2,3-Dehydro-4-epi-N-acetylneuraminic acid; a neuraminidase inhibitor

Use of Phenols as Nucleophiles in the Zbiral Oxidative Deamination of N-Acetyl Neuraminic Acid: Isolation and Characterization of Tricyclic 3-Keto-2-deoxy-nonulosonic Acid (KDN) Derivatives via an Intermediate Vinyl Diazonium Ion

It is well established that the N-nitrosoamide derived from peracetylated derivatives of N-acetyl neuraminic acid on treatment with a mixture of sodium isopropoxide and trifluoroethanol, followed by the addition of acetic acid, gives an oxidative deamination product, in which the AcN(NO)-C5 bond is replaced with a AcO-C5 bond with the retention of configuration, affording a practical synthesis of 2-keto-3-deoxy-d-glycero-d-galactononulosonic acid (KDN) derivatives. Application of other strong acids, including hydrogen fluoride, thioacetic acid, trifluoromethanesulfonic acid, and hydrogen azide, functions similarly to afford KDN derivatives functionalized at the 5-position. We describe our attempts to extend the range of useful nucleophiles employed in this oxidative deamination process to include phenols and thiophenols, resulting in the discovery of a new branch of the general reaction and the formation of a series of products resulting from substitution of the 5-acetamido group and of the 4-acetoxy group from neuraminic acid. A mechanistic rationale for the formation of these products is advanced according to which, in the absence of acids of pKa ≤ 8, the intermediate diazonium ion resulting from the elimination of acetic acid and nitrogen from the nitrosoacetamide undergoes elimination of acetic acid from the 4-position to afford a highly electrophilic alkenediazonium ion. Reversible conjugate addition of the nucleophile to the 4-position then initiates the reaction cascade leading to the ultimate products.

Synthetic study of 3-fluorinated sialic acid derivatives

Sialic acid derivatives, analogs, and their conjugates are expected to be pharmaceutical candidates such as anti-influenza drugs and also useful probes for investigating the biological role of glycoconjugates. Derivatives of 3-fluorinated sialic acid (3-F-Sia) have been found to be excellent probes in investigating functions and mechanisms of a series of proteins. Here, we describe the syntheses of 3-F-Sia derivatives, which are useful in making biologically important conjugate probes. A practical method for the construction of 3-fluorinated sialosides based on the stereoselective formation of the corresponding anomeric O-trimethylsilyl ether and their nucleophilic attack by an alkyl halide, an allyl halide in particular, was developed. In addition, details of the synthesis of cytidine monophosphate (CMP)-3-F-Sia bearing a fluorescent tag, which has been proven to show dual functions as a substrate of CMP-sialic acid transporter (CST) and an inhibitor of sialyltransferase (STase), are described.

One-pot SSA-catalyzed β-elimination: an efficient and inexpensive protocol for easy access to the glycal of sialic acid

Neu5Ac2en1Me per-OAc, the fully protected glycal of sialic acid, is a key intermediate in the discovery of therapeutics and diagnostics, including anti-influenza drugs and proteolysis resistant peptidomimetic foldamers. The synthesis of this sialic acid derivative, however, still relies on standard sugar chemistry that utilizes multi-step methodologies. Herein we report a facile and highly efficient microwave-assisted preparation of Neu5Ac1Me using silica sulfuric acid (SSA) as solid-supported acid catalyst that is one- to two-orders of magnitude faster than standard procedures. We also describe the microwave-assisted and SSA-catalyzed one-pot, rapid, solvent free reaction that combines both peracetylation and β-elimination reactions in one step to generate the glycal from Neu5Ac1Me. We coined the term One-pot SSA-catalyzed Technology for β-Elimination Protocol (OneSTEP) to describe this least laborious, most efficient, and practical preparation to date of Neu5Ac2en1Me per-OAc in terms of yield, time, reagent cost, and waste generation.

