Structure and Reactivity of Xanthocorrinoids. Part III. The first example of a pinacol-type rearrangement in the corrin series

The transformation of the c-acetic-acid chain of hexamethyl Coα, Coβ-dicyanocobyrinate into an ethyl group (→ 2 ) as well as the synthesis of the pentadecaalkyl-cobalticorrin 6d from commercial cyanocobalamin are described. On reaction of 2 or 6d with O₂ in the presence of ascorbic acid, migration of the CH₃ group at C(5) to the vicinal position C(6) takes place concomitantly with the introduction of a carbonyl group at C(5).     

Palladium-catalyzed C-O bond formation: direct synthesis of phenols and aryl/alkyl ethers from activated aryl halides

A simple and efficient palladium-catalyzed carbon-oxygen bond formation is reported. The palladium-tri-tert-butylphosphine complex was found to be effective in converting haloarenes to corresponding substituted phenols. This methodology offers a direct transformation of aryl halides to phenols, as well as the straightforward application to generate a wide variety of diaryl or alkyl/aryl ethers.     

Analysis of tinuvin 1577 polymer additive in edible oils using on-line coupled HPLC-GC

An application of automated on-line HPLC-HRGC is described for direct analysis of edible oils for migrated polymer additives. The sample preparation, separating the additive from the oil triglycerides, is carried out using normal phase HPLC. The fraction of the eluent containing the additive is automatically transferred to a HRGC where a second and final separation of the additive from minor oil components takes place. The method compares well with off-line separation methods. Migration data for Tinuvin 1577 from PET and PC polymers as well as an unspecified experimental polymer is given. The advantages and disadvantages of using different edible oils as food simulants are discussed.     

Coulometrisches Verfahren zur Bestimmung von Gesamt-, Carbonat- und Nichtcarbonat-Kohlenstoff in magmatischen, metamorphen und sediment?ren Gesteinen

Zusammenfassung Für die Bestimmung von Gesamt-, Carbonat- und Nichtcarbonat-Kohlenstoff in magmatischen, metamorphen und sedimentären Gesteinen (auch bei höheren Anteilen an organischem C) ist ein Verfahren nach dem Prinzip der coulometrischen Titration geeignet. Der Gesamt-Kohlenstoff wird ermittelt durch Erhitzung der auf <0,125 mm zerkleinerten Probe bei etwa 1250°C im Sauerstoffstrom ohne irgendwelche Zusätze. Zur Bestimmung von Nichtcarbonat-Kohlenstoff wird eine bestimmte Menge Gesteinspulver mit Salzsäure versetzt und auf einem Aluminiumblock HCl abgeraucht. Der Carbonat-Kohlenstoff entweicht als CO₂. Zurück bleibt der Nichtcarbonat-Kohlenstoff, welcher wie der Gesamt-Kohlenstoff coulometrisch bestimmt wird. Der Carbonat-Kohlenstoff bzw. die äquivalente Menge CO₂ ergibt sich dann aus der Differenz von Gesamt- zu Nichtcarbonat-Kohlenstoff. Das Verfahren ist anwendbar auf Kohlenstoffgehalte in Gesteinen von etwa 10 ppm bis 20 Gew.-% bei mittleren Standardabweichungen von etwa 0,0002–0,05% C (Richtwerte). Die Analysendauer für eine Probe beträgt etwa 3–5 min.

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Coulometric method for the determination of total, carbonate, and non-carbonate carbon in igneous, metamorphic, and sedimentary rocks

For the measurement of total carbon the sample, ground finer than 0.125 mm and without the addition of any reagents, is ignited in a current of oxygen at about 1250°C. Non-carbonate carbon can be analysed after another portion of the sample is treated with conc, hydrochloric acid and evaporated on a hot plate; the carbonates are decomposed and the carbonate carbon is removed as carbon dioxide. The residue is non-carbonate carbon which is also determined by the coulometric method. The difference between total carbon and non-carbonate carbon corresponds to carbonate carbon or its equivalent as carbon dioxide. The method is applicable to carbon contents in rocks from 10 ppm to 20 wt.-%. The standard deviation is approximately 0.0002 to 0.05% C. Each carbon analysis takes about 3 to 5 min.

