¹H And ¹³C NMR chemical shifts of the diastereotopic methyl groups of valyl and leucyl residues in peptides and proteins

Stereospecific ^1H and ¹³C NMR assignments for the diastereo-topic methyl groups of the valyl and leucyl residues in a cyclic peptide and in two globular proteins were obtained using biosynthetically direc-ted fractional isotope labeling with ¹³C. The methyl chemical shifts are analyzed with respect to possible correlations with the stereochemistry of these amino acid side chains.