Zanamivir sialidase

Fig. 5 Key interactions of 4-deoxy-4-guanidino-Neu5Ac2en (zanamivir) 12 with the active site of influenza A virus sialidase [Figure generated from crystal strucmre data (PDB - Innc) using LIGPLOT (Wallace et al. 1995)]. To the right is shown zanamivir 12 in the same orientation...

The discovery of the potent in vitro sialidase inhibitory activity and in vivo efficacy of zanamivir 12, and the increasing availability of 3D structural data for influenza virus sialidases in the 1990s, particularly with Neu5Ac and various inhibitors bound into the active site, provided a platform for further drug discovery efforts targeting... 

Functionalisation Through the C-7 Position of Zanamivir The Development of Long Acting Sialidase Inhibitors... 

Importantly, the crystal structure of 34 complexed with N9 sialidase (Fig. 8) indicated differences in the orientation of the guanidino group in subsite S2, and in its interaction with the active site residues, compared to that of zanamivir (Babu et al. 2000). These differences have implications for cross-reactivity of 34 with zanamivir-resistant influenza viruses that have Glul 19 mutations in the sialidase S2 subsite (see Sect. 5.1). 

Smith PW, Sollis SL, Howes PD, Cherry PC, Starkey ID, Cobley KN, Weston H, Scicinski J, Merritt A, Whittington A, Wyatt P, Taylor N, Green D, BetheU R, Madar S, Fenton RJ, Motley PJ, Pateman T, Beresford A (1998) Dihydropyrancarboxamides related to zanamivir a new series of inhibitors of influenza virus sialidases. 1. Discovery, synthesis, biological activity, and structure-activity relationships of 4-guanidino- and 4-amino H-pyran-6-carboxamides. J Med Chem 41 787-797... 

Fig. 3 Zanamivir , an antiviral drug which inhibits viral sialidases and below the mechanism of hydrolysis of sialosides with the transition state 4 mimed by Zanamivir .

Fig. 5. The important interactions of Zanamivir (1) with the active site of influenza virus A sialidase.70 This figure was generated from crystal structure data (PDB-1NNC) using LIGPLOT.63...

The discovery of Zanamivir as a potent and selective inhibitor of influenza virus sialidase prompted several researchers to investigate the synthesis and structure-activity relationship studies of Neu5Ac2en-based compounds as potential sialidase inhibitors. Exploration of these SAR studies were undertaken to optimize inhibitory activity and to improve the physicochemical properties of the sialic acid-based influenza virus sialidase inhibitor. A few in vitro assays are commonly employed to measure the effectiveness of influenza virus sialidase inhibitors. The first involves a fluorometric assay that measures release of a synthetic fluorophore following its cleavage from Neu5Ac by sialidase. Dye-uptake assay, such as the Neutral Red uptake assay, measures the uptake of a vital stain, Neutral Red in cell culture. The process requires intact membranes and active metabolism in the cell, and is expressed as percent protective rate against virus infection. The plaque-reduction assay is used to measure sialidase inhibition indirectly in cell culture, and provides some measure of the inhibitor s effect on the viability of the influenza virus. In vitro and in vivo systems for analysis of inhibitors of influenza virus enzymes have been reviewed.71... 

The majority of other modifications examined at the C-4 position of Neu5Ac2en involved A -alkylation or /V-acylation of 4-amino-4-deoxy-Neu5Ac-2en or modification of the guanidino substituent of Zanamivir. IV-Methylamino (22), A -al lyl (23), and Ar,Ar-dimethylamino (24) derivatives of amine 9 were effective inhibitors of NA from influenza A and B viruses (A) = 10 5-10 7M) though they showed diminished activity against a number of bacterial sialidases.57,65... 

A series of fourteen 4-triazole-modified Zanamivir analogues were synthesized from the 4-azido-4-deoxy-Neu5Ac2en derivative using click chemistry, and their inhibitory potencies against influenza virus sialidase were determined. These modifications were not that successful as 33-35 demonstrated only 6-40% protective rate at a concentration of 50 pM against the virus infection compared to Zanamivir which shows 86% at the same concentration. The best result was obtained for compound 36, which showed a protective rate of >61%.76... 

Fig. 8. Zanamivir derivatives modified by replacement of the C-7 hydroxyl. Values in parentheses reflect the relative ability of the compounds to inhibit influenza A virus sialidase. The reference value for Zanamivir 1 is 1.0.

A virus in both sialidase inhibition and plaque-reduction assays. Alkyl ethers up to twelve carbon atoms in length exhibited similar inhibitory activity to Zanamivir against influenza A virus sialidase, however, showed a pronounced improvement in plaque-reduction assay compared to the parent triol 1. Alkylation of the C-7 hydroxyl with two-carbon substituents bearing terminal hydroxyl, amino, azido, and acetamido groups yielded inhibitors 61-64 and did not significantly affect the binding and had similar potency to that of ethyl or propyl ethers 65 or 66 (Fig. 9). 

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