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Crystal structures of Boc‐ D ‐ and L ‐Iva‐ L ‐Pro‐OB Z l: Unturned conformation of Aib‐Pro sequence unaffected by replacement of Me with Et in Aib
Author(s) -
Kawai Masao,
Omori Yoshimasa,
Yamamura Hatsuo,
Butsugan Yasuo,
Taga Tooru,
Miwa Yoshihisa
Publication year - 1993
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.360330807
Subject(s) - chemistry , stereochemistry , steric effects , residue (chemistry) , peptide , dipeptide , alkyl , crystal structure , methylene , side chain , diastereomer , crystallography , medicinal chemistry , biochemistry , organic chemistry , polymer
The crystal structures of the isovaline (Iva) containing dipeptides, Boc‐ D ‐Iva‐ L ‐Pro‐OB z l and Boc‐ L ‐Iva‐ L ‐Pro‐OB z l, were determined by x‐ray diffraction. The diastereomeric peptides were shown to adopt unturned conformations closely similar to each other (ϕ Iva 52°, ψ Iva 46°, ϕ Pro –65°, and ψ Pro 143° for D ‐Iva‐ L ‐Pro sequence and ϕ Iva 52°, ψIva 44°, ϕ Pro −63°, and ψ pro 148° for L ‐Iva‐ L ‐Pro sequence). The Pro ring of each peptide was in C γ ‐ endo conformation. The unusually large ∠C Iva ‐N Pro ‐C δ Provalues (131° in both peptides) were observed, that was due to steric repulsion between the δ‐methylene of Pro and the alkyl side chain of Iva residue. These conformations were essentially the same as that of the corresponding α‐aminoisobutyric acid (Aib)‐containing peptide Boc‐Aib‐ L ‐Pro‐OB z l. The result has demonstrated that replacement of either one of the two methyl groups of the Aib residue in Boc‐Aib‐ L ‐Pro‐OB z l with an ethyl group does not cause any significant change in the unturned conformation of the dipeptide. © 1993 John Wiley & Sons, Inc.