We aimed to access the selenium-modified nucleosides 1a-2b in a biocatalytic one-pot approach using thermostable NPs (Scheme 2). For this study we selected the commercially available pyrimidine nucleoside phosphorylase PyNP-04 due to its thermostability and broad substrate spectrum. Analytical-scale experiments in our previous report indicated that these compounds can, in principle, be synthesized via transglycosylation starting from the natural nucleosides uridine or thymidine and a selenium-containing nucleobase.