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V Langer

Publications and source records attributed to V Langer.

15 recordsLinked to original sources
PubMed2001

Synthesis and structure determination of some sugar amino acids related to alanine and 6-deoxymannojirimycin.

(5'R)-5'-Methyl-5'-[methyl (4S)-2,3-O-isopropylidene-beta-L-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione was synthesised starting from methyl 6-deoxy-2,3-O-isopropylidene-alpha-D-lyxo-hexofuranosid-5-ulose applying the Bucherer-Bergs reaction. Its 5'-R configuration was confirmed by X-ray crystallography. Corresponding alpha-amino acid-methyl (5R)-5-amino-5-C-carboxy-5,6-dideoxy-alpha-D-lyxo-hexofuranoside (alternative name: 2-[methyl (4S)-2,3-O-isopropylidene-beta-L-erythrofuranosid-4-C-yl]-D-alanine) was obtained from the above hydantoin by acid hydrolysis of the isopropylidene group followed by basic hydrolysis of the hydantoin ring. Total deprotection afforded 5-C-carboxy-6-deoxymannojirimycin. Analogously, methyl (5S)-5-amino-5-C-carboxy-5,6-dideoxy-alpha-L-lyxo-hexofuranoside and 5-C-carboxy-6-deoxy-L-mannojirimycin were prepared from the corresponding (5'S)-5'-methyl-5'-[methyl (4R)-2,3-O-isopropylidene-beta-D-erythrofuranosid-4-C-yl]-imidazolidin-2',4'-dione starting from methyl 6-deoxy-2,3-O-isopropylidene-alpha-L-lyxo-hexofuranosid-5-ulose.

1-Deoxynojirimycin↗
PubMed2001

Copper(II)-mediated oxidative coupling of 2-aminonaphthalene homologues. Competition between the straight dimerization and the formation of carbazoles.

Whereas the Cu(II)-mediated oxidative coupling of 2-aminonaphthalenes 7a and 7b results in the clean formation of 1,1'-binaphthyls 13a and 13b, respectively, their higher homologues and congeners 8-12 have been found to exhibit a different reaction pattern. Thus, 2-aminoanthracene (8) gave a approximately 1:1 mixture of the expected bianthryl derivative 15 and the carbazole 16, whereas the 9-aminophenanthrene (10), 3-phenyl-1-aminonaphthalene (11), and 2-aminochrysene (12) produced almost exclusively the corresponding carbazoles 19, 20, and 21, respectively. By contrast, the isomeric 3-aminophenanthrene (9) gave rise to the azo compound 17 as a result of the preferential oxidation on the nitrogen. The carbazoles have been shown to arise directly from the coupling reactions rather than from the primarily formed binaphthyls. Alternatively, carbazole 19 can also be prepared from 1b on reaction with hydrazine. On the other hand, treatment of 3a with hydrazine resulted in the formation of a approximately 2:7 mixture of amine 11 and arylhydrazine 22. 2,2'-Diamino-1,1'-bianthryl (15) has been resolved into enantiomers via cocrystallization with (-)-N-benzylcinchonidinium chloride and shown to have (R)-(-)-15 configuration by X-ray crystallography.

Journal Article↗
PubMed2000

Preparation and structure determination of two sugar amino acids via corresponding hydantoin derivatives.

(4R)-2,3-O-Isopropylidene-methylspiro[4,6-dideoxy-alpha-L-lyxo+ ++-hexopyranosid-4,5'-imidazolidin]-2',4'-dione and (4R)-2,3-O-isopropylidene-methylspiro[4,6-dideoxy-beta-D-ribo-h exopyranosid-4,5'-imidazolidin]-2',4'-dione were prepared under various reaction conditions starting from methyl 6-deoxy-2,3-O-isopropylidene-alpha-L-lyxo-hexopyranosid-4-++ +ulose. Corresponding alpha-amino acids methyl (4R)-4-amino-4-C-carboxy-4,6-dideoxy-alpha-L-lyxo-hexopyranosid e and methyl (4R)-4-amino-4-C-carboxy-4,6-dideoxy-beta-D-ribo-hexopyranoside were obtained from the above hydantoins by selective acid hydrolysis of the isopropylidene group, followed by basic hydrolysis of the hydantoin ring. The crystal structures of both hydantoin derivatives are also presented.

Amino Acids↗
PubMed2000

Absolute configuration of a diaryldiacyloxy spiroselenurane and resolution of a carbon analog.

The enantiomers of 3,3'-spirobi(3-selenaphthalide) (2) were obtained via direct separation by liquid chromatography on a chiral stationary phase. Determination of the absolute configuration was made by X-ray crystallography with the use of the anomalous dispersion technique. The first eluted (+)-form (lambda = 302 and 365 nm) of 2 was found to have (S)-configuration. By a comparison of CD-spectra, the same (S)-configuration could be assigned to the (+)-forms of the sulfur (1) and tellurium (7) analogs of 2. An asymmetric dichloro-substituted spirobilactone (4) was also synthesized and separated into its enantiomers. Relative configurations between 4 and its parent compound (3) were established from the corresponding chiroptical data obtained. Chirality 12: 71-75, 2000.

