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  • Electronic Resource  (13)
  • 2000-2004
  • 1980-1984  (13)
  • Chemistry  (13)
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  • Electronic Resource  (13)
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  • 1
    Electronic Resource
    Electronic Resource
    Circular dichroism studies of α-aminoisobutyric acid-containing peptides: Chain length and solvent effects in alternating Aib-L-Ala and Aib-L-Val sequences (1984)
    New York : Wiley-Blackwell
    Biopolymers 23 (1984), S. 877-886 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The CD spectra of the peptides Boc-X-(Aib-X)n-OMe (n = 1, 2, 3) and Boc-(Aib-X)5-OMe, where X = L-Ala or L-Val have been examined in several solvents. The X = Ala and Val peptides behave similarly in all solvents, suggesting that the Aib residues dominate the folding preferences of these peptides. The decapeptides adopt helical conformations in methanol and trifluoroethanol, with characteristic negative CD bands at 222 and 205 nm. In the heptapeptides, similar spectra with reduced intensities are observed. Comparison with nmr studies suggest that estimates of helical content in oligopeptides by CD methods may lead to erroneous conclusions. The pentapeptides yield solvent-dependent spectra indicative of conformational perturbations. Peptide association in dioxane results in an unusual spectrum with a single negative band at 210 nm for the decapeptides. Disaggregation is induced by the addition of methanol or water to dioxane solutions. Aggregation of the heptapeptides is less pronounced in dioxane, suggesting that a critical helix length may be necessary to promote association stabilized by helix dipole-dipole interactions.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360230505
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  • 2
    Electronic Resource
    Electronic Resource
    Temperature dependence of peptide NH chemical shifts in benzene: Delineation of solvent-shielded and exposed amide protons (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 625-628 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Additional Material: 1 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1981.360200313
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  • 3
    Electronic Resource
    Electronic Resource
    X-Pro peptides: Synthesis and solution conformation of benzyloxycarbonyl-(Aib-Pro)4methyl ester. Evidence for a novel helical structure (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1137-1145 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the octapeptide, benzyloxycarbonyl-(α-aminoisobutyryl-L-prolyl)4-methyl ester [Z-(Aib-Pro)4-OMe] and an analysis of its solution conformation is reported. The octapeptide is shown to possess three strong intramolecular hydrogen bonds on the basis of studies of the solvent and temperature dependence of NH chemical shifts and rates of hydrogen-deuterium exchange. 13C studies are consistent with a structure involving only trans Aib-Pro bonds, while ir experiments support a hydrogen-bonded conformation. The Aib 3, 5, and 7 NH groups are shown to participate in hydrogen bonding. A 310 helical conformation compatible with the spectroscopic data is suggested. The proposed conformation consists of three type III β-turns with Aib and Pro at the corners and stabilized by 4 → 1 intramolecular hydrogen bonds.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1981.360200605
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  • 4
    Electronic Resource
    Electronic Resource
    Infrared spectroscopic study of C7 intramolecular hydrogen bonds in peptidesContribution No. 156 from the Solid State and Structural Chemistry Unit. (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 2091-2104 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The ir-spectra in the N—H stretching region of Piv-Pro-NHMe and Boc-Pro-NHMe have been studied in carbon tetrachloride and chloroform solutions over a wide range of concentrations. Based on the concentration dependence of the N—H stretching bands, it has been shown that the characteristic N—H stretching band due to the C7 intramolecular hydrogen bond is around 3335 cm-1. Intermolecular hydrogen bonding also occurs to a small extent in these peptides, giving rise to a slight concentration dependence of the N—H stretching bands. The band around 3335 cm-1 need not necessarily be due to C7 hydrogen bonds alone as proposed by Tsuboi et al. or to intermolecular hydrogen bonding alone as proposed by Maxfield et al.; this conclusion is supported by studies on Boc-Leu-NHMe, which undergoes only intermolecular hydrogen bonding. We have shown that Z-Aib-Aib-OMe and Z-Aib-Ala-OMe form C7 intramolecular hydrogen bonds in addition to C5 intramolecular hydrogen bonds. The present studies also show that all the peptides studied exist in more than one conformation in solution.
