The first structurally analysed nucleic acid building block containing the Reese protecting group: 2'-O-[1-(2-fluorophenyl)-4-methoxypiperidin-4-yl]-β-D-(1'R,2'R,3'R,4'R)-uridine.

The title compound, C21H26FN3O7, is assembled by N—H...O and O—H...O hydrogen bonds into well-separated two-dimensional layers of about 15 A thickness. The crescent conformation of the molecules is stabilized by weak intramolecular C—H...O and C—H...F hydrogen bonds. The uridine moiety adopts an anti conformation. The ribofuranose ring exists in an envelope conformation. All the endocyclic uracil bonds are shorter than normal single C—N and C—C bonds, and five of them have comparable lengths, which implies a considerable degree of delocalization of the electron density within this ring.