RESUMO
The similar conformations and interaction modes of Ac-DL-Leu-NMe2 and Ac-delta-Leu-NMe2 molecules in the solid state allow the comparison of their geometrical parameters. The most evident variations are essentially restricted to the alpha, beta-unsaturated side-chain which adopts the Z-disposition. The dimensions of the peptide backbone are much less sensitive to alpha, beta-unsaturation, with a small shortening by 0.04 A and 0.02 A of the N--C alpha and C alpha--C' bonds, respectively, and an increase by 6 degrees of the N--C alpha--C' bond angle. The ethylenic and amide groups in the delta-Leu derivative are far from coplanarity, and a significant electronic conjugation of the pi-orbital is likely to be rejected.
Assuntos
Leucina/análogos & derivados , Peptídeos/química , Cristalização , Ligação de Hidrogênio , Leucina/síntese química , Leucina/química , Estrutura Molecular , Conformação Proteica , Difração de Raios XRESUMO
N-(tert-Butylcarbonylglycylaminoethyl)-N-(ethyl)ammonium tetraphenylborate, C11H24N3O+2.C24H20B-, Mr = 549.57, triclinic, P-1, a = 11.567 (2), b = 11.922 (2), c = 14.484 (3) A, alpha = 70.99 (2), beta = 74.83 (2), gamma = 59.33 (1) degrees, V = 1613.1 A3, Z = 2, D chi = 1.13 g cm-3, lambda(Cu K alpha) = 1.5418 A, mu = 4.69 cm-1, mu Rmax much less than 1, F(000) = 592, T = 293 K, R = 0.058 for 3491 observed reflections. This pseudopeptide is folded by a short N(+)-H ... O = C hydrogen bond (N3 ... O1 = 2.81 A) which closes a ten-membered ring. This results in a beta-turn structure that can be classified as type II on the basis of the conformational angles for the N-terminal glycine. The conformational angles phi 1, psi 1, phi 2 and psi 2 are -53.4 (6), 139.7 (4), 91.5 (5) and -62.6 (6) degrees respectively.
Assuntos
Dipeptídeos/química , Peptídeos/química , Tetrafenilborato/análogos & derivados , Sequência de Aminoácidos , Cristalização , Modelos Químicos , Conformação Molecular , Dados de Sequência Molecular , Tetrafenilborato/química , Difração de Raios XRESUMO
N-Isobutylidenedipivalamide, C14H28N2O2, Mr = 256.39, orthorhombic, P2(1)2(1)2(1), a = 16.656 (2), b = 9.751 (2), c = 10.583 (2) A, V = 1718.8 A3, Z = 4, D chi = 0.99 g cm-3, lambda(Cu K alpha) = 1.5418 A, mu = 4.56 cm-1, mu Rmax much less than 1, F(000) = 568, T = 293 K, R = 0.081 for 887 observed reflections. The geometrical parameters of this retro-peptide molecule are quite similar to the standard values for peptides. Conformational angles are phi = -101 (1), phi' = 99 (1) degrees.
Assuntos
Dipeptídeos/química , Peptídeos/química , Sequência de Aminoácidos , Cristalização , Modelos Químicos , Conformação Molecular , Dados de Sequência Molecular , Difração de Raios XRESUMO
N,N'-Methylenediacetamide, C5H10N2O2, Mr = 130.15, orthorhombic, Pna2(1), a = 17.218 (1), b = 4.489 (1), c = 18.124 (1) A, V = 1400.8 A3, Z = 8, D chi = 1.23 g cm-3, lambda(Cu K alpha) = 1.5418 A, mu Rmax much less than 1, mu = 7.19 cm-1, F(000) = 560, T = 293 K, R = 0.044 for 1318 observed reflections. This retro-peptide molecule assumes two nearly identical conformational states (A phi = 93.2, phi' = 77.0; B phi = 90.6, phi' = 79.6 degrees) with planar trans amide functions. The bond lengths and bond angles are very close to the standard dimensions of the peptide group.
Assuntos
Acetamidas/química , Glicina/análogos & derivados , Peptídeos/química , Sequência de Aminoácidos , Cristalização , Glicina/química , Modelos Químicos , Conformação Molecular , Dados de Sequência Molecular , Difração de Raios XRESUMO
N,N'-Dimethylisopropylmalonamide, C8H16N2O2, Mr = 172.23, orthorhombic, Pbcm, a = 4.859 (1), b = 13.523 (2), c = 15,469 (2) A, V = 1016.4 A3, Z = 4, Dx = 1.12 g cm-3, lambda(Cu K alpha) = 1.5418 A, microRmax much less than 1, mu = 5.88 cm-1, F(000) = 376, T = 293 K, R = 0.060 for 665 observed reflections. Dimensions of this retropeptide molecule are quite similar to the standard values for peptides. The C alpha and C beta atoms are in a mirror (z = 1/4), so conformational angles are psi' = -psi = -110.4 degrees (2).
Assuntos
Malonatos/química , Peptídeos/química , Valina/análogos & derivados , Sequência de Aminoácidos , Cristalização , Modelos Químicos , Conformação Molecular , Dados de Sequência Molecular , Valina/química , Difração de Raios XRESUMO
The three retro-analogs of the tBuCO-Ala-Gly-NHiPr dipeptide, in which each amide bond had been successively reversed, were studied in solution by 1H-n.m.r. and i.r. spectroscopy with reference to the conformational properties of their parent dipeptide. Reversal of the Ala-Gly amide bond proved to perturb the folding tendency of the backbone less than the inversion of either of the terminal amide bonds. The crystal structure of the retro-peptide containing a reversed Ala-Gly amide bond was also solved by X-ray diffraction and constitutes the first available data for this retro-peptide series. In contrast to the beta II-folded structure of the parent dipeptide, the retro-peptide molecule adopts an open conformation in the crystal.
