ISSN:
0006-3525
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
It is noteworthy that the dehydro-Ala residue adopts an extended conformation that is different than those observed in dehydro-Phe, dehydro-Leu, and dehydro-Abu. The peptide N-Boc-L -Phe-dehydro-Ala-OCH3 (C18H24N2O5) was synthesized by the usual workup procedure and finally by converting N-Boc-L-Phe-L-Ser-OCH3 to N-Boc-L-Phe-dehydro-Ala-OCH3. It was crystallized from its solution in a methanol-water mixture at room temperature. The crystals belong to the monoclinic space group P21 with a = 9.577(1) Å, b = 5.195 (3) Å, c = 19.563 (3) Å, β = 94.67 (5)°, V = 970.1(6) Å3, Z = 2, dm = 1.201(5) Mg m-3, dc = 1.197 (5) Mg m-3. The structure was determined using direct method procedures. It was refined by a full-matrix least-squares procedure to an R value of 0.048 for 1370 observed reflections. The C2α-C2β distance is 1.327 (8) Å, while the bond angles N2-C2α-C2' and C1'-N2-C2α are 109.8 (5)° and 127.8 (5)°, respectively. The backbone adopts a nonspecific conformation with dehydro-Ala in a fully extended conformation with the following torsion angles: θl = 175.2 (4)°, ω, 0 = 170.2 (4)°, ø1 = 135.8 (5)°, ψ 1 = -22.6(6)°, ω1 = 168.5 (5)°, ψ2,= -170.3(5)°, ψ2T = -178.6(5)°', θT = 178.4(7)°. The rigid planar and trans conformation of dehydro-Ala forces Phe to adopt a strained conformation. The Boc group has a trans-trans conformation. The side-chain torsion angles of the Phe residue are χ1 = 63.3(6)°, χ12,1 = -92.1(6)°, χ12,2 = 89.5 (6)°. The observed conformation is stabilized by three nonlinear intramolecular C - H---O type of interactions. The crystal structure is stabilized by an intermolecular hydrogen bond N1 - H1---O2 of distance 2.938(7) Å along the b axis while the van der Waals forces are the stabilizing interactions in the ac plane. The low-energy conformation found by calculations corresponds to the solid state conformation established by the crystal structure analysis. © 1992 John Wiley & Sons, Inc.
Additional Material:
3 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/bip.360321002
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