Enzymatic regioselective acylation of nucleosides in biomass-derived 2-methyltetrahydrofuran: kinetic study and enzyme substrate recognition.

Enzymatic regioselective acylation of pyrimidine nucleosides was mediated by immobilized lipase from Penicillium expansum in 2-methyltetrahydrofuran (MeTHF), a bio-solvent derived from biomass. Despite of the moderate dissolution ability of MeTHF toward nucleosides, the initial enzymatic reaction rate was much higher in this eco-friendly solvent than in other commonly used organic solvents. This could be explained by the lower apparent activation energy of the enzymatic reaction (24.5 vs. 43.3-57.1kJ/mol) and the higher catalytic efficiency of the enzyme (Vmax/Km, 5.8 vs. 1.1-2.9h(-1)) in MeTHF. The enzymatic acylation of a group of ribonucleosides afforded the desirable 5'-esters with the conversions of 96-99% and 5'-regioselectivities of 96 to >99%. In enzymatic acylation of 2'-deoxynucleosides, however, 5'-regioselectivities showed a clear dependence on the 5-substituents present in the base moiety although the substrate conversions reached >98% within 1-3h. In the cases of 2',3'-dideoxynucleoside analogs, the reaction rate decreased markedly due to the lack of 3'-hydroxyl.