Sialidase inhibition

Oseltamivir carboxylate 18 is used in sialidase inhibition assays Numbering used is that of A/N2 Abed et al. (2008)... 

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... 

In a study from Vibrio cholerae, a 1000-fold drop in inhibitory potency was observed for 42 relative to Neu5Ac2en, indicating that the acyl group contributes heavily to binding.79 Interestingly, similar modification in the 4-amino-4-deoxy-Neu5Ac2en to give compound 43 and applied to influenza virus sialidase, inhibition was reduced only 10-fold relative to its /V-acyl counterpart 9.65... 

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). 

Fig. 14. A comparison of influenza virus sialidase inhibition by C-6 diethylcarboxamide 107 with related C-6-keto, -ether, and -hydroxy derivatives 108-110.

Comparative early work on the influenza virus sialidase inhibition of the cyclohexene isomers 132 and 133 revealed that 133 was a much more potent compound (IC50 = 6.3 pM) than its isomer 132, which failed to demonstrate inhibition of the enzyme at concentrations up to 200 pM, supporting the significance of the position of the unsaturation.121 Interestingly in seeming contrast... 

Fig. 20. A comparison of influenza virus A sialidase inhibition by derivatives of 142 with various C-5 nitrogen substituents. IC50 values are given in parentheses.

P. Florio, R. J. Thomson, A. Alafaci, S. Abo, and M. von Itzstein, Synthesis of 8 4-P-d-glucopyranosiduronic acids as mimetics of 2,3-unsaturated sialic acids for sialidase inhibition, Bioorg. Med. Chem. Lett., 9 (1999) 2065-2068. 

Derivative 13, with its extremely potent sialidase inhibition in vitro and in vivo [31, 89], was subsequently developed as zanamivir (Relenza ) by Glaxo for treatment of influenza A and B viral infection. Zanamivir was revealed to be rapidly excreted and to have poor oral bioavailability [98, 99] because of its highly polar nature. It is therefore administered through inhalation however, intravenous administration has also been explored and proven effective [100],... 

C. A. Vercelli, A. M. Hidalgo, S. H. Hyon, and P. F. Argibay, Trypanosoma cruzi tram-sialidase inhibits human lymphocyte proliferation by nonapoptotic mechanisms implications in pathogenesis and transplant immunology, Transplant. Proc., 37 (2005) 4594 1597. 

The 5-acetamido group in zanamivir is also important in terms of influenza sialidase inhibition. Removal of this group, to give the 5-desacetamido derivative (19) resulted in a compound with a 25,000-fold reduced affinity for influenza virus sialidase [103]. However both the 5-trifluoroacetamido zanamivir analogue (20) and the 5-sulphonamide derivative (21) retain potent inhibitory activity against both influenza A and B strains, although the reported [104] IC50 values [2 x 10"8 M and 9 x 10 8 M, respectively, for (20)... 

Takada, K., Hamada, T, Hirota, H., Nakao, Y, Matsunaga, S., Van Soest, R.W.M., and Fusetani, N. (2006) Asteropine A, a sialidase-inhibiting conotoxin-like peptide from the marine sponge Asteropus simplex. Chem. Biol, 13, 569-574. 

---