| | 1 | Author
| Atta-Ur -Rahman, Irshad Ali, M. Iqbal, ChaudharyH E J | Requires cookie* | | | Title
| NMR and Mass Spectroscopic Studies on Catharine  | | | | Abstract
| The 13 C NMR of Catharine is reported. A temperature-dependent study of the 'H NMR of Catharine indicates that it exists as two conformers at room temperature. At higher temperatures, the distinction between the two conformers disappears with the higher rate of equilibration. The mass spectral fragmentation of Catharine as established by link scan measurements is also re-ported. | | | |
Reference
| Z. Naturforsch. 40b, 543—545 (1985); received August 20/December 20 1984 | | | |
Published
| 1985 | | | |
Keywords
| Catharine, Conformational Analysis, 13 C NMR | | | |
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| default:Reihe_B/40/ZNB-1985-40b-0543.pdf | | | | Identifier
| ZNB-1985-40b-0543 | | | | Volume
| 40 | |
| 3 | Author
| RobertA. Shaw | Requires cookie* | | | Title
| The Reactions of Halogenocyclophosphazenes with Nitrogenous Bases | | | | Abstract
| The reactions of hexachlorocyclotriphosphazatriene, N3P3CI6, and to a lesser extent octachlorocyclotetraphosphazatetraene, N4P4CI8, and other halogenocyclophosphazenes with primary, secondary, and tertiary amines, are described. The effect on the substitution pattern of variables such as the structure of the amine, nature of the reaction solvent, etc., are discussed in some detail. Attention is drawn to the importance of steric effects. Isomerisation reactions are referred to. The physical properties of aminocyclophosphazenes and aminohalogenocyclophos-phazenes are discussed in some detail. These include basicity studies, X H and 31 P NMR and 35 C1 NQR studies, Faraday effect measurements, etc. Attempts are made to correlate the above properties with X-ray crystallographic studies and quantum chemical calculations. The distinction between ground state and perturbed state properties is emphasised. Synthesis, structure, and properties of phosphazenylcyclophosphazenes and related com-pounds are described and a novel conformational behaviour is discussed and rationalised. | | | |
Reference
| (Z. Naturforsch. 31b, 641—667 [1976]; received October 20 1975) | | | |
Published
| 1976 | | | |
Keywords
| Halogenocyclophosphazenes, Substitution Patterns, Nitrogenous Bases, Quantum Chemistry, Conformational Analysis | | | |
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| | | | | TEI-XML for
| default:Reihe_B/31/ZNB-1976-31b-0641.pdf | | | | Identifier
| ZNB-1976-31b-0641 | | | | Volume
| 31 | |
| 4 | Author
| Ulrich Burkert | Requires cookie* | | | Title
| The Conformations of Oxacyclooctanes | | | | Abstract
| The geometries and energies of the conformers of oxocane, the isomeric di-and trioxocanes, and of 1,3,5,7-tetroxocane were calculated by molec-ular mechanics. A boat-chair conformation was preferred by all molecules. From the preference of oxygen in the boat-chair conformations of oxocane (position 3 over 1 over 4) the preferred boat-chair form of all other oxocanes can be derived. The results are compared to experi-mental data, which in part can be reinterpreted. Additional CNDO/2 and MINDO/3 calculations were performed for 1,3,5,7-tetroxocane. | | | |
Reference
| Z. Naturforsch. 35b, 1479—1481 (1980); received July 18 1980 | | | |
Published
| 1980 | | | |
Keywords
| Molecular Mechanics, Force Field Calculations, Oxocanes, Cyclooctane, Conformational Analysis | | | |
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| | | | | TEI-XML for
| default:Reihe_B/35/ZNB-1980-35b-1479_n.pdf | | | | Identifier
| ZNB-1980-35b-1479_n | | | | Volume
| 35 | |
| 5 | Author
| Zofia Plesnar3, Stanisław Malanowski3, Zenon Lotowskib, JacekW. Morzyckib, Jadwiga Frelek, Jacek Wójcikd | Requires cookie* | | | Title
| Stereospecific Association of C-20 Epimers of 3/?-Hydroxy-16-oxo-24-nor-17-azachol-5-eno-23-nitryle | | | | Abstract
