The Inhibition of Liposaccharide Heptosyltransferase WaaC with Multivalent Glycosylated Fullerenes: A New Mode of Glycosyltransferase Inhibition

l,d-Heptosides (L-glycero-D-manno-heptopyranoses) are found in important bacterial glycolipids such as lipopolysaccharide (LPS), the biosynthesis of which is targeted for the development of novel antibacterial agents. This work describes the synthesis of a series of fullerene hexa-adducts bearing 12 copies of peripheral sugars displaying the mannopyranose core structure of bacterial l,d-heptoside. The multimers were assembled through an efficient copper-catalyzed alkyneazide cycloaddition reaction as the final step. The final fullerene sugar balls were assayed as inhibitors of heptosyltransferase WaaC, the glycosyltransferase catalyzing the incorporation of the first L-heptose into LPS. Interestingly, the inhibition of the final molecules was found in the low micromolar range (IC50=745 mu M), whereas the corresponding monomeric glycosides displayed high micromolar to low millimolar inhibition levels (IC50 always above 400 mu M). When evaluated on a per-sugar basis, these inhibition data showed that, in each case, the average affinity of a single glycoside of the fullerenes towards WaaC was significantly enhanced when displayed as a multimer, thus demonstrating an unexpected multivalent effect. To date, such a multivalent mode of inhibition had never been evidenced with glycosyltransferases.