title: Structure of 3-acetyl-5-fluorouracil (5-FU): implication for its rearrangements during hydrolysis and upon heating.
abstract: Single-crystal X-ray diffraction data show that the 3-acetyl group in 1,3-diacetyl-5-FU (FU = fluorouracil) is perpendicular to the plane of the 5-FU ring, while the 1-acetyl group is coplanar with the ring. Analyses of 1H NMR and IR spectra provide evidence that the 1- and 3-acyl groups are in different electronic environments, which is consistent with the X-ray diffraction structure. 3-Acetyl-5-FU is thermally unstable, giving mainly 1-acetyl-5-FU (80%) and 5-FU (20%) upon heating. The hydrolysis of 3-acyl derivatives of 5-FU showed a biexponential relationship between in concentration and time which had not been previously observed. The behavior of 3-acetyl-5-FU during hydrolysis can be explained by postulating its initial rapid equilibrium with an intermediate, 2-acetyl-5-FU, which subsequently hydrolyzes to 5-FU or rearranges to 1-acetyl-5-FU, which hydrolyzes to 5-FU. The 2-acetyl intermediate was trapped by its reaction with formaldehyde. The formaldehyde adducts of the symmetrical 2-acetyl intermediate rearranged to yield equal amounts of 1- and 3-acetyloxymethyl-5-FU.
authors.affiliation: Department of Medicinal Chemistry, University of Florida, Gainesville 32610.
authors.forename: H D
authors.initials: HD
authors.lastname: Beall
authors.forename: R J
authors.initials: RJ
authors.lastname: Prankerd
authors.forename: L J
authors.initials: LJ
authors.lastname: Todaro
authors.forename: K B
authors.initials: KB
authors.lastname: Sloan
mesh_terms: D005472:Fluorouracil / Q000031:analogs & derivatives* / Q000737:chemistry; D006358:Hot Temperature; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared; D014961:X-Ray Diffraction
chemical_list: C082012:3-acetyl-5-fluorouracil; D005472:Fluorouracil