| The cryoscopic measurements show that title compounds are strongly associated in CHC13 solutions. The association of the 20 R epimer is distinctly less pronounced than that of the 205 epipmer. Self-association of the 205 epimer leads to the formation of very large com plexes. The 20 R epimer forms associates via water molecules. The dissimilarity may be ex plained in terms of different accessibility of the lactam carbonyl groups in the two epimers for the association. It is proposed that the association process is controlled by the configura tion at the carbon atom C(20) and conformation around the C(20)-C(22) bond. Populations of side chain conformations of both epimers were determined by means of proton nuclear magnetic resonance. It was found for the 20 R epimer that the t and the -g rotamers are almost equally populated, and the rotamer +g is excluded. For the 205 epimer the +g rotamer predominates over the t one, and the -g rotamer is excluded. The N M R data are fully consistent with the results of the molecular modelling studies. | | | |
Reference
| Z. Naturforsch. 52b, 749—756 (1997); received | | | |
Published
| 1997 | | | |
Keywords
| Self-Association, Cryoscopic Measurements, Conformational Analysis, CD Spectra, Azasteroids | | | |
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| default:Reihe_B/52/ZNB-1997-52b-0749.pdf | | | | Identifier
| ZNB-1997-52b-0749 | | | | Volume
| 52 | |
| 6 | Author
| PaavoH. Hynninen, Gunnel Sievers | Requires cookie* | | | Title
| Conformations of Chlorophylls a and a' and their Magnesium-Free Derivatives as Revealed by Circular Dichroism and Proton Magnetic Resonance | | | | Abstract
| The electronic absorption (UV/VIS), circular dichroism (CD) and proton magnetic resonance (*H NMR) spectra have been recorded for C-l0 epimeric chlorophylls a and a', pheophytins a and a' as well as pheophorbides a and a'. Although the epimers in each pair showed virtually identical UV/VIS spectra, their CD spectra were profoundly different and exhibited opposite signs at most wavelengths in the UV region. The differences were interpreted as arising, in part, from different C-10 configurations, and, in part, from conformational alterations induced by the steric strain in the crowded periphery of the macrocycle. The conformational alterations were also clearly indicated by the X H NMR zJö-values observed for the a,ß and <5 methine protons, the C-10 protons and most methyl group protons of the epimers in each pair. This was considered to imply changes in the geometry of the whole macrocycle. The A 6-values were larger for the Mg-free epimers than for the chlorophyll epimers, which shows that the central Mg-atom makes the macrocycle more rigid. Correlations between the signs of the CD bands and configurations are discussed. | | | |
Reference
| Z. Naturforsch. 36b, 1000—1009 (1981); received May 19 1981 | | | |
Published
| 1981 | | | |
Keywords
| Stereochemistry, Conformational Analysis, Chlorophyll and Pheophytin Epimers, X H NMR Spectra, Circular Dichroism | | | |
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| default:Reihe_B/36/ZNB-1981-36b-1000.pdf | | | | Identifier
| ZNB-1981-36b-1000 | | | | Volume
| 36 | |
| 7 | Author
| Reinhold Tacke, Haryanto Linoh, MoayadT. Attar-Bashi, WilliamS. Sheldrick, Ludger Ernst, Roland Niedner, Joachim Frohnecke | Requires cookie* | | | Title
| Sila-Pharmaka, 26. Mitt. [1] Darstellung und Eigenschaften potentiell curarewirksamer Silicium-Verbindungen, III Sila-Pharmaca, 26th Communication [1] Preparation and Properties of Silicon Compounds with Potential Curare-Like Activity, III | | | | Abstract
| The potentially curare-hke silicon compounds 8a-Sf were synthesized and investigated with respect to their structure-activity relationships. The conformations of the com-pounds in the solid state and in solution were studied by X-ray diffraction analysis (8a-8e) and *H NMR spectroscopy (8a-8f), respectively. The muscle relaxing properties of 8a-8f were investigated on the mouse. The observed structure-activity relationships are not in accordance with the classical "14 A model" for neuromuscular blocking agents. Einführung | | | |
