Crystal structure and conformational features of α-panose

✍ Scribed by Anne Imberty; Serge Pérez

• Publisher: Elsevier Science
• Year: 1988
• Tongue: English
• Weight: 944 KB
• Volume: 181
• Category: Article
• ISSN: 0008-6215
• DOI: 10.1016/0008-6215(88)84021-7

✦ Synopsis

The crystal structure of cY-panose [@a-D-glucopyranosyl-(1-+6)-O-a-Dglucopyranosyl-( l-4)-cY-D-glucose],

(C,sOIhH3J, has been established by direct methods from 1491 independent reflections, and refined to a final R-value of 0.077. The crystal belongs to the monoclinic system, space group P2,, and has a unit cell of dimensions a = 0.9662(3), b = 0.8505(3), c = 1.2955(S) nm, and p = 102.4(l)". The three D-glucose residues have the 4C, pyranose conformation.

The orientation of the a-(l-6)-glycosidic linkage is characterized by torsion angles of @ = 71.4", Zy = 165.2", and w = 75.7". The orientation of the cy-(1+4)-glycosidic linkage is characterized by torsion angles @' = 92.9" and V' = -131.3", which results in an intramolecular hydrogen-bonding between secondary hydroxyl groups belonging to contiguous residues (O-3". . . O-2' = 299.6 pm). The intramolecular conformation is also stabilized by the occurrence of another intramolecular hydrogen-bond between the nonreducing and the reducing residues (O-2 *. * O-6" = 283.9 pm). This is made possible because of a unique, eclipsed orientation of the primary hydroxyl group at O-6". As a result, the trisaccharide molecule adopts a folded conformation. Molecules are held together by a complicated network of hydrogen bonding involving all of the hydroxyl groups; this explains the high density of 1.63 g.cmW3 measured for the crystals. The structural features observed have been rationalized through the use of conformational analysis and packing computations.