Structure of Ursodeoxycholic Acid

Abstract

Ursodeoxycholic acid, C₂₄H₄₀O₄, crystallizes in the orthorhombic space group P2₁2₁2₁ with eight molecules in the unit cell. The cell dimensions are a=26.617 (7), b=13.272 (2), and c=12.320 (2) Å. The structure was solved by use of direct methods and refined to a residual of 0.079 for 1619 independent significant reflections. The conformations of the D rings and 17β side-chains of the two molecules in the asymmetric unit are different from each other. All the hydroxyl and carboxyl groups are involved in hydrogen bonding extended nearly parallel to the bc plane.