Reference
| Z. Naturforsch. 37b, 1461—1471 (1982); eingegangen am 19. April 1982 | | | |
Published
| 1982 | | | |
Keywords
| Silicon Compounds, Curare-Like Activity, X-ray, Conformational Analyses, Structure-Activity Relationships | | | |
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| default:Reihe_B/37/ZNB-1982-37b-1461.pdf | | | | Identifier
| ZNB-1982-37b-1461 | | | | Volume
| 37 | |
| 8 | Author
| Udo Kunze, Rolf Tittmann | Requires cookie* | | | Title
| Phosphinsubstituierte Chelatliganden, XXIII [1] Darstellung und NMR-Spektren von Alkyl-arylphosphinothioformamiden, R(Ph)PC(S)NHMe Phosphine-Substituted Chelate Ligands, XXIII [1] Synthesis and NMR Spectra of Alkyl-arylphosphinothioformamides, R(Ph)PC(S)NHMe | | | | Abstract
| A series of alkyl-arylsubstituted N-methyl phosphinothioformamides, R(Ph)PC(S)NHMe (2 a—g), with varying bulkiness of the alkyl rest was synthesized from the racemic secondary phosphines la—g and methyl isothiocyanate. 'H and 13 C NMR spectra of 2a—g reveal signal sets of diastereotopic nuclei due to the asymmetry of the molecule. The chemical shift and coupling constants were confirmed by simulation in case of 2b, c. The vicinal 31 P— 13 C cou-plings of the menthyl and neomenthyl compounds 2f, g show an "anti-Karplus" behaviour CJ(gauche) > ? J(trans)) and allow the conformational assignment of the alicyclic group. The 31 P chemical shifts of 2a—d give a linear correlation with the cone angle of the alkyl substituents quoted from literature. | | | |
Reference
| (Z. Naturforsch. 42b, 77—83 [1987]; eingegangen am 8. August 1986) | | | |
Published
| 1987 | | | |
Keywords
| Alkyl-arylphosphinothioformamides, Menthyl and Neomenthyl Derivatives, NMR Spectra, Conformational Analysis, Substituent Influence | | | |
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| default:Reihe_B/42/ZNB-1987-42b-0077.pdf | | | | Identifier
| ZNB-1987-42b-0077 | | | | Volume
| 42 | |
| 9 | Author
| M. Ath, O. S. Enge | Requires cookie* | | | Title
| A Conformational Study of 5,10,15,20-Tetraalkyl-22//+,24//+-porphyrindiium Salts (Dication Salts) | | | | Abstract
| N-protonation of 5,10,15,20-tetraalkylporphyrins with n-butyl, isobutyl, isopropyl, 1-ethyl-propyl or ferf-butyl substituents yields the respective 22,24-dihydroporphyrins (22//+,24//+-porphyrindiium salts) that exhibit highly nonplanar conformations. Depending on the steric demand of the meso substituents, the free base porphyrins have planar to moderately ruffled macrocycles (primary or secondary alkyl residues) or are severely ruffled (tertiary alkyl resi dues). X-ray crystallographic studies show that protonation of porphyrins with «-Bu (2), i-Pr (3) or EtPr (4) substituents leads to steric congestion of the core resulting in symmetric, saddle distorted macrocycles as evidenced by average displacements of the Cb positions from the mean plane ranging from 0.79 to 1.01 A. The structures observed for these porphyrin diacids are very similar in distortion mode and degree of nonplanarity to 5,10,15,20-tetraaryl-22f/+,24//+-porphyrindiium salts and to 2,3,7,8,12,13,17,18-octaalkyl-5,10,15,20-tetraaryl-porphyrins. In contrast, protonation of the highly ruffled 5,10,15,20-tetrakis(teA-r-butyl)porph-yrin results in a switch of the conformational distortion mode. The dication 6 shows both saddle distortion (Cb displacements -1.3 A) and ruffling of the macrocycle (Cm displacements of approx. 0.48 A). Thus, the need to accomodate four N-H units in the porphyrin core with its associated out-of-plane tilting of the pyrrole rings and the steric strain induced at the meso carbon atoms results in a highly nonplanar porphyrin with mixed distortion modes. | | | |
Reference
| Z. Naturforsch. 55b, 336—344 (2000); received January 20 2000 | | | |
Published
| 2000 | | | |
Keywords