    Additional Material: 12 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360220908
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  • 5
    Electronic Resource
    Electronic Resource
    Crystal structures of diketopiperazines containing α-aminoisobutyric acid: Cyclo(Aib-Aib) and cyclo(Aib-L-Ile) (1982)
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 1847-1855 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal and molecular structures of two α-aminoisobutyric acid (Aib)-containing diketopiperazines, cyclo(Aib-Aib) 1 and cyclo(Aib-L-Ile) 2, are reported. Cyclo(Aib-Aib) crystallizes in the space group P1 with a = 5.649(3), b = 5.865(2), c = 8.363(1), α = 69.89(6), β = 113.04(8), γ = 116.0(3), and Z = 1, while 2 occurs in the space group P212121 with a = 6.177(1), b = 10.791(1), c = 16.676(1), and Z = 4. The structures of 1 and 2 have been refined to final R factors of 0.085 and 0.086, respectively. In both structures the diketopiperazine ring shows small but significant deviation from planarity. A very flat chair conformation is adopted by 1, in which the Cα atoms are displaced by 0.07 Å on each side of the mean plane, passing through the other four atoms of the ring. Cyclo(Aib-Ile) favors a slight boat conformation, with Aib Cα and Ile Cα atoms displaced by 0.11 and 0.05 Å on the same side of the mean plane formed by the other ring atoms. Structural features in these two molecules are compared with other related diketopiperazines.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360210912
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  • 6
    Electronic Resource
    Electronic Resource
    Molecular structure of t-butyloxycarbonyl-Leu-Aib-Pro-Val-Aib-methyl ester, a fragment of alamethicin and suzukacillin: A 310-helical pentapeptide (1982)
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 2461-2472 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The pentapeptide Boc-Leu-Aib-Pro-Val-Aib-OMe, a fragment of alamethicin and suzukacillin, crystallizes in the space group P21, with a = 11.034 (2), b = 10.894 (2), c = 15.483 (2) Å, β = 104.80 (2)° and Z = 2. The crystal structure has been solved by direct methods and refined to an R value of 0.069. The peptide backbone folds into a right-handed 310-helical conformation, stabilized by two intramolecular 4 → 1 hydrogen bonds between the Leu(1) CO and Val(4) NH and Aib(2) CO and Aib(5) NH groups. The solid-state conformation is consistent with results of spectroscopic analysis in solution.
    Additional Material: 4 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360211210
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  • 7
    Electronic Resource
    Electronic Resource
    Stereochemistry of α-aminoisobutyric acid peptides in solution: Helical conformations of protected decapeptides with repeating Aib-L-Ala and Aib-L-Val sequences (1983)
    New York : Wiley-Blackwell
    Biopolymers 22 (1983), S. 2133-2140 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The decapeptides Boc-(Aib-L-Ala)5-OMe and Boc-(Aib-L-Val)5-OMe have been studied by 270-MHz 1H-nmr in CDCl3 and (CD3)2SO solutions. Intramolecular hydrogen-bonded NH groups have been delineated using the temperature and solvent dependence of the NH chemical shifts and differential broadening of the NH resonances, induced by addition of a nitroxide radical. Both peptides have eight solvent-shielded NH groups, suggesting that 310-helical conformations are maintained in the two solvents. In alternating Aib-X sequences, the Aib residues appear to play a dominant role in determining the preferred conformations, overriding the intrinsic stereochemical preferences of the X residues.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360220911
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  • 8
    Electronic Resource
    Electronic Resource
    X-Pro peptides: Solution and solid-state conformation of benzyloxycarbonyl-(Aib-Pro)2methyl ester, a type I β-turn (1981)
    New York : Wiley-Blackwell
