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  • General Chemistry  (3)
  • molecular dynamics  (2)
  • β-bend  (2)
  • CD spectroscopy  (1)
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  • 1
    Electronic Resource
    Electronic Resource
    Solid State and Solution Conformation of 6-[4-[N-tert-ButoxycarbonylN-(N′-ethyl)propanamide]imidazolyl]-6-deoxycyclomaltoheptaose: Evidence of Self-Inclusion of the Boc Group within the β-Cyclodextrin Cavity (2000)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 2000 (2000), S. 1065-1076 
    Details
    ISSN: 1434-193X
    Keywords: Cyclodextrins ; Inclusion compounds ; Carcinine ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: ---A new modified β-cyclodextrin (β-CD) derivative 1 that was functionalized in position 6 with Boc-Carcinine was synthesised and its crystal structure was determined. The structure reveals a “sleeping swan”-like shape, the covalently bonded Boc-Carcinine moiety forming a folded structure with the Boc group inserted within the hydrophobic cavity of the β-cyclodextrin. The conformation of the Carcinine moiety is determined by the inclusion of the Boc group and is further stabilised by three intramolecular hydrogen bonds, two between the amide N1-H group, the carbonyl C′1=O1 group and a primary hydroxylic group of the glucose unit 5, one between the carbonyl C′0=O0 group and the primary hydroxylic group of the glucose unit 2. The β-CD macrocycle differs only slightly from unmodified β-CDs, maintaining an approximate sevenfold symmetry. The solution structure of the new β-CD derivative was investigated by NMR spectroscopy and circular dichroism (c.d.) spectroscopy. In addition to a complete (1H and 13C) assignment of the pendant Boc-Carcinine group, the NMR study allowed the assignment of all the proton resonances associated with the β-CD macrocycle. Furthermore, NMR and c.d. results indicated that the self-inclusion of the Boc group within the β-CD cavity is retained in aqueous solution. In order to estimate the strength of this self-inclusion complex a series of competition experiments with the external guest 1-adamantanol was carried out using c.d. spectroscopy.
    Additional Material: 9 Ill.
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  • 2
    Electronic Resource
    Electronic Resource
    Solution conformational preferences of a peptidic analogue of a natural macrolide (1997)
    New York : Wiley-Blackwell
    Biopolymers 42 (1997), S. 349-361 
    Details
    ISSN: 0006-3525
    Keywords: cyclic peptides ; molecular dynamics ; nmr ; conformation ; FK506 ; FK506 binding proteins ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The conformational behavior in solution of a cyclic peptide with sequence cyclo-(Pro1-Pro2-Dab3 (cHexA)ψ[N7HCO]-Leu4ψ[NHCO]-Suc5-Gly6-) has been throughly investigated with the combined use of nmr and molecular dynamic techniques. The compound, which has been modeled to mimic the FK506 macrolide bound to the FK506 binding protein structure, can be considered as a peptidic analogue of the FK506 system.The synthesis was carried out on a phenylacetoamidomethyl resin using an appropriate protocol for the peptide chain elongation. The conformational properties of the cyclic hexapeptide were studied in DMSO and water. The nmr data in DMSO and restrained molecular dynamics simulations show the presence of two contiguous cis peptide bonds involving the -Gly-Pro-Pro- segment. This segment in water exhibits conformational heterogeneity presenting at least two distinct conformational families, characterized the first by cis-cis and the second by a trans-cis Gly-Pro-Pro configuration; the trans-cis isomer was fully characterized. © 1997 John Wiley & Sons, Inc. Biopoly 42: 349-361, 1997
    Additional Material: 6 Ill.
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  • 3
    Electronic Resource
    Electronic Resource
    Conformational behaviour of Cα,α-diphenylglycine: folded vs. extended structures in DφG-containing tripeptides (1998)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 4 (1998), S. 21-32 
    Details
    ISSN: 1075-2617
    Keywords: Cα,α-disubstituted amino acids ; crystal structure ; molecular dynamics ; conformation ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal structures of three fully protected tripeptides containing the Dφg residue (Cα,α-diphenylglycine) in the central position are reported, namely Z-Gly-Dφg-Gly-OMe (a), Z-Gly-Dφg-Aib-OMe (b) and Z-Aib-Dφg-Aib-OMe (c). The molecular conformations are quite unusual because the Dφg residue adopts a folded conformation in the 310-helical region when the following residue adopts a folded conformation of opposite handedness (peptidesbandc). In contrast, the Dφg residue adopts the more frequently observed fully extended conformation when the following residue adopts a semi-extended conformation (peptidea). These findings are in agreement with the theoretical calculations on Ac-Dφg-Aib-NHCH3 and Ac-Aib-Dφg-NHCH3 also reported in this work. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
    Additional Material: 9 Ill.
