Enzymatic Synthesis of Nucleoside Analogues by Nucleoside Phosphorylases

With the world moving toward green chemistry approaches, the enzymatic synthesis of nucleoside analogues offers several advantages over chemical methods, which include higher total yields, a higher regio- and stereo-selectivity, and higher product purity. This chapter focuses on enzymatic approaches using nucleoside phosphorylases (NPs). NPs are of high interest as biocatalysts because of their wide substrate spectrum and abundance in almost all living organisms. Since NPs were first described by Kalckar, many research projects were conducted to test whether definite nucleoside analogues are used as substrates for NPs. NPs from different mesophiles, like Escherichia coli or Bacillus subtilis, were applied in the synthesis of pharmacologically active compounds. An interesting feature of purine NPs (PNPs) is their ability to accept pyrimidine nucleosides as substrate. Thus, they may be interesting catalysts for the synthesis of cytidine and deoxycytidine that are not utilized by many pyrimidine NPs.