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1Author    H.-D Liidemann, H. Pladi, E. W. Esthof, L. B. TownsendRequires cookie*
 Title    Conformations of 3-Deazaadenosine, 3-Deaza-8-azaadenosine, and Benzimidazole-1-ß-D-riboside in Solution: H RNM R-, Proton-Relaxation-Time-, and Nuclear-Overhauser- Effect Studies  
 Abstract    The solution conformations of 3-deazaadenosine, 3-deaza-8-azaadenosine, and benzimidazole-l-/5-D-riboside have been determined by nuclear magnetic resonance methods in aqueous and ammonia solutions. The two-state S N model of Altona and Sundaralingam is used to analyse the ribose moiety. In order to characterize the orientation of the base relative to the ribose, longitudinal proton relaxation time and nuclear Overhauser enhancement measurements have been carried out. It is shown that 3-deazaadenosine and benzimidazole-l-/?-D-riboside exist preferentially in the S-syn-g+/t (70%) and the N-anti-g+/t (30%) conformation families. In the case of 3-deaza-8-aza-adenosine, some destabilization of the g+ rotamer occurs. In this case, the pulsed methods seem to indicate a preference of the base for the anti range. 
  Reference    Z. Naturforsch. 33c, 305 (1978); received February 17/March 30 1978 
  Published    1978 
  Keywords    Nucleosideanalogs, Conformations, NMR, NOE 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0305.pdf 
 Identifier    ZNC-1978-33c-0305 
 Volume    33 
2Author    G. Klimke, I. Cuno, H.-D Lüdem, R. Mengel, M. J. RobinsRequires cookie*
 Title    Arabinose Conformations of 9-ß -D-Arabinofuranosyladenine (ARA-A) Analogues Modified at the 2',3' or 5' Positions  
 Abstract    The solution conformations o f 9-/?-D-arabinofuranosyladenine analogues modified at the 2',3' or 5' positions are derived from the HRNMR spectra and the longitudinal relaxation rates o f the protons. The compounds studied are: 9-/?-D-arabinofuranosyladenine and its 2/-amino-2'-deoxy, 2'-chloro-2'-deoxy, 2'-azido-2'-deoxy, 3'-amino-3'-deoxy, 3'-bromo-3'-deoxy, 3'-chloro-3'-deoxy, 3'-fluoro-3'-deoxy, 3'-azido-3'-deoxy, 2',3'-diamino-2/,3'-dideoxy, 2',5'-diamino-2',5'-di-deoxy and 2',5'-diazido-2',5'-dideoxy analogues. It is derived from the data that the conforma­ tional equilibria o f the furanoside rings can be described by the two state N <*> S model of Altona and Sundaralingam. The emphasis in this work is to study systematically the influence o f the different chemical modifications upon the conformational equilibria o f the nucleosides. For the arabinosides it is found that substitution o f the hydroxyl groups at C2' or C3' by other atoms or groups always stabilizes the N conformation of the arabinose ring. The only exception is fluorine, where S is stabilized. The preference for the N state is correlated with an increasing population o f the g + rotamer of the exocyclic 5'-CH2OD group. From the relaxation study o f 2'-chloro-2'-deoxy-arabinofuranosyladenine the position of the syn <=> anti equilibrium o f the base was estimated to be predominantly anti. Thus a preference for the anti-N-g+ conformation was derived for the arabinosides excluding an intramolecular hydrogen bond between the 2' and 5' hydroxyl groups that was found in the solid state. The stabilization o f the N conformer in the modified compounds can be qualitatively explained by steric effects. 
