Abstract: A method for producing cladribine (2-chloro-2? deoxyadenosine) comprising the steps of: a) reaction of 2-deoxyuridine with 2-chloroadenine, in the presence of uridine phosphorylase (UPase) and purine nucleoside phosphorylase (PNPase) in an aqueous reaction medium possibly containing up to 40% v/v of an aprotic dipolar solvent, to obtain cladribine dissolved in said reaction medium; b) isolation of the cladribine by precipitation by means of concentration and alkalinisation of the reaction medium up to pH 11.5-12.5.

Abstract: A method for producing cladribine (2-chloro-2?-deoxyadenosine) comprising the steps of: a) reaction of 2-deoxyuridine with 2-chloroadenine, in the presence of uridine phosphorylase (UPase) and purine nucleoside phosphorylase (PNPase) in an aqueous reaction medium possibly containing up to 40% v/v of an aprotic dipolar solvent, to obtain cladribine dissolved in said reaction medium; b) isolation of the cladribine by precipitation by means of concentration and alkalinisation of the reaction medium up to pH 11.5-12.5.

Abstract: A process for immobilizing cells is described, particularly procaryotic cells, which includes a step of adsorbing said cells on a resin, wherein such a resin is a weak anionic exchange resin and preferably has amino moieties; when the immobilized cells are UPase and/or PNPase producing cells, nucleosides can be produced by reaction of a pentose-1-phosphate with a purine or pyrimidine base, and transglycosylation reactions can be performed; advantageously, as immobilized UPase or PNPase producing cells, Escherichia cells of the DH5alpha strain transformed by the plasmid vectors having the sequences reported in Seq. Id. No. 1 and 2. are used.