Asymmetric solution-phase mixture aldol reaction using oligomeric ethylene glycol tagged chiral oxazolidinones

Sorting tags are oligomeric structures that can be used as protecting groups or chiral auxiliaries enabling solution-phase mixture syntheses of multiple tagged compounds in one pot and allowing for facile and predictable chromatographic separation of products at the end of synthetic sequences. Perfluorinated hydrocarbon and oligomeric ethylene glycol (OEG) derivatives are known classes of sorting tags. Herein we describe the preparation of OEGylated chiral oxazolidinones and their use in asymmetric solution-phase mixture aldol reactions. Through the use of such oxazolidinones based on tyrosine four different individually tagged aldol adducts were obtained as a mixture, chromatographically demixed, detagged, and it was shown that these processes gave the desired aldol products in good yield and enantioselectivity.     

Interaction of giant extracellular Glossoscolex paulistus hemoglobin (HbGp) with zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS): effects of oligomeric dissociation

The present work focuses on the interaction between the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (HPS) and the giant extracellular hemoglobin of Glossoscolex paulistus (HbGp). Electronic optical absorption, fluorescence emission and circular dichroism spectroscopy techniques, together with Gel-filtration chromatography, were used in order to evaluate the oligomeric dissociation as well as the autoxidation of HbGp as a function of the interaction with HPS. A peculiar behavior was observed for the HPS–HbGp interaction: a complex ferric species formation equilibrium was promoted, as a consequence of the autoxidation and oligomeric dissociation processes. At pH 7.0, HPS is more effective up to 1 mM while at pH 9.0 the surfactant effect is more intense above 1 mM. Furthermore, the interaction of HPS with HbGp was clearly less intense than the interaction of this hemoglobin with cationic (CTAC) and anionic (SDS) surfactants. Probably, this lower interaction with HPS is due to two factors: (i) the lower electrostatic attraction between the HPS surfactant and the protein surface ionic sites when compared to the electrostatic interaction between HbGp and cationic and anionic surfactants, and (ii) the low cmc of HPS, which probably reduces the interaction of the surfactant in the monomeric form with the protein. The present work emphasizes the importance of the electrostatic contribution in the interaction between ionic surfactants and HbGp. Furthermore, in the whole HPS concentration range used in this study, no folding and autoxidation decrease induced by this surfactant were observed. This is quite different from the literature data on the interaction between surfactants and tetrameric hemoglobins, that supports the occurrence of this behavior for the intracellular hemoglobins at low surfactant concentration range. Spectroscopic data are discussed and compared with the literature in order to improve the understanding of hemoglobin–surfactant interaction as well as the acid isoelectric point (pI) influence of the giant extracellular hemoglobins on their structure–activity relationship.     

Two novel carbonic acid esters conjugated with oligophenyl glucosides from Rhamnus nakaharai

Two novel carbonic acid esters conjugated with oligomeric phenyl glycosides have been isolated and characterized from the wood of Rhamnus nakaharai. The structures are characterized as 5,7-dihydroxyphthalide 5-O-β-[6-O-{3″-methoxy-4″-O-β-[6?-O-(4?-O-carboxy-3?,5?-dimethoxy)phenyl]glucopyranosyl}phenyl]glucopyranoside (1) and 6-O-{3′-methoxy-4′-O-β-[6″-O-(3?-mercapto-5?-methoxy-4?-O-methylcarboxy)phenyl]glucopyranosyl}phenyl β-glucopyranose (2), namely, rhamnakoside A (1) and B (2), all by NMR and other spectral methods, respectively. They could be a novel case of phase II detoxification products and biogenetic diversity in plant kingdom.     

Synthesis of Nonionic Oligomeric Manganese（ Ⅱ ） Complexes and Investigation of Their Toxicity and T1 -Relaxation Enhancement

Six nonionic oligomeric manganese （ Ⅱ ） complexes with oligomeric phosphate-polyglycol-EDTA ester ligands were synthesized and characterized. The longitudinal relaxivities of these complexes were measured. One of these complexes, which showed the highest relaxivity, was chosen to be used in the acute toxicity test and the T1-weighted imaging experiment. It has been found that compared to Gd-DTPA, this nonionic oligomeric Mn（ Ⅱ ） complex exhibits no acute toxicity, generates highly enhanced MRI signals and increases the intention time in the rat liver tissue.     

Influence of temperature and mobile phase composition on retention properties of oligomeric bonded phases in reversed-phase liquid chromatography (RPLC)

Summary The effect of temperature and mobile phase composition (methanol-water) on the retention behaviour of an oligomeric series of n-octylsilyl bonded phases in reversed-phase liquid chromatography has been investigated. Plots of lnk against 1/T (van't Hoff plot) and the enthalpy of transfer (ΔH^o) yields linear relationships under the conditions studied. The ΔH^o values of the aromatic hydrocarbons and n-alkyl benzoates are higher than those of the polar compounds due to their higher level of interaction with the stationary phase. A linear plot of ΔH^o vs. ΔS^o suggest that the retention process, which is essentially controlled by non-specific (dispersive) interactions between the solutes and the bonded ligands, is identical for all cases evaluated. The existence of similar retention mechanisms is confirmed by the constant value of the enthalpy-entropy compensation temperature of the columns for a given class of componds. As expected, decreasing the methanol content (% v/v) of the mobile phase results in increased eluite retention times. The methylene and phenyl selectivities are found to be independent of the carbon content of the stationary phases and varied only with the eluent composition. In addition to their high stability under aggressive mobile phase conditions as previously reported, the results of this study generally showed that the solute retention process on oligomeric phases are similar to those exhibited by the conventional reversed phases.     