Pneumococcal neuraminidase A: an essential upper airway colonization factor for Streptococcus pneumoniae

Streptococcus pneumoniae colonizes the upper respiratory tract from where the organisms may disseminate systemically to cause life threatening infections. The mechanisms by which pneumococci colonize epithelia are not understood, but neuraminidase A (NanA) has a major role in promoting growth and survival in the upper respiratory tract. In this article we show that mutants of S. pneumoniae D39 deficient in NanA or neuraminidase B (NanB) are abrogated in adherence to three epithelial cell lines, and to primary nasopharyngeal cells. Adherence levels were partly restored by nanA complementation in trans. Enzymic activity of NanA was shown to be necessary for pneumococcal adherence to epithelial cells, and adherence of the nanA mutant was restored to wild-type level by pre-incubation of epithelial cells with Lactococcus lactis cells expressing NanA. Pneumococcal nanA or nanB mutants were deficient in biofilm formation, while expression of NanA on L. lactis or Streptococcus gordonii promoted biofilm formation by these heterologous host organisms. The results suggest that NanA is an enzymic factor mediating adherence to epithelial cells by decrypting receptors for adhesion, and functions at least in part as an adhesin in biofilm formation. Neuraminidase A thus appears to play multiple temporal roles in pneumococcal infection, from adherence to host tissues, colonization, and community development, to systemic spread and crossing of the blood-brain barrier.

A simple synthesis of N-perfluoroacylated and N-acylated glycals of neuraminic acid with a cyclic aminic substituent at the 4α position as possible inhibitors of sialidases

A simple protocol for the synthesis of N-perfluoroacylated and N-acylated glycals of neuraminic acid, with a secondary cyclic amine (morpholine or piperidine) at the 4α position, has been set-up, starting from peracetylated N-acetylneuraminic acid methyl ester that undergoes, sequentially to its direct N-transacylation followed by a C-4 amination, a β-elimination, and a selective hydrolysis of the ester functions, without affecting the sensitive perfluorinated amide.

X-ray crystal structure analysis of 4,7,8,9-tetra-O-acetyl-N-acetyl-2,3-dehydro-2-deoxy-4-epineuraminic acid methyl ester

X-ray crystallographic analysis was performed on a single crystal of 4,7,8,9-tetra-O-acetyl-N-acetyl-2,3-dehydro-2-deoxy-4-epi-neuraminic acid methyl ester. The pyranoid ring adopts the 5H6 conformation.

Novel practical synthesis of Kdn2en and its C-4 nitrogen-modified derivatives

A practical synthesis of Kdn2en and 4-amino-4-deoxy-Kdn2en has been achieved via a key intermediate, methyl 4,5,7,8,9-penta-O-acetyl-2,6-anhydro-3-deoxy-D-glycero-D-galacto-non-2- enonate, which has been prepared from Kdn in three steps in 91% overall yield.

An efficient short-step total synthesis of ganglioside GM3: effective usage of the neighbouring group participation strategy

We have developed an efficient methodology for highly stereoselective sialylation using 3-position substituted sialic acids and have prepared 2a having a 3 beta-phenylthio group as a sialic donor. Glycosylation of suitably protected lactoside 3 with 2a gave only the alpha-sialyl trisaccharide 16 in good yield. Condensation of the azidosphingosine 4 with the acetate 17 using promotors, DMTST or NIS-TfOH, afforded the glycolipid 18, which was directly transformed to 20 by reduction with Bu3P and subsequent acylation with octadecanoic acid in the presence of WSC. Removal of the protecting groups generated ganglioside GM3 (1).

Synthesis of transition-state analogues as potential inhibitors of sialidase from Influenza virus

Sodium 5-acetamido-2,6-anhydro-3,4,5-trideoxy-D-manno-non-2-enonate (2) has been synthesized from N-acetyl-4-deoxy-neuraminic acid methyl ester (4). Sodium 2,6-anhydro-3-deoxy-L-arabino-hept-2-enonate (3), 4-acetamido-2,6-anhydro-3,4-dideoxy-L-arabino-hept-2-enonic acid (18e), and 4-acetamido-2,6-anhydro-3,4-dideoxy-L-ribo-hept-2-enonic acid (18a) have been prepared from L-arabinose. The above compounds were investigated as inhibitors of sialidase from Influenza virus. Only compound 2 showed a significant inhibitory activity (Ki 8 x 10(-2) mM) against the enzyme.

