A 13C T1 study of conformational and molecular mobility of mono‐ and difucosyllactosesfv

Overall and internal motions of lactose Galβ(1 → 4)Glcα and its three fucosylated derivatives Fucα(1 → 2)Galβ(1 → 4)Glcα, Galβ(1 → 4) [Fucα(1 → 3)] Glcα and Fucα(1 → 2)Galβ(1 → 4) [Fucα(1 → 3)] Glcα were investigated in Me2SO‐d6 using the spin–lattice relaxation times of 13C nuclei, T1(13C), measured at 8.5 and 11.7T. The relaxation data of the ring carbons in lactose and the lactosyl core of its derivatives were well described by the axially symmetric motion of the molecule. However, the interpretation of the T1(13C) of ring carbons in fucose residues required the assumption of a conformational mobility about the appropriate glycosidic bonds. For this purpose, a bistable, jump model of internal motion with a varying angle between the rotation axis and the symmetry axis of the overall tumbling was developed. The internal rotation of hydroxymethyl groups in Glc and Gal residues was also analysed quantitatively; the rotation in Glc was found to be slower than that in Gal. The internal rotation of methyl groups in fucoses undergoing a complex motion was interpreted semi‐quantitatively

Identification of constituent sugar residues in oligosaccharides by two‐dimensional spectroscopy

Pure absorption phase‐sensitive shift‐correlated 1H NMR spectra were shown to furnish complete information on chemical shifts, their connectivities (including one‐ and two‐step remote connectivities) and coupling constants for oligosaccharides of considerable complexity. Therefore, a strategy using these spectra as a first step in ab initio structure elucidation of carbohydrates may require less effort and spectrometer time than alternative strategies exploiting J‐resolved, double quantum and relayed coherence transfer spectra. All these methods and also triple quantum filtered spectra were applied in order to compare their merits and to identify the constituent sugar residues of three peracetylated glycosphingolipids, viz. Galα(1–3)Galβ(1–4)GlcNAcβ(1–3)Galβ(1–4)Glcβ(1–1)Cer(Cer=ceramide),Galα(1–3)Galβ(1–4)GlcNAcβ(1–3)[Galα(1–3)Galβ(1–4)GlcNAcβ(1–6)]Galβ(1–4)GlcNAcβ(1–3)Galβ(1–4)Glcβ(1–1)Cer and GalNAcβ(1–3)Galα(1–4)Galβ(1–4)Glcβ(1–1)Cer(globoside)

Application of 1H/13C inversely correlated NMR spectroscopy to the determination of the stereochemistry of a polysubstituted [2.2]paracyclophane

The relative orientation of substituents in the opposite rings of one of the isomeric 4,7-Dichloro-5,8,12,15-tetramethoxy-13,6-bis[4-(2-methoxycarbonylphenyl) butyl][2.2]paracyclophanes was determined by establishing by NOE their orientation relative to the bridge protons, which thus served as ‘space-spy nuclei’. The mutual orientation of these bridge protons was ascertained by the analysis of their coupling constants, obtained from a phasesensitive COSY spectrum. The 1H and 13C resonances were assigned with the aid of 1H COSY and 1H/13C inversely correlated spectra

The quest for simplicity: Remarks on the free-approach models.

Nuclear magnetic relaxation provides a powerful method giving insight into molecular motions at atomic resolution on a broad time scale. Dynamics of biological macromolecules has been widely exploited by measuring 15N and 13C relaxation data. Interpretation of these data relies almost exclusively on the use of the model-free approach (MFA) and its extended version (EMFA) which requires no particular physical model of motion and a small number of parameters. It is shown that EMFA is often unable to cope with three different time scales and fails to describe slow internal motions properly. In contrast to EMFA, genuine MFA with two time scales can reproduce internal motions slower than the overall tumbling. It is also shown that MFA and simplified EMFA are equivalent with respect to the values of the N–H bond length and chemical shift anisotropy. Therefore, the vast majority of 15N relaxation data for proteins can be satisfactorily interpreted solely with MFA

Solution conformation of mono‐ and difucosyllactoses as revealed by rotating‐frame NOE‐based distance mapping and molecular mechanics and molecular dynamics calculations

The solution conformation of two fucosyllactoses, Fucα(1 → 2)Galβ(1 → 4)Glcα,β and Galβ(1 → 4) [Fucα(1 → 3)] Glcα,β, and a difucosyllactose, Fucα(1 → 2)Galβ(1 → 4)[Fucα(1 → 3)]Glcα,β, were investigated in Me2SO‐d6 with the use of distance mapping, molecular mechanics (MM) energy minimization and molecular dynamics (MD) simulations. The distance mapping procedure, which was based on rotating‐frame NOE constraints involving C‐ and O‐linked protons, and hydrogen bonding constraints, suggested the occurrence of two conformations for each of the fucose residues. The MM calculations resulted in two minima that were located reasonably near to the regions demarcated in the Θ, Ψ conformational space by distance mapping; 500 ps MD trajectories showed transitions between two conformations characterized by glycosidic angles Θ and Ψ that only deviated insignificantly from those found by the first two methods. No similar transitions were observed for the Galβ14Glc linkage

The structure of 3'-O-anthraniloyladenosine, an analogue of the 3'-end of aminoacyl-tRNA.

3'-O-Anthraniloyladenosine, an analogue of the 3'- terminal aminoacyladenosine residue in aminoacyl-tRNAs, was prepared by chemical synthesis, and its crystal structure was determined. The sugar pucker of 3'-O-anthraniloyladenosine is 2'-endo resulting in a 3'-axial position of the anthraniloyl residue. The nucleoside is insynconformation, which is stabilized by alternating stacking of adenine and benzoyl residues of the neighboring molecules in the crystal lattice. The conformation of the 5'-hydroxymethylene in 3'-O- anthraniloyladenosine is gauche-gauche. There are two intramolecular and two intermolecular hydrogen bonds and several H-bridges with surrounding water molecules. The predominant structure of 3'-O-anthraniloyladenosine in solution, as determined by NMR spectroscopy, is 2'-endo,gauche-gauche and anti for the sugar ring pucker, the torsion angle around the C4'-C5'bond and the torsion angle around the C1'-N9 bond, respectively. The 2'-endo conformation of the ribose in 2'(3')-O-aminoacyladenosine, which places the adenine and aminoacyl residues in equatorial and axial positions, respectively, could serve as a structural element that is recognized by enzymes that interact with aminoacyl-tRNA or by ribosomes to differentiate between aminoacylated and non-aminoacylated tRNA