We describe a synthetic sialic acid analogue, 9-thioacetamido-N-acetylneuraminic acid (9-thioacetamido-Neu5Ac), which is recognized by the receptor-binding activity of influenza C virus, but is resistant to the receptor-destroying enzyme (acetylesterase) of this virus. Following transfer of the analogue to the surface of receptor-negative cells, influenza C virus is able to attach to these cells, but is unable to infect the cells. This result suggests that inactivation of virus receptors by the receptor-destroying enzyme is essential for initiation of infection. Because of their unique properties such analogues promise to be powerful chemotherapeutic agents.
