Synthesis and influenza virus sialidase inhibitory activity of analogues of 4-guanidino-Neu5Ac2en (GG167) with modified 5-substituents

Five Novel Non-Sialic Acid-Like Scaffolds Inhibit In Vitro H1N1 and H5N2 Neuraminidase Activity of Influenza a Virus

Neuraminidase (NA) of influenza viruses enables the virus to access the cell membrane. It degrades the sialic acid contained in extracellular mucin. Later, it is responsible for releasing newly formed virions from the membrane of infected cells. Both processes become key functions within the viral cycle. Therefore, it is a therapeutic target for research of the new antiviral agents. Structure–activity relationships studies have revealed which are the important functional groups for the receptor–ligand interaction. Influenza virus type A NA activity was inhibited by five scaffolds without structural resemblance to sialic acid. Intending small organic compound repositioning along with drug repurposing, this study combined in silico simulations of ligand docking into the known binding site of NA, along with in vitro bioassays. The five proposed scaffolds are N-acetylphenylalanylmethionine, propanoic 3-[(2,5-dimethylphenyl) carbamoyl]-2-(piperazin-1-yl) acid, 3-(propylaminosulfonyl)-4-chlorobenzoic acid, ascorbic acid (vitamin C), and 4-(dipropylsulfamoyl) benzoic acid (probenecid). Their half maximal inhibitory concentration (IC₅₀) was determined through fluorometry. An acidic reagent 2′-O-(4-methylumbelliferyl)-α-dN-acetylneuraminic acid (MUNANA) was used as substrate for viruses of human influenza H1N1 or avian influenza H5N2. Inhibition was observed in millimolar ranges in a concentration-dependent manner. The IC₅₀ values of the five proposed scaffolds ranged from 6.4 to 73 mM. The values reflect a significant affinity difference with respect to the reference drug zanamivir (p < 0.001). Two compounds (N-acetyl dipeptide and 4-substituted benzoic acid) clearly showed competitive mechanisms, whereas ascorbic acid reflected non-competitive kinetics. The five small organic molecules constitute five different scaffolds with moderate NA affinities. They are proposed as lead compounds for developing new NA inhibitors which are not analogous to sialic acid.

Synthesis of novel pentacyclic triterpene-Neu5Ac2en derivatives and investigation of their in vitro anti-influenza entry activity

Sialic acid derivatives, analogs, and their conjugates are important pharmacophores. Modification of the C-4 hydroxyl group of sialic acid can lead to derivatives, such as zanamivir, with potent anti-influenza activities. Herein, we described the synthesis of C-4-modified sialic acid derivatives via conjugation with naturally derived pentacyclic triterpenes, which are active ingredients of traditional Chinese medicine, and the evaluation of their in vitro anti-influenza virus activity in MDCK cells. Interestingly, a set of configurational isomers was obtained during the de-O-acetylation reaction of two pentacyclic triterpene-sialic acid conjugates under Zemplén conditions, and a mechanism was proposed. Owing to the attachment of the Neu5Ac2en moiety, all synthesized conjugates displayed lower hydrophobicity than their parent compounds. In comparison with ursane- and lupane-type triterpenes, oleanane-type triterpene-functionalized Neu5Ac2en conjugates were most promising. The insertion of a (1,2,3-triazol-4-yl)-methyl between the amide bond and Neu5Ac2en caused a substantial decrease in activity. Compound 15a exhibited the highest inhibitory activity (IC50 = 8.3 μM) and selectivity index (SI = 22.7). Further studies involving hemagglutination inhibition and neuraminidase inhibition suggested that compound 15a inhibited virus-induced hemagglutination with no effect on the enzymatic activity of neuraminidase, indicating that the antiviral activity appeared to be mediated via interaction with hemagglutinin at the initial stage of viral infection.

Influenza Neuraminidase Inhibitors: Synthetic Approaches, Derivatives and Biological Activity

Despite being a common viral disease, influenza has very negative consequences, causing the death of around half a million people each year. A neuraminidase located on the surface of the virus plays an important role in viral reproduction by contributing to the release of viruses from infected host cells. The treatment of influenza is mainly based on the administration of neuraminidase inhibitors. The neuraminidase inhibitors zanamivir, laninamivir, oseltamivir and peramivir have been commercialized and have been demonstrated to be potent influenza viral neuraminidase inhibitors against most influenza strains. In order to create more potent neuraminidase inhibitors and fight against the surge in resistance resulting from naturally-occurring mutations, these anti-influenza drugs have been used as templates for the development of new neuraminidase inhibitors through structure-activity relationship studies. Here, we review the synthetic routes to these commercial drugs, the modifications which have been performed on these structures and the effects of these modifications on their inhibitory activity.

Oxidative Deamination of N-Acetyl Neuraminic Acid: Substituent Effects and Mechanism

A study of the mechanism of the oxidative deamination of the N-nitroso-N-acetyl sialyl glycosides leading with overall retention of configuration to the corresponding 2-keto-3-deoxy-D-glycero-D-galacto-nonulopyranosidonic acid (KDN) glycosides is described, making use of a series of differentially O-protected N-nitroso-N-acetyl sialyl glycosides and of isotopic labeling studies. No evidence is found for stereodirecting participation by ester groups at the 4- and 7-positions. Comparisons are drawn with oxidative deamination reactions of 4-amino-4-deoxy and 2-amino-2-deoxy hexopyranosides and a common mechanism is formulated involving the intermediacy of 1-oxabicyclo[3.1.0]hexyl oxonium ions following participation by the pyranoside ring oxygen. A minor reaction pathway has been uncovered by labeling studies in the β-thiosialosides that results in the exchange of the 4-O-acetyl group by the glacial acetic acid that serves as external nucleophile in the general oxidative deamination process. A mechanism is proposed for this exchange involving participation by the thioglycoside at the level of an intermediate diazoalkane.

