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  • 1
    ISSN: 1573-3904
    Keywords: homo-β-Amino acids ; β-Amino acid residue ; X-ray diffraction ; Crystal structure ; Solid-state conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract An N- and C-protected derivative of homo-β-leucine, Fmoc-homo-β-(S)-leucine methyl ester, synthesized from the corresponding proteinogenic parent α-amino acid in enantiopure form has been fully characterized in the solid state by X-ray diffraction analysis. The crystal conformation of this new residue indicates an extended conformation for this homo-β-residue, with the ϕ torsion angle being more constrained than the µ and ψ angles.
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  • 2
    ISSN: 1573-3904
    Keywords: homo-β-Amino acids ; β-Amino acid residue ; X-ray diffraction ; Crystal structure ; Solid-state conformation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Summary An N- and C-protected derivative ofhomo-β-leucine, Fmoc-homo-β-(S)-leucine methyl ester, synthesized from the corresponding proteinogenic parent α-amino acid in enantiopure form has been fully characterized in the solid state by X-ray diffraction analysis. The crystal conformation of this new residue indicates and extended conformation for thishomo-β-residue, with the ϕ torsion angle being more constrained than the μ and ψ angles.
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  • 3
    ISSN: 1075-2617
    Keywords: conformational analysis ; NMR spectroscopy ; X-ray diffraction ; peptide-based taste ligands ; artificial sweeteners ; computer simulations ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: A dipeptide taste ligand L-aspartyl-D-2-aminobutyric acid-(S)-α-ethylbenzylamide was found to be about 2000 times more potent than sucrose. To investigate the molecular basis of its potent sweet taste, we carried out conformational analysis of this molecule and several related analogues by NMR spectroscopy, computer simulations and X-ray crystallographic studies. The results of the studies support our earlier model that an ‘L’-shape molecular array is essential for eliciting sweet taste. In addition, we have identified an aromatic group located between the stem and the base of the ‘L-shape’, which is responsible for enhancement of sweetness potency. In this study, we also assessed the optimal size of the essential hydrophobic group (X) and the effects of the chirality of the second residue toward taste. ©1997 European Peptide Society and John Wiley & Sons, Ltd.
    Additional Material: 11 Ill.
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  • 4
    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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  • 5
    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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  • 6
    ISSN: 1075-2617
    Keywords: Conformational analysis ; peptide-based taste ligands ; artificial sweeteners ; X-ray crystal structures ; Chemistry ; Biochemistry and Biotechnology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The molecular basis of sweet taste was investigated by carrying out the crystal state conformational analysis by X-ray diffraction of the following dipeptide taste igands:N-3,3-dimethylbutyl-aspartyl-phenylalanine methyl ester,I(N-DMB-Asp-Phe-OMe), its sodium salt (N-DMB-Asp-Phe-ONa),II, aspartyl-D-2-aminobutyric acid-(S)-α-ethylbenzylamide,III(Asp-D-Abu-(S)-α-ethylbenzylamide), aspartyl-N′-((2,2,5,5-tetramethylcyclopentanyl)-carbonyl)-(R)-1,1-diamino-ethane,IV(Asp-(R)-gAla-TMCP), and aspartyl-D-valine-(R)-α-methoxymethylbenzyl amide,V(Asp-D-Val-(R)-α-methoxymethylbenzylamide). With the exception of the sodium saltII, all compounds are sweet-tasting, showing in some cases considerable potency enhancement with respect to sucrose. The results of this study confirm the earlier model that an ‘L-shape’ molecular array is essential for eliciting sweet taste for dipeptide-like ligands. In addition, it was established that (i) substitution of the N-terminal group does not inhibit sweet taste, if its zwitterionic character is maintained; (ii) a hydrophobic group located between the stem and the base of the L-shape could be responsible for sweetness potency enhancement, as found inI, IIIandIV; in fact, the extraordinary potency of the N-alkylated analogueIwould support a model with an additional hydrophobic binding domain above the base of the ‘L’; (iii) removal of the methyl ester at the C-terminus of compoundIwith the salt formation gives rise to the tasteless compoundII; (iv) for the first time all possible side-chain conformers (g-,g+andt) for the N-substituted aspartyl residue were observed; and (v) a retro-inverso modification, incorporated at position 2 of the dipeptide chain, confers greater flexibility to the molecule, as demonstrated by the contemporary presence of six conformationally distinct independent molecules in the unit cell and yet sweet taste properties are maintained, as found inIV. © 1998 European Peptide Society and John Wiley & Sons, Ltd.
    Additional Material: 4 Ill.
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  • 7
    ISSN: 1075-2617
    Keywords: β-turn ; 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 pentamer level) from the cycloaliphatic Cα,α,-dialkylated glycine 1-aminocyclononane-1-carboxylic acid (Ac9c) and two Ala/Ac9c tripeptides have been 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 mClAc-Ac9c-OH and Z-Ac9c-OtBu, the dipeptide pBrBz-(Ac9c)2-OtBu, the tetrapeptide Z-(Ac9c)4-OtBu, and the pentapeptide Z-( Ac9c)5-OtBu were determined in the crystal state by X-ray diffraction. Based on this information, the average geometry and the preferred conformation for the cyclononyl moiety of the Ac9c residue have been assessed. The backbone conformational data are strongly in favour of the conclusion that the Ac9c residue is a strong β-turn and helix former. A comparison with the structural propensity 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=3-8) is made and the implications for the use of the Ac9c residue in conformationally constrained analogues of bioactive peptides are briefly examined. © 1997 European Peptide Society and John Wiley & Sons, Ltd.J. Pep. Sci. 3: 367-382No. of Figures: 10. No. of Tables: 6. No. of References: 62
    Additional Material: 10 Ill.
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  • 8
    ISSN: 0006-3525
    Keywords: Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: No abstract.
    Additional Material: 2 Ill.
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  • 9
    ISSN: 0006-3525
    Keywords: Aib peptides ; crystal state structure ; helical peptides ; peptide helices ; x-ray crystallography ; Chemistry ; Polymer and Materials Science
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The crystal-state preferred conformations of six Nα-blocked pentapeptide esters, each containing four helicogenic, achiral α-aminoisobutyric acid (Aib) residues followed by one chiral L-valine (L-Val) or Cα-methyl-L-valine [(αMe)Val] residue at the C-terminus, have been assessed by x-ray diffraction analysis. In all of the compounds the —(Aib)4— sequence is folded in a regular 310-helical conformation. In the four pentapeptides characterized by the L-(αMe)Val residue two conformationally distinct molecules occur in the asymmetric unit. Conversely, only one molecule is observed in the asymmetric unit of two pentapeptides with the C-terminal L-Val residue. In the L-Val based peptides the helical screw sense of the —(Aib)4— sequence is right-handed, whereas in the L—(αMe)Val— analogues both right- and left-handed helical screw senses concomitantly occur in the two crystallographically independent molecules. © 1998 John Wiley & Sons, Inc. Biopoly 46: 433-443, 1998
    Additional Material: 4 Ill.
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