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Vibrational CD studies of the solution conformation of N ‐urethanyl‐ L ‐amino acid derivatives
Author(s) -
Chernovitz Anita C.,
Freedman Teresa B.,
Nafie Laurence A.
Publication year - 1987
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.360261105
Subject(s) - chemistry , vibrational circular dichroism , molecule , stereochemistry , ring (chemistry) , circular dichroism , chloroform , hydrogen bond , amino acid , alanine , phenylalanine , crystallography , organic chemistry , biochemistry
The solution conformations of several N ‐urethanyl‐ L ‐amino acids in 0.2–0.002 M chloroform and 0.2 M dimethylsulfoxide have been investigated by using vibrational circular dichroism (VCD), ir absorption, and 13 C‐nmr spectroscopies. Both the N ‐carbobenzoxy (N‐CBZ) and N ‐ t ‐butoxycarbonyl derivatives of L ‐alanine, L ‐proline, L ‐valine, and L ‐phenylalanine, and N‐CBZ‐serine were studied. The 13 C‐nmr results indicate that the molecules occur predominantly as the cis isomer about the CN peptide bond at room temperature. The interpretation of the strong VCD couplet in the carbonyl‐stretching region using the degenerate coupled oscillator model is consistent with the conformational range of ϕ = −60° to −90° and ψ = 30° to 90° for molecules forming acid dimers. Conformations with an intramolecularly hydrogen‐bonded C 7 ring are also present, which give rise to biased VCD features in the NH‐, CH‐, and CO‐stretching regions that can arise due to vibrationally generated ring currents.