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

The pKa and pH dependence of the formation of nitroxide radicals from the following drugs that contain an aliphatic secondary amino group, by oxidation with hydrogen peroxide, have been studied by ESR spectroscopy: Ephedrine, (1R,2S)-1-phenyl-2-methyl-aminopropanol, timolol, (S)-1-(tert-butyl-amino)-3-[(4-morpholino-1,2,3-thiadiazol-3-yl)ox y]-2- propanol, metoprolol, 1-[4-(2-methoxyethyl)phenoxy]-3-[(1-methylethyl)amino]-2-propanol and terodiline, N-tert-butyl-3,3-diphenyl-1-methylpropylamine. Radicals were formed from the non-ionized base only. Therefore, the pKa value of the amine and the pH of the reaction mixture is of crucial importance for the yield of nitroxide radical. At 37 degrees C the pKa values of 1-3 are about 9.2, and of 4 about 9.6, which means that 1.5% of 1-3, and 0.6% of 4, are present in the reactive base form at the physiological pH of 7.4. Horse-radish peroxidase was found both to enhance radical production and to decrease the life-time of the radicals formed in the reaction with hydrogen peroxide.

The short-lived radionuclide 11C (t1/2 = 20.4 min) has been used in the asymmetric synthesis of L-2-amino[3-11C]butyric acid, L-[3-11C]-norvaline and L-[3-11C]valine. The syntheses were performed by alkylation of [(+)-2-hydroxypinanyl-3-idene]-glycine tert-butyl ester under anhydrous conditions in tetrahydrofuran/1,3-dimethyl-3,4,5,6-tetrahydro-2-pyrimidinone with lithiated 2,2,6,6-tetramethylpiperidine as base, using the appropriate 11C-alkyl iodides prepared in a one-pot reactor from [11C]carbon dioxide. Following removal of the protecting groups, the -[3-11C]amino acids were obtained in 80-82% enantiomeric excess and in 9-25% radiochemical yields, decay corrected and calculated on the basis of the amount of [11C]carbon dioxide at the start of the syntheses within 50-55 min.

A fragment, GIP1-31, of the human Glucose-dependent Insulinotropic Polypeptide (GIP1-42) Tyr-Ala-Glu-Gly-Thr-Phe-Ile-Ser-Asp-Tyr-Ser-Ile-Ala-Met-Asp-Lys-Ile-His- Gln-Gln-Asp-Phe-Val-Asn-Trp-Leu-Leu-Ala-Gln-Lys-Gly has been synthesized by solid phase methodology under continuous flow conditions. The peptide was assembled on a polydimethylacrylamide kieselguhr support by using 9-fluorenylmethoxycarbonyl amino acid pentafluorophenyl esters. The crude peptide, obtained after trifluoroacetic acid cleavage, was purified by gel filtration and by reverse-phase HPLC. This synthetic replicate, corresponding to human GIP1-31, retains the ability of naturally occurring GIP to stimulate insulin release.

(A) The effects of phosphate, chloride, nitrate, pyruvate, malate, succinate and glutamate ions on the kinetics of yeast phosphoglycerate kinase (ATP: 3-phospho-D-glycerate 1-phosphotransferase, EC 2.7.2.3) were studied with MgATP2- and 3-P-glycerate as variable substrates. Three types of patterns were obtained: (1) Nitrate, succinate, malate and glutamate ions, strictly noncompetitive versus both the substrates. (2) Phosphate and chloride ions, noncompetitive versus MgATP2- and mixed versus 3-P-glycerate. (3) Pyruvate ions, being very weak inhibitors, competitive with MgATP2- and noncompetitive with 3-P-glycerate. (B) Based on experiments with simultaneous inhibition by various combinations of two anions the following suggestions were made: The type 1 anions presumably bind to a site outside the active centre. These ions appear to bind to the enzyme independently of type 2. The latter also appears to include sulfate ions, which are competitive versus both the substrates as well as versus the phosphate and chloride ions. Sulfate and phosphate ions are electronically similar, but show different inhibition patterns, presumably due to various effects on the protein conformation. Type 3 inhibition exerted by pyruvate ions was shown earlier for 1-anilino-8-naphthalenesulfonate and salicylate ions, but as these two anions are supposed to bind to the adenine binding pocket of the catalytic centre, the results indicate that pyruvate ions might preferably compete with the nucleotide substrate for the polyphosphate binding site.

The absolute configuration of the more active (-)-enantiomer of the anticholinergic trihexyphenidyl hydrochloride has been established as (R) by syntheses of (S)-(+)-procyclidine hydrochloride, whose absolute configuration has been established previously, and (S)-(+)-trihexyphenidyl hydrochloride from the same chiral building block, viz. (S)-(-)-cyclohexyl-3-hydroxy-3-phenylpropanoic acid. Both enantiomers of this chiral synthon were prepared by optical resolution of the corresponding racemate, employing (R)- and (S)-1-phenylethylamine, respectively, as resolving agents.

ATP-stimulated DNA polymerase activity involving DNA polymerase I has been found to be present in cell extracts from wild type and recC mutant strains of Escherichia coli, but not in extracts from recB strain. The activity has been separated from recBC DNase by DEAE-cellulose ion exchange. It is suggested that recB-dependent factor is involved in the ATP-stimulation of polymerase. Evidence is provided that this stimulation may be due to the interaction of recB-dependent factor with DNA polymerase I.

The structure of a sponge metabolite from Microciona prolifera, previously considered to be (6S)-2,3-didehydro- or 3,4-didehydro-gamma, chi-carotene, has been further studied. Attempted total synthesis of the 3,4-didehydro derivative provided the hitherto unknown gamma, chi-carotene, the synthesis of which is described. Hydrolysis of lutein methanesulfonate diester (dimesylate) gave elimination products possessing the 3,4-didehydro gamma end-group. 1H NMR data for this gamma end-group were identical with those for the sponge carotenoid. The mesylate elimination reaction described may mimic the metabolic formation of the 3,4-didehydro-gamma-carotenoid end-group. In connection with other investigations on functionalized carotenoids we further report the preparation of zeaxanthin and lutein mesylates and their base-catalyzed elimination reactions. SN2 type substitution reactions of zeaxanthin dimesylate with appropriate nucleophiles did not produce beta, beta-carotene, zeaxanthin diacetate or thiozeaxanthin.

The substrate specificity of purified human protein kinase C was modulated by 12-O-tetradecanoyl-4 beta-phorbol-13-acetate (TPA), dioleoylglycerol, arachidonic acid and lipid A when histone type III-S and myelin basic protein were used as phosphate acceptors. Each activator also showed a distinct pattern in the stimulation of phosphorylation of the kinase itself and of cytosolic placental proteins. The nature of the substrate and the presence of calcium and phospholipid determined the magnitude of the effect observed upon addition of all activators and also the dose dependency of kinase activation by TPA. The apparent Km value for phosphorylation of histone type III-S by the kinase activated by phorbol ester alone and with calcium was 20-30 fold higher than that observed for the enzyme activated by calcium and phospholipid. These observations indicate that the nature and extent of cellular response induced by the activation of C-kinase(s) may be determined by the type of cellular stimulus.

A rabbit liver enzyme preparation oxidised racemic iminium ions 1 and 2 to optically active lactams 3 and 4 with enantiomer ratios ER/S = 5.5 and 0.14, respectively.