Fluorinated compounds play an important role in enzymology as well as clinical medicine. Based on the stereochemical preferences of
dihydroorotate oxidase and
enzymes that use fluoroaspartate, it was anticipated that threo-5-fluoro-L-dihydroorotate (
t-FDHO) would have the properties of an
antimetabolite. Thus,
t-FDHO was synthesized via the reduction of 5-fluoroorotate using
NADH and
dihydroorotate dehydrogenase that was free of
dihydroorotase. When the product was purified and studied by high field
proton and
carbon 13 NMR, the
fluorine, the five carbons, and all the nonexchangeable
protons were readily observed. Confirmation of threo configuration was obtained by examining the vicinal coupling constants between the substituents on
carbon 5 and
carbon 6 of the newly synthesized compound. Additionally,
t-FDHO could be reoxidized to 5-fluoroorotate in the presence of
dihydroorotate dehydrogenase and NAD+. Treatment of
t-FDHO with
dihydroorotase generated N-carbamyl-threo-3-fluoro-L-aspartate (CTF-ASP) which was also purified and characterized by NMR. The antiproliferative activity of
t-FDHO was determined against a diploid human
fibrosarcoma cell line (HT-1080). Fifty microM
t-FDHO caused 50% inhibition of HT-1080 cell proliferation. During the 48-h toxicity study, extracellular
t-FDHO underwent significant hydrolysis to CTF-ASP. Further extracellular degradation to fluoroaspartate was not seen. The antiproliferative activity of
t-FDHO was not due to extracellular degradation since CTF-ASP itself was essentially nontoxic.