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  • 4
    Electronic Resource
    Electronic Resource
    Conformational Analysis by NMR and Distance-Geometry Techniques of Deltorphin Analogs (1998)
    Weinheim : Wiley-Blackwell
    Liebigs Annalen 1998 (1998), S. 2279-2287 
    Details
    ISSN: 1434-193X
    Keywords: Receptor selectivity ; Agonist activity ; Distance geometry ; Conformation ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: To identify the peptide conformation that is preferentially recognized by the receptor, we have synthetized by solid-phase method a series of deltorphin I analogs with increasing selectivity for δ- and μ-opioid receptor. Structure-selectivity relationship of these peptides were evaluated on the basis of receptor-binding properties and conformational features, computed by two-dimensional NMR spectra and distance-geometry techniques. These compounds in solution are present with a large number of conformers with no defined secondary structural elements. The analysis of the average properties of these compounds indicate the presence of some distinct conformational preferences that can be related to the observed opioid receptor selectivities. Selectivity for the δ- and μ-opioid receptors can be ascribed to the spatial arrangement of the aromatic moieties. In addition, substitutions in position 2 and 4 are important for the correct arrangement and must be taken into account in the design of δ-opioid receptor-selective ligands.
    Additional Material: 6 Ill.
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  • 5
    Electronic Resource
    Electronic Resource
    A Modified Cyclodextrin with a Fully Encapsulated Dansyl Group: Self-Inclusion in the Solid State and in Solution (1996)
    Weinheim : Wiley-Blackwell
    Chemistry - A European Journal 2 (1996), S. 373-381 
    Details
    ISSN: 0947-6539
    Keywords: crystal structure ; cyclodextrins ; dansyl derivatives ; fluorescent sensors ; self-inclusion ; Chemistry ; General Chemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A monofunctionalized β-cyclodextrin containing a dansyl moiety, 6- deoxy- 6 - N - ( N′- (5- dimethylamino - 1 - naphthalenesulfonyl)diaminoethane) - β-cyclodextrin (CD-en-DNS, 2), was synthesized and its crystal structure determined. It was shown that the dansyl group is fully encapsulated within the cyclodextrin cavity, with the dimethylamino and sulfonyl groups emerging from opposite sides. The shape of the cavity is considerably flattened, since O(4)-O(4) distances parallel to the naphtalene ring were found to be longer than the others. The conformation of the diaminoethane linker was found to be determined by the inclusion of the dansyl group and by a hydrogen bond between the sulfonamide NH and one of the O(6)-H groups on the cyclodextrin rim. The self-inclusion features of the aromatic moiety were found to be consistent with the solution data: 1H NMR ROESY spectra suggested that the orientation of the dansyl moiety observed in the solid state was retained in aqueous solution; the circular dichroism spectrum was consistent with an axial complexation model. Fluorescence spectra showed that the inclusion of the dansyl group in the cyclodextrin cavity considerably increases the quantum yield: time-resolved fluorescence experiments showed the presence of a long-lifetime component (16.1 ns), which was attributed to the included fluorophore. The ability of 2 to act as a fluorescence sensor was evaluated by the addition of several guests of different shape: fluorescence intensity was lowered, especially upon addition of adamantanecarboxylic acid. All the data obtained were consistent with the model of the in-out movement of the dansyl group from the self-included conformation observed in the solid state to a position more exposed to the bulk solvent. Copper(II) was shown to enhance the difference in the fluorescence of 2 in the presence of guests by additional static quenching.
