Substrate Specificity of a Purine Nucleoside Phosphorylase from <i>Aeromonas hydrophila</i> Toward 6-Substituted Purines and its Use as a Biocatalyst in the Synthesis of the Corresponding Ribonucleosides

A purine nucleoside phosphorylase from Aeromonas hydrophila (AhPNP) was found to catalyze the regio- and stereoselective transfer of the ribofuranosyl moiety from 7-methylguanosine iodide (1) to a library of 6- substituted purines, resulting in moderate to high conversions (18-65%) into their ribonucleoside counterparts (26- 34, 36-49). Exploring of substrate recognition by AhPNP with regard to 6-position of purine base provided the necessary information to exploit this biocatalyst for the chemoenzymatic synthesis of nucleoside analogues through a transglycosylation reaction. Keywords: Purine nucleoside phosphorylase, transglycosylation, chemoenzymatic synthesis, 6-substituted purine ribonucleosides, Aeromonas hydrophila.