Novel sialidase inhibitors suppress mumps virus replication and infection.

The prevalent human pathogen, mumps virus (MuV; orthorubulavirus parotitidis) causes various complications and serious sequelae, such as meningitis, encephalitis, deafness, and impaired fertility. Direct-acting antivirals (DAAs) targeting MuV which can prevent mumps and mumps-associated complications and sequelae are yet to be developed. Paramyxoviridae family members, such as MuV, possess viral surface hemagglutinin-neuraminidase (HN) protein with sialidase activity which facilitates efficient viral replication. Therefore, to develop DAAs targeting MuV we synthesized MuV sialidase inhibitors. It is proposed that the viral HN has a single functional site for N-acetylneuraminic acid (Neu5Ac) binding and sialidase activity. Further, the known MuV sialidase inhibitor is an analog of Neu5Ac-2,3-didehydro-2-deoxy-N-acetylneuraminic acid (DANA)-which lacks potency. DANA derivatives with higher MuV sialidase inhibitory potency are lacking. The MuV-HN-Neu5Ac binding site has a hydrophobic cavity adjacent to the C4 position of Neu5Ac. Exploiting this, here, we synthesized DANA derivatives with increasing hydrophobicity at its C4 position and created 3 novel sialidase inhibitors (Compounds 1, 2, and 3) with higher specificity for MuV-HN than DANA; they inhibited MuV replication step to greater extent than DANA. Furthermore, they also inhibited hemagglutination and the MuV infection step. The insight-that these 3 novel DANA derivatives possess linear hydrocarbon groups at the C4-hydroxyl group of DANA-could help develop highly potent sialidase inhibitors with high specificity for MuV sialidase, which may function as direct-acting MuV-specific antivirals.

The Function of Sialidase Revealed by Sialidase Activity Imaging Probe.

Sialidase cleaves sialic acid residues from glycans such as glycoproteins and glycolipids. In the brain, desorption of the sialic acid by sialidase is essential for synaptic plasticity, learning and memory and synaptic transmission. BTP3-Neu5Ac has been developed for sensitive imaging of sialidase enzyme activity in mammalian tissues. Sialidase activity in the rat hippocampus detected with BTP3-Neu5Ac increases rapidly by neuronal depolarization. It is presumed that an increased sialidase activity in conjunction with neural excitation is involved in the formation of the neural circuit for memory. Since sialidase inhibits the exocytosis of the excitatory neurotransmitter glutamate, the increased sialidase activity by neural excitation might play a role in the negative feedback mechanism against the glutamate release. Mammalian tissues other than the brain have also been stained with BTP3-Neu5Ac. On the basis of information on the sialidase activity imaging in the pancreas, it was found that sialidase inhibitor can be used as an anti-diabetic drug that can avoid hypoglycemia, a serious side effect of insulin secretagogues. In this review, we discuss the role of sialidase in the brain as well as in the pancreas and skin, as revealed by using a sialidase activity imaging probe. We also present the detection of influenza virus with BTP3-Neu5Ac and modification of BTP3-Neu5Ac.

Rapid regulation of sialidase activity in response to neural activity and sialic acid removal during memory processing in rat hippocampus.

