The crystal structure of methyl 5-O-acetyl-2-O-benzo1-3,4-O-isopropylidene-β-l-idoseptanoside

✍ Scribed by Carol J. Bailey; Donald C. Craig; Colin T. Grainger; Veronica J. James; John D. Stevens

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 264 KB
• Volume: 284
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(96)00025-0

✦ Synopsis

Vicinal proton-proton spin-coupling constants for methyl 5-O-acetyl-2-O-benzoyl-3,4-O-isopropylidene-fl-L-idoseptanoside (1) have led to the assignment [1] of the twist-chair conformation, °'ITC2, 3 [2], for the seven-membered ring in 1 in which the pseudo-axis of symmetry passes through C-5. Since this is in contrast to a structure isomeric at C-5, methyl 2,5-di-O-acetyl-3,4-O-isopropylidene-a-D-glucoseptanoside (2), in which the seven-membered ring adopts the twist-chair conformation 4'5TC6, O with the pseudo-axis of symmetry passing through C-2 [3], we have carried out a single-crystal X-ray diffraction study of 1 in order to determine its solid state conformation.

Bond angles within the Seven-membered ring are all greater than the tetrahedral angle. This is in keeping with the values found for a large number of septanose carbohydrates [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] and for the parent heterocycle, oxepane, as determined by Bocian and Strauss [20,21 ].

An examination of the ring torsional angles shows that the ring conformation is a twist-chair with the pseudo-axis of symmetry passing through C-5, conformation °'1TC2, 3 [2]. In their study of oxepane, Bocian and Strauss [20] concluded that there are two pairs of low-energy twist-chair conformations, with the pseudo-axis of symmetry passing through a carbon atom attached to oxygen (twist-chair C and C') and passing through a carbon atom once removed from oxygen (twist-chair B and B'). For