The crystal and molecular structure of a diglycosylamine: the N-analogue of peracetylated α,β-trehalose

Crystals of the disaccharide, (2,3,4,6-tetra-O-acetyl-α-d-glucopyranosyl) (2,3,4,6–tetra-O-acetyl-β-d-glucopyranosyl)amine belong to the space group P21 with a=14.848(2), b=21.838(3), c=11.534(2) Å, and β=113.72(4)° and Z=4. The crystal structure was solved by direct methods and refined by the full-matrix least squares procedure to an R value of 0.049 (Rw=0.46) for 4262 observed reflections. This work provides the first crystalline features in the diglycosylamine series and this molecule can be considered as a N-analogue of peracetylated α,β-trehalose. The conformational features of the two independent diglycosylamine molecules do not display any major significant differences. The d–glucopyranose residues have the usual 4C1 chair conformations, whereas all the primary and secondary acetate groups display usual orientations. In the crystal structure the hydrogen atom covalently linked to the nitrogen at the glycosidic linkage could be located; its configuration is (R) providing the priority is given to the (R) carbon neighbor (C-1β). The torsional angles at the glycosidic linkages Φα (O-5–C-1α–N-1–C-1β), Φβ (C-1α–N-1–C-1β–O-5) of the two molecules have values of (57.6°,−78.8°) and (59.8°,−85.9°), respectively, slightly different from the conformation found in α,β-trehalose monohydrate. These conformations have been rationalized through the use of molecular mechanics calculations. The packing mode is highly anisotropic, with the existence of chains of molecules along the c axis, stabilized by numerous van der Waals contacts and by a strong hydrogen bond, involving the NH group of the glycosidic linkage and the carbonyl group of one acetate.