    Biopolymers 20 (1981), S. 1123-1136 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The synthesis of the tetrapeptide benzyloxycarbonyl(α-aminoisobutyryl-L-prolyl)2-methyl ester (Z-(Aib-Pro)2-OMe) and an analysis of its conformation in solution and the solid state are reported. Stepwise synthesis using dicyclohexylcarbodiimide leads to racemization at Pro(2). Evidence for the presence of diastereomeric tetrapeptides is obtained from 270-MHz1H-nmr and 67.89-MHz 13C-nmr. The all-L tetrapeptide is obtained by fractional crystallization from ethyl acetate. The NH of Aib(3) is shown to be involved in an intramo-lecular hydrogen bond by variable-temperature 1H-nmr and the solvent dependence of NH chemical shifts. The results are consistent with a β-turn conformation with Aib(1) and Pro(2) at the corners stabilized by a 4 → 1 hydrogen bond. The molecule crystallizes in the space group P212121, with a = 8.839, b = 14.938, and c = 22.015 Å. The structure has been refined to an R value of 0.051. The peptide backbone is all-trans, and a 4 → 1 hydrogen bond, between the CO group of the urethane moiety and Aib(3) NH, is observed. Aib(1) and Pro(2) occupy the corner positions of a type I β-turn with φ = -55.4°, Ψ = -31.3° for Aib(1) and φ = -71.6°, Ψ = -38° for Pro(2). The tertiary amide unit linking Pro(2) and Aib(3) is significantly distorted from planarity (Δω = 14.3°).
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.1981.360200604
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  • 9
    Electronic Resource
    Electronic Resource
    Type II β-turn conformation of pivaloyl-L-prolyl-α-aminoisobutyryl-N-methylamide: Theoretical, spectroscopic, and X-ray studies (1982)
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 1261-1273 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Pivaloyl-L-Pro-Aib-N-methylamide has been shown to possess one intramolecular hydrogen bond in (CD3)2SO solution, by 1H-nmr methods, suggesting the existence of β-turns, with Pro-Aib as the corner residues. Theoretical conformational analysis suggests that Type II β-turn conformations are about 2 kcal mol-1 more stable than Type III structures. A crystallographic study has established the Type II β-turn in the solid state. The molecule crystallizes in the space group P21 with a = 5.865 Å, b = 11.421 Å, c = 12.966 Å, β = 97.55°, and Z = 2. The structure has been refined to a final R value of 0.061. The Type II β-turn conformation is stabilized by an intramolecular 4 → 1 hydrogen bond between the methylamide NH and the pivaloyl CO group. The conformational angles are φPro = -57.8°, ψPro = 139.3°, φAib = 61.4°, and ψAib = 25.1°. The Type II β-turn conformation for Pro-Aib in this peptide is compared with the Type III structures observed for the same segment in larger peptides.
    Additional Material: 5 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360210702
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  • 10
    Electronic Resource
    Electronic Resource
    Aggregation of apolar peptides in organic solvents. Concentration dependence of 1H-nmr parameters for peptide NH groups in 310 helical decapeptide fragment of suzukacillin (1982)
    New York : Wiley-Blackwell
    Biopolymers 21 (1982), S. 1427-1433 
    Details
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Peptide NH chemical shifts and their temperature dependences have been monitored as a function of concentration for the decapeptide, Boc-Aib-Pro-Val-Aib-Val-Ala-Aib-Ala-Aib-Aib-OMe in CDCl3 (0.001-0.06M) and (CD3)2SO (0.001-0.03M). The chemical shifts and temperature coefficients for all nine NH groups show no significant concentration dependence in (CD3)2SO. Seven NH groups yield low values of temperature coefficients over the entire range, while one yields an intermediate value. In CDCl3, the Aib(1) NH group shows a large concentration dependence of both chemical shift and temperature coefficient, in contrast to the other eight NH groups. The data suggest that in (CD3)2SO, the peptide adopts a 310 helical conformation and is monomeric over the entire concentration range. In CDCl3, the 310 helical peptide associates at a concentration of 0.01M, with the Aib(1) NH involved in an intermolecular hydrogen bond. Association does not disrupt the intramolecular hydrogen-bonding pattern in the decapeptide.
    Additional Material: 2 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/bip.360210711
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