Biocatalysed synthesis of nucleosides

ELIZABETH S. LEWKOWICZ, JORGE TRELLES, SILVIA PORRO, MARÍA A. ZINNI, LUIS E. IGLESIAS AND ADOLFO M. IRIBARREN

Leuven

Simposio; XV International Round Table. Nucleosides, Nucleotides and Nucleic Acids; 2002

IS3N

We focus our efforts on the generation of modified nucleosides, both because they are the starting materials for the preparation of modified oligonucleotides and because they are powerful molecules with widespread applications as antiviral and anticancer agents. Alternatives to the traditional chemical routes are biotransformations, which are promising processes because such reactions take place under very mild conditions. We apply biotransformations, using free or immobilised enzymes and whole cells as biocatalysts, to develop simple, regio- and stereoselective and environmentally clean processes for the preparation of nucleosides. For example, selectively acylated nucleosides are of interest not only as synthetic intermediates, but also for the generation of more lypophlilic prodrugs, with improved bioavailability. Results obtained so far in the search of regioselective alcoholysis of peracylated nucleosides by means of isolated hydrolases will be discussed. Other examples of useful enzymes are phosphorylases. The utility of these enzymes relies on their ability to catalyse the formation of purine or pyrimidine nucleosides from cheaper precursors. As in this synthesis two intracellular enzymes are necessary, the process can be improved by using whole cells. Moreover, the use of microorganisms provides a wide range of related enzymes with differential substrate tolerance and lower costs, since isolation and purification of the enzymatic system is avoided. Therefore, we developed a screening assay that allow us the selection of the strain that catalyses the conversion of a particular substrate. Immobilisations of cells on different supports have also been achieved, providing catalysts with increased stability and high activity. Results regarding the preparation of natural and modified nucleosides as well as studies with immobilsed cells will be analysed