Proton NMR of the protected tetrapeptides TFA-Gly-Gly- l- X- l-Ala-OCH 3, where X stands for One of the 20 common amino acids

Abstract

The 1H NMR parameters for the 20 common amino acid residues have been measured in the protected linear peptides TFA-Gly(1)-Gly(2)- l- X(3)- l-Ala(4)OCH 3 in d 6-DSMO solution. In view of their potential use as “random coil” NMR parameters for studies of peptide conformations in DSMO solutions, these data were further qualified by investigations of the molecular conformations of the tetrapeptides. 1H, 13C, and 19F NMR were all consistent with a predominantly extended flexible random coil form of the peptide backbone. Correspondingly, the amino acid sequence effects are small, i.e., the NMR parameters of Gly(1), Gly(2), and Ala(4) were found to be only little affected by the difference in residue X(3). On the other hand there is evidence for a nonrandom spatial orientation of bulky side chains of X in these peptides.