Stereoselectivity of the in vitro metabolism of thalidomide

The stereoselective metabolism of the former sedative thalidomide and the metabolism of its analogue EM 12 were studied in vitro with liver homogenates. In our study we focused on hydroxylated nonhydrolyzed metabolites of thalidomide. An analytical HPLC method was developed to determine these metabolites directly. The investigations showed a highly stereoselective biotransformation of thalidomide. 5-Hydroxy thalidomide was preferentially formed by (?)-(S)-thalidomide, whereas (+)-(R)-thalidomide was metabolized to two hitherto unknown compounds (Met A and B). Mass spectrometry of these metabolites Met A and B indicated that oxidation or hydroxylation took place in the glutarimide moiety. Biotransformation studies with the more stable thalidomide analogue EM 12 revealed four new metabolites (Met C? F) whose quantities differed in the selected liver homogenate. © 1994 Wiley-Liss, Inc.     

Preparative and analytical separation of the zopiclone enantiomers and determination of their affinity to the benzodiazepine receptor binding site

We report the preparative separation of rac-zopiclone using malic acid as the resolving agent. Furthermore, two different methods for the analytical determination of zopiclone enantiomers by HPLC on chiral stationary phases are described. The benzodiazepine receptor binding of the isolated enantiomers was investigated. Half-maximal inhibitory concentrations of (+)- and (?)-zopiclone were 21 or 1,130 nmol/liter, respectively, indicating a more than 50 times higher affinity of the (+)-enantiomer toward the receptor. © 1993 Wiley-Liss, Inc.     

Microsequecing and cDNA cloning of the Calvin cycle/OPPP enzyme ribose-5-phosphate isomerase (EC 5.3.1.6) from spinach chloroplasts

Ribose-5-phosphate isomerase (RPI) catalyses the interconversion of ribose-5-phosphate and ribulose-5-phosphate in the reductive and oxidative pentose phosphate pathways in plants. RPI from spinach chloroplasts was purified and microsequenced. Via PCR with degenerate primers designed against microsequenced peptides, a hybridisation probe was obtained and used to isolate several cDNA clones which encode RPI. The nuclear-encoded 239 amino acid mature RPI subunit has a predicted size of 25.3 kDa and is translated as a cytosolic precursor possessing a 50 amino acid transit peptide. The processing site of the transit peptide was identified from protein sequence data. Spinach leaves possess only one type of homodimeric RPI enzyme which is localized in chloroplasts and is encoded by a single nuclear gene. Molecular characterization of RPI supports the view that a single amphibolic RPI enzyme functions in the oxidative and reductive pentose phosphate pathways of spinach plastids.Abbreviations RPI ribose-5-phosphate isomerase - OPPP oxidative pentose phosphate pathway - CNBr cyanogen bromide - R5P ribose-5-phosphate - Ru5P ribulose-5-phosphate     

A 5, 6-dimethoxylated flavone in the leaf resin of Adenostoma sparsifolium

A new flavone 5,6-dimethoxy-3,7,4′-trihydroxyflavone was isolated from the external leaf resin of Adenostoma sparsifolium and identified by spect     

Characterization of the isolated calcium-binding vesicles from the green alga Mougeotia scalaris,and their relevance to chloroplast movement

The calcium-binding vesicles from the green alga Mougeotia scalaris were isolated and characterized after staining in vivo by neutral red or rhodamine B. They were found to possess, a protonated group with a pK_a-9.9, typifying phenolic hydroxyl groups; upon titration, both, phenolic compound(s) and vital dye were concomitantly released from the vesicular matrix. A shift in peak absorbance from 450 nm to 540 nm of the vitally stained vesicles indicated that the neutral form of neutral red was bound to the vesicular, matrix as an intermediate form, stabilized via intermolecular hydrogen bonds to the phenolic compound(s). Up to 8.5.10⁹ dye molecules were calculated to be adsorbed to a mean-size vesicle. Analysis of Langmuir adsorption isotherms, indicated that there were two binding sites each for both neutral red and rhodamine B. The isolated vesicles were devoid of calcium, probably because vesicular calcium, bound to the vesicle matrix, was displaced upon dye binding. Dye adsorption to the vesicles in vivo results in substantial inhibition of the reorientational movement of the Mougeotia chloroplast and is explained by dye-mediated disorder of the cellular calcium homoeostasis.Abbreviations NR neutral red - RB rhodamine B - SDS sodium dodecyl sulfate This paper is part of the Ph.D. thesis of F. Grolig at Justus-Liebig-Universität Giessen, FRG