Sialidase cleaves sialic acids on the extracellular cell surface as well as inside the cell and is necessary for normal long-term potentiation (LTP) at mossy fiber-CA3 pyramidal cell synapses and for hippocampus-dependent spatial memory. Here, we investigated in detail the role of sialidase in memory processing. Sialidase activity measured with 4-methylumbelliferyl-α-d-N-acetylneuraminic acid (4MU-Neu5Ac) or 5-bromo-4-chloroindol-3-yl-α-d-N-acetylneuraminic acid (X-Neu5Ac) and Fast Red Violet LB was increased by high-K+-induced membrane depolarization. Sialidase activity was also increased by chemical LTP induction with forskolin and activation of BDNF signaling, non-NMDA receptors, or NMDA receptors. The increase in sialidase activity with neural excitation appears to be caused not by secreted sialidase or by an increase in sialidase expression but by a change in the subcellular localization of sialidase. Astrocytes as well as neurons are also involved in the neural activity-dependent increase in sialidase activity. Sialidase activity visualized with a benzothiazolylphenol-based sialic acid derivative (BTP3-Neu5Ac), a highly sensitive histochemical imaging probe for sialidase activity, at the CA3 stratum lucidum of rat acute hippocampal slices was immediately increased in response to LTP-inducible high-frequency stimulation on a time scale of seconds. To obtain direct evidence for sialic acid removal on the extracellular cell surface during neural excitation, the extracellular free sialic acid level in the hippocampus was monitored using in vivo microdialysis. The free sialic acid level was increased by high-K+-induced membrane depolarization. Desialylation also occurred during hippocampus-dependent memory formation in a contextual fear-conditioning paradigm. Our results show that neural activity-dependent desialylation by sialidase may be involved in hippocampal memory processing.

Chemoenzymatic synthesis and characterization of N-glycolylneuraminic acid-carrying sialoglycopolypeptides as effective inhibitors against equine influenza virus hemagglutination.

A series of novel sialoglycopolypeptides carrying N-glycolylneuraminic acid (Neu5Gc)-containing trisaccharides having α(2 â†’ 3)- and α(2 â†’ 6)-linkages in the side chains of γ-polyglutamic acid (γ-PGA) were designed as competitive inhibitors against equine influenza viruses (EIV), which critically recognize the Neu5Gc residue for receptor binding. Using horse red blood cells (HRBC) we successfully evaluated the binding activity of the multivalent Neu5Gc ligands to both equine and canine influenza viruses in the hemagglutination inhibition (HI) assay. Our findings show the multivalent α2,3-linked Neu5Gc-ligands (3a-c and 7) selectively inhibit hemagglutination mediated by both influenza viruses and display a strong inhibitory activity. Our results indicate that the multivalent Neu5Gc-ligands can be used as novel probes to elucidate the mechanism of infection/adhesion of Neu5Gc-binding influenza viruses.

Substrate Specificity of Equine and Human Influenza A Virus Sialidase to Molecular Species of Sialic Acid.

Most equine influenza A viruses (IAVs) show strong binding to glycoconjugates containing N-glycolylneuraminic acid (Neu5Gc) as well as N-acetylneuraminic acid (Neu5Ac). Therefore, the progeny of equine IAV is thought to be released from the infected cell surface through removal of sialic acids by the viral sialidase. In the present study, equine IAV sialidases showed significantly lower substrate affinity than that of human IAV sialidases to artificial and natural Neu5Gc-conjugated substrates. The substrate specificity of equine IAV sialidases is in disagreement with their binding specificity to molecular species of sialic acid. The results suggest that substrate specificity of equine IAV sialidase for Neu5Ac, rather than for Neu5Gc, is important for an advantage at the early infection stage and the process of progeny virus release from the surface of infected cells.

N-glycolylneuraminic acid on human epithelial cells prevents entry of influenza A viruses that possess N-glycolylneuraminic acid binding ability.

