Figure 3. The cone-like (left) and umbrella-like (right) topologies presented by Chandrasekaran et al.

The umbrella conformation is unique to sialic acids with an α2–6 linkage and chains of sufficient length. As illustrated above, the topology is alleged to result from both the angle constrained by the linkage and the open spread allowed by the longer chain. (Reprinted by permission from Macmillan Publishers Ltd: Chandrasekaran et al. Nat Biotechnol 2008 Jan;26(1):107–13).