The reaction of 3-O-acetyl-5-O-benzoyl-2-deoxy-2-fluoro-D-arabinofuranosyl bromide (I) with tris(trimethylsilyl)cytosine (II) in methylene chloride gives 1-(3-O-acetyl-5-O-benzoyl-2-deoxy-2-fluoro-beta-D-arabinofuranosyl)cytosine (III), which is hydrolyzed by treatment with methanol NH3 to afford 1-(2-deoxy-2-fluoro-beta-D-arabinofuranosyl)cytosine (IV). Finally, this compound is iodinated by treatment with HIO3 - I2 in CCl4 - H2O - acetic acid.
FMAU is prepared by condensation of 3-O-benzoyl-2-fluoro-D-arabinosyl bromide (I) with trimethylsilylated thymine (II) followed by saponification of the protected nucleoside (III).