[10] Galactosylation of nucleosides at 5′-position of pentofuranoses

The evaluation of biological activity requires absolutely pure compounds in relatively large quantities. Because glycosylation of carbohydrate primary hydroxyls usually proceeds smoothly, in principle such galactosylated nucleosides should be obtainable by organic synthesis. Several synthetic analogs of naturally occurring nucleosides are clinically useful anticancer or antiviral agents. A practical problem with their use arises from the low selectivity of such agents: they kill normal cells, albeit more slowly, as well as neoplastic or virally infected cells. An increase in selectivity would substantially increase the curative potential of such drugs. For instance, if the cytotoxicity can be abolished by glycosylation of the drug, and if a suitable glycosidase were present only in a cancer cell, then this glycosylation would provide the needed increase in the selectivity.