Mobilization of sialidase from intracellular stores to the surface of human neutrophils and its role in stimulated adhesion responses of these cells

Desialation of cell surfaces has been associated with the initiation or modification of diverse cellular functions. In these studies we have examined the subcellular distribution of sialidase (SE) in human neutrophils as well as the mobilization of this enzyme following neutrophil activation. Separation of subcellular fractions by density gradient centrifugation showed that SE is present not only in neutrophil primary and secondary granule populations, like lysozyme, but also in plasma membrane fractions. Neutrophil activation was associated with a redistribution of SE from secondary granule-enriched fractions to the plasma membrane. Furthermore, SE activity detected on the surface of intact neutrophils with a fluorescent SE substrate increased rapidly after activation with kinetics that matched both the loss of total cell-associated sialic acid and release of free sialic acid from the cells. These activation-dependent events were in each case blocked by incubation of neutrophils with the SE inhibitor, 2-deoxy-N-acetyl-neuraminic acid. Aggregation responses of neutrophils as well as adhesion responses to nylon and plastic surfaces were also inhibited by 2-deoxyNANA. Our findings indicate that the activation-dependent desialation of the neutrophil surface is associated with mobilization of an endogenous SE to the plasma membrane and has a role in stimulated adhesion responses of these cells.

On the side-chain conformation of N-acetylneuraminic acid and its epimers at C-7, C-8, and C-7,8

The side-chain conformation of N-acetylneuraminic acid and analogs has been studied by n.m.r. spectroscopy. The results of the 1H-, 13C-n.m.r.-, and 1H-nuclear-Overhauser-enhancement measurements were used to distinguish between different local-minima conformations suggested by hard-sphere calculations. Attempts were made to correlate the major conformation determined for each compound with the behavior towards activation with N-acetylneuraminic acid-CMP-synthetase.

4,8-anhydro-N-acetylneuraminic acid. Isolation from edible bird's nest and structure determination

A new, sialic-acid-derived compound was isolated from the acid hydrolysate of edible bird's nest by ion-exchange chromatography. Combined use of mass spectroscopy and 1H- and 13C-NMR spectroscopy established that it is the 4,8-anhydro derivative of N-acetylneuraminic acid and that in solutions it exists in two tautomeric forms. The formation of the new compound supports and earlier findings that in the glycoprotein of edible bird's nest at least a portion of N-acetylneuraminic acid is acetylated at HO-4.

Structural parameters and natural occurrence of 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid

2-Deoxy-2,3-didehydro-N-glycoloylneuraminic acid has been found to occur in porcine, bovine and equine submandibular glands as well as in the urine of pig, horse and rat. This novel, unsaturated sialic acid was isolated by gel filtration and ion-exchange chromatography. Final purification was achieved by column chromatography or by preparative thin-layer chromatography on cellulose. The structural analysis was performed by combined capillary gas-liquid chromatography/mass spectrometry. The various data were compared with those from synthetic 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid. Besides of the unsaturated N-glycoloylated sialic acid, also the corresponding N-acetylated derivative was present in the materials analyzed. The inhibitory effect of 2-deoxy-2,3-didehydro-N-glycoloylneuraminic acid on Vibrio cholerae sialidase using N-acetylneuraminyl-(alpha 2----3)-lactose as substrate is slightly higher (50% inhibition at 10 microM) when compared with 2-deoxy-2,3-didehydro-N-acetylneuraminic acid (50% inhibition at 15 microM).

Removal of sialic acids from the purified insulin receptor results in enhanced insulin-binding and kinase activities

Neuraminidase treatment of the purified insulin receptor resulted in an increase in both insulin-binding and kinase activities. Neuraminidase-treated alpha and beta subunits moved further than native subunits on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) under reducing conditions. The enhancement of insulin-binding and kinase activities and increased mobility of the subunits on SDS-PAGE were not observed when the receptor was treated with neuraminidase in the presence of neuraminidase inhibitor. These results suggest that terminal sialic acid residues have a significant role in insulin-binding and kinase activities. The involvement of sialic acid residues in the activities of the receptor has not been detected by previous studies.