     

Gas-liquid chromatographic method for the measurement of plasma levels of d-7,8-dimethoxy-3-methyl-phenyl-2,3,4,5-tetrahydro-1h-3-benzazepine acid maleate (SCH-12679) and its major metabolites in aggressive mental retardites

A sensitive gas-liquid chromatographic technique for the quantitative analysis of SCH-12679 (d-7,8-dimethoxy-3-methyl-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine acid maleate) and its major metabolites in plasma of aggressive mental retardates receiving therapeutic doses of the medicament has been developed. The lower limits of detection are 20 ng/ml for SCH-12679, 0.5 ng/ml for 3-desmethyl SCH-12679 and 0.4 ng/ml for 7-desmethyl plus 8-desmethyl SCH-12679. SCH-12679 is estimated with a flame ionization detector. Its metabolites are quantitated using an electron-capture detector after conversion of the compounds to their heptafluorobutyryl derivatives by reaction with the appropriate anhydride. Data on plasma levels of unchanged SCH-12679, 3-desmethyl SCH-12679 and a combination of 7-desmethyl and 8-desmethyl SCH-12679 in fifteen patients treated with the medicament are presented.     

Synthesis of unsymmetrical 2,4-dialkylpyrazolo[1,5-a]-1,3,5-triazines

The reaction of 3-aminopyrazole with imidate esters such as ethyl acetimidate, gave N-(pyrazol-3-yl)acetamidine (1) rather than the isomeric 2-acetamidoyl-3-aminopyrazole. Ring closure of 1 with orthoesters such as ethyl propionimidate, afforded unsymmetrically substituted 2.4-dialkylpyrazolo[1,5-a]-1,3,5-triazines such as 4-ethyl-2-methylpyrazolo[1,5-a]-1,3,5-triazine (3). The structure of 1 was confirmed by several alternate syntheses. The unique feature of this two-step synthetic approach to the synthesis of pyrazolo[1,5-a]-1,3,5-triazines is that it is a convenient method of preparing fused triazines based on available pyrazoles rather than the less accessible dialkyltriazines.     

REACTIVITY OF SINGLET OXYGEN TOWARD LARGE PEPTIDES

Abstract— The reactions of singlet oxygen, ¹O₂, with amino acids and their derivatives have been studied previously. It was found that only five amino acid residues interact readily with ¹O₂. Here we describe its reactions with the large peptides melittin, neuropeptide Y (NPY) and insulin in their native and in their denatured forms. The singlet oxygen quenching by a polypeptide was compared with that of a solution at the same concentration as those of its constituent amino acids, which are known to react efficiently with ¹O₂. It was found that the quenching rate by such a mixture exceeded that of the polypeptides in their native form. The ratio of the rate constants for NPY to that of the corresponding amino acid mixture in solution was 0.75. For melittin in its monomeric form it was 0.83 and for a tetramer of melittin (at high ionic strength) it was 0.70. For native insulin the ratio of the rate constants was 0.55. For oxidized insulin with its -S-S- bridges opened the figure became 0.80. However, the quenching by all the polypeptides in their fully denatured form (in the presence of 6 M urea) equalled that of the corresponding amino acid mixtures. Although polypeptides are generally supposed not to possess a stable secondary structure in solution the effects are explained by shielding of some of the reactive amino acid residues in the chain by temporary folding or incipient secondary structures of the native polypeptide.
It is shown that the kinetics for a homogeneous solution of quenchers applies also to measurements in a polypeptide solution where the quenchers are localized along the polypeptide backbone and thus form clusters in solution.     

Electrocyclic ring opening reaction of a 1,3,4-oxadiazin-6-one into its azaketene tautomer

5-Methyl-2-phenyl-1,3,4-oxadiazin-6-one undergoes cycloaddition with 2-methylpropenylpyrrolidine. One of the cycloadducts is derived from the Diels-Alder reaction of a transient azaketene tautomer.     

Über den sterischen Verlauf der Umsetzung von Enaminen aus offenkettigen Aldehyden und Ketonen mit Nitroolefinen zu 2,3-disubstituierten 4-Nitroketonen

On the Steric Course of the Reaction of Enamines Derived from Open-Chain Aldehydes and Ketones with Nitro-olefins Yielding 2,3-Disubstituted 4-Nitroketones The relative configuration of the nitro-ketone 12 obtained by the title reaction has been proved by a Baeyer-Villiger degradation and subsequent reduction to the amino-alcohol (±)-(u)- 20 , the relative configuration of which is identical with a sample prepared from 2-methyl-3-hydroxybutyrate of known configuration (Scheme 1). The stereochemical course of the title reaction is thus as predicted by our topological rule. It is assumed that the other nitro-ketones 13–18 described here are also formed by (lk)-combination of the trigonal centers of the educts (diastereoselectivity > 90%, see Formulae and Fig. 1). It is not possible to reverse this relative topicity by employing (Z)- instead of (E)-components of the starting materials, due to the reversibility of the primary step of these Michael additions (Schemes 2 and 3, and Fig. 2).