Characterization of mixtures of biocidal oligoguanidines by capillary electrophoresis and high-performance liquid chromatography coupled to mass spectrometry

The polycondensation of guanidine hydrochloride and 2,2′-(ethylenedioxy)bis(ethylamine) leads to various types of oligomeric guanidines exhibiting a broad spectrum of biocidal activities. In the present work a reversed-phase high-performance liquid chromatographic method with a gradient consisting of aqueous 0.1% trifluoroacetic acid and acetonitrile as mobile phase has been developed to separate these oligoguanidines according to type and chain length. The combination with electrospray mass spectrometry allowed the identification of the various compounds. By this technique, some structures already suggested in the literature could be confirmed, and several additional oligoguanidines not yet reported could be identified. As a complementary technique, capillary zone electrophoresis was investigated. Best results were obtained with carrier electrolytes consisting of phosphoric acid in water/acetonitrile mixtures. Although the number of peaks that could be separated by the electrophoretic method was considerably lower than in case of the chromatographic method, capillary electrophoresis in combination with UV detection at 195 nm may still be a fast method suitable for quantitation of some of the major compounds and for monitoring the reaction rate during the polycondensation reaction.     

Bis(η5-cyclopentadienyl)-brenzkatechinato-titan(IV) — ein oligomerer Mehrkernkomplex

Cp ₂TiCl₂ reacts with 1,2-(LiO)₂C₆H₄ producing the pyrocatecholato complex [Cp ₂Ti(O₂C₆H₄-o)] _n . Osmometric molecular weight determination, temperature-variable¹H NMR, and MS indicate an oligomeric polynuclear complex (2n4). Its MS fragmentation behaviour is observed by metastable transitions.

     

示波极谱法测定葡萄籽提取物中原花青素

提出了测定葡萄籽提取物中原花青素的电化学分析新方法。在碱性硼砂底液中,原花青素与Zn(Ⅱ)在(-1.02±0.02V)(vs.SCE)电位处产生灵敏络合吸附波。其峰电流IP与原花青素在40～200mg·L-1范围内呈良好的线性关系,方法的检出限为25mg·L-1。该方法已用于保健食品中原花青素的含量测定,重现性好,结果满意。     

Das erste Vanadium(III)‐Borophosphat: Darstellung und Kristallstruktur von CsV3(H2O)2[B2P4O16(OH)4]

The First Vanadium(III) Borophosphate: Synthesis and Crystal Structure of CsV₃(H₂O)₂[B₂P₄O₁₆(OH)₄] CsV₃(H₂O)₂[B₂P₄O₁₆(OH)₄] was prepared under mild hydrothermal conditions (T = 165 °C) from mixtures of CsOH_(aq), VCl₃, H₃BO₃, and H₃PO₄ (molar ratio 1 : 1 : 1 : 2). The crystal structure was determined by X‐ray single crystal methods (monoclinic; space group C2/m, No. 12): a = 958.82(15) pm, b = 1840.8(4) pm, c = 503.49(3) pm; β = 110.675(4)°; Z = 2. The anionic partial structure contains oligomeric units [BP₂O₈(OH)₂]^5–, which are built up by a central BO₂(OH)₂ tetrahedron and two PO₄ tetrahedra sharing common corners. V^III is octahedrally coordinated by oxygen of adjacent phosphate tetrahedra and OH groups of borate tetrahedra as well as oxygen of phosphate tetrahedra and H₂O molecules, respectively (coordination octahedra VO₄(OH)₂ and VO₄(H₂O)₂). The oxidation state +3 for vanadium was confirmed by measurements of the magnetic susceptibility. The trimeric borophosphate groups are connected via vanadium centres to form layers with octahedra‐tetrahedra ring systems, which are likewise linked via V^III‐coordination octahedra. Overall, a three‐dimensional framework constructed from VO₄(OH)₂ and VO₄(H₂O)₂ octahedra as well as BO₂(OH)₂ and PO₄ tetrahedra results. The structure contains channels running along [001], which are occupied by Cs⁺ in a distorted octahedral coordination (CsO₄(H₂O)₂).     

酰胺衍生寡聚DTPA钆配合物的合成、表征及弛豫性能

以寡聚二乙撑三胺-N,N′-二(乙酰苯胺)-N,N′,N″-三乙酸([H₃L]_n)为配体, 与GdCl₃在二甲基甲酰胺-水混合溶剂中组装得到了寡聚金属螯合物. 采用傅里叶变换红外光谱(FTIR)、元素分析、核磁共振氢谱(¹H NMR)和热重及差热分析(TG-DTA)确定了寡聚金属螯合物的组成单元为[GdL(H₂O)]·4H₂O, 即寡聚配体的每个链节与1个金属离子配位. 采用反转恢复法测试了寡聚金属螯合物和小分子配合物Gd-DTPA(DTPA为二乙撑三胺五乙酸)的纵向弛豫时间T₁, 该寡聚金属螯合物体外弛豫率为8.526 mmol·L^-1·s^-1, 与配合物Gd-DTPA的弛豫率(4.370 mmol·L^-1·s^-1) 相比, 弛豫性能明显提高.