Structure sialidase inhibitors

Fig. 3 Sialidase inhibitor Neu5Ac2en 4 bound in the active site of influenza A virus sialidase (from PDB structure IfSb (Smith et al, 2001)), Left Stick model of 4 surrounded by some important active site residues. Right Electrostatic potential surface rendering of the active site (blue -positive, red - negative), (Amino acid numbering for influenza A/N2 sialidase is used throughout this review)...

Structural Basis of Resistance, and Cross-Resistance, to Sialidase Inhibitors... 

Chan T-H, Xin Y-C, von Itzstein M (1997) Synthesis of phosphonic add analogs of siaUc acids (Neu5Ac and KDN) as potential sialidase inhibitors. J Org Chem 62 3500-3504 Chand P, Kotian PL, Dehghani A, El-Kattan Y, Lin T-H, Hutchison TL, Babu YS, Bantia S, Elliott AJ, Montgomery JA (2001) Systematic structure-based design and stereoselective synthesis of novel multisubstituted cyclopentane derivatives with potent antiinfluenza activity. J Med Chem 44 4379 392... 

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... 

S. Singh, M. J. Jedrzejas, G. M. Air, M. Luo, W. G. Laver, and W. J. Brouillette, Structure-based inhibitors of influenza virus sialidase A benzoic acid lead with novel interaction, J. Med. Chem., 38 (1995) 3217-3225. 

X-ray crystal structures of a-Neu5Ac and 11 in complex with influenza virus sialidases in the 1980s and early 1990s led to the opportunity for structure-based design and development of influenza virus sialidase inhibitors [66, 85],... 

Structure-Based Sialidase Inhibitor Design on a Sialic Acid Scaffold Development of Zanamivir... 

FIGURE 17.8 Developed sialidase inhibitors following structural modifications of compound 11. 

In the challenge to develop potent influenza virus sialidase inhibitors, a large amount of research has been dedicated to the manipulation of every position on 11 except C3. Structure-activity relationship (SAR) studies carried out on compounds derived from 11 before and during the development of zanamivir (reviewed in [101-103]) revealed structural requirements to conserve the main interactions between the substrate inhibitor and the active site of NA, particularly with regards to the carboxylate, C4-guanidino, and C5-acetamido moieties. 

The discovery, in the early 1990s, that zanamivir was a potent and selective inhibitor of influenza virus sialidase prompted several researchers to investigate the synthesis of Neu5Ac2en based analogues of zanamivir. Much of this effort was a consequence of the fact that zanamivir (12) must be administered as a nasal spray, due to its poor oral bioavailability and rapid excretion [101,102], and the desire to identify new sialidase inhibitors with modified physicochemical properties. Several researchers have described structure-activity relationship studies based on zanamivir (vide infra), with most modifications reported at C-4, C-5, and the glycerol side-chain. 

Starting from the knowledge of the structurally invariant active site of influenza A and sialidases, von Itzstein et al postulated that substitution of the 4-hydroxyl group of the nonselective sialidase inhibitor 2-deoxy-2,3-didehydro-D-acetylneuraminic acid 7 (Fig. 20.5) with a positively charged substituent would fill an occupied pocket lined with anionic residues. Synthesis and testing of the 4-guanidino analogue 8 revealed a reduction in K, from... 

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