Double diastereoselection in aldol reactions mediated by dicyclohexylchloroborane between chiral aldehydes and a chiral ethyl ketone derived from L-erythrulose. synthesis of a C1-C9 fragment of the structure of the antifungal metabolite soraphen A1alpha

[Chemical reaction: See text] Both matched and mismatched diastereoselections have been observed in the aldol reactions of a range of chiral aldehydes with the dicyclohexylboron enolate of a chiral ethyl ketone related to L-erythrulose. As was previously observed in the corresponding aldol reactions with L-erythrulose derivatives, the Felkin-Anh model provides an adequate explanation for the stereochemical outcome of reactions with chiral alpha-methyl aldehydes. However, a satisfactory account of the results observed with alpha-oxygenated aldehydes was only possible with the Cornforth model. As a practical application of the methodology described herein, a C1-C9 fragment of the structure of the antifungal macrolide soraphen A1alpha has been prepared in a convergent and stereoselective way.     

Synthesis of double C-glycoside analogue of sTn

A sTn double C-glycoside, sTn analogue 2, was synthesized using samarium chemistry developed in our laboratory. Complications in the oxidation reaction affording aldehyde acceptor were overcome by double protection of amide and the use of a room-temperature ionic liquid as solvent. Studies are underway to conjugate the sTn double C-glycoside hapten 2 to KLH carrier protein for biological evaluation as a vaccine.     

Batch immunoextraction method for efficient purification of aromatic cytokinins

A range of benzylaminopurines naturally occur in plants and exhibit high biological activity. Others have been synthesized, such as 6-(2-hydroxy-3-methoxybenzylamino)purine riboside (2OH3MeOBAPR), which has shown interesting anti-cancer activity under in vitro conditions. In order to study the biological activity of this interesting compound in more detail, a rapid and highly efficient method for its purification from complex samples (e.g. blood and plant extracts) is needed. Therefore, we prepared monoclonal antibodies against 2OH3MeOBAPR. The antibody had undetectable cross-reactivity with all natural isoprenoid cytokinins, but relatively high cross-reactivity with aromatic cytokinins as well as some synthetic di- and tri-substituted 6-benzylaminopurines and the corresponding ribosides. The antibody also showed strong responses and specificity in enzyme-linked immunoassays (ELISAs). In addition, it was used to prepare, for the first time, an immunoaffinity sorbent with high specificity and capacity for aromatic cytokinins. A batch immunoextraction method was then developed and optimized for the purification of 2OH3MeOBAPR from murine blood samples. The high efficacy and simplicity of this method (in off-line combination with HPLC-MS) for the isolation of target analytes from biological material is demonstrated in this study.     

Fractionation of glycoforms of recombinant human erythropoietin by preparative capillary isotachophoresis

This feasibility study deals with the use of preparative capillary isotachophoresis (CITP), operating in a discontinuous fractionation mode, to the separations and isolations of glycoforms of recombinant human erythropoietin (rhEPO). The preparative CITP separations were monitored by capillary zone electrophoresis (CZE) with a hydrodynamically closed separation unit. Such a CZE system, suppressing fluctuations of the migration data linked with fluctuations of EOF and hydrodynamic flow, made possible to evaluate and compare the preparative CITP separations performed within a longer time frame. Preparative CITP, carried out in the separation unit with coupled columns of enhanced sample loadability, separating 100 microg of rhEPO in a run lasting ca. 30 min, gave the production rate higher than 55 ng/s for the rhEPO glycoforms. The preparative separations included valve isolations of the glycoforms from the ITP stack into four or six fractions. Such numbers of the fractions corresponded to typical numbers of the major glycoform peaks as resolved in CZE of rhEPO. With respect to close effective mobilities of the glycoforms and a multicomponent nature of rhEPO, the fractions contained mixtures of glycoforms with the dominant glycoforms enriched 10-100-fold, relative to the original rhEPO sample.     

SMM Behaviour of the Butterfly {CrIII2DyIII2} Pivalate Complex and Magneto-structurally Correlated Relaxation Thermal Barrier

We are reporting the synthesis, single-crystal X-ray structure characterization, and magnetic property investigations of the pivalate butterfly {Cr^III₂Ln^III₂} complexes with Ln= Gd and Dy and the isostructural Y(III) sample. We found an anti-ferromagnetic Cr(III)-Ln(III) exchange interaction, which, as previously observed in related Cr(III)/Ln(III) systems, plays a key role in suppressing quantum tunnelling of magnetization and enhances the SMM performance in the Dy(III) complex. In fact, a pure Orbach relaxation mechanism, with absence of QT regime, is observed with a thermal barrier of 50 cm⁻¹, leading to magnetization hysteresis opening, measured with a commercial magnetometer, up to 3.6 K with a coercive field of 2.9 T. Analysis of SMM behaviour in literature-known butterfly {Cr^III₂Dy^III₂} complexes, reveals the existence of a magneto-structural correlation between U_eff, the thermal barrier size, and the mean Cr−Dy bond distances. Moreover, a clear correlation is found for the thermal barrier magnitude and the maximum temperature hysteresis opening and coercive field.     

Flexural strength of silica fume,fly ash,and metakaolin of hardened cement paste after exposure to elevated temperatures

Journal of Thermal Analysis and Calorimetry - The mechanical properties of concrete based mainly on flexural and compressive bearing capacity. Generally, researchers have an interest in the...     

Synthesis of bis(amidoxime)s and evaluation of their properties as uranyl-complexing agents

Uranium pollution involves high toxicity and radioactivity and, therefore, constitutes a grave threat to human health and the environment. Chelation is an effective method for sequestering uranium. It is well known that chelators based on oxime groups are able to complex uranyl cations efficiently. To this end, various bis(amidoxime)s were synthesized by reaction of hydroxylamine with the corresponding dinitriles. In these compounds the amidoximes are separated by chains of various lengths, some including a heterocycle (pyridine or 1,3,5-triazine). The abilities of these bis(amidoxime)s to complex uranyl cation in water were evaluated by determining their affinity constants and thermodynamic parameters by means of Isothermal Titration Calorimetry (ITC). DFT calculations were also performed, to determine the optimum structures of the complexes formed between uranyl cations and the oximate groups. A tetrakis(amidoxime), also synthesized in this work, shows good affinity for uranium, and a single molecule is able chelate several uranyl cations. These results are of importance for the remediation of uranium-polluted wastewaters, and open up several perspectives for the design and synthesis of new amidoxime compounds.     

Exploiting Synergistic Effects in Organozinc Chemistry for Direct Stereoselective C‐Glycosylation Reactions at Room Temperature

Pairing a range of bis(aryl) zinc reagents ZnAr₂ with the stronger Lewis acidic [(ZnAr^F₂)] (Ar^F=C₆F₅), enables highly stereoselective cross‐coupling between glycosyl bromides and ZnAr₂ without the use of a transition metal. Reactions occur at room temperature with excellent levels of stereoselectivity, where ZnAr^F₂ acts as a non‐coupling partner although its presence is crucial for the execution of the C(sp²)–C(sp³) bond formation process. Mechanistic studies have uncovered a unique synergistic partnership between the two zinc reagents, which circumvents the need for transition‐metal catalysis or forcing reaction conditions. Key to the success of the coupling is the avoidance of solvents that act as Lewis bases versus diarylzinc compounds (e.g. THF).