STRUCTURES OF ISOMERS OF URSODEOXYCHOLIC ACID - 3-BETA,7-ALPHA-DIHYDROXY-5-BETA-CHOLAN-24-OIC AND 3-BETA,7-BETA-DIHYDROXY-5-BETA-CHOLAN-24-OIC ACIDS

Isomers of ursodeoxycholic acid, 3-beta,7-alpha- and 3-beta,7-beta-dihydroxy-5-beta-cholan-24-oic acids (3-beta-7-alpha-U and 3-beta-7-beta-U) crystallize in the orthorhombic space group P2(1)2(1)2(1) containing one molecule and in the monoclinic group P2(1) containing two independent molecules in an asymmetric unit. The cell dimensions are a = 28.032(17), b = 9.973(5), c = 8.049(6) angstrom for 3-beta-7-alpha-U, and a = 11.771(8), b = 27.999(12), c = 6.637(2) angstrom, beta = 90.78(6)-degrees for 3-beta-7-beta-U, respectively. Both structures were solved by the direct method and refined to the residual values of 0.065 (3-beta-7-alpha-U) and 0.059 (3-beta-7-beta-U). The conformations of the D rings of each molecule are different from each other: 3-beta-7-alpha-U intermediate, 3-beta-7-beta-U (A and B) half-chair form. In the crystal, 3-beta-7-alpha-U molecules are connected by a hydrogen bond extended nearly parallel to the bc plane and 3-beta-7-beta-U molecules are connected by the helical hydrogen bond system or by the zigzag one parallel to the ac plane.