Chromatography, Liquid↗
PubMed1999

Structure of

The crystal structure of the title compound, dimethylammonium tetrachlorocobaltate(II), has been determined at four temperatures between 297 and 366 K, in order to investigate possible phase transitions at 313 and 353 K [Kapustianik, Polovinko & Kaluza et al. (1996). Phys. Status Solidi A, 153, 117-122]. We found that there is no significant change either in the hydrogen-bonding network or in the cell parameters, apart from a linear dilatation with temperature. This study reveals that the anomalous variation in electric conductivity and some of the other physical properties of the compound cannot be explained by structural changes.

Journal Article↗
PubMed1998

Improved hardware and software for single-crystal NMR spectroscopy.

Design of state-of-the-art instrumentation and software for acquisition and analysis of single-crystal NMR spectra is presented. The design involves highly accurate rotation of a goniometer, and the acquisition of all the spectra for each rotation axis is automatically controlled by the host computer of the spectrometer using a homebuilt interface between the computer and the single-crystal probe. Moreover, a software package (ASICS) for fast and routine assignment/analysis of complex single-crystal spectra has been developed. Employing this equipment, the acquisition and complete analysis of single-crystal NMR spectra may be performed in about the same time as required for powder methods (spinning or static). The hardware and software are compared to recent alternative approaches within single-crystal NMR. Finally, it has been observed that single-crystal NMR techniques may provide the desired data for samples where powder methods fail.

Computers↗
PubMed1997

X-ray structure determination and characterization of the Pseudomonas aeruginosa azurin mutant Met121Glu.

The Met121Glu azurin mutant has been crystallized and the structure determined at a resolution of 2.3 A. In the crystal structure a carboxyl oxygen of Met121Glu is coordinated to the metal at a distance of 2.2 A. Single-crystal resonance Raman spectroscopy was used to show that the glutamic acid residue in the copper site was in the protonated state. Titration of this residue gives rise to a number of unusual, pH-dependent properties: as the pH is increased from 4 to 8, the S(Cys)-Cu ligand-to-metal charge transfer bands are blue shifted and their intensity ratio is reversed, the EPR signal changes from type 1 copper to a new form of protein-bound copper, and the redox potential changes from 370 to 180 mV. The spectroscopic changes in this pH interval are consistent with a two-state model. From the pH dependence of the optical and EPR spectra, pKa = 5.0 for the glutamic acid in the oxidized protein was determined.

Azurin↗
PubMed1997

The metal site of Pseudomonas aeruginosa azurin, revealed by a crystal structure determination of the Co(II) derivative and Co-EPR spectroscopy.

The crystal structure of cobalt-substituted azurin from Pseudomonas aeruginosa has been determined to final crystallographic R value of 0.175 at 1.9 A resolution. There are four molecules in the asymmetric unit in the structure, and these four molecules are packed as a dimer of dimers. The dimer packing is very similar to that of the wild-type Pseudomonas aeruginosa azurin dimer. Replacement of the native copper by the cobalt ion has only small effects on the metal binding site presumably because of the existence of an extensive network of hydrogen bonds in its immediate neighborhood. Some differences are obvious, however. In wild-type azurin the copper atom occupies a distorted trigonal bipyramidal site, while cobalt similar to zinc and nickel occupy a distorted tetrahedral site, in which the distance to the Met121,S(delta) atom is increased to 3.3-3.5 A and the distance to the carbonyl oxygen of Gly45 has decreased to 2.1-2.4 A. The X-band EPR spectrum of the high-spin Co(II) in azurin is well resolved (apparent g values gx' = 5.23; gy' = 3.83; gz' = 1.995, and hyperfine splittings Ax' = 31; Ay' = 20-30; Az' = 53 G) and indicates that the ligand field is close to axial.

Azurin↗
PubMed1992

Crystallization and preliminary crystallographic data for the azurin mutant Ala 114 from Pseudomonas aeruginosa.

The site-specific mutant alanine 114 of the blue copper protein azurin from Pseudomonas aeruginosa in Escherichia coli has been crystallized from PEG 4000 in a new crystal form compared to the wild type utilizing the hanging-drop procedure. The crystals are blue well-formed prisms. Monoclinic, P2(1), a = 51.03 (5), b = 83.36 (5), c = 66.30 (6) A and beta = 111.0 (1) degrees. 14,875 reflections up to 2.7 A have been collected using a modified Syntex P2(1) automated four-circle diffractometer.

Azurin↗