text: 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (Neu5Ac2en) is a pan-selective inhibitor for neuraminidase. Neu5Ac2en is a dehydrogenated Neu5Ac and can be synthesized by the hNEU enzyme if Neu5Ac is in high enough concentration. Neu5Ac is also a mild inhibitor for the enzyme but as Neu5Ac2en is a transition-state analogue it is a much better inhibitor.