  Reference    Z. Naturforsch. 35c, 853 (1980); received June 25 1980 
  Published    1980 
  Keywords    Arabinofuranosyladenine Analogues, Conformation, NMR 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0853.pdf 
 Identifier    ZNC-1980-35c-0853 
 Volume    35 
3Author    G. Klimke, I. Cuno, H.-D Lüdemann, R. Mengel, M. J. RobinsRequires cookie*
 Title    Xylose Conformations of 9-/?-D-Xylofuranosyladenine Analogues Modified at the 2'3' or 5'-Positions and Lyxose Conformations of 9-^-D-Lyxofuranosyladenine  
 Abstract    Proton magnetic resonance studies o f 9-/?-D-xylofuranosyladenine (xyloA), its 2'-amino-2'-deoxy, 2'-azido-2'-deoxy, 2'-bromo-2'-deoxy, 3'-thio-3'-deoxy, 3'-amino-3'-deoxy, 3'-azido-3'-deoxy, 3'-chloro-3'-deoxy, 3'-fluoro-3'-deoxy, 3'-0-methyl, 3',5'-diazido-3',5'-dideoxy analogues and 9-/?-D-lyxofuranosyladenine (lyxoA) have been carried out to study the effect o f chemical modifications at the sugar moiety on the solution conformational equilibria in these classes of nucleosides. Analogously to previous studies the xylose pucker can be described in the two-state N <=> 5 model o f Altona and Sundaralingam. For the xylosides, however, a somewhat different N state (C3'-endo-C4'-exo) has to be used than for the ribosides and arabinosides (C2'-exo-C3'-endo). The results o f the conformational analysis are that xyloA exists almost exclusively as an N conformer. The effect o f the substitutions in the modified compounds is to destabilize the N state. This decrease in the mole fraction o f N is accompanied by an increase in the population of the g + rotamer o f the exocylic 5'-CH2OD group. Thus for the xylosides a correlation N-t/g~ or S-g +, respectively, can be derived. Proton relaxation rate measurements on 2'-azido-2'-deoxyxylo-furanosyladenine indicate that in the xylosides the standard syn or anti ranges do not represent stable positions for the adenine base, but that a glycosyl torsion angle (* ~ 160°, T ~ 80°) be­ tween syn and anti is preferred. LyxoA behaves similar to the xylosides and also favours the N state o f the sugar pucker. In a summarizing discussion the conformational equilibria o f the different modified pentosides -ribose, arabinose, xylose and lyxose -are compared. It is shown that generally intramolecular hydrogen bonding does not yield an important contribution to the stabilization o f conformational equilibria in solution. It is also not possible to derive a quantitative relationship between such parameters as Van-der-Waals' radii or electronegativity o f the substituents and the mole fractions of the different conformers. It can, however, be seen that in all cases, where the hydroxyl groups at C2' or C3' are substituted by a more voluminous atom or group, steric effects become dominant and allow a qualitative explanation o f the changes of the conformational equilibria. Only for the smallest and most electronegative substituents, like fluorine, other interactions (e. g. electrostatic) may become important. It is thus suggested that the purine(/7)nucleoside conforma­ tion is essentially determined by steric interactions between the different parts o f the molecule. 
  Reference    Z. Naturforsch. 35c, 865—877 (1980); received June 251980 
  Published    1980 
  Keywords    Adenosine Analogues, Conformation, NMR 
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 TEI-XML for    default:Reihe_C/35/ZNC-1980-35c-0865.pdf 
 Identifier    ZNC-1980-35c-0865 
 Volume    35 
4Author    Hugo Scheer, W. Erner KuferRequires cookie*
 Title    Conformational Studies on C-Phycocyanin from Spirulina platensis  
 Abstract    The chromophore-protein interactions of C-phycocyanin (C-PC) from Spirulina platensis have been studied by following the partial and complete denaturation with UV-Vis spectroscopy. From comparison with published MO calculations, an elongated conformation of the chromophore is sug­ gested for native C-PC, a cyclic one for denatured C-PC. By means of partial denaturation, a step­ wise unfolding of the protein has been demonstrated. The presence of at least two sets of spectro­ scopically different diromophores is suggested from the partial denaturation and low temperature experiments. 