| Porphyrins, Steric Strain, Porphyrin Dications, Crystal Structure, Conformational Analysis, 22, 24-Dihydroporphyrins | | | |
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| default:Reihe_B/55/ZNB-2000-55b-0336.pdf | | | | Identifier
| ZNB-2000-55b-0336 | | | | Volume
| 55 | |
| 10 | Author
| Zygmunt Kazimierczuka, Ryszard Stolarskia, Lech Dudyczb, David Shugara> | Requires cookie* | | | Title
| Solution Conformation of Benzimidazole Nucleosides with the Aid of Model Analogues | | | | Abstract
| The 4,6-dibromo-and 5,7-dibromo-derivatives o f l-/?-D-ribofuranosylbenzimidazole, and the 4,6-dibromo-derivative o f 1-a-D-arabinofuranosylbenzimidazole, have been synthesized by condensation of the trimethylsilylated derivative of 4,6-dibromobenzimidazole with the appro priate protected sugar in the presence o f SnCl4. Application of the fusion method led to the ß-ribofuranoside o f 2-methyl-5,6-dichlorobenzimidazole. Two additional analogues o f the biologi cally active ribofuranoside of 5,6-dichlorobenzimidazole, viz. the 2',3'-0-isopropylidene and the 5'-chloro-5'-deoxy derivatives have been synthesized. Analyses o f the 'H N M R spectra of the foregoing, and o f previously synthesized 5(6)-mono-halogeno and 5,6-dihalogeno derivatives, were employed to determine solution conformations of these nucleosides. Conformations o f the sugar rings and exocyclic groups were evaluated from vicinal proton-proton coupling constants, as for purine nucleosides. The conformation of the benzimidazole ring about the glycosidic bond was determined from the chemical shifts of the sugar protons, principally H(2'), with the aid of model analogues in fixed syn and anti conforma tions; and, independently, from the chemical shifts o f the benzimidazole ring protons, principally H(4) and H(7). The halogenated benzimidazole ribofuranosides exhibit conformations of the sugar ring similar to those for purine /7-nucleosides, but differ from the latter in their preference for the conformation syn about the glycosidic bond. | | | |
Reference
| Z. Naturforsch. 36c, 126—1 (1981); received August 19 1980 | | | |
Published
| 1981 | | | |
Keywords
| Benzimidazole Nucleosides, Synthesis of Halogeno Analogues, Model syn and anti Conformations, Conformational Analysis | | | |
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| | | | | TEI-XML for
| default:Reihe_C/36/ZNC-1981-36c-0126.pdf | | | | Identifier
| ZNC-1981-36c-0126 | | | | Volume
| 36 | |
| 11 | Author
| M. Artin Bohl, Z. En, O. Simon | Requires cookie* | | | Title
| MTD Approach to Quantitative Structure-Activity Relationships for Cardiotonic Steroids | | | | Abstract
| A minimal topological difference (MTD) approach is made to describe quantitative structure-activity relationships (OSAR) for the N a+, K+-ATPase inhibitory activity of cardiotonic steroids. The calculations take into account 20 derivatives of digitoxigenin, digoxigenin, and gitoxigenin with small substituents at different sites of the steroid backbone. A multiple correlation coeffi cient of r = 0.916 is obtained using the MTD and an indicator variable for the presence of a 15 ß substituent. The corresponding receptor map reveals receptor wall vertices in the C l l , C12, C15, and C22 regions. Both 3ß and 16ß substituents are found to contain receptor cavity vertices. The MTD results are discussed with respect to lactone-ring conformational investigations presented and they are compared with findings of previous structure-activity studies. | | | |
Reference
| Z. Naturforsch. 40c, 858—862 (1985); received August 27 1985 | | | |
Published
| 1985 | | | |
Keywords
| Receptor Site Mapping, MTD Method, Conformational Analysis, Cardiotonic Steroids, Na+, K -ATPase Inhibition | | | |
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| | | | | TEI-XML for
| default:Reihe_C/40/ZNC-1985-40c-0858.pdf | | | | Identifier
| ZNC-1985-40c-0858 | | | | Volume
| 40 | |
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