Production, characterization and synthetic application of a purine nucleoside phosphorylase from Aeromonas hydrophila

Purine nucleoside phosphorylase (PNP) from Aeromonas hydrophila encoded by the deoD gene has been over-expressed in Escherichia coli, purified, characterized about its substrate specificity and used for the preparative synthesis of some 6-substituted purine-9-ribosides. Substrate specificity towards natural nucleosides showed that this PNP catalyzes the phosphorolysis of both 6-oxo- and 6-aminopurine (deoxy)ribonucleosides. A library of nucleoside analogues was synthesized and then submitted to enzymatic phosphorolysis as well. This assay revealed that 1-, 2-, 6- and 7-modified nucleosides are accepted as substrates, whereas 8-substituted nucleosides are not. A few transglycosylation reactions were carried out using 7-methylguanosine iodide (4) as a D-ribose donor and 6-substituted purines as acceptor. In particular, following this approach, 2-amino-6-chloropurine-9-riboside (2c), 6-methoxypurine-9-riboside (2d) and 2-amino-6-(methylthio)purine-9-riboside (2g) were synthesized in very high yield and purity.