Influence of the solvent ability to form hydrogen bonds in the crystal structure of ([3beta,5beta,7alpha,12alpha]-3[(norbornyl-2-acetyl)-amino]-7,12-dihydroxycholan-24-oic acid (a norbornyl derivative of cholic acid).

A norbornyl-2-acetyl derivative of cholic acid ([3beta,5beta,7alpha,12alpha]-3[(norbornyl-2-acetyl)-amino]-7,12-dihydroxycholan-24-oic acid -NbCH2CA-) was synthesized and recrystallized in two dipolar aprotic solvents (acetone, DMSO) and in one protic solvent (2-propanol). In DMSO and acetone the crystals are orthorhombic, P2(1)2(1)2(1) (all their parameters being very similar) while in 2-propanol the crystal is monoclinic, P2(1). The inclusion complexes with the solvent have a 1:1 stochiometry with DMSO and acetone and 1:2 with 2-propanol. All solvents are forming a hydrogen bond with the amide bond of the bridge between the norbornyl residue and the steroid nucleus of the bile acid. In DMSO and acetone the beta side of the steroid groups lies in the same region facilitating hydrophobic interactions, and the molecules are disposed in an antiparallel orientation (the methyl groups having a beta interdigitation) forming bilayers. The width of the bilayers is 9.231 A and 8.859 A in DMSO and acetone, respectively. A lamellar structure is also evident for the crystal in 2-propanol (the width being 11.908 A), but the packing is different from the previous one since a sliding between the steroid groups is observed and the methyl groups are not interdigitated. Four different hydrogen bonds are established by every steroid molecule in the NbCH2CA/DMSO (or acetone) crystal. This hydrogen bond network interconnects the hydrophilic regions of the lamellar structure. The hydrogen bond network of the NbCH2CA:2-propanol crystal is different because of the different abilities of 2-propanol to form hydrogen bonds. The side chain has a ttti conformation in the two orthorhombic crystals, and a tgtg one in the monoclinic crystal.