UNLABELLED: Some animal influenza A viruses (IAVs) bind not only to N-acetylneuraminic acid (Neu5Ac) but also to N-glycolylneuraminic acid (Neu5Gc), which has been discussed as a virus receptor. Human cells cannot synthesize Neu5Gc due to dysfunction of the CMP-Neu5Ac hydroxylase (CMAH) gene, which converts CMP-Neu5Ac to CMP-Neu5Gc. However, exogenous Neu5Gc from Neu5Gc-rich dietary sources is able to be metabolically incorporated into surfaces of tissue cells and may be related to enhancement of the infectivity and severity of IAV. Here, we investigated the receptor function of Neu5Gc on IAV infection in Neu5Gc-expressing cells by transfection of the monkey CMAH gene into human cells or by incubation with human cells in the presence of N-glycolylmannosamine. Expression of Neu5Gc on human cells clearly suppressed infectivity of IAVs that possess Neu5Gc binding ability. Furthermore, there was no difference in infectivity of a transfectant virus that included the wild-type HA gene from A/Memphis/1/1971 (H3N2), which shows no Neu5Gc binding, between parent MCF7 cells and cells stably expressing the monkey CMAH gene (CMAH-MCF7 cells). On the other hand, cell entry of the transfectant virus that included the Neu5Gc-binding HA gene with a single mutation to Tyr at position Thr155 was arrested at the stage of internalization from the plasma membrane of the CMAH-MCF7 cells. These results indicate that expression of Neu5Gc on the surface of human epithelial cells suppresses infection of IAVs that possess Neu5Gc binding ability. Neu5Gc is suggested to work as a decoy receptor of Neu5Gc-binding IAVs but not a functional receptor for IAV infection. IMPORTANCE: Influenza A viruses (IAVs) bind to the host cell surfaces through sialic acids at the terminal of glycoconjugates. For IAV binding to sialic acids, some IAVs bind not only to N-acetylneuraminic acid (Neu5Ac) as a receptor but also to N-glycolylneuraminic acid (Neu5Gc). Neu5Gc has been discussed as a receptor of human and animal IAVs. Our results showed that Neu5Gc expression on human epithelial cells suppresses infection of IAVs that possess Neu5Gc binding ability. Neu5Gc is suggested to be a "decoy receptor" of Neu5Gc-binding IAVs but not a functional receptor for IAV infection. Human cells cannot synthesize Neu5Gc because of dysfunction of the CMP-N-acetylneuraminic acid hydroxylase gene but can exogenously and metabolically incorporate Neu5Gc from dietary sources. The expression of Neu5Gc on human epithelial cells by taking in exogenous Neu5Gc from Neu5Gc-rich dietary sources may be related to restriction of the infection of IAVs that have acquired Neu5Gc binding ability.

Rapid Fluorescent Detection Assay for Human Parainfluenza Viruses.

Human parainfluenza virus type 1 (hPIV1) does not form clear plaque by the conventional plaque formation assay because of slightly a cytopathic effects in many cell lines infected with hPIV1, thus making in virus titration, isolation and inhibitor evaluation difficult. We have succeeded in fluorescent histochemical visualization of sialidase activities of influenza A and B viruses, Newcastle disease virus and Sendai virus by using a novel fluorescent sialidase substrate, 2-(benzothiazol-2-yl)-4-bromophenyl 5-acetamido-3,5-dideoxy-α-D-glycero-D-galacto-2-nonulopyranosidonic acid (BTP3-Neu5Ac). In this study, we applied the BTP3-Neu5Ac assay for rapid detection of hPIV1 and hPIV type 3. The BTP3-Neu5Ac assay could histochemically visualize dot-blotted hPIVs on a membrane and hPIV-infected cells as local fluorescence under UV irradiation. We succeeded in distinct fluorescent visualization of hPIV1-infected cells in only 3 d using the BTP3-Neu5Ac assay. Due to there being no fixation, hPIV1 was isolated directly from fluorescent stained focus cells by the BTP3-Neu5Ac assay. Establishment of a sensitive, easy, and rapid fluorescent focus detection assay for hPIV, hPIV1 in particular will contribute greatly to progress in hPIV studies.

Computational design of a sulfoglucuronide derivative fitting into a hydrophobic pocket of dengue virus E protein.

We performed first-principles calculations based on the ab initio fragment molecular orbital method on dengue virus envelope protein with a hydrophobic ligand, octyl-ß-D-glucose to develop an entry inhibitor. As several polar amino acid residues are present at the edge of the pocket, the glucose moiety was chemically modified with hydrophilic groups. Introduction of both sulfated and carboxylated groups on glucose enhanced not only binding affinity to the protein but also inhibition of dengue virus entry. Octyl-2-O-sulfo ß-D-glucuronic acid may serve as a molecular probe to study the dengue virus entry process.

