title: Design of peptides: synthesis, crystal structure, molecular conformation, and conformational calculations of N-Boc-L-Phe-Dehydro-Ala-OCH3.
abstract: 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 monoclonic space group P2(1), with a = 9.577(1) A, b = 5.195(3) A, c = 19.563(3) A, beta = 94.67(5) degrees, V = 970.1(6) A3, 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 C2 alpha-C2 beta distance is 1.327(8) A, while the bond angles N2-C2 alpha-C2' and C1'-N2-C2 alpha are 109.8(5) degrees and 127.8(5) degrees, respectively. The backbone adopts a nonspecific conformation with dehydro-Ala in a fully extended conformation with the following torsion angles: theta 1 = 175.2(4) degrees, omega 0 = 170.2(4) degrees, phi 1 = 135.8(5) degrees, psi 1 = -22.6(6) degrees, omega 1 = 168.5(5) degrees, phi 2 = -170.3(5) degrees, psi 2T = -178.6(5) degrees, theta T = 178.4(7) degrees. The rigid planar and trans conformation of dehydro-Ala forces Phe to adopt a strained conformation. The Boc group has a trans-trans conformation.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biophysics, All India Institute of Medical Sciences, New Delhi.
authors.forename: B
authors.initials: B
authors.lastname: Padmanabhan
authors.forename: S
authors.initials: S
authors.lastname: Dey
authors.forename: B
authors.initials: B
authors.lastname: Khandelwal
authors.forename: G S
authors.initials: GS
authors.lastname: Rao
authors.forename: T P
authors.initials: TP
authors.lastname: Singh
mesh_terms: D004151:Dipeptides / Q000138:chemical synthesis / Q000737:chemistry*; D015195:Drug Design; D015394:Molecular Structure; D011487:Protein Conformation; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D004151:Dipeptides; C078070:N-butyloxycarbonylphenylalanyl-dehydroalanyl-methyl ester