Conformational Dynamics and Exchange Kinetics of N‑Formyl and N‑Acetyl Groups Substituting 3‑Amino-3,6-dideoxy-α‑d‑galactopyranose, a Sugar Found in Bacterial O‑Antigen Polysaccharides

• Published in: The journal of physical chemistry. B 2017-10, Vol.121 (41), p.9487-9497
• Main Authors: Engström, Olof, Mobarak, Hani, Ståhle, Jonas, Widmalm, Göran
• Format: Article
• Language: English
• Subjects: Organic Chemistry; organisk kemi
• ISSN: 1520-6106; 1520-5207; 1520-5207
• DOI: 10.1021/acs.jpcb.7b05611

Three dimensional shape and conformation of carbohydrates are important factors in molecular recognition events and the N-acetyl group of a monosaccharide residue can function as a conformational gatekeeper whereby it influences the overall shape of the oligosaccharide. NMR spectroscopy and quantum mechanics (QM) calculations are used herein to investigate both the conformational preferences and the dynamic behavior of N-acetyl and N-formyl substituents of 3-amino-3,6-dideoxy-α-d-galactopyranose, a sugar and substitution pattern found in bacterial O-antigen polysaccharides. QM calculations suggest that the amide oxygen can be involved in hydrogen bonding with the axial OH4 group primarily but also with the equatorial OH2 group. However, an NMR J coupling analysis indicates that the θ1 torsion angle, adjacent to the sugar ring, prefers an ap conformation where conformations