The design, synthesis and biological evaluation of neuraminic acid-based probes of Vibrio cholerae sialidase

2-Deoxy-2,3-didehydro-N-acetylneuraminic acid analogues structurally modified at the C-4 position: Synthesis and biological evaluation as inhibitors of human parainfluenza virus type 1

To explore the influence of binding to human parainfluenza virus type 1 (hPIV-1), a series of 4-O-substituted Neu5Ac2en derivatives 6a-e was synthesized and tested for their ability to inhibit hPIV-1 sialidase. Among compounds 6a-e, the 4-O-ethyl-Neu5Ac2en derivative 6b showed the most potent inhibitory activity (IC50 6.3 microM) against hPIV-1 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.

Preparation of a fluorous protecting group and its application to the chemoenzymatic synthesis of sialidase inhibitor

2-(Perfluorohexyl)ethoxymethyl chloride was prepared as a novel fluorous protecting reagent. Neu5Ac aldolase-catalyzed chemoenzymatic transformation of N-acetyl-D-mannosamine to Neu5Ac derivatives was achieved successfully by using the fluorous reagent not only for hydroxy group protection but also for fluorous tagging. This chemoenzymatic method was applied to the synthesis of 2-deoxy-2,3-didehydrosialic acid 1 known as a potent sialidase inhibitor.

One-Bead-One-Inhibitor-One-Substrate Screening of Neuraminidase Activity

Given the eminent threat of a 21st century flu pandemic, the search for novel antiviral compounds is an increasingly important area of research. Recent developments in antiviral research have established the viability of targeting viral neuraminidase (NA), an enzyme that cleaves sialic acid from the cell-surface-mediating passage of the virus in the respiratory tract. N-acetyl neuraminic acid (NeuAc) is the substrate for NA, and analogues of this core structure have been commercialized as antiviral therapeutics. Recent studies have established that this system is well suited for combinatorial approaches to drug discovery. An important step in the process is to develop solid-phase screening technologies. The feasibility of performing competitive solid-phase NA assays is reported herein. Initially, a fluorogenic NeuAc substrate was immobilized on solid support, and the ability of three NAs (Clostridium perfringens, Salmonella typhimurium, and Vibrio cholerae) to cleave the substrate was shown to be analogous to solution-phase assays. The solid support was then bifunctionalized with the fluorogenic NeuAc substrate and one of two known inhibitors (DANA and Zanamivir). The ability of NA to cleave NeuAc from the solid support when simultaneously presented with an inhibitor was shown to be enzyme dependent. As expected, simultaneous presentation of NeuAc and DANA, a nonspecific inhibitor, led to diminished activity for all three enzymes tested. In contrast, dual presentation of NeuAc and the selective inhibitor Zanamivir only showed significant activity against Vibrio cholerae.

2β,3β-Difluorosialic acid derivatives structurally modified at the C-4 position: synthesis and biological evaluation as inhibitors of human parainfluenza virus type 1

A series of 4-O-substituted 2beta,3beta-difluorosialic acid derivatives (3a-d) has been synthesized. A key intermediate was synthesized efficiently by the electrophilic syn-addition of fluorine to the double bond of a glycal precursor using molecular fluorine or xenon difluoride in the presence of BF(3).OEt(2). Among compounds 3a-d, the 4-O-thiocarbamoylmethyl derivative 3c showed the most potent inhibitory activity against sialidase of human parainfluenza virus type 1. [structure: see text].

Saturation transfer difference (STD) 1H-NMR experiments and in silico docking experiments to probe the binding of N-acetylneuraminic acid and derivatives to Vibrio cholerae sialidase

Saturation transfer difference (STD) (1)H NMR experiments were used to probe the epitope binding characteristics of the sialidase [EC 3.2.1.18] from the bacterium Vibrio cholerae, the causative agent of cholera. Binding preferences were investigated for N-acetylneuraminic acid (Neu5Ac, 1), the product of the sialidase catalytic reaction, for the known sialidase inhibitor 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enoic acid (Neu5Ac2en, 2), and for the uronic acid-based Neu5Ac2en mimetic iso-propyl 2-acetamido-2,4-dideoxy-alpha-L-threo-hex-4-enopyranosiduronic acid (3), in which the native glycerol side-chain of Neu5Ac2en is replaced with an O-iso-propyl ether. The STD experiments provided evidence, supporting previous studies, that Neu5Ac (1) binds to the sialidase as the alpha-anomer. Docking experiments using DOCK (version 4.0.1) revealed further information regarding the binding characteristics of the enzyme active site in complex with Neu5Ac2en (2) and the Neu5Ac2en mimetic (3), indicating an expected dominant interaction of the acetamide moiety with the protein.

Oxidation of 3-C-(2-amino-2-deoxy-D-glucopyranosyl)-1-propene compounds and the structure of 3-C-(2-amino-2-deoxy-D-glucopyranosyl)-1,2-propanediol derivatives for a synthesis of 2,3-didehydro-2,7-dideoxy-N-acetylneuraminic acid

Oxidation of 5-acetamido-4,8-anhydro-1,2,3,5-tetradeoxy-D-glycero-D-ido-non-1-enitol [3-C-(2-amino-2-deoxy-beta-D-glucopyranosyl)-1-propene] was studied to search for preparative routes to aminodeoxy didehydro nonulosonic acid derivatives. Since only moderate chiral induction was observed with osmium tetroxide dihydroxylation as well as with peracid epoxidation, the catalytic asymmetric dihydroxylation conditions were applied to give the stereocontrolled formation of 1,2-propanediol derivatives. The structures of these diastereoisomeric 1,2-propanediol derivatives were determined by X-ray crystallographic analyses. The formation of diastereoisomeric 1,2-propanediols also varied with the nature of 2-substituent on the aminodoexy glycosyl moiety. Thus 5-acetamido-4,8-anhydro-3,5-dideoxy-D-erythro-L-ido-nonitol [(2S)-3-C-(2-acetamido-2-deoxy-beta-D-glucopyranosyl)-1,2-propanediol] was obtained predominantly up to 70% from 3-C-(2-acetamido-2-deoxyglycosyl)-1-propene by the use of ADmixbeta reagent. The (2S)-propanediol derivative was transformed in a five-step reaction sequence to 2,3-didehydro-2,7-dideoxy-N-acetylneuraminic acid.

Synthesis of 2-deoxy-2,3-didehydro-N-acetylneuraminic acid analogues modified at the C-4 and C-9 positions and their behaviour towards sialidase from influenza virus and pig liver membrane

The synthesis of novel 2-deoxy-2,3-didehydro-N-acetylneuraminic acid analogues structurally varied at C-4 and C-9 by transformation from versatile key intermediates and their inhibitory activity against sialidase from influenza virus A and pig liver membrane are described.