Crystal structure and molecular mechanics analysis of methyl 6-O-(N-heptylcarbamoyl)-α-d-glucopyranoside (Hecameg)

The crystal structure of methyl 6-O-(N-heptylcarbamoyl)-α-d-glucopyranoside (trivial name: Hecameg), C15H29NO7, was determined using MoKα X-ray data at 110 K. The space group is P212121, with four molecules in a unit cell having dimensions of a=5.070 (5), b=8.282 (4), and c=43.16 (2) . Because all the crystals which could be grown were twinned, a high-resolution data set could not be collected. Consequently, a highly refined structure could not be reached. Therefore, the crystalline structure was submitted to a further refinement based on optimization of both intramolecular and intermolecular interactions using molecular mechanics methods. The present work provides structural information about the fairly uncommon carbamoyl group, as well as on the amphiphilic components of Hecameg. A 4C1 conformation is maintained for the glucopyranoside, and the orientation around C-5-C-6 is gauche-gauche; the polymethylene chain is observed in its fully extended, all anti conformation. Whereas there is no intramolecular hydrogen bonding, three intermolecular H bonds are observed. One involves the N-H of the carbamoyl group linked to the carbonyl oxygen of a neighboring group. The two others link the secondary hydroxyl groups of the glucopyranose through a network which propagates along one of the 21 screw axis. A complete analysis of the intermolecular arrangement has been performed, which yields a detailed analysis of the crystal packing. To the best of our knowledge this is the first amphiphilic carbohydrate structure which crystallizes in a bilayer type of arrangement not having interdigitized hydrophobic acyl chains.