Verification of the Projection Resultant Method for Two-Bond13C–13C Coupling Sign Determinations in Carbohydrates

✍ Scribed by Anthony S. Serianni; Paul B. Bondo; Jaroslav Zajicek

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 143 KB
• Volume: 112
• Category: Article
• ISSN: 1064-1866
• DOI: 10.1006/jmrb.1996.0111

✦ Synopsis

Structural analysis of carbohydrates in solution has de-An empirical method was proposed recently ( 14) that predicts the magnitudes and signs of 2 J CCC and 2 J COC values pended heavily on the interpretation of vicinal 1 H-1 H spin couplings ( 3 J HH ) which can be related to molecular H-C-in carbohydrates based on the use of a projection resultant.

The method predicts 2 J C1,C3 in a-D-glucopyranose 1 to be C-H dihedral angles [i.e., Karplus relationship ( 1)]. However, 3 J HH values cannot be used to assess certain structural small or zero and 2 J C1,C3 in b-D-glucopyranose 2 to be positive (/4.5 Hz), whereas 2 J C1,C3 in 2-deoxy-a-D-arabino-and conformational features of complex sugars. For example, the conformation about the O-glycoside linkages of hexopyranose 3 was predicted to be negative (02.3 Hz): oligo-and polysaccharides cannot be assessed via 3 J HH , since H-C-C-H coupling pathways across these linkages do not exist (2-4). On the other hand, three-bond 13 C-1 H ( 3 J CH ) and 13 C-13 C ( 3 J CC ) spin couplings are available and can be used effectively in such studies (2-6):

This study concluded that a key determinant of 2 J CCC in carbohydrates is the relative orientation of the hydroxyl substituents on the C-C-C fragment, with anti arrangements (relative to the coupled carbons) making a positive contribution to the coupling. This behavior is similar to that observed for 2 J CH in NOTES FIG. 4. Schematic representations of the 13 C-13 C COSY C1-C5 cross peak (A) and the C1-C6 cross peak (B) for the a-pyranose of 6. In (A) and (B), those signals that remain in the COSY-45 spectrum are indicated and produce the different relative displacements (dashed lines) observed in the spectral data shown in Figs. 3D and 3E, respectively.