title: Crystal structures of Boc-D- and L-Iva-L-Pro-OBzl: unturned conformation of Aib-Pro sequence unaffected by replacement of Me with Et in Aib.
abstract: The crystal structures of the isovaline (Iva) containing dipeptides, Boc-D-Iva-L-Pro-OBzl and Boc-L-Iva-L-Pro-OBzl, were determined by x-ray diffraction. The diastereomeric peptides were shown to adopt unturned conformations closely similar to each other (phi Iva 52 degrees, psi Iva 46 degrees, phi Pro -65 degrees, and psi Pro 143 degrees for D-Iva-L-Pro sequence and phi Iva 52 degrees, psi Iva 44 degrees, phi Pro -63 degrees, and psi Pro 148 degrees for L-Iva-L-Pro sequence). The Pro ring of each peptide was in C gamma-endo conformation. The unusually large angle CIva-NPro-C delta Pro values (131 degrees in both peptides) were observed, that was due to steric repulsion between the delta-methylene of Pro and the alkyl side chain of Iva residue. These conformations were essentially the same as that of the corresponding alpha-aminoisobutyric acid (Aib)-containing peptide Boc-Aib-L-Pro-OBzl. The result has demonstrated that replacement of either one of the two methyl groups of the Aib residue in Boc-Aib-L-Pro-OBzl with an ethyl group does not cause any significant change in the unturned conformation of the dipeptide.
authors.affiliation: Department of Applied Chemistry, Nagoya Institute of Technology, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Kawai
authors.forename: Y
authors.initials: Y
authors.lastname: Omori
authors.forename: H
authors.initials: H
authors.lastname: Yamamura
authors.forename: Y
authors.initials: Y
authors.lastname: Butsugan
authors.forename: T
authors.initials: T
authors.lastname: Taga
authors.forename: Y
authors.initials: Y
authors.lastname: Miwa
mesh_terms: D000621:Aminoisobutyric Acids / Q000737:chemistry*; D004151:Dipeptides / Q000737:chemistry*; D015394:Molecular Structure; D011392:Proline / Q000737:chemistry; D011487:Protein Conformation; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D014633:Valine / Q000737:chemistry; D014961:X-Ray Diffraction
chemical_list: D000621:Aminoisobutyric Acids; D004151:Dipeptides; C100049:2-aminoisobutyric acid; C032737:isovaline; D011392:Proline; D014633:Valine