Synthesis of 5R-Acetamido-4S-amino-4H-pyran-6R-O-(1-ethyl)propyl and 6R-(1-oxo-2-ethyl)butyl 2-carboxylic acids (4 and 5) and their evaluation as inhibitors of influenza virus sialidase is described. Both compounds showed good inhibitory activity with marked selectivity for influenza A sialidase.

A novel synthesis of the bicyclo [2.2.2] octane ring system has been achieved utilising a tandem Henry cyclisation as the key stage. This chemistry has been employed in the synthesis of a potential inhibitor of influenza virus sialidase.

Two methods for the synthesis of 4-acetylamino benzoic acids substituted at the 3-position with imidazoles are described. Many of the compounds are inhibitors of influenza virus sialidases with levels of activity similar to the recently described 4-acetylamino-3-guanidino-benzoic acid (BANA 113).

Background: Inhibitors of the influenza virus neuraminidase have been shown to be effective antiviral agents in humans, Several studies have reported the selection of novel influenza strains when the virus is cultured with neuraminidase inhibitors in vitro, These resistant viruses have mutations either in the neuraminidase or in the viral haemagglutinin, Inhibitors in which the glycerol sidechain at position 6 of 2-deoxy-2,3-dehydro-N-acetylneuraminic acid (Neu5Ac2en) has been replaced by carboxamide-linked hydrophobic substituents have recently been reported and shown to select neuraminidase variants. This study seeks to clarify the structural and functional consequences of replacing the glycerol sidechain of the inhibitor with other chemical constituents.Results: The neuraminidase variant Arg292-->Lys is modified in one of three arginine residues that encircle the carboxylate group of the substrate, The structure of this variant in complex with the carboxamide inhibitor used for its selection, and with other Neu5Ac2en analogues, is reported here at high resolution, The structural consequences of the mutation correlate with altered inhibitory activity of the compounds compared with wild-type neuraminidase,Conclusions: The Arg292-->Lys variant of influenza neuraminidase affects the binding of substrate by modification of the interaction with the substrate carboxylate. This may be one of the structural correlates of the reduced enzyme activity of the variant, Inhibitors that have replacements for the glycerol at position 6 are further affected in the Arg292-->Lys variant because of structural changes in the binding site that apparently raise the energy barrier for the conformational change in the enzyme required to accommodate such inhibitors. These results provide evidence that a general strategy for drug design when the target has a high mutation frequency is to design the inhibitor to be as closely related as possible to the natural ligands of the target.

4-Amino- and 4-guanidino-4H-pyran-6-carboxamides 4 and 5 related to zanamivir (GG167) are a new class of inhibitors of influenza virus sialidases. Structure-activity studies reveal that, in general, secondary amides are weak inhibitors of both influenza A and B viral sialidases. However, tertiary amides, which contain one or more small alkyl groups, show much greater inhibitory activity, particularly against the influenza A virus enzyme. The sialidase inhibitory activities of these compounds correlate well with their in vitro antiviral efficacy, and several of the most potent analogues displayed useful antiviral activity in vivo when evaluated in a mouse model of influenza A virus infection. Carboxamides which were highly active sialidase inhibitors in vitro also showed good antiviral activity in the mouse efficacy model of influenza A infection when administered intranasally but displayed modest activity when delivered by the intraperitoneal route.

The first paper in this series (see previous article) described structure-activity studies of carboxamide analogues of zanamivir binding to influenza virus sialidase types A and B and showed that inhibitory activity of these compounds was much greater against influenza A enzyme. To understand the large differences in affinities, a number of protein-ligand complexes have been investigated using crystallography and molecular dynamics. The crystallographic studies show that the binding of ligands containing tertiary amide groups is accompanied by the formation of an intramolecular planar salt bridge between two amino acid residues in the active site of the enzyme. It is proposed that the unexpected strong binding of these inhibitors is a result of the burial of hydrophobic surface area and salt-bridge formation in an environment of low dielectric. In sialidase from type A virus, binding of the carboxamide moeity and salt-bridge formation have only a minor effect on the positions of the surrounding residues, whereas in type B enzyme, significant distortion of the protein is observed. The results suggest that the decreased affinity in enzyme from influenza B is directly correlated with the small changes that occur in the amino acid residue interactions accompanying ligand binding. Molecular dynamics calculations have shown that the tendency for salt-bridge formation is greater in influenza A sialidase than influenza B sialidase and that this tendency is a useful descriptor for the prediction of inhibitor potency.

