No abstract

Synthesis and reactions of optically active phosphine-boranes have been investigated. Optically active secondary phosphine-boranes, (Sp)-and (Rp)-menthyloxyphenylphosphine-boranes, and (S)-methylphenylphosphine-borane underwent palladium(0)-catalyzed electrophilic arylation withand a number of investigations on these compounds have been made so far, revealing the inherent nature of the phosphorus-boron bond [ 1,21. We have been interested in the characteristic properties of phosphine-boranes and have investigated the syntheses and reactions of this class of compounds from the viewpoint of organic synthesis [3-It is known that optically active phosphorus compounds possessing a chiral center at phosphorus occupy a central position in the study of the stereochemistry of reactions occurring at phosphorus [ 6 ] . Previous investigations in this area have utilized a great number of chiral phosphorus compounds. However, little attention has been paid to optically active phosphine-boranes. Recently, we have initiated the syntheses and stereochemical studies of optically active phosphine-boranes [7]. In this article, we describe new stereochemical aspects of reactions occurring at a chiral phosphorus as well as novel synthetic routes to optically pure C2-symmetric bisphosphine-boranes [S] . 51. RESULTS AND DISCUSSION Palladium-Catalyzed Cross-Coupling Reactions of Secondary Phosphine-Boranes with I odoa n isolesRecently, Xu et al. reported that palladium-catalyzed cross-coupling reactions of optically pure phosphinates with aromatic or vinylic halides proceed with almost complete retention of configuration [9]. We have been interested in palladium-catalyzed phosphorus-carbon bond forming reactions and have studied the reactions of optically active secondary phosphine-boranes and related substrates. Our initial experiments were conducted with the reactions of diastereomerically pure 0 1992 VCH Publishers, Inc.

Rat plasma glutathione peroxidase (GSH-Px) was purified 1,400-fold from rat serum by a combination of phenyl Sepharose, DEAE Sephacel, blue Sepharose and Sephacryl S-200 column chromatographies. The purified GSH-Px migrated as a single band corresponding to a molecular weight of 22,500 on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme was used for the immunization of chickens to obtain a specific antibody and for determination of its amino acid sequence. Two overlapping cDNA clones for rat plasma GSH-Px were isolated from a placental cDNA library. The composite nucleotide sequence is 1,529 base-pairs long and encodes 226 amino acids. The deduced amino acid sequence completely coincided with the sequences of five individual peptide fragments derived from the purified plasma GSH-Px on digestion with lysyl endopeptidase. In order to identify the tissue(s) generating this plasma GSH-Px, immunoblot analysis was performed on homogenates prepared from 13 tissues. A single immunoreactive band of 22.5 kDa, corresponding to plasma GSH-Px, was detected for the kidney homogenate. A much fainter band was observed for the lung preparation, but liver, spleen, bone marrow, and other tissues examined were negative. Northern blot analysis further revealed that the expression level of the plasma GSH-Px gene was high in kidney and low in lung. No transcript was detected in liver or spleen. These results indicate that plasma GSH-Px is predominantly synthesized and secreted by renal cells.

cDNAs of metallothioneins (MTs) in the nematode Caenorhabditis elegans were characterized. The MT-II clone encodes 62 amino acid residues and the predicted Mr is 6462. The MT-I clone contains an additional 12 residues at the C-terminal end, and the predicted Mr is 7959. There is a considerable similarity between MT-I and MT-II. Both of these proteins are cysteine-rich and, with a few exceptions, show a good alignment of cysteine residues. No obvious sequence relationship in the coding region was discernible between C. elegans MTs and mammalian MTs, aside from Cys-Cys, Cys-Xaa-Cys, and Cys-Xaa-Xaa-Xaa-Cys segments. However, 3'-untranslated region of cDNAs of C. elegans MT-I and -II have some consensus sequences found in mammalian MT cDNAs, suggesting that these regions may have some roles in the regulation of MT-gene expression.

The mechanism by which yeast rus2 mutant hyperaccumulates glycogen has been investigated. Total glycogen synthase activity WHS between 2.5 and 1.3 times higher in the rus2 mutant than in an isogenic strain. In addition, while in the normal strain the glycogen synthase activation state decreased along the exponential phase, in the mutant strain the opposite behaviour was observed: glycogen synthase activation state rose continuously reaching full activation at the beginning of the stationary phase. Glycogen phosphorylase a activity was up to 40 times higher in the mutant than in the normal strain. Glucose 6-phospha'te and fructose 2,G-bisphosphate levels were slightly more elevated in the mutants. The increase in total glycogen synthase and, particularly, the full activation of this enzyme may explain glycogen hyperaccumulation in the rus2 mutant even in the presence of elevated levels of glycogen phosphorylase a.