¹³C nuclear magnetic resonance study of the cis-trans isomerism in X-Pro-Pro tripeptides

Abstract

13C nuclear magnetic resonance has been used to characterize quantitatively the cis-trans isomerism about both peptide bonds in the tripeptides Ser-Pro-Pro and Arg-Pro-Pro. Detailed pH titration data indicate that the configuration about both peptide bonds is closely linked to titration of the terminal carboxyl group and, to a lesser extent, to titration of the terminal amino group. The Pro2 C-3 resonance has been found particularly useful for interpretation due to its sensitivity to the isomerization about both peptide bonds. Analysis of the probabilities of the trans-trans, cic-cis, cis-trans, and trans-cis isomers in aqueous solution indicates a stability decrease in the order given. Similarities in the isomerization behavior of the two peptides indicate that side chain interactions involving the first residue have very little effect on the observed cis/trans ratios. The sensitivity of the cis/trans ratio to titration of the terminal amino group is most readily explained on the basis of an indirect effect on carbonyl-carbonyl repulsion.

Conformational state of a 25-mer peptide from the cyclophilin-binding loop of the HIV type 1 capsid protein

“…The existence of only two out of sixteen theoretically possible isomers (Figure 3) suggests the formation of a structure stabilizing just these two conformers. Multiple proline-containing random coil peptides usually occur as a mixture of all possible cis\trans isomers ( [29][30][31], and U. Reimer and G. Fisher, unpublished work). In addition we found a temperature dependence of the CD spectra in peptide 1 in buffered solution.…”

13C-NMR study of the inhibition of δ-chymotrypsin by a tripeptide-glyoxal inhibitor

“…(Table 1) were observed when there was irreversible breakdown of the glyoxal in the presence or absence of enzyme. These signals had similar titration characteristics to the major signals, and could reflect the formation of diastereoisomers [39] or proline cis-trans isomers [40,41] of the α-hydroxy acid breakdown product.…”

Peptide δ‐Turn: Literature Survey and Recent Progress

“…Experimental NMR spectroscopy data in aqueous solution of small linear peptides partially or fully deprotected at their N/C termini provided some support in favor of the occurrence of the C 8 form stabilized by interactions involving charged species, in which for example the H‐bonding donor is either an ammonium or an amide moiety, and the H‐bonding acceptor is the carboxylate moiety 42–47…”