Synthesis and conformational studies of 2-beta-chloro, 1-alpha-fluoro, and 2-beta-fluoro derivatives of 2-deoxy-N-acetyl-neuraminic acid

5-Acetamido-4,7,8,9-tetra-O-acetyl-2,3,5-trideoxy-2-fluoro-D-glycero-alp ha- and -beta-D- galacto -2- nonulosonic acid methyl esters and the beta-chloro analog were synthesized from N-acetylneuraminic acid. Their 1H- and 13C-n.m.r.spectra were completely assigned by using single-frequency decoupling, off-resonance decoupling, and spin-simulation programs. Bond angles estimated from the 1H coupling-constants indicate that all of the compounds adopt the 2C5 (L) conformation with minor conformational differences in the C3 side chain. 5-Acetamido-2,3,5,-tri-deoxy-2-fluoro-D-glycero-alpha- and -beta-D- galacto -2- nonulosonic acid and their methyl esters were also prepared.

The interaction of substrate-related ketals with bacterial and viral neuraminidases

Arthrobacter sialophilus neuraminidase catalyzes the hydration of 5-acetamido-2,6-anhydro-3,5-dideoxy-D-glycero-D-galacto-non-2-enonic acid (2,3-dehydro-AcNeu) with Km and kcat values of 8.9 X 10(-4) M and 6.40 X 10(-4) s-1, respectively. The methyl ester of 2,3-dehydro-AcNeu as well as 2,3-dehydro-4-epi-AcNeu are also hydrated by the enzyme. The product resulting from the enzymatic hydration of 2,3-dehydro-AcNeu is N-acetylneuraminic acid. A series of derivatives of 2,3-dehydro-AcNeu (K1, 1.60 X 10(-6) M) including 2,3-dehydro-4-epi-AcNeu (2.10 X 10(-4) M) and 2,3-dehydro-4-keto-AcNeu (K1 = 6.10 X 10(-5) M) were each competitive inhibitors of the enzyme. The methyl esters of these ketal derivatives were also competitive enzyme inhibitors. Dissociation constants for these ketals were determined independently by fluorescence enzyme titrations which gave values similar to those found kinetically. These six relatives of 2,3-dehydro-AcNeu were also competitive inhibitors for the influenza viral neuraminidases. For the viral neuraminidases, the dissociation constant for 2,3-dehydro-AcNeu and its methyl ester were 2.40 X 10(-6) and 1.17 X 10(-3) M, respectively. The interpretation placed upon the K1 values determined for these ketals against the Arthrobacter versus influenza neuraminidases is that the bacterial enzyme has a more flexible glycone binding site.

Histochemical localization of neuraminidase in the CNS of mice and fish by means of 5-brom-3-indolyl-alpha-ketoside of 5-N-acetyl-D-neuraminic acid (BI-NeuAc)

The applicability of the 5-brom-3-indolyl-alpha-ketoside of N-acetyl-D-neuraminic acid (BI-NeuAc) as substrate for the histochemical indication of neuraminidase (GOSSRAU et al. 1977) was examined in frozen sections of brain, small intestine and kidney from suckling and adult mice and respectively from a cichlid fish (Sarotherodon mosambicus) with and without formaldehyde fixation. Following biochemical investigations using tritiated gangliosides as substrate a decrease in the activity of neuraminidase took place from about 50 to 80% after tissue fixation with formaldehyde. Nevertheless significant histochemical reactions were found only in fixed tissue sections. The specificity of this reaction was shown by means of inhibitions tests using 2,3-dehydro-2-desoxy-N-acetyl-neuraminic acid according to KUMAR et al. (1981). In contrast to distinct staining of neuraminidase activity in the small intestine and kidney, only faint reactions occurred in brain sections. From this it is concluded that the application of the new synthetic substrate for quantitative staining of neuraminidase seems to be not very suitable for the CNS.

Structural requirements for neuraminidase induction in Arthrobacter sialophilus

The effectiveness of 13 N-acetylneuraminic acid derivatives as potential inducers of Arthrobacter sialophilus neuraminidase were examined. N-Acetylneuraminic acid nitrogen and thioglycosides were not inducers, whereas 2,3-dehydro-N-acetylneuraminic acid, a transition state analog for neuraminidases, was the most effective inductive ligand. The C-4 hydroxyl function of N-acetylneuraminic acid was essential for enzyme derepression.