Biocatalytic approaches to nucleoside analogues.
(a) Enzyme cascade
for the synthesis of didanosine involving a ribokinase (RK), phosphopentomutase
(PPM), and purine nucleoside phosphorylase (PNP). The RK variant D16A
has mechanistic promiscuity and can catalyze direct 1′-ribose
phosphorylation, avoiding the requirement for PPMs. (b) Enzyme cascade
for the synthesis of Islatravir. The first step involves a galactose
oxidase (GOase) catalyzed desymmetrization using auxiliary enzymes
catalase and HRP. In the second step, pantothenate kinase (PanK) catalyzes
substrate phosphorylation using ATP, which is recycled by acetate
kinase (AcK) and acetylphosphate. The final step involves deoxyribose
5-phosphate aldolase (DERA), PPM and PNP, and a sucrose phosphorylase
(SP) auxiliary enzyme to drive the equilibrium.