The synthesis of 5-(2-deoxy-2-fluoro-/3-D-arabinofuranosyl)-l-methyluracil (1, C-FMAU), an isostere of the potent antiviral and antitumor nucleoside 1-(2-deoxy-2-fluoro-/?-D-arabinofuranosyl)thymine (2'-fluoro-5-methyl-ara-U or FMAU), was achieved. Pseudouridine (2) was converted into 4,5'-anhydro-3'-0-acetyl-2'-0-triflylpseudouridine (4), which was treated with tris(dimethylamino)sulfur(l+) difluorotrimethylsilicate (TASF) to give 4,5'-anhydro-5-(3-0-acetyl-2-deoxy-2-fluoro-/3-D-arabinofuranosyl)-l-methyluracil (5b) in 40% yield. Acid hydrolysis of the 4,5'-anhydro linkage of 5b with Dowex 50 (H+) afforded C-FMAU. The inhibitory activity of C-FMAU against HSV-1 and HSV-2 was about 10-fold less than that of FMAU in tissue culture. This compound, however, did not show significant activity in mice inoculated with HSV-1 or HSV-2.