An enantioselective synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid via asymmetric hydrogenation

A concise enantioselective synthesis of (S)-(+)-3-aminomethyl-5-methylhexanoic acid (1, Pregabalin) has been developed. The key step is the asymmetric hydrogenation of a 3-cyano-5-methylhex-3-enoic acid salt 2 with a rhodium Me-DuPHOS catalyst, providing the desired (S)-3-cyano-5-methylhexanoate 3 in very high ee. Subsequent hydrogenation of the nitrile 3 with a heterogeneous nickel catalyst provides Pregabalin 1 in excellent overall yield and purity.     

Regioselective synthesis of 4-(2-alkyl-5-methyl-2H-pyrazol-3-yl)-piperidines

The regioselective, scaleable synthesis of three 4-(2-alkyl-5-methyl-2H-pyrazol-3-yl)-piperidines is discussed.     

Recent computational developments with the self-consistent electron pairs method and application to the stability of glycine conformers

Significant improvements in calculational efficiency and capability with the self-consistent electron pairs (SCEP ) method has resulted from several new computational developments. A new procedure for constructing the important internal Coulomb and exchange operators has substantially reduced the preiteration time. A general scheme for utilizing molecular symmetry has been used to advantage in reducing the number of pair functions and external operators that must be found explicitly at each iteration. A projection operator tool has been implemented and found to be quite effective at minimizing the number of iterations required at some point on a potential energy surface when an SCEP wavefunction exists for some nearby point. These and other improvements in the program construction have yielded sizable reductions in time for some representative test cases, including water and a potential energy curve for formaldehyde. The new SCEP program also performs low-order perturbation theory treatments and coupled electron pair approximation (CEPA ) calculations using the same operator approach. The usefulness of the approach is demonstrated by very large scale calculations on the stability of the two interstellar glycine conformers. These calculations involve the variational treatment of 82,205 symmetry-adapted singly and doubly substituted configurations involving 225 internal electron pairs.     

Trace elements in western Canadian hard red spring wheat (Triticum aestivum L.): levels and quality assurance.

A monitoring program was conducted for trace elements in Western Canadian Hard Red Spring wheat (Triticum aestivum L.). Samples were selected from harvest survey samples submitted by producers from crop districts in Manitoba, Saskatchewan, and Alberta for 1996, 1997, and 1998 crops. The analytical quality control measures used in these surveys are described along with the results for Cd, Cu, Fe, Mn, Se, and Zn. Accuracy and precision for the analyses fell within the acceptable control limits. Year-to-year variations in grain chemistry were small for Cd, Mn, Se, and Zn, but Cu and Fe contents showed 12 and 9% decreases, respectively, over the 3 years. The overall variability for the plant-essential trace elements-Cu, Fe, Mn, and Zn-was low compared with that for Cd and Se. The spatial variation in crop chemistry across the Canadian Prairie wheat-producing region was greater than the year-to-year variations. Soil properties were major factors in controlling Cd and Se levels in grain.     

Alkalien

Ohne Zusammenfassung     

DESCANT – the deuterated scintillator array for neutron tagging

The DESCANT array is a new device for neutron detection based on deuterated liquid scintillator. It has been designed to be coupled with the TIGRESS and GRIFFIN γ-ray spectrometers to enable neutron tagging in fusion-evaporation reactions, and β-delayed neutron studies.     

Improved lateral-flow immunoassays for chlamydia and immunoglobulin M by sequential rehydration of two-phase system components within a paper-based diagnostic

Microchimica Acta - Frequent screening of at-risk individuals using paper-based point-of-care diagnostics is a promising method for attenuating the spread of chlamydia and HIV. However, such...