Toward direct determination of conformations of protein building units from multidimensional NMR experiments. V. NMR chemical shielding analysis of N‐formyl‐serinamide, a model for polar side‐chain containing peptides

Knowledge of chemical shift–structure relationships could greatly facilitate the NMR chemical shift assignment and structure refinement processes that occur during peptide/protein structure determination via NMR spectroscopy. To determine whether such correlations exist for polar side chain containing amino acid residues the serine dipeptide model, For‐ L ‐Ser‐NH 2 , was studied. Using the GIAO‐RHF/6‐31+G(d) and GIAO‐RHF/TZ2P levels of theory the NMR chemical shifts of all hydrogen ( 1 H N , 1 H α , 1 H β1 , 1 H β2 ), carbon ( 13 C α , 13 C β , 13 C′) and nitrogen ( 15 N) atoms have been computed for all 44 stable conformers of For‐ L ‐Ser‐NH 2 . An attempt was made to establish correlation between chemical shift of each nucleus and the major conformational variables (ω 0 , ϕ, ψ, ω 1 , χ, 1 and χ 2 ). At both levels of theory a linear correlation can be observed between 1 H α /ϕ, 13 C α /ϕ, and 13 C α /ψ. These results indicate that the backbone and side‐chain structures of For‐ L ‐Ser‐NH 2 have a strong influence on its chemical shifts. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1157–1171, 2003