Rapid and flexible synthesis of 1-deoxy-D-xylulose-5-phosphate, the substrate for 1-deoxy-D-xylulose-5-phosphate reductoisomerase

1-Deoxy-D-xylulose-5-phosphate (DXP) is a key intermediate in the non-mevalonate pathway to terpenoids in bacteria, and it is the substrate for the enzyme 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXP-R). In order to study the mechanism of DXP-R, we required a flexible synthesis of the substrate which would allow the incorporation of isotopic labels, and the variation of the two stereocentres. Thus 1,4-dihydroxypent-2-yne was selectively reduced to give the E-olefin, and selective phosphorylation of the primary alcohol followed by oxidation of the secondary alcohol gave a substrate suitable for dihydroxylation. Dihydroxylation using stoichiometric OsO4 in the presence of chiral ligands gave protected DXP in high ee. Final hydrogenolysis gave DXP in quantitative yield and high purity. DXP-R was produced by rapid cloning of the dxr gene from Escherichia coli through controlled expression and ion exchange chromatography. The synthetic DXP was fully active in enzyme assays catalysed by recombinant DXP-R.     

An evaluation of various computational methods for the treatment of organoselenium compounds

A reliable computational method for the prediction of organoselenium geometries and bond dissociation energies (BDEs) has been determined on the basis of the performance of density functional theory (DFT: B3LYP and B3PW91) and ab initio molecular orbital procedures (Hartree-Fock (HF)) in conjunction with various Pople basis sets including (but not limited to) the 6-31G(d), 6-31G(d,p), 6-311G(d), 6-311G(d,p), 6-311G(2df,p), and 6-311G(3df,3pd) sets. Predicted geometries and BDEs are compared with available experimental data and quadratic configuration interaction including single and double substitutions (QCISD) results. The B3PW91/6-311G(2df,p) level of theory is recommended for the prediction of the geometries and energetics of organoselenium compounds.     

High pressure-temperature Raman measurements of H2O melting to 22 GPa and 900 K

The melting curve of H(2)O has been measured by in situ Raman spectroscopy in an externally heated diamond anvil cell up to 22 GPa and 900 K. The Raman-active OH-stretching bands and the translational modes of H(2)O as well as optical observations are used to directly and reliably detect melting in ice VII. The observed melting temperatures are higher than previously reported x-ray measurements and significantly lower than recent laser-heating determinations. However, our results are in accord with earlier optical determinations. The frequencies and intensities of the OH-stretching peaks change significantly across the melting line while the translational mode disappears altogether in the liquid phase. The observed OH-stretching bands of liquid water at high pressure are very similar to those obtained in shock-wave Raman measurements.     

Structure, stereochemistry, and biological activity of integramycin, a novel hexacyclic natural product produced by Actinoplanes sp. that inhibits HIV-1 integrase

[structure: see text] HIV-1 integrase is a critical enzyme for viral replication, and its inhibition is an emerging target for potential antiviral chemotherapy. We have discovered a novel inhibitor, integramycin, from screening of fermentation extracts using an in vitro assay. Integramycin possesses a hexacyclic ring system and exhibited an IC50 value of 4 microM against HIV-1 integrase (strand transfer). The isolation, structure elucidation, stereochemistry, conformation, and biological activity has been described.     

Thermochemistry on the Complex of Erbium Perchlorate with L-α-Glutamic Acid [Er2（L-Glu）2（H2O）6]（ClO4）4·6H2O（s）

A coordination compound of erbium perchlorate with L-α-glutamic acid, [Er2（Glu）2（H2O）6]（ClO4）4·6H2O（s）, was synthesized. By chemical analysis, elemental analysis, FTIR, TG/DTG, and comparison with relevant literatures, its chemical composition and structure were established. The mechanism of thermal decomposition of the complex was deduced on the basis of the TG/DTG analysis. Low-temperature heat capacities were measured by a precision automated adiabatic calorimeter from 78 to 318 K. An endothermic peak in the heat capacity curve was observed over the temperature region of 290-318 K, which was ascribed to a solid-to-solid phase transition. The temperature Ttrans, the enthalpy △transHm and the entropy △transSm of the phase transition for the compound were determined to be： （308.73±0.45） K, （10.49±0.05） kJ·mol^-1 and （33.9±0.2） J·K^-1·mol^-1. Polynomial equation of heat capacities as a function of the temperature in the region of 78-290 K was fitted by the least square method. Standard molar enthalpies of dissolution of the mixture [2ErCl3·6H2O（s）＋2L-Glu（s）＋6NaClO4·H2O（s）] and the mixture {[Er2（Glu）2（H2O）6]（ClO4）4·6H2O（s）＋6NaCl（s）} in 100 mL of 2 mol·dm^-3 HClO4 as calorimetric solvent, and {2HClO4（1）} in the solution A＇ at T=298.15 K were measured to be, △dHm,1=（31.552±0.026） kJ·mol^-1, △dHm,2 = （41.302±0.034） kJ·mol^-1, and △dHm,3 = （ 14.986 ± 0.064） kJ·mol^-1, respectively. In accordance with Hess law, the standard molar enthalpy of formation of the complex was determined as △fHm-=-（7551.0±2.4） kJ·mol^-1 by using an isoperibol solution-reaction calorimeter and designing a thermochemical cycle.     

Preparation of sinapinaldehyde modified mesoporous silica materials and their application in selective extraction of trace Pb(II)

A new solid phase extractant, sinapinaldehyde (SA) modified SBA-15 mesoporous silica, was developed for selective extraction and preconcentration of trace Pb(II) from aqueous solutions. The successful immobilization of SA on SBA-15 and the strong interaction between SA-SBA-15 and Pb(II) were characterized and confirmed by FTIR spectroscopy and scanning electron microscopy. Parameters such as solution pH, shaking time, eluent condition and sample volume were optimized so that the maximum removal of Pb(II) from solution could be achieved. At pH 4.0, the maximum adsorption capacity of the sorbent for Pb(II) was found to be 33.6?mg?g^?1 and the adsorbed Pb(II) could be completely eluted using a mixed solution of 2?M HCl and 5% CS(NH₂)₂. Some common metal ions such as K(I), Na(I), Mg(II), Ca(II), Cr(III), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Cd(II) and Hg(II) did not interfere with the adsorption of trace Pb(II). The detection limit of the present method was found to be 1.3?ng?mL^?1 and the relative standard deviation was less than 2.0% (n?=?8). These results suggested that this new sorbent is very efficient and selective for the removal of trace Pb(II) in water samples.     

Book review

Matrix Analysis, by Rajendra Bhatia, Graduate Texts in Mathematics, 169, Springer, New York, 1997, 347 + xi pages. ISBN 0-387-94846-5