The known 5-decynyl-2'-deoxyuridine (I) was protected as the bis-silyl ether (II) with chlorotrimethylsilane and triethylamine. Treatment of (II) with POCl3 and triazole produced the triazolyl derivative (III). Finally, reaction of (III) with thioacetic acid gave rise to the desired thienopyrimidine.

In another synthetic route, the starting 3',5'-di-O-acetyl-5-iodo-2'-deoxyuridine (IV) was converted to the corresponding 4-thio derivative (V) upon treatment with P2S5. This was S-methylated with iodomethane and triethylamine to give the 4-methylthio pyrimidinone (VI). Palladium-catalyzed coupling of this 5-iodopyrimidine (VI) with 1-decyne (VII) furnished the 5-decynyl nucleoside (VIII). Removal of the methylthio group with NaSH in DMF gave directly the cyclized thienopyrimidine (IX). The remaining acetate esters were finally hydrolyzed by treatment with a methanolic solution of ammonium hydroxide.