    Additional Material: 7 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/chem.19960020404
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  • 6
    Electronic Resource
    Electronic Resource
    Inversion of 310-helix screw sense in a (D-αMe)Leu homotetrapeptide induced by a guest D-(αMe)val residue (1995)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 1 (1995), S. 396-402 
    Details
    ISSN: 1075-2617
    Keywords: (αMe) amino acids ; CD spectroscopy ; 310-helix ; peptide 3D-structure ; X-ray structure ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The terminally blocked tetrapeptide pBrBz-[D-(αMe)Leu]2-D-(αMe)Val-D-(αMe)Leu-OtBu is folded in the crystal state in a left-handed 310-helical structure stabilized by two consecutive 1 ← 4 C=O⃛H—N intramolecular H-bonds, as determined by X-ray diffraction analysis. A CD study strongly supports the view that this conformation is also that largely prevailing in MeOH solution. A comparison with the published conformation of pBrBz-[D-(αMe)Leu]4-OtBu indicates that incorporation of a single internal β-branched (αMe)Val guest residue into the host homo-tetrapeptide from the γ-branched (αMe)Leu residue is responsible for a dramatic structural perturbation, i.e. an inversion of the 310 screw sense from right to left-handed.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/psc.310010607
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  • 7
    Electronic Resource
    Electronic Resource
    Preferred conformation of peptides rich in Ac8c, a medium-ring alicyclic Cα,α-disubstituted glycine (1996)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 2 (1996), S. 14-27 
    Details
    ISSN: 1075-2617
    Keywords: β-bend ; cyclic amino acid ; 310-helix ; peptide conformation ; X-ray diffraction ; Chemistry ; Biochemistry
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A complete series of terminally blocked, monodispersed homo-oligopeptides (to the pentamer level) from the sterically demanding, medium-ring alicyclic Cα,α-disubstituted glycine 1-aminocyclooctane-1-carb oxylic acid (Ac8c), and two Ala/Ac8c tripeptides, were synthesized by solution methods and fully characterized. The preferred conformation of all the oligopeptides was determined in deuterochloroform solution by IR absorption and 1H-NMR. The molecular structures of the amino acid derivative Z-Ac8c-OH, the dipeptide pBrBz- (Ac8c)2-OH and the tripeptide pBrBz-(Ac8c)3-OtBu were assessed in the crystal state by X-ray diffraction. Conformational energy computations were performed on the monopeptide Ac-Ac8c-NHMe. Taken together, the results obtained strongly support the view that the Ac8c residue is an effective β-turn and helix former. A comparison is also made with the conformational preferences of α-aminoisobutyric acid, the prototype of Cα, α-disubstituted glycines, and of the other members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n=3, 5-7) investigated so far. The implications for the use of the Ac8c residue in peptide conformational design are considered.
    Additional Material: 8 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/psc.43
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  • 8
    Electronic Resource
    Electronic Resource
    Conformational Characterization of the 1-Aminocyclobutane-1-carboxylic Acid Residue in Model Peptides (1997)
    New York, NY [u.a.] : Wiley-Blackwell
    Journal of Peptide Science 3 (1997), S. 110-122 
    Details
    ISSN: 1075-2617
    Keywords: β-bend ; cyclic amino acid ; 310-helix ; peptide conformation ; X-ray diffraction ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A series of N- and C-protected, monodispersed homo-oligopeptides (to the dodecamer level) from the small-ring alicyclic Cα,α-dialkylated glycine 1-aminocyclobutane-1-carboxylic acid (Ac4c) and two Ala/Ac4c tripeptides were synthesized by solution methods and fully characterized. The conformational preferences of all the model peptides were determined in deuterochloroform solution by FT-IR absorption and 1H-NMR. The molecular structures of the amino acid derivatives Z-Ac4c-OH and Z2-Ac4c-OH, the tripeptides Z-(Ac4c)3-OtBu, Z-Ac4c-(L-Ala)2-OMe and Z-L-Ala-Ac4c-L-Ala-OMe, and the tetrapeptide Z-(Ac4c)4-OtBu were determined in the crystal state by X-ray diffraction. The average geometry of the cyclobutyl moiety of the Ac4c residue was assessed and the τ(N-Cα-C′) bond angle was found to be significantly expanded from the regular tetrahedral value. The conformational data are strongly in favour of the conclusion that the Ac4c residue is an effective β-turn and helix former. A comparison with the structural propensities of α-aminoisobutyric acid, the prototype of Cα,α-dialkylated glycines, and the other extensively investigated members of the family of 1-aminocycloalkane-1-carboxylic acids (Acnc, with n=3, 5-8) is made and the implications for the use of the Ac4c residue in conformationally constrained peptide analogues are briefly examined. © 1997 European Peptide Society and John Wiley & Sons, Ltd
    Additional Material: 8 Ill.
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