Biological diversity from a structurally diverse library: systematically scanning conformational space using a pyranose scaffold.

Success in discovering bioactive peptide mimetics is often limited by the difficulties in correctly transposing known binding elements of the active peptide onto a small and metabolically more stable scaffold while maintaining bioactivity. Here we describe a scanning approach using a library of pyranose-based peptidomimetics that is structurally diverse in a systematic manner, designed to cover all possible conformations of tripeptide motifs containing two aromatic groups and one positive charge. Structural diversity was achieved by efficient selection of various chemoforms, characterized by a choice of pyranose scaffold of defined chirality and substitution pattern. A systematic scanning library of 490 compounds was thus designed, produced, and screened in vitro for activity at the somatostatin (sst(1-5)) and melanin-concentrating hormone (MCH(1)) receptors. Bioactive compounds were found for each target, with specific chemoform preferences identified in each case, which can be used to guide follow-on drug discovery projects without the need for scaffold hopping.

Complexity in influenza virus targeted drug design: interaction with human sialidases.

With the global spread of the pandemic H1N1 and the ongoing pandemic potential of the H5N1 subtype, the influenza virus represents one of the most alarming viruses spreading worldwide. The influenza virus sialidase is an effective drug target, and a number of inhibitors are clinically effective against the virus (zanamivir, oseltamivir, peramivir). Here we report structural and biochemical studies of the human cytosolic sialidase Neu2 with influenza virus sialidase-targeting drugs and related compounds.

A versatile synthetic approach toward diversity libraries using monosaccharide scaffolds.

The pyranose scaffold is unique in its ability to position pharmacophore substituents in various ways in 3D space, and unique pharmacophore scanning libraries could be envisaged that focus on scanning topography rather than diversity in the type of substituents. Approaches have been described that make use of amine and acid functionalities on the pyranose scaffolds to append substituents, and this has enabled the generation of libraries of significant structural diversity. Our general aim was to generate libraries of pyranose-based drug-like mimetics, where the substituents are held close to the scaffold, in order to obtain molecules with better defined positions for the pharmacophore substituents. Here we describe the development of a versatile synthetic route toward peptide mimetics build on 2-amino pyranose scaffolds. The method allows introduction of a wide range of substituent types, it is regio- and stereospecific, and the later diversity steps are performed on solid phase. Further, the same process was applied on glucose and allose scaffolds, in the exemplified cases, and is likely adaptable to other pyranose building blocks. The methods developed in this work give access to molecules that position the three selected binding elements in various 3D orientations on a pyranose scaffold and have been applied for the production of a systematically diverse library of several hundred monosaccharide-based mimetics.

Sugar nucleotide recognition by Klebsiella pneumoniae UDP-D-galactopyranose mutase: fluorinated substrates, kinetics and equilibria.

A series of selectively fluorinated and other substituted UDP-D-galactose derivatives have been evaluated as substrates for Klebsiella pneumoniae UDP-D-galactopyranose mutase. This enzyme, which catalyses the interconversion of the pyranose and furanose forms of galactose as its UDP adduct, is a prospective drug target for a variety of microbial infections. We show that none of the 2''-, 3''- or 6''-hydroxyl groups of UDP-D-galactopyranose are essential for substrate binding and turnover. However, steric factors appear to play an important role in limiting the range of substitutions that can be accommodated at C-2'' and C-6'' of the sugar nucleotide substrate. Attempts to invert the C-2'' stereochemistry from equatorial to axial, changing D-galacto- to D-talo-configuration, in an attempt to exploit the higher percentage of furanose at equilibrium in the talo-series, met with no turnover of substrate.

Unsaturated N-acetyl- D-glucosaminuronic acid glycosides as inhibitors of influenza virus sialidase.

The threat of pandemic influenza is a significant concern of governments worldwide. There is a very limited and relatively expensive armament to tackle such a pandemic should it occur. This fact provides much impetus to the scientific community for the discovery of new and less expensive anti-influenza drugs. Our longstanding interest in the inhibition of influenza virus sialidase, coupled with the development of simple carbohydrates that mimic an unsaturated derivative of the enzyme's naturally-occurring ligand, N-acetylneuraminic acid, has led us to investigate the development of influenza virus sialidase inhibitors based on these mimetics. We have successfully prepared a range of these compounds, in good yield, from the relatively inexpensive carbohydrate N-acetylglucosamine utilising a short synthetic procedure. We have employed a sialidase inhibition assay for biological evaluation of the target compounds and to our delight these mimetics have displayed significant inhibition of influenza virus sialidase.

Modelling, synthesis and biological evaluation of novel glucuronide-based probes of Vibrio cholerae sialidase.

The development of sialidase inhibitors is an area of continuing interest due to their potential use as therapeutic agents to combat viral and bacterial infections. Herein, we report our studies involving the sialidase from the pathogen Vibrio cholerae, through the modelling, synthesis and biological evaluation of mimetics of 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enonic acid (Neu5Ac2en, 1), a naturally occurring sialidase inhibitor. These mimetics are O- and S-glycosides of N-acetyl-D-glucosaminuronic acid in which the aglycone portion effectively replaces the C-6 glycerol side chain of Neu5Ac2en (1). The choice of aglycones was aided by use of the X-ray crystal structure of V. cholerae sialidase complexed with Neu5Ac2en (1). All Neu5Ac2en mimetics tested were found to inhibit V. cholerae sialidase as determined using a standard fluorometric assay.

An efficient approach to N-acetyl-D-glucosaminuronic acid-based sialylmimetics as potential sialidase inhibitors.

A novel approach to the synthesis of beta-glycosides of N-acetyl-D-glucosaminuronic acid, in six steps and good overall yield from N-acetyl-d-glucosamine, has been developed. The key synthetic step was the Lewis acid mediated O-glycosidation of methyl 1,3,4-tri-O-pivaloyl-N-acetyl-D-glucosaminuronate (11). Elaboration of glucosaminuronides 15 and 18 provided novel sialylmimetics 21 and 22, which showed inhibition of Vibrio cholerae sialidase.