Natural abundant solid state NMR studies in designed tripeptides for differentiation of multiple conformers

Solid state NMR (SSNMR) experiments on heteronuclei in natural abundance are described for three synthetically designed tripeptides Piv‐ L Pro‐ L Pro‐ L Phe‐OMe ( 1 ), Piv‐ D Pro‐ L Pro‐ L Phe‐OMe ( 2 ), and Piv‐ D Pro‐ L Pro‐ L Phe‐NHMe ( 3 ). These peptides exist in different conformation as shown by solution state NMR and single crystal X‐ray analysis (Chatterjee et al., Chem Eur J 2008, 14, 6192). In this study, SSNMR has been used to probe the conformations of these peptides in their powder form. The 13 C spectrum of peptide ( 1 ) showed doubling of resonances corresponding to cis/cis form, unlike in solution where the similar doubling is attributed to cis/trans form. This has been confirmed by the chemical shift differences of C β and C γ carbon of Proline in peptide ( 1 ) both in solution and SSNMR. Peptide ( 2 ) and ( 3 ) provided single set of resonances which represented all trans form across the di‐Proline segment. The results are in agreement with the X‐ray analysis. Solid state 15 N resonances, especially from Proline residues provided additional information, which is normally not observable in solution state NMR. 1 H chemical shifts are also obtained from a two‐dimensional heteronuclear correlation experiment between 1 H 13 C. The results confirm the utility of NMR as a useful tool for identifying different conformers in peptides in the solid state. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 851–860, 2009. This article was originally published online as an accepted preprint. The “Published Online“ date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com