Abstract
Isomers of ursodeoxycholic acid, 3β, 7α- and 3β, 7β-dihydroxy-5β-cholan-24-oic acids (3β7αU and 3β7βU) crystallize in the orthorhombic space group P212121 containing one molecule and in the monoclinic group P21 containing two independent molecules in an asymmetric unit. The cell dimensions are a=28.032(17), b=9.973(5), c=8.049(6)Å for 3β7αU, and a=11.771(8), b=27.999(12), c=6.637(2)Å, β=90.78(6)° for 3β7βU, respectively. Both structures were solved by the direct method and refined to the residual values of 0.065 (3β7αU) and 0.059 (3β7βU). The conformations of the D rings of each molecule are different from each other : 3β7αU intermediate, 3β7βU (A and B) half-chair form. In the crystal, 3β7αU molecules are connected by a hydrogen bond extended nearly parallel to the bc plane and 3β7βU molecules are connected by the helical hydrogen bond system or by the zigzag one parallel to the ac plane.