A series of substituted 4-amino-4H-pyran-2-carboxylic acid 6-triazoles and oxadiazoles are described. The compounds are inhibitors of influenza virus sialidases which, in general, show a similar pattern of activity and selectivity to recently reported 4H-pyran-2-carboxylic acid 6-carboxamides.

Analogues of 4-guanidino-Neu5Ac2en (GG167) have been prepared containing alternative amide and sulfonamide substituents at the 5-position. (4S,5R,6R)-4-guanidino-5-(2,2,2-trifluoroacetylamino)-6-(1R,2R,3-trihydroxypropyl)-5,6-dihydro-4H-pyran-2-carboxylic acid 5 and (4S,5R,6R)-4-guanidino-5-methanesulfonylamino-6-(1R,2R,3-trihydroxypropyl)-5,6-dihydro-4H-pyran-2-carboxylic acid 6 were the only analogues which approached the activity of GG167, showing potent inhibition of influenza virus sialidases and good antiviral activity in vitro.

The structure-activity relationships of a series of 4-amino and guanidino-4H-pyran-2-carboxylic acid 6-carboxamides are described. These compounds represent a new class of inhibitor of influenza sialidases and are particularly active against influenza A sialidase. The binding of the N-phenethyl-N-propylamide 41 to influenza A and B sialidases has been investigated using X-ray crystallography and molecular dynamics simulations. Our results suggest that formation of a hitherto unobserved intramolecular salt bridge within the enzymes may account for the observed activity and selectivity of the series.

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The title compound 2b has been synthesised in 8 steps from 2-deoxy-D-glucose (2-DG). Key transformations were an aldolase reaction utilising 2-DG to form the 9 carbon sugar 3, and then introduction of the required unsaturation and a 4-amino substitutent in a one-pot process. The poor inhibitory activity of 2b demonstrates that the 5-acetamido substitutent in 2,3-didehydro-2,4-dideoxy-4-guanidinyl-N-acetylneuraminic acid (GG167) 1 is critical for sialidase binding.

A series of benzophenone derivatives has been synthesized and evaluated as inhibitors of HIV-1 reverse transcriptase (RT) and the growth of HIV-1 in MT-4 cells. Through the use of the structure-activity relationships within this series of compounds and computational chemistry techniques, a binding conformation is proposed. The SAR also indicated that the major interactions of 1h with the RT enzyme are through hydrogen bonding of the amide and benzophenone carbonyls and pi-orbital interactions with the benzophenone nucleus and an aromatic function separated from the benzophenone by a suitable spacer group. The crystal structure of compound 1h has been determined. A number of compounds with potent inhibitory activity against HIV-1 RT and HIV in cellular assays at levels comparable with AZT and our efforts to identify a metabolically stable analogue are described.

A short high yielding synthesis of the potent anti-varicella-zoster virus (VZV) carbocyclic nucleoside analogue carba-BVDU 1 starting from aminodiol 2 is described. Reaction of 2 with acyl carbamate 3 and subsequent ring closure under acidic conditions afforded 5-ethyl-2'-deoxy-4'a-carbauridine 5. In situ acetylation of 5 afforded 3',5'-di-O-acetyl-5-ethyl-2'-deoxy-4'a-carbauridine 6 in 78% overall yield from 2. Radical bromination of 6 with either bromine or NBS and subsequent treatment with triethylamine gave an efficient conversion to 3',5'-di-O-acetyl-5-(E)-(2-bromovinyl)-2'-deoxy-4'a-carbauridine 7. Deacetylation of 7 afforded 1 in an overall 45-53% yield from 2.