  Reference    (Z. Naturforsch. 32c, 513 [1977]; received April 25 1977) 
  Published    1977 
  Keywords    Bile Pigments, Protein Interaction, Conformation, Denaturation 
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 TEI-XML for    default:Reihe_C/32/ZNC-1977-32c-0513.pdf 
 Identifier    ZNC-1977-32c-0513 
 Volume    32 
5Author    Ryszard Stolarskia, JaroslawM. Cieslab, David ShugarabRequires cookie*
 Title    Monophosphates and Cyclic Phosphates of Some Antiviral Acyclonucleosides: Synthesis, Conformation and Substrate/Inhibitor Properties in Some Enzyme Systems  
 Abstract    Chemical and enzymatic procedures are described for the synthesis o f the m onophosphates and cyclic phosphates o f the antiviral acyclonucleoside 9-(1,3-dihydroxy-2-propoxym ethyl)-guanine (D H PG), its 3-hydroxymethyl-4-hydroxybutyl analogue, the (/?)-and (S)-epimers o f 9-(3,4-dihydroxybutyl)guanine, and 9-(2,3-dihydroxypropyl)guanine. The structures, and some conform ational features, o f all the foregoing, were determined by 'H and 3IP N M R spectroscopy. Their substrate/inhibitor properties have been examined in several enzyme systems, including ribonucleases, snake venom phosphodiesterase, beef heart and higher plant cyclic nucleotide phosphodiesterases, nuclease P I, and 3'-and 5'-nucleo-tidases. The enzymatic results are considered in relation to the mechanism o f the antiviral ac­ tivity o f the cyclic phosphate o f D H PG . 
  Reference    Z. Naturforsch. 45c, 293 (1990); received October 31 1989 
  Published    1990 
  Keywords    Acyclonucleosides, M onophosphates, Cyclic Phosphates, Conformation, Substrate/Inhibitor Properties 
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 TEI-XML for    default:Reihe_C/45/ZNC-1990-45c-0293.pdf 
 Identifier    ZNC-1990-45c-0293 
 Volume    45 
6Author    Lech Dudycz, Ryszard Stolarski, Reynaldo Pless, David ShugarRequires cookie*
 Title    A 1H NM R Study of the Syn-Anti Dynamic Equilibrium in Adenine Nucleosides and Nucleotides with the Aid of Some Synthetic Model Analogues with Fixed Conformations  
 Abstract    The syn-anti equilibrium about the glycosidic bond in adenosine and some related analogues was studied by means of *H NMR spectroscopy, with the aid of several model analogues fixed in given conformations either by intramolecular bonding, or by introduction of a bulky substituent. A model unambiguously and exclusively in the syn conformation is 8-(a-hydroxyisopropyl) adenosine; while one fixed in the a n ti conformation is 8,5'-anhydro-8-oxoadenosine. A new analogue, fixed in the high an ti conformation, is 8,2'-0-isopropylidenearabinofuranosyladenine. Several additional new model compounds were synthesized and their properties are described. With the aid of these models, the syn-anti dynamic equilibrium was examined for adenosine and some related compounds in different solvent systems, and the conformer populations evaluated quantitatively. The validity of the procedure applied, and the accuracy of the results, are critically examined, and compared with findings obtained by other procedures. Available literature data on the syn-anti equilibrium in other 8-substituted adenosines are re analyzed in the light of the present results. An analysis is also presented of the interdependence of the various conformational parameters, i. e. conformation about the glycosidic bond and those of the sugar ring and exocyclic carbinol group, in adenosine and 2',3'-0-isopropylideneadenosine. 
  Reference    Z. Naturforsch. 34c, 359 (1979); received November 21 1978 
  Published    1979 
  Keywords    NMR Spectroscopy, Conformation, S yn -A n ti Equilibrium, Purine Nucleosides and Nucleotides, Chemical Syntheses 
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 TEI-XML for    default:Reihe_C/34/ZNC-1979-34c-0359.pdf 
 Identifier    ZNC-1979-34c-0359 
 Volume    34 
7Author    Reynaldo Pless, Lech Dudycz, Ryszard Stolarski, David ShugarRequires cookie*
 Title    Purine Nucleosides and Nucleotides Unequivocally in the Syn Conformation' .Guanosine and 5-GM P with 8-ter/-Butyl and 8-( ß-Hydroxyisopropyl) Substituents  
  Reference    Z. Naturforsch. 33c, 902 (1978); received July 3 1978 
  Published    1978 
  Keywords    8 -Substituted Purines, Purine Nucleosides, Nucleotides, NMR Spectroscopy, Conformation, S yn -A n ti E quilibrium, 5'-Nucleotidase 
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 TEI-XML for    default:Reihe_C/33/ZNC-1978-33c-0902.pdf 
 Identifier    ZNC-1978-33c-0902 
 Volume    33