Synthesis of naturally occurring β-d-glucopyranoside based on enzymatic β-glycosidation

For the purpose of synthesis of naturally occurring β-d-glucopyranoside, direct β-glycosidation for seven kinds of the functionalized primary alcohol in the presence of d-glucose using native or immobilized β-glucosidase (EC 3.2.1.21) from almonds under equilibrium condition was carried out. The utilization of high concentration of the alcohol acceptor, 3-methyl-2-buten-1-ol (3) or 2-methyl-2-propen-1-ol (4) using the immobilized enzyme gave the corresponding β-d-glucopyranoside (21, natural product) or (22) in 65 or 51% yield, respectively. On the other hand, the utilization of 4-equivalents of the functionalized alcohols (5–9) using the immobilized enzyme in 90% tert-butanol/H2O solution afforded the naturally occurring β-d-glucopyranosides (23–27), respectively, in moderate yield. Among them, five kinds of β-d-glucopyranosides (21, 22, 24, 25, and 27) were converted into the cyanoglucosides (rhodiocyanoside A (28), osmaronin (29)) and other naturally occurring β-d-glucopyranosides (30–32), respectively.