Histochemical imaging of alkaline phosphatase using a novel fluorescent substrate.

Histochemical visualization of phosphatase is exclusively required for Western immunoblotting and antigen-positive cell staining using an alkaline phosphatase (AP)-labeled secondary antibody. This detection has been performed by several reagents including 5-bromo-4-chloro-3-indolyl-phosphate (X-Phos), nitro blue tetrazolium (NBT), 3-(2'-spiroadamantane)-4-methoxy-4-(3″-phosphoryloxy)phenyl-1,2-dioxetane and 2-(5'-chloro-2'-phosphoryloxyphenyl)-6-chloro-4-[3H]-quinazolinone (ELF® 97 Phosphate). We previously reported that 2-(benzothiazol-2-yl)-4-bromophenol bonded with N-acetylneuraminic acid (BTP3-Neu5Ac), enabled fluorescent histochemical visualization of sialidase activity. 2-(Benzothiazol-2-yl)-4-bromophenol (BTP3), which is formed from BTP3-Neu5Ac by sialidase reaction, is a crystalline, insoluble and stable fluorogenic compound, deposited at the site of enzyme activity. We developed a BTP3 phosphate ester (BTP3-Phos) for the purpose of fluorescent histochemical visualization of phosphatase activity. BTP3-Phos emitted fluorescence in a manner dependent on the concentration of the AP-labeled antibody. BTP3-Phos also enabled fluorescent histochemical visualization of AP-blotted dots in a manner dependent on the concentration of the AP-labeled antibody. The detection sensitivity of BTP3-Phos was estimated to be greater than that of the conventional method using X-Phos and NBT. Influenza A virus-infected cells were fixed and reacted with anti-influenza A virus antibodies and incubated continuously with an AP-labeled secondary antibody. BTP3-Phos stained the infected cells with distinct green fluorescence. These results indicate that BTP3-Phos can enable fluorescent immunohistochemical staining analysis using an AP-labeled antibody. BTP3-Phos would be beneficial for histochemical staining of AP activity, and may be applicable for multi-color staining or a cell sorter.

Visualizing intracellular sialidase activity of influenza A virus neuraminidase using a fluorescence imaging probe.

In influenza A virus-infected cells, newly synthesized viral neuraminidases (NAs) transiently localize at the host cell Golgi due to glycosylation, before their expression on the cell surface. It remains unproven whether Golgi-localized intracellular NAs exhibit sialidase activity. We have developed a sialidase imaging probe, [2-(benzothiazol-2-yl)-5-(non-1-yn-1-yl) phenyl]-α-D-N-acetylneuraminic acid (BTP9-Neu5Ac). This probe is designed to be cleaved by sialidase activity, resulting in the release of a hydrophobic fluorescent compound, 2-(benzothiazol-2-yl)-5-(non-1-yn-1-yl) phenol (BTP9). BTP9-Neu5Ac makes the location of sialidase activity visually detectable by the BTP9 fluorescence that results from the action of sialidase activity. In this study, we established a protocol to visualize the sialidase activity of intracellular NA at the Golgi of influenza A virus-infected cells using BTP9-Neu5Ac. Furthermore, we employed this fluorescence imaging protocol to elucidate the intracellular inhibition of laninamivir octanoate, an anti-influenza drug. At approximately 7 h after infection, newly synthesized viral NAs localized at the Golgi. Using our developed protocol, we successfully histochemically stained the sialidase activity of intracellular viral NAs localized at the Golgi. Importantly, we observed that laninamivir octanoate effectively inhibited the intracellular viral NA, in contrast to drugs like zanamivir or laninamivir. Our study establishes a visualization protocol for intracellular viral NA sialidase activity and visualizes the inhibitory effect of laninamivir octanoate on Golgi-localized intracellular viral NA in infected cells.

