Analysis of Carbon-13 Nuclear Magnetic Resonance of Some Enriched Amino Acids and Related Peptides

摘要

In view of the importance of exp 13 C magnetic resonance in the study of the configurations and chemical properties of peptides and proteins in solution, isotopically enriched amino acids and peptides have been studied. The main characteristics of the nuclear magnetic resonance (NMR) spectra are presented. The enriched amino acids were obtained by biosynthesis and therefore were uniformly enriched (80%). Some also were labeled with exp 15 N. The following were studied in particular: L-serine, L-threonine, L-aspartic acid, L-glutamic acid, cyclo (L-thr-L-thr),cyclo (L-thr-L-his) and cyclo (D-thr-L-his)dissolved in D sub 2 O. Fourier transform spectroscopy was used, so that good spectral resolutions were obtained within a reasonable time. However, multiple couplings and nuclear isomers lead to complex and strongly coupled spectra, which were interpreted with the help of the ITR CAL Program. The values of the enrichment rates, chemical shifts, coupling constants, and isotopic shifts are given. The isotopic shifts of the exp 13 C signal for adjacent substitution are on the average +0.25 ppM for exp 1 H implies exp 2 H, + 0.010 ppM for exp 12 C implies exp 13 C and + 0.020 ppM for exp 14 N implies exp 15 N; on the other hand, there is no shift of the C' nucleus signal for the substitution exp 12 C implies exp 13 C. From exp 13 C - exp 13 C couplings one can derive information about the charge distribution. In the case of cyclo (L-thr-L-his), the vicinal coupling constants appear to indicate a preferential configuration in solution. On the basis of these results it will be possible to make a thorough study of natural amino acids and their derivatives. The methods developed in this work will be used in studying peptides of biological interest and selectively enriched proteins. (ERA citation 05:009292)