Peptide conformations. Part 30. Assignment of the 1H-, 13C-, and 15N-NMR spectra of cyclosporin A in CDCl3 and C6D6 by a combination of homo- and heteronuclear two-dimensional techniques

The ¹H-, ¹³C-, and ¹⁵N-NMR spectra of the immunosuppressive cyclic undecapeptide cyclosporin A ( 1 ) have been analyzed at 300 MHz in CDCl₃, C₆D₆, and mixtures of these solvents. A combination of different homo- and heteronuclear two-dimensional NMR techniques enable complete assignment of all H-, C- and 4 N-signals. Recognition of the proton spin systems has been achieved via ¹H,¹H–COSY and double-quantum-¹H-NMR spectroscopy. NOESY spectra yield some sequence assignments, but two techniques using coupling across amide bonds have been applied to get independent assignments of all amino acids in the sequence: (i) An ¹H,¹H-COSY spectrum optimized for small coupling constants enables the detection of long-range couplings from N-methyl groups to both α-protons attached to that amide bond. (ii) An ¹H, ¹³C-COSY spectrum optimized for C,H-long-range couplings (J = 5 to 10 Hz) to the eleven CO groups again yields coupling to both α-protons attached to that amide bond. Additionally these two experiments yield the assignment of N-methyl protons and carbonyl C-atoms. Normal and relayed ¹H,¹³C-COSY in both solvents have been applied to assign all C-atoms via their directly attached and remote protons. An ¹H,¹³C-COLOC spectrum at 500 MHz in CDCl₃, which uses H,C-long-range couplings confirms the assignment of all proton spin systems as well as the C-signals of each individual amino acid. Ambiguities in the assignment of the C(δ)'s of MeLeu have thus been removed. An ¹H,¹⁵N-COSY spectrum enables the assignment of the 4 NH N-atoms.     

Röntgenographische und spektroskopische Untersuchungen an zwei Modifikationen von Dichloro-2,2′-dipyridyl-platin(II)

X-ray and Spectroscopic Studies on the two Modifications of Dichloro-2,2′-bipyridyl Platinum(II) Two modifications of PtCl₂(2,2′-bipyridyl) are investigated by X-ray diffraction and spectroscopic methods. The difference between both forms consists only in the packing of the planar complex units within the crystal. For the red coloured modification a columnar structure is derived from X-ray single crystal data, in which the nearest distance between planar complex units stacked above each other is 3.40 Å. The yellow form, however, does not form a columnar structure. It is built up from essentially isolated complex molecules without any feasible Pt–Pt-interaction (shortest Pt–Pt-distance: ca. 4.5 Å). Infrared and electronic spectra confirm the proposed structures. In the visible range only electronic transitions of the type 5d(Pt) → π*(bipyridyl) are observed which are also responsible for the different colours of the two modifications.     

Die Kristallstruktur des Tetragermanats K2Ba[Ge4O9]2

The crystal structure of the compound K₂Ba[Ge₄O₉]₂ has been determined by means of three-dimensional X-ray data resulting a finalR-value of 0.034. The lattice constants of the trigonal unit cell ( ) are:a=11.729 (I) andc=19.278 (3) Å. There is a close structural relationship to the tetragermanates K₂Ge₄O₉ and BaGe₄O₉. The new compound also consists of three-membered rings built up by [GeO₄] tetrahedra, which are linked by [GeO₆] octahedra forming a three-dimensional network.According to their powder diagrams the following compounds are isostructural to K₂Ba[Ge₄O₉]₂: Na₂Ba[Ge₄O₉]₂, Rb₂Ba[Ge₄O₉]₂, Na₂Sr[Ge₄O₉]₂ and K₂Sr[Ge₄O₉]₂.     

Addition von Acetylendicarbonsäuredimethylester an Imidazole; Aminierung der Addukte: neue Synthesen von 3-(2-Imidazolyl)-2-pyridon-4,5-dicarbonsäureamiden und Pyrido[1,2-a]pyrazinen

The reaction between dimethyl acetylene dicarboxylate and 2-amino-1-methylimidazole affords dimethyl 2-amino-1-methyl-1,3-diazepine-5,6-dicarboxylate in low yield. This 1:1 – adduct was formed by addition of the acetylenic compound to the enamine double bond of the imidazole ring followed by ring enlargement. On the other hand, 2:1 – adducts to the imine bond are isolated in moderate yield when dimethyl acetylene dicarboxylate is treated with either 1-methyl-2-methylmercapto-imidazole or 1-methyl-2-methylmercapto-imidazoline. These adducts behave differently on heating with ethylamine: the adduct of the imidazole series cyclizes to the pyridone 15 with concomittant loss of one carboxamide group whereas that of the imidazoline series forms a pyrido[1,2-a]pyrazine derivative 20 , both in high yield. The possible reaction mechanisms are discussed. ¹³C–NMR.-spectroscopy and X-ray analysis were used in the determination of several structures.     

Titanium distributions in zone melted materials measured by SIMS

Using a zone melting apparatus the influence of the different solidification processes on the Ti distribution has been investigated in model alloys and a technical steel. The concentration profiles after the conventional zone melting process have been measured using secondary ion mass spectrometry and were used for the determination of the distribution coefficients of Ti in pure Fe-Ti- and Fe-C-Ti-alloys. The registration of lateral elemental maps helps to identify and to eliminate measuring artefacts and allows the investigation of dendritic solidification structures.     

