and gold(III) complexes with a triphosphine ligand

We have synthesized and characterized a series of trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (triphos = bis(2-diphenylphosphinoethyl)phenylphosphine; X = Cl 1, Br 2, I 3, C(6)F(5) 4) and di- and trinuclear gold(III) complexes [[Au(C(6)F(5))(3)](n)(mu-triphos)] (n = 2 (5), 3 (6)). The crystal structure of 6 [[Au(C(6)F(5))(3)](3)(mu-triphos)] has been determined by X-ray diffraction studies, which show the triphosphine in a conformation resulting in very long gold-gold distances, probably associated with the steric requirements of the tris(pentafluorophenyl)gold(III) units. Complex 6 crystallizes in the triclinic space group P(-1) with a = 12.7746(16) A, b = 18.560(2) A, c = 21.750(3) A, alpha = 98.215(3) degrees, beta = 101.666(3) degrees, gamma = 96.640(3) degrees, and Z = 2. Chloride substitutions in complex 1 afford trinuclear gold(I) complexes [(AuX)(3)(mu-triphos)] (X = Fmes (1,3,5-tris(trifluoromethyl)phenyl) 7, p-SC(6)H(4)Me 8, SCN 9) and [Au(3)Cl(3)(-)(n)()(S(2)CNR(2))(n)(mu-triphos)] (R = Me, n = 3 (10), 2 (12), 1 (14); R = CH(2)Ph, n = 3 (11), 2 (13), 1 (15)). The luminescence properties of these complexes in the solid state have been studied; at low temperature most of them are luminescent, including the gold(III) derivative 6, with the intensity and the emission maxima being clearly influenced by the nature and the number of the ligands bonded to the gold centers.