The glycan portion of macrolide antibiotics modulates their efficacy. High-level expression of three macrolide GTs and kinetic analysis has revealed a highly selective synthetic "tool kit" with such plasticity that 12 glycan-modified macrolide antibiotics have been readily created. One of these (1-Gal) is enhanced over its parent oleandomycin (1) by "glycotargeting", allowing higher uptake through active internalization by virtue of the attachment of a glycan (Gal) not normally found on 1. Subsequent release of the targeting glycan by endogenous galactosidase activity releases 1.