Solid state molecular assemblies of five bile acid derivatives

The crystal structures of five bile acid derivatives are reported: 1: 6a,7a-Dihydroxy-5b-cholan-24-oic acid; 2: 3a,6a-Dihydroxy-5b-cholan-24-oic acid (Hyodeoxycholic acid); 3: 3a,7a,12a-Trihydroxy-5b-cholan- 24-hydrazide hemihydrate; 4: 3-Dimethyl ketal,7,12-dioxo- 5b-cholan-24-oic acid and 5: 3a,7a-Di-O-acetyl-12-oxo- 5b-cholan-24-oic acid methyl ester. In all the structures the four saturated cycles, forming the common alicyclic steroidal skeleton, have the same conformation, while the flexible side chain adopts different conformations. Whereas all the crystal structures of Cholic Acid inclusion compounds are characterized by the formation of a bilayer- type structure with channels within the lipophilic layers, the chemical variations of the substituents on the cholanic framework induce remarkable changes in the Hbond scheme and in the crystal packing arrangements. For instance, the structures 1, 2, having a different number and position of the hydroxyl groups on the rigid skeleton, display a variety of supramolecular architectures dominated by networks of cooperative . . .O––H. . .O. . . H-bonds which do not produce typical molecular layers and channels of Cholic Acid inclusion compounds. Cholic hydrazide hemihydrate, 3, where both the hydrazide group and water molecule are strongly involved in the H-bond system, forms an overall structural motif similar to that observed in CA inclusion compounds containing hydrophilic and lipophilic layers and small channels. Compound 4, containing only the carboxylic OH group as H-bond donor, makes simple antiparallel chains of molecules, while compound 5, lacking of H-bond donors, forms a crystal aggregation dominated by weak C––H. . .O contacts and van der Waals interactions leading to a crystal packing where neither molecular layers nor channels are recognizable.