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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of computer aided molecular design 4 (1990), S. 239-253 
    ISSN: 1573-4951
    Keywords: Chirality ; Energy calculations ; Flexible-geometry maps ; Interactive computer graphics ; N-Methylated γ-lactams ; β-Turns
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary The conformational constraints imposed by γ-lactams in peptides have been studied using valence force field energy calculations and flexible geometry maps. It has been found that while cyclisation restrains the Ψ of the lactam, non-bonded interactions contribute to the constraints on ϕ of the lactam. The γ-lactam also affects the (ϕ,Ψ) of the residue after it in a peptide sequence. For an l-lactam, the ring geometry restricts Ψ to about-120°, and ϕ has two minima, the lowest energy around-140° and a higher minimum (5 kcal/mol higher) at 60°, making an l-γ-lactam more favourably accommodated in a near extended conformation than in position 2 of a type II′ β-turn. The energy of the ϕ∼+60° minimum can be lowered substantially until it is more favoured than the-140° minimum by progressive substitution of bulkier groups on the amide N of the l-γ-lactam. The (ϕ,Ψ) maps of the residue succeeding a γ-lactam show subtle differences from those of standard N-methylated residues. The dependence of the constraints on the chirality of γ-lactams and N-substituted γ-lactams, in terms of the formation of secondary structures like β-turns is discussed and the comparison of the theoretical conformations with experimental results is highlighted.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of Melanin-concentrating hormone (MCH) fragments have been synthesized and their biological activities compared with the parent peptide. The substructural units, 5-14 linear and 5-14 cyclic, have been used as models for MCH -  in 1H-nmr conformational studies. Conformational features predicted by molecular dynamics analyses find support in the nmr experiments.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Molecular dynamics simulations have been used to search for the accessible conformations of the melanin-concentrationg hormone (MCH). The studies have been performed on native MCH and two of its peptide fragments, a cyclic MCH(5-14) fragment and a linear MCH(5-14) fragment. An analysis of the molecular dynamics trajectories of the three peptides indicates that two regions of the peptide have characteristic conformational properties that may be important for the biological activity. One is a region around Gly8, which is conformationally mobile, and the other is around Pro13, which shows unusual rigidity. The molecular dynamics simulation results are discussed in terms of backbone structural features like β turns, side-chain interactions, and orientations of the disulfide bridge. The results of this analysis are used to suggest new analogues that will modify the conformational features of the peptide and further define the conformational requirements for activity. Finally, the results are related to nmr studies of the peptide and reveal agreements between the experimental nuclear Overhauser effect constraints and some of the accessible conformations obtained from the simulation.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
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