Acta chemica Scandinavica. Series B: Organic chemistry and biochemistry最新文献

A synthetic scheme from N-benzyloxycarbonyl S-benzyl homocysteine peptide benzyl ester, assembled using well-established procedures in solution and purified, to the corresponding free methionine peptide, has been explored preparatively. Deprotection by sodium in liquid ammonia followed by alkylation on sulfur with methyl iodide gave, after purification by semipreparative HPLC, in the case of methionine-enkephalin a pure product in high yield. No evidence from side-reactions on tyrosine could be detected by HPLC. The scheme was primarily designed to be adaptable to the preparation of 11C-labelled methionine-enkephalin and, in particular, to exploit 11C-methyl iodide, now in routine production in our laboratory, in peptide synthesis, thus providing access to 11C-labelled enkephalins with high specific radioactivity for in vivo experiments. Applying 2H-, 3H-, 13C- or 14C-methyl iodide instead, however, this approach should be equally useful for the preparation of the corresponding peptides. Provided overalkylation by methyl iodide and fatal splitting of peptide bonds by the sodium/ammonia reagent can be avoided, the scheme should be applicable also to the synthesis of other methionine-containing peptides.

Two stable glucopyranosylpalladium complexes, chloro[1,3-dimethyl-5-(3,4,6-tri-O-acetyl-2-deoxy-alpha-D -arabinohexopyranosyl)-2,4(1H,3H)-pyrimidinedionnato] (triphenylphosphine)-palladium and the corresponding triphenylarsine analog, were studied using fast atom bombardment mass spectrometry, 1H, 13C and 31P nuclear magnetic resonance, UV and IR spectroscopy to establish structures for these complexes. The data obtained indicate that the pyranosyl ring is in a chair conformation in which palladium (C2'), acetoxy (C3' C4') and acetoxymethyl (C5') are equatorial and 1,3-dimethyl-2,4(1H,3H) pyrimidinedion-5-yl (C1') is axial. The palladium(II) ion is encompassed in a six-membered ring metallocycle in which C2' of the glucopyranosyl ring and the oxygen of the C4 carbonyl of the pyrimidinedionyl group occupy adjacent ligand sites. The other two ligand sites on square planar palladium are occupied by triphenylphosphine (or triphenylarsine) cis to C2' and trans to carbonyl oxygen, and chloride trans to C2' and cis to oxygen. This stable metallocycle has three unusual features, a cis-beta-hydrogen, a six-membered Pd-containing ring and an oxygen donor ligand. Its surprising stability is due to conformational barriers to the proper alignment of Pd with pyranosyl ring substituents required for elimination reactions.

Calcium and phospholipid-dependent protein kinase (protein kinase C) from isolated rat adipocytes has been partially purified using DEAE-Sepharose CL-6B and characterized. The enzyme was shown to have similar properties as the kinase isolated from brain or spleen. When histone was used as substrate, an equal amount of cAMP-dependent and calcium and phospholipid-dependent kinase activity was detected from the DEAE Sepharose CL-6B fractions. The major part of protein kinase C (72%) was isolated from the soluble adipocyte fraction. Of the membranous fractions, the plasma membrane exhibited the highest specific activity. The protein kinase preparations bound [3H]-phorbol-12,13-dibutyrate (PDBU) with high affinity (Kd = 2 nM) and the number of PDBU binding sites per cell was calculated to 63 000.

The chemical heterogeneity of radiolabelled neuroblastoma heparan sulfate has been studied by ion exchange chromatography and by affinity chromatography on heparan sulfate-agarose. Although the entire population of chains shows considerable homogeneity in charge density, the deaminative cleavage products ranged in size from disaccharides to eicosasaccharides. Under appropriate conditions neuroblastoma heparan sulfate could be separated into two pools of low or high affinity for lung heparan sulfate-agarose. Analyses of periodate oxidation-alkaline elimination indicated that the high affinity chains contained larger proportions of heparin-like segments, i.e. iduronate-rich and N-sulfated ones.

Influenza virus mRNA synthesis is primed by a capped oligonucleotide which is cleaved off from a cellular mRNA by a viral protein. The dinucleotide A3'p5'G can be used as a primer for the viral RNA polymerase mediated RNA synthesis in a cell-free system. Analogues of A3'p5'G have therefore been synthesized using the phosphotriester approach, and their priming ability for the influenza virus mRNA synthesis has been determined. An absence of the 2'-hydroxyl function in the guanosine residue in the dinucleotide, as in A3'p5'dG, drastically decreased its priming ability. Similarly, an alteration of the 3'----5' phosphate linkage to a 2'----5' phosphodiester linkage affected the priming ability quite severely. However a dinucleotide, with the 2'-hydroxyl function omitted in the adenosine moiety, as in dA3'p5'G, could still stimulate the mRNA synthesis. None of the modified dinucleotides inhibited A3'p5'G or globin mRNA primed influenza mRNA synthesis.