Effects of Glycosylation of (2S,4R)-4-Hydroxyproline on the Conformation, Kinetics, and Thermodynamics of Prolyl Amide Isomerization

conformational implications of Hyp-glycosylation on peptide backbone conformation. Hyp and proline (Pro) are unique among the proteinogenic amino acids since they are characterized by limited rotation of the o dihedral angle (Figure 1) as their side chain is fused to the peptide backbone. As a consequence, there is a reduction in the energy difference between the prolyl amide cis and trans isomers, making them nearly isoenergetic; this leads to higher cis N-terminal amide content relative to the other amino acids. Moreover, the isomerization of the prolyl amide bond has been shown to be the ratedetermining step in the folding pathways of many peptides and proteins. 4 Herein we describe the effects of galactosylation of Hyp on the conformation as well as the thermodynamics and kinetics of prolyl N-terminal amide isomerization. Compounds 4a AcHyp(R-D-Gal)NHMe and 4b AcHyp(‚-D-Gal)NHMe were selected as glycopeptide mimics, while AcProNHMe 1, AcHypNHMe 2, and AcHyp(Otert-butyl)NHMe 3 served as non-glycosylated reference compounds