Synthesis and anticancer evaluation of 4’-thio and 4’-sulfinyl pyrimidine nucleoside analogues

Analogues of the canonical nucleosides required for nucleic acid synthesis have a longstanding presence and proven capability within antiviral and anticancer research. Despite their success, newer generations of such analogues are required, to overcome issues surrounding cellular proficiency and growing resistance profiles. The chemical synthesis of a series of nucleoside analogues that incorporate bioisosteric replacement of furanose oxygen with sulfur is presented herein. Developing access to a common 4-thioribose building block enables access to thio-ribo and thio-arabino pyrimidine nucleosides, alongside their 4’-sulfinyl derivatives. In addition, this building block methodology is templated to deliver 4’-thio and 4’-sulfinyl analogues of the established anticancer drug gemcitabine. Cytotoxic capability of these new analogues is evaluated against human pancreatic cancer and human primary glioblastoma cell lines, with observed activities ranging from low μM to >200 μM; explanation for this reduced activity, compared to established nucleoside analogues, is yet unclear. Access to these chemotypes, with thiohemiaminal linkages, will enable a wider exploration of such materials for resistance towards relevant hydrolytic enzymes within nucleotide and nucleic acid biochemistries.