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.

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.

1,4-Addition of sulphur nucleophiles to the diene (12) derived via the pen-2-em (5) from clavulanic acid provides the thiadeoxa analogues (14–15). X-ray analysis of the ester (14) shows the thermodynamically stable isomers to have the same relative stereochemistry as clavulanic acid.

AbstractAus dem Penemcarbonester‐Derivat (Ia) erhält man die Substitutionsprodukte (Ib) und (Ic), die zum Lacton (II) cyclisiert werden können.

AbstractClavulansäure wird als Ester (I) zum Lactam (II) gespalten, das nach Cyclisierung mit n‐Butanthiol zum Enol (IV) gespalten wird.

Allylic halides (e.g.2), prepared from 4-nitrobenzyl clavulanate, react with salts of thiocarboxylic, thiocarbamic, and sulphinic acids to give thioesters, thiocarbamates, and sulphones; dehydrohalogenation of the halides affords the diene (4), from which sulphur derivatives may also be prepared via a stereospecific 1,4-addition reaction.

AbstractDie Behandlung von (I) mit Triethylamin ergibt das Ringspaltungsprodukt (II), das beim Erhitzen zum Isomeren (III) cyclisiert und mit Triethylamin wieder in (II) übergeht.

Treatment of the derivative (5) of clavulanic acid with triethylamine leads to the endocyclic double bond isomer (6) and thence to the salt (10) which is a powerful inhibitor of β-lactamases; cleavage of the oxazoline ring of (6) with triethylamine or with pyridine gives the novel zwitterions (7) and (9) which are readily recyclised to (6) by thermolysis.