2-(Benzothiazol-2-yl)-phenyl-ß-d-galactopyranoside derivatives as fluorescent pigment dyeing substrates and their application for the assay of ß-d-galactosidase activities.

2-(Benzothiazol-2-yl)-phenyl-ß-d-galactopyranoside derivatives were synthesized as novel artificial fluorescent pigment dyeing substrates for ß-d-galactosidase. The substrates, which exhibited non-fluorescence or weak fluorescence in solution phase, were smoothly hydrolyzed by ß-d-galactosidase from Aspergillus oryzae and yielded a water-insoluble strong fluorescent pigment. The difference of fluorescent intensity exhibited a linear relationship with the amount of enzyme.

Syntheses of 2-deoxy-2,3-didehydro-N-acetylneuraminic acid analogues modified by α-acylaminoamido groups at the C-4 position using isocyanide-based four-component coupling and biological evaluation as inhibitors of human parainfluenza virus type 1.

Novel sialidase inhibitors 11 having an α-acylaminoamido group at the C-4 position of Neu5Ac2en 1 against human parainfluenza virus type 1 (hPIV-1) were synthesized using one-pot isocyanide-based four-component condensation, and their inhibitory activities against hPIV-1 sialidase were studied. Compound 11b showed inhibitory activity (IC(50)=5.1 mM) against hPIV-1 sialidase. The degree of inhibition of 11b was much weaker than that of 1 (IC(50)=0.3 mM).

3-O-sulfated glucuronide derivative as a potential anti-dengue virus agent.

A series of 12 carbohydrate compounds were synthesized by introduction of a sulfated group at specific positions and evaluated for their activities against dengue virus (DENV) infection as well as binding to BHK-21 cells. 3-O-sulfated GlcA was active against DENV infection, whereas 2-O-sulfated GlcA and 3,6-di-O-sulfated Glc showed negligible activity. Persulfated compounds did not inhibit DENV infection. These results provided a rationale for designing sulfated carbohydrate compounds with low molecular mass as anti-DENV agents targeting E protein functions. 3-O-Sulfated GlcA showed no significant cytotoxicity at 1mM. The EC(50) value (120 µM) was lower than that of sucrose octasulfate (SOS), a small molecular weight inhibitor of DENV infection. Two negatively charged groups, 3-O-sulfate and 6-C-carboxylic acid, appear to be essential for anti-DENV activity. We performed docking study to investigate the binding potential of 3-O-sulfated GlcA with respect to DENV E protein. The docking study showed that distance and conformation of these negative charges on the carbohydrate may be suitable for association with three amino acid residues of E protein critically involved in virus adsorption (Lys295, Ser145, and Gly159). This interaction may competitively prevent functional DENV binding to receptor(s) on host cells. In conclusion, 3-O-sulfated GlcA is a chemical probe that may facilitate exploration of the molecular mechanisms underlying manifestations of dengue diseases.

Origin of the inhibitory activity of 4-O-substituted sialic derivatives of human parainfluenza virus.

Human parainfluenza virus (hPIV) is a serious human pathogen causing upper and lower respiratory tract disease, yet there are no effective vaccines or therapies to control parainfluenza virus infections. Recently, we found that 4-O-substituted sialic derivatives have potent inhibitory activity against hPIV-1, whereas the anti-influenza inhibitor Zanamivir was less inhibitory. To elucidate the origin of the high potency inhibitory activities of these 4-O-substituted derivatives, we performed correlated fragment molecular orbital (FMO)-interfragment interaction energy (IFIE) analysis for hemagglutinin-neuraminidase (HN) glycoprotein complexes of hPIV with the derivatives and compared them with those for Zanamivir. We found key interactions between the inhibitors and the hPIV HN glycoprotein and identified important factors for the inhibitory activity. These theoretical results will be useful for the development of novel anti-hPIV drugs.

