From the compounds synthesised, 4'-thioarabinocytidine was shown to have moderate cytotoxicity towards U87-MG cells, but generally all the thionucleosides evaluated showed little cytotoxicity. This is not unexpected, if conversion to an active triphosphate form is limited by substrate tolerance within nucleotide-forming kinase pathways. Further work to access monophosphate prodrug forms of these analogues is currently underway and will be reported in due course.