Structural features and kinetic characterization of alanine racemase from Staphylococcus aureus (Mu50)

The tertiary structure and kinetic properties of alanine racemase from Staphylococcus aureus are described and compared to other related alanine racemase structures

Catalytic intramolecular hydroamination of aminoallenes using titanium complexes of chiral, tridentate, dianionic imine-diol ligands

Alkylation of D- or L-phenylalanine or valine alkyl esters was carried out using methyl or phenyl Grignard reagents. Subsequent condensation with salicylaldehyde, 3,5-di-tert-butylsalicylaldehyde, or 5-fluorosalicylaldehyde formed tridentate, X_2L type, Schiff base ligands. Chiral shift NMR confirmed retention of stereochemistry during synthesis. X-ray crystal structures of four of the ligands show either inter- or intramolecular hydrogen bonding interactions. The ligands coordinate to the titanium reagents Ti(NMe_2)_4 or TiCl(NMe_2)_3 by protonolysis and displacement of two equivalents of HNMe_2. The crystal structure of one example of Ti(X_2L)Cl(NMe_2) was determined and the complex has a distorted square pyramidal geometry with an axial NMe_2 ligand. The bis-dimethylamide complexes are active catalysts for the ring closing hydroamination of di- and trisubstituted aminoallenes. The reaction of hepta-4,5-dienylamine at 135 °C with 5 mol% catalyst gives a mixture of 6-ethyl-2,3,4,5-tetrahydropyridine (40–72%) and both Z- and E-2-propenyl-pyrrolidine (25–52%). The ring closing reaction of 6-methyl-hepta-4,5-dienylamine at 135 °C with 5 mol% catalyst gives exclusively 2-(2-methyl-propenyl)-pyrrolidine. The pyrrolidine products are obtained with enantiomeric excesses up to 17%

New molecular charge transfer salts of BEDT-TTF, bis(ethylenedithio) tetrathiafulvalene, with thiocyanato-complex anions: (BEDT-TTF)₄ Fe(NCS)₆·CH₂Cl₂ and (BEDT-TTF)₂ Cr(NCS)₄(bipym)·0.15H₂O

Two new charge transfer salts of BEDT-TTF, bis (ethylenedithio) tetrathiafulvalene, with thiocyanato-metal complex anions have been synthesized and characterized as (BEDT-TTF)4[Fe(NCS)6].CH2Cl2 and (BEDT-TTF)2[Cr(NCS)4 (bipym)]·0.15H2O, where bipym = 2,2 ' -bipyrimidine. The Fe salt, I, crystallizes in the P-l (No. 2) space group at 150 K with a = 10.629(1) Angstrom, b = 12.099(1) Angstrom, c = 16.062(2) Angstrom, alpha = 99.61(1)degrees, beta = 90.87(1)degrees, gamma = 112.92(1)degrees, and V = 1868.5(6) Angstrom (3). At 150 K th, C, salt, II, crystallizes in the P-1 (No. 2) space group with a = 9.243(2), b = 11.781(2), c = 22.925(5) Angstrom. alpha = 93.76(3), beta = 101.51(3), gamma = 105.45(3)degrees, V= 2339.0(8) Angstrom (3), and Z = 2. Both salts exhibit close S···S contacts between the anion and cation components and in II there is no pi -stacking between the bipym group and the BEDT-TTF molecules. Both salts are paramagnetic with C = 4.926 I and C = 1.819 II with small negative Weiss constants of -0.19 and -0.26, respectively. Therefore, the S S contacts alone do not promote correlated magnetic effects as seen in other thiocyanato salts that also contain pi -stacking. Each compound is a semiconductor and has two crystallographically independent BEDT-TTF molecules for which bond length analysis give charges of +0.9 ± 0.1/ +0.6 ± 0.1 for I and +0.3 ± 0.1/ +0.9 ± 0.1 for II