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. Author manuscript; available in PMC: 2014 Oct 27.
Published in final edited form as: J Am Chem Soc. 2013 Mar 11;135(11):4333–4363. doi: 10.1021/ja3109664

Figure 7.

Figure 7

Representative 1H NMR spectra (5 mM phosphate (pH 4 unless an ionizable proton is present), 25 mM NaCl, 90% H2O/10% D2O) of Ac-TYP(4-substituted)N-NH2 peptides with 4-substituted prolines, with species with trans and cis amide bonds and Ktrans/cis indicated. The largest differences between 4R- versus 4S-substituted peptides are observed in Ktrans/cis, the δ of Tyrcis and Asntrans, and the 3JαN of Tyrcis. These effects are modulated as a function of the nature of the substituent with the 4R or 4S series. (a) Stereoelectronic effects of 4-substituents. (b) Disubstituted prolines. The NMR spectrum of 4-oxo-proline also includes the hydrate, which is in equilibrium with the ketone (Khydrate/ketone = 0.15).67b (c) Steric effects of 4-substituted prolines and the interplay of steric versus stereoelectronic effects in chalcogen-substituted prolines. (d) Steric effects versus stereoelectronic effects as a result of sulfur oxidation. NMR spectra for all peptides are in the Supporting Information (part 1: amide regions of the NMR spectra for all peptides; part 3: full NMR spectra for all peptides).