Synthesis and evaluation of tripeptidic plasmin inhibitors with nitrile as warhead.

Plasmin is best known as the key molecule in the fibrinolytic system, which is critical for clot lysis and can initiate matrix metalloproteinase (MMP) activation cascade. Along with MMP, plasmin is suggested to be involved in physiological processes that are linked to the risk of carcinoma formation. Plasmin inhibitors could be perceived as a promising new principle in the treatment of diseases triggered by plasmin. On the basis of the peptidic sequence derived from the synthetic plasmin substrate, a series of peptidic plasmin inhibitors possessing nitrile as warhead were prepared and evaluated for their inhibitory activities against plasmin and other serine proteases, plasma kallikrein and urokinase. The most potent peptidic inhibitors with the nitrile warhead exhibit the potency toward plasmin (IC(50) = 7.7-11 µM) and are characterized by their selectivity profile against plasma kallikrein and urokinase. The results and molecular modeling of the peptidic inhibitor complexed with plasmin reveal that the P2 residue makes favorable contacts with the open binding pocket comprising the S2 and S3 subsites of plasmin.

Pseudorenal failure due to intraperitoneal bladder rupture after blunt trauma: usefulness of examining ascitic fluid sediment.

A 42-year-old man noted decreased urine output and visited our emergency department. He said that 3 days previously, he had gotten drunk and fallen down a set of stairs. Blood tests and abdominal contrast-enhanced computed tomography revealed no abnormalities. A serum creatinine level of 5.89 mg/dL led to a diagnosis of acute renal failure and his hospitalization. After admission, his ascitic fluid level gradually increased, suggesting urine leakage into the peritoneal cavity. Microscopic examination of his ascitic fluid sediment revealed the presence of hyaline casts enclosing renal tubular epithelial cells. Cystography demonstrated contrast medium leakage into the peritoneal cavity, which led to a diagnosis of bladder rupture. Examination of ascitic fluid sediment is simple and very useful for diagnosing bladder rupture.

Autologous extracellular cytochrome c is an endogenous ligand for leucine-rich alpha2-glycoprotein and beta-type phospholipase A2 inhibitor.

Beta-type phospholipase A(2) inhibitory protein (PLIbeta) from the serum of the venomous snake Gloydius brevicaudus neutralizes basic phospholipase A(2) (PLA(2)) from its own venom, and it has 33% sequence homology with human leucine-rich alpha(2)-glycoprotein (LRG), which has been recently reported to bind cytochrome c (Cyt c) (Cummings, C., Walder, J., Treeful, A., and Jemmerson, R. (2006) Apoptosis 11, 1121-1129). In the present study, PLIbeta was found to bind Cyt c. The interactions of LRG and PLIbeta with Cyt c were compared by surface plasmon resonance analysis. Human LRG bound horse and snake Cyt c with dissociation constants of 1.58 x 10(-13) M and 1.65 x 10(-10) M, respectively, but did not bind yeast Cyt c, while G. brevicaudus PLIbeta bound horse, snake, and yeast Cyt c with dissociation constants of 1.05 x 10(-10) M, 2.37 x 10(-12) M, and 1.67 x 10(-6) M, respectively. On the other hand, LRG did not show any PLA(2) inhibitory activity and did not bind G. brevicaudus basic PLA(2), whereas PLIbeta bound the basic PLA(2) with a dissociation constant of 1.21 x 10(-9) M, which is smaller than those with the Cyt c described above. The PLA(2) inhibitory activity of PLIbeta was also found to be suppressed by the binding of Cyt c to PLIbeta. These results suggest that autologous Cyt c is an endogeneous ligand for LRG and PLIbeta and that these serum proteins neutralize the autologous Cyt c released from the dead cells.

Inhibitory activities of the heterotrimers formed from two α-type phospholipase A2 inhibitory proteins with different enzyme affinities and importance of the intersubunit electrostatic interaction in trimer formation.

