[13C]Enriched Methyl Aldopyranosides: Structural Interpretations of 13C-1H Spin-Coupling Constants and 1H Chemical Shifts

A nonprotein thermal hysteresis-producing xylomannan antifreeze in the freeze-tolerant Alaskan beetle Upis ceramboides

“…1 H-1 H spin-coupling constants involving the anomeric (H1) proton were used to assign anomeric configuration. The value of 3 J H1,H2 (7.8 Hz) in the xylopyranose (Xylp) constituent was virtually identical to that reported in methyl ␤-D-xylopyranoside (27). The anomeric configuration of the Xylp residues was also confirmed with endo ␤-(134)xylosidase treatment, which reduced the TH activity of a R1 sample from 0.6 Ϯ 0.1°C (ϮSD) to zero within 1 h of treatment at 22°C.…”

“…In authentic methyl D-mannopyranosides, 3 J H1,H2 for the ␣ and ␤ anomers are 1.8 and 0.9 Hz, respectively (27). This coupling in the R1 THF was obscured by line broadening (Ϸ3 Hz); when resolution enhancement was applied, the mannopyranose (Manp) H1 signal still appeared nearly symmetric and unsplit, suggesting a 3 J H1,H2 coupling Ͻ1 Hz, indicative of a ␤-configuration.…”

“…This coupling in the R1 THF was obscured by line broadening (Ϸ3 Hz); when resolution enhancement was applied, the mannopyranose (Manp) H1 signal still appeared nearly symmetric and unsplit, suggesting a 3 J H1,H2 coupling Ͻ1 Hz, indicative of a ␤-configuration. To gain more information on the Manp anomeric configuration, we measured the one-bond 1 J C1,H1 coupling, which is very sensitive to anomeric configuration in Manp structures (27). The observed value of Ϸ160 Hz supported a ␤-configuration (27); however, broad signals and relatively poor signal/noise observed in the proton-coupled 13 C NMR spectrum led to uncertainty (Ϯ 10 Hz) in this measurement, allowing for a slight possibility that the Manp ring is in the ␣-configuration.…”

Structural Features of Dinoflagellate Toxins Underlying Biological Activity as Viewed by NMR

“…12,47,48 Vicinal carbon-proton spin-coupling constants ( 3 J C,H ) show Karplustype dihedral dependence [49][50][51] (Fig. 4); applications of 2;3 J C,H to conformational analyses and/or stereospecific assignments of methylene protons have been reported for proteins, [52][53][54] carbohydrates, 55,56 and polynucleotides. 57,58 In addition, geminal carbon-proton coupling constants ( 2 J C,H ) also provide stereochemical information; 59 when an oxygen atom on a carbon atom is gauche to its geminal proton, 2 J C,H becomes large (in minus sign), and when it is anti, the value becomes small (Fig.…”

New phenanthrene glycosides from Dendrobium denneanum and their cytotoxic activity

“…The sugar moieties in 4 were confirmed to be D-glucose and L-rhamnose by HPLC analysis (Section 3). The glucose was determined to be b configuration based on its large 3 J H1,H2 value (7.2 Hz), while the a orientation for L-rhamnose was assigned from its large 1 J H-1,C-1 value (168.2 Hz) (Podlasek et al, 1995;Paradowska et al, 2008;Timité et al, 2011). The rhamnose residue was determined to be connected to C-6 of glucose according to the HMBC correlation of H-1 00 ( (Table 2) of 5 indicated the existence of one more pentose unit than 1.…”