Synthese optisch aktiver 2-Methyl- und 2-Äthyl-1, 6-dioxaspiro [4.4]-nonan- und -[4.5]decan-Pheromone aus einem gemeinsamen chiralen Vorläufer

Synthesis of Optically Active 2-Methyl- and 2-Ethyl-1, 6-dioxaspiro [4.4]nonane- and -[4.5]decane Pheromones from a Common Chiral Precursor The versatility of the bromoepoxide 6 as chiral building block, which is readily available in both enantiomeric forms from malic acid, and which has previously been used for a vermiculine synthesis, is further demonstrated by the preparation of the title compounds 1, 3, 4 and 5 . Alkylation of 1,3-dithiane, first with the 1-ethoxyethyl-protected ω-chloroalcohols 8b or 9b and then with the (S)-(?)-bromoepoxide 6 , followed by oxirane opening with Selectride or methyl Gilman-reagent creates the desired carbon skeletons and functionality patterns 14–17 , in overall yields of 60–80%. Acetal and thioacetal hydrolyses directly furnish the spiroacetal target structures 1 and 3–5 as 3:2-diastereomeric mixtures; the E/Z-epimers 3 are separated by preparative GC. (Fig.).     

Rubidium-Pentafluoromanganat(III) und dessen Monohydrat,strukturelle Daten und Topotaxiebeziehungen

Rubidiumpentafluoromanganate (III) and its monohydrate, crystal data and topotaxy The unit cells and most probable space groups of the new compounds Rb₂MnF₅ · H₂O and Rb₂MnF₅ have been determined from single crystal X-ray diffraction data and the powder diffraction patterns indexed. . By analogy to the stoichiometrically similar phases high temperature K₂MnF₅ · H₂O, the unit cell of which has also been determined and its powder diffraction pattern indexed, and (NH₄)₂MnF₅, model structures for the rubidium salts are proposed. Both structures consist of infinite chains of corner sharing coordination octahedra [MnF₆], between which the rubidium ions and in the case of the hydrate additional water molecules are located. X-ray diffraction and scanning electron microscopical investigations of the dehydration of the hydrate clearly point to a chain controlled topotactic reaction mechnism. This supports the proposed model structures and confirms the possibility of predicting topotactic reaction mechanisms.     

GaSb based lasers operating near 2.3 microm for high resolution absorption spectroscopy

The paper describes results obtained with a new type of GaSb based semiconductor distributed feedback multiple quantum well lasers operating in continuous wave mode well above room temperature. The lasers show good tunability both by current and temperature from 0 to +60 degrees C and current from threshold up to 120 mA. They all operate in high power (1-3 mW) single mode regime and can be tuned in the methane and ammonia overtone absorption spectral range over up to 12 cm(-1) and can be used for the detection of these and other gases.     

Bemerkungen zur Synthese von 5-Amino-m-xylol-2-sulfonsäure und 5-Amino-m-xylol-4-sulfonsäure

Some comments on the syntheses of 5-amino-m-xylene-2-sulfonic acid and 5-amino-m-xylene-4-sulfonic acid Treatment of 5-amino-m-xylene ( 1 ) with oleum led to a 55:45 mixture of 5-amino-m-xylene-2-sulfonic acid ( 2 ) and 5-amino-m-xylene-4-sulfonic acid ( 3 ). The structure of both isomers was proven by reaction of sulfur dioxide with the diazonium chlorides derived from 2-amino-5-nitro-m-xylene ( 5 ) and 4-amino-5-nitro-m-xylene ( 8 ) giving 5-nitro-m-xylene-2-sulfonyl chloride ( 6 ) and 5-nitro-m-xylene-4-sulfonyl chloride ( 9 ) respectively, followed by hydrolyses to the corresponding sulfonic acids 7 and 10 , and final Béchamp reductions. The sulfonic acid 2 was also prepared by sulfonation of 5-acetylamino-m-xylene ( 4 ) to 5-acetylamino-m-xylene-2-sulfonic acid ( 11 ) and subsequent hydrolysis. A further procedure for the synthesis of 3 was sulfonation of 5-amino-2-chloro-m-xylene ( 12 ) – prepared by Béchamp reduction of 2-chloro-5-nitro-m-xylene ( 13 ) – or of 5-amino-2-bromo-m-xylene ( 15 ) – prepared by bromination of 4 and subsequent hydrolysis – to 5-amino-2-chloro-m-xylene-4-sulfonic acid ( 16 ) and 5-amino-2-bromo-m-xylene-4-sulfonic acid ( 17 ) respectively, followed by hydrogenolysis.     

Influence of Insulin and Glucagon on the Cholesterol Synthesis in Rat Liver in vivo. Evidence against a Rate Limiting Function of the HMG-Coenzyme A Reductase

Physiological doses of insulin and glucagon in the range of 0.5–2.5 m unit and 0.05-2 μg respectively per 100 g body weight stimulate first and inhibit afterwards the cholesterol synthesis from labeled acetate in rat liver in vivo. It could be shown that these effects are not caused by a regulating influence of the HMG-coenzyme A reductase.