Covalent attachment of recombinant Lactobacillus reuteri 2'-deoxyribosyltransferase to Sepabeads EC-EP303 leads to the immobilized biocatalyst SLrNDT4, which displayed an enzymatic activity of 65.4 IU/g of wet biocatalyst in 2'-deoxyadenosine synthesis from 2'-deoxyuridine and adenine at 40A degrees C and pH 6.5. Response surface methodology was employed for the optimization of SLrNDT4 activity. Optimal conditions for SLrNDT4 highest activity were observed at 40A degrees C and pH 6.5. Immobilized biocatalyst retained 50% of its maximal activity after 17.9 h at 60A degrees C, whereas 96% activity was observed after storage at 40A degrees C for 110 h. This novel immobilized biocatalyst has been successfully employed in the enzymatic synthesis of different natural and therapeutic nucleosides effective against cancer and viral diseases. Among these last products, enzymatic synthesis of therapeutic nucleosides such as 5-ethyl-2'-deoxyuridine and 5-trifluorothymidine has been carried out for the first time. Importantly for its potential application, SLrNDT4 could be recycled for 26 consecutive batch reactions in the synthesis of 2,6-diaminopurine-2'-deoxyriboside with negligible loss of catalytic activity.