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  • 1
    Electronic Resource
    Electronic Resource
    Conformational restriction of Tyr and Phe side chains in opioid peptides: Information about preferred and bioactive side-chain topology (1996)
    New York : Wiley-Blackwell
    Biopolymers 38 (1996), S. 1-12 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The side chain of Tyr and Phe was fixed into the gauche (-) or gauche (+) conformation by using the Tic or Htc structures, and into the trans conformation by using an aminobenzazepine-type (Aba) structure. When incorporated into dermorphin or deltorphin II, the Tic and Htc analogues all showed a large decrease in both μ and δ affinities and activities. Fixation of Phe3 in the trans rotamer resulted in a large increase in δ affinity in the dermorphin analogue, whereas in the [Aba3-Gly4] deltorphin II analogue, good δ affinity is maintained despite the removal of the Glu side chain. Whereas several authors propose a gauche (-) preferred conformation for the Phe3 side chain, these results suggest a trans conformation at the δ receptor. The use of these conformationally constrained residues for evaluating the preferred solution conformation in the flexible N-terminal tripeptide Tyr-D-Ala-Phe is illustrated. The 1H-nmr parameters - chemical shift, temperature dependence, and nuclear Overhauser effects to the D-Ala2 methyl protons in the different analogues - provide direct evidence to confirm the proposed sandwich conformation in the native peptides. © 1996 John Wiley & Sons, Inc.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
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    Paper (German National Licenses)
  • 2
    Electronic Resource
    Electronic Resource
    Assignment of the 1H-nmr resonances of the four rotamers of β-casomorphin-5 in DMSO (1991)
    New York : Wiley-Blackwell
    Biopolymers 31 (1991), S. 1409-1416 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: We report the complete assignment of the 1H-nmr spectrum of β-casomorphin-5 in DMSO-d6 solution. With a combination of one-dimensional, double quantum filtered correlated spectroscopy, homonuclear Hartmann-Hahn, and rotating frame nuclear Overhauser enhancement spectroscopy (ROESY) spectra, we were able to differentiate the four conformers originating from two Xxx-Pro bonds present in the sequence. Exchange peaks in the ROESY spectra confirmed the presence of four interchanging conformational isomers. Based on integrations, the relative populations of the four species were estimated, while characteristic sequential nuclear Overhauser enhancements (NOEs) were used to determine the orientation of the Xxx-Pro bonds. This orientation was also shown to correlate with the chemical shift changes for the α protons of both the Xxx and Pro residues. Finally, interresidue NOEs indicate conformational preferences for the aromatic side chains, especially in the all-trans conformer.
    Additional Material: 3 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360311207
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  • 3
    Electronic Resource
    Electronic Resource
    Morphiceptin and β-casomorphin-5 analogues containing a reduced peptide bond: Selective μ-receptor agonists and a novel μ antagonist, H-Tyr-Proψ(CH2-NH)Phe-Pro-Gly-OH (1992)
    New York : Wiley-Blackwell
    Biopolymers 32 (1992), S. 957-969 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In order to prevent enzymatic degradation of β-casomorphin-5 (1) and morphiceptin, reduced peptide bonds were incorporated at the 2-3 and 3-4 bonds, respectively. The analogues were synthesized by a combination of solid phase methodology and reductive alkylation of resin-bound peptide amines with Boc-amino acid aldehydes (Boc: tert-butyloxycarbonyl) in the presence of NaBH3CN. During reversed phase high pressure liquid chromatography purification, peak shape distortions could be observed. Epimerization was excluded, based on gas chromatography/mass spectroscopy analysis, which indicated acceptable levels of racemization (〈3%) in the crude product. Instead, the phenomena could be attributed to slow cis/ trans isomerizations originating from the Xxx-Pro bonds in the sequence. The presence of different conformational isomers was also established by 1H-nmr spectroscopy in DMSO-d6. All analogues showed high stability in blood plasma, enhanced binding affinity for the μ receptor, and very low binding to the δ receptor. While the Phe3Ψ(CH2-N) Pro4 analogues (3) and (5) displayed agonist activity, the Pro2Ψ(CH2-NH) Phe3 modified analogue (2) showed antagonist activity comparable to D-Phe-Cys-Tyr-D -Trp-Arg-Thr-Pen-Thr-NH2.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360320807
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