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NMR analysis of the configuration and conformation of N ‐acetylneuraminosyl‐(2 → 3)‐lactose
Author(s) -
Schulte J.,
Lauterwein J.,
Höweler U.
Publication year - 2000
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/1097-458x(200009)38:9<751::aid-mrc717>3.0.co;2-d
Subject(s) - chemistry , geminal , glycosidic bond , dihedral angle , vicinal , coupling constant , crystallography , stereochemistry , sialic acid , nuclear magnetic resonance , hydrogen bond , molecule , organic chemistry , physics , biochemistry , particle physics , enzyme
1D and 2D 13 C NMR spectra of N ‐acetylneuraminosyl‐(2 → 3)‐lactose were recorded and the sign and magnitude of the geminal couplings between C‐2 and the H‐3 protons of the N ‐acetylneuraminic acid residue were determined. The C‐2,H‐3ax coupling constant was −8.0 Hz, indicative of an α‐configuration at C‐2. The vicinal coupling between C‐2 and H‐3′ of the β‐ D ‐galactose unit was measured to be 5.2 Hz. This result gave a set of four solutions for the dihedral angle ψ at the 2 → 3 glycosidic linkage: ±16 ° ; ±149 ° . NOE experiments established close contacts between the sialic acid and the galactose protons. Force field calculations determined up to eight conformational minima with comparable energy distributed over the whole range of ϕ angles but only within a band of ψ angles, −60° < ψ <60°. This indicated a highly flexible 2 → 3 glycosidic linkage. However, by considering only the two most favored conformations (ϕ, ψ = −161°, −21° and −67°,−4°), good agreement with the coupling constant and the NOE data was found. Copyright © 2000 John Wiley & Sons, Ltd.