α-type phospholipase A2 inhibitory protein (PLIα) isolated from the serum of the venomous snake Glyoidius brevicaudus, GbPLIα, is a homotrimer of subunits having a C-type lectin-like domain. The serum protein from nonvenomous snake Elaphe quadrivirgata, EqPLIα-LP, is homologous to GbPLIα, but it does not show any inhibitory activity against PLA2s. When a mixture of denaturant-treated monomeric forms of GbPLIα and EqPLIα-LP was used to reconstitute their trimers, no significant amounts of heterotrimers composed of GbPLIα and EqPLIα-LP subunits could be formed. On the other hand, when a mixture of denaturant-treated monomeric forms of GbPLIα and the recombinant chimeric EqPLIα-LP, Eq13Gb37Eq, in which the residues 13-36 were replaced by those of GbPLIα, was used to reconstitute their trimers, significant amounts of their heterotrimers were observed. Furthermore, when a mixture of denaturant-treated monomeric forms of EqPLIα-LP and the recombinant chimeric GbPLIα, Gb13Eq37Gb, in which the residues 13-36 were replaced by those of EqPLIα-LP, was used, significant amounts of their heterotrimers were observed. By comparison of the respective inhibitory activities of the heterotrimeric subspecies, it was suggested that the inhibitory activity of the trimer was governed by one subunit with the highest activity, and not affected by the number of these subunits. The intermolecular electrostatic interactions between Glu23 and Lys28 of GbPLIα were also suggested to be important in stabilizing the trimeric structure. The importance of the electrostatic interaction was supported by the less stability of the homotrimeric structure of a mutant GbPLIα with a single amino acid substitution, GbPLIα(K28E).

Imaging of sialidase activity in rat brain sections by a highly sensitive fluorescent histochemical method.

Sialidase (EC 3.2.1.18) removes sialic acid from sialoglycoconjugates. Since sialidase extracellularly applied to the rat hippocampus influences many neural functions, including synaptic plasticity and innervations of glutamatergic neurons, endogenous sialidase activities on the extracellular membrane surface could also affect neural functions. However, the distribution of sialidase activity in the brain remains unknown. To visualize extracellular sialidase activity on the membrane surface in the rat brain, acute brain slices were incubated with 5-bromo-4-chloroindol-3-yl-α-d-N-acetylneuraminic acid (X-Neu5Ac) and Fast Red Violet LB (FRV LB) at pH 7.3. After 1h, myelin-abundant regions showed intense fluorescence in the rat brain. Although the hippocampus showed weak fluorescence in the brain, mossy fiber terminals in the hippocampus showed relatively intense fluorescence. These fluorescence intensities were attenuated with a sialidase-specific inhibitor, 2,3-dehydro-2-deoxy-N-acetylneuraminic acid (DANA, 1mM). Additionally, the fluorescence intensities caused by X-Neu5Ac and FRV LB were correlated with the sialidase activity measured with 4-methylumbelliferyl-α-d-N-acetylneuraminic acid (4MU-Neu5Ac), a classical substrate for quantitative measurement of sialidase activity, in each brain region. Therefore, staining with X-Neu5Ac and FRV LB is specific for sialidase and useful for quantitative analysis of sialidase activities. The results suggest that white matter of the rat brain has intense sialidase activity.

Syntheses of 2-deoxy-2,3-didehydro-N-acetylneuraminic acid analogues modified by N-sulfonylamidino groups at the C-4 position and biological evaluation as inhibitors of human parainfluenza virus type 1.

Eleven novel sialidase inhibitors 9 and 10 with an N-sulfonylamidino group at the C-4 position of Neu5Ac2en 1 against human parainfluenza virus type 1 (hPIV-1) were synthesized using copper-catalyzed three-component coupling reactions, and their inhibitory activities against hPIV-1 sialidase were studied.