The molecular and crystal structures of the terminally blocked homo-tri- and homo-pentapeptides from 1-amino-l-cyclopentane-carboxylic acid, Z-(Ac5c)3- OtBu (1) and Z-(Ac5C)5-OtBu (2), were determined by X-ray diffraction. The two compounds exhibit the following parameters: (1) orthorhombic, P212121, a= 11.539(7) Å, b = 16.185(2) Å, c = 30.925(4) Å and Z = 8; (2) triclinic, P1, a = 10.835(5) Å, b = 11.631(9) Å, c = 18.212(5) Å, α = 92.20(7)°, β = 94.79(10)°, γ = 107.6(3)° and Z = 2. The crystal structures were solved by direct methods. The least-squares refinements led to R values of 0.080 and 0.060 for 4061 and 4018 reflections with I ≥2Ã(I) (according to the SHELXL-93 computer program weighting scheme) for (1) and I ≥ 3σ(I) (Structure Determination Programs, SDP crystallographic package weighting scheme) for (2), respectively. The two independent molecules, A and B, in the asymmetric unit of the tripeptide (1) are folded into a type-I/III and a type-I’ β-bend conformation, respectively, each stabilized by an intramolecular C=O. H-N H-bond. The pentapeptide molecules adopt a 310-helical structure, stabilized by three consecutive, intramolecularly H-bonded type-Ill (III') β-bend conformations. © 1996, Walter de Gruyter. All rights reserved.
Molecular and crystal structures of two terminally-blocked Ac(5)c homo-oligopeptides
IACOVINO, Rosa;
1996
Abstract
The molecular and crystal structures of the terminally blocked homo-tri- and homo-pentapeptides from 1-amino-l-cyclopentane-carboxylic acid, Z-(Ac5c)3- OtBu (1) and Z-(Ac5C)5-OtBu (2), were determined by X-ray diffraction. The two compounds exhibit the following parameters: (1) orthorhombic, P212121, a= 11.539(7) Å, b = 16.185(2) Å, c = 30.925(4) Å and Z = 8; (2) triclinic, P1, a = 10.835(5) Å, b = 11.631(9) Å, c = 18.212(5) Å, α = 92.20(7)°, β = 94.79(10)°, γ = 107.6(3)° and Z = 2. The crystal structures were solved by direct methods. The least-squares refinements led to R values of 0.080 and 0.060 for 4061 and 4018 reflections with I ≥2Ã(I) (according to the SHELXL-93 computer program weighting scheme) for (1) and I ≥ 3σ(I) (Structure Determination Programs, SDP crystallographic package weighting scheme) for (2), respectively. The two independent molecules, A and B, in the asymmetric unit of the tripeptide (1) are folded into a type-I/III and a type-I’ β-bend conformation, respectively, each stabilized by an intramolecular C=O. H-N H-bond. The pentapeptide molecules adopt a 310-helical structure, stabilized by three consecutive, intramolecularly H-bonded type-Ill (III') β-bend conformations. © 1996, Walter de Gruyter. All rights reserved.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
