Convenient synthesis of beta-galactosyl nucleosides using the marine beta-galactosidase from Aplysia fasciata

A convenient synthesis of beta-galactosyl derivatives of antiviral and anticancer nucleosides, which utilizes the purified beta-galactosidase activity from the hapatopancreas of Aplysia fasciata, is reported. All reactions were extremely stereo- and regioselective, since only anomerically pure 5'-O-beta-galactosyl conjugates were formed. 5'-O-beta-Galactosyl-5-fluorouridine was synthesized with a 60% yield and 5'-O-beta-galactosyl-3-azido- 3'-deoxythymidine, the derivative of the anti-HIV drug, was obtained in 43% yield.