Structural and functional-group tuning in the design of neuraminidase inhibitors

Analogues of the disaccharide alpha-NeuAc-(2-->6)-beta-D-Gal-OR have been made by modifications at C-1 and C-6 of the galactose and at C-4 of the NeuAc unit, for structure-activity relationship studies with influenza virus neuraminidase. These studies indicate that for the influenza neuraminidase, a larger aglycon at C-1 of galactose is less preferred, whereas the restriction of the rotamer orientation at C-6 of galactose in the "tg" mode favors enzyme binding. Substitution at C-4 of the NeuAc unit has the most profound effect in the influenza neuraminidase hydrolysis and inhibition. For example, azido and acetamido groups at C-4 of the NeuAc units render the sialosides resistant to neuraminidase hydrolysis. However, these derivatives are not inhibitors of the neuraminidase, indicating their lack of binding. On the other hand, a 4-amino substitution of the NeuAc unit not only renders the corresponding sialosides neuraminidase-resistant, but also makes them potent neuraminidase inhibitors. This potent inhibition indicates that the 4-amino groups in these sialosides may engage in favorable interaction with amino acids at the neuraminidase active-site. The conclusion is also supported by docking studies of the carbohydrate structures at the neuraminidase active-site.