Conformational analysis of sugar-peptide adducts in the solution state by NMR spectroscopy and molecular modelling

A combined use of NMR spectroscopy and molecular modelling has enabled insi ght into conformational features., of the novel sugar-peptide adducts 1-3. Cyclic neoglycopeptide 1, having the beta -D-glucopyranose moiety which con nects terminal parts of the Tyr-Pro-Phe sequence into a 14-membered ring, h as been found in a rigid conformation with a sandwich-like arrangement of t he proline residue flanked by the tyrosine, and the phenylalanine side-chai ns. However, cyclic Tyr-Pro-Phe-Val-related Amadori compound 2, with an 18- membered glycopeptide ring, has shown more flexibility in the peptide backb one and amino, acid side-chains. Nevertheless, mutarotation was obstructed and the 1-deoxy-D-fructofuranose moiety was found in the beta configuration exclusively. The analysis of the Amadori compound 3, with an unsubstituted C-terminal of the Tyr-Pro-Phe-Val peptide, as revealed the presence of con formational isomers arising from trans-cis isomerism of the Tyr(1)-Pro(2) p eptide bond, while the 1-deoxy-D-fructose has been found in the beta -pyran ose form. The results presented here point towards peptide sequence-governe d overall conformation of the studied neoglycopeptides.