From neuraminidase inhibitors to conjugates: a step towards better anti-influenza drugs?

For the treatment of seasonal flu and possible pandemic infections the development of new anti-influenza drugs that have good bioavailability against a broad spectrum of influenza viruses including the resistant strains is needed. In this review, we summarize previous methods for the structural modification of zanamivir, a potent neuraminidase inhibitor that has rare drug resistance, in order to develop effective anti-influenza drugs. We also report recent research into the design of multivalent zanamivir drugs and bifunctional zanamivir conjugates, some of which have shown better efficacy in animal experiments. As a step towards developing improved antivirals, conjugating anti-influenza drugs with anti-inflammatory agents can improve oral bioavailability and also exert synergistic effect in influenza therapy.

Exploring human parainfluenza virus type-1 hemagglutinin-neuraminidase as a target for inhibitor discovery

Human parainfluenza virus type 1 is the major cause of croup in infants and young children. There is currently neither vaccine nor clinically effective treatment for parainfluenza virus infection. Hemagglutinin-neuraminidase glycoprotein is a key protein in viral infection, and its inhibition has been a target for 2-deoxy-2,3-didehydro-d-N-acetylneuraminic acid (Neu5Ac2en)-based inhibitor development. In this study, we explore the effect of C-5 modifications on the potency of Neu5Ac2en derivatives that target the human parainfluenza type-1 hemagglutinin-neuraminidase protein. Our study demonstrates that the replacement of the Neu5Ac2en C-5 acetamido moiety with more hydrophobic alkane-based moieties improves the inhibitory potency for both hemagglutinin-neuraminidase functions. These findings shed light on the importance of C-5 substitution on Neu5Ac2en in the design of novel sialic acid-based inhibitors that target human parainfluenza type-1 hemagglutinin-neuraminidase.

A DNA-templated synthesis of encoded small molecules by DNA self-assembly

Encoded libraries can be prepared by DNA-templated synthesis without any DNA template.

Regioselective synthesis of 4azido-Neu2en5,7Ac(2)1Me and its intramolecular transformation to 4azido-Neu2en5,9Ac(2)1Me

Methyl 5-N-acetyl-7-O-acetyl-4-azido-2,3-didehydro-2,4-dideoxy-neuraminic acid (4azido-Neu2en5,7 Ac(2)1Me) was synthesized regioselectively starting from 4azido-Neu2en5Ac1Me in high yield. The transformation of 4azido-Neu2en5,7Ac(2)1Me to the corresponding thermodynamically stable 4azido-Neu2en5,9Ac(2)1Me via intramolecular acetyl migration was confirmed by single-crystal X-ray diffraction analysis. The proposed rearrangement mechanism is discussed.

Anti-influenza virus agents: synthesis and mode of action

Annual epidemics of influenza virus infection are responsible for considerable morbidity and mortality, and pandemics are much more devastating. Considerable knowledge of viral infectivity and replication has been acquired, but many details still have to be elucidated and the virus remains a challenging target for drug design and development. This review provides an overview of the antiviral drugs targeting the influenza viral replicative cycle. Included are a brief description of their chemical syntheses and biological activities. For other reviews, see References1-9.

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.

Synthesis and anti-influenza virus activity of 4-guanidino-7-substituted Neu5Ac2en derivatives

Substitution of 7-OH by small hydrophobic groups on zanamivir resulted in the retaining of low nanomolar inhibitory activities against not only influenza A virus sialidase but also influenza A virus in cell culture. These compounds were prepared by treatment of the corresponding 7-substituted sialic acids derived from 4-modified N-acetyl-D-mannosamine (ManNAc) using enzyme-catalyzed aldol condensation.

Sialidase inhibitors related to zanamivir. Further SAR studies of 4-amino-4H-pyran-2-carboxylic acid-6-propylamides

SAR investigations of the 4- and 5-positions of a series of 4-amino-4H-pyran-2-carboxylic acid 6-carboxamides are reported. Potent inhibitors of influenza A sialidase with marked selectivity over the influenza B enzyme were obtained when the basic 4-amino substituent was replaced by hydroxyl or even deleted. Modifications at the 5-position exhibited a tight steric requirement, with trifluoroacetamide being optimal.

Synthesis and influenza virus sialidase inhibitory activity of analogues of 4-Guanidino-Neu5Ac2en (Zanamivir) modified in the glycerol side-chain

Analogues of 4-Guanidino-Neu5Ac2en (Zanamivir) have been prepared containing carbamate substituents at the 7-hydroxy position. (4S,5R,6R)-5-Acetylamino-6-[1R-[(6-aminohexyl)carbamoyloxy]-2R,3-dihydroxypropyl]-4-guanidino-5,6-dihydro-4H-pyran-2carboxylic acid and (4S,5R,6R)-5-Acetylamino-6-[1R-[heptylcarbamoyloxy]-2R,3-dihydroxypropyl]-4-guanidino-5,6-dihydro4H-pyran2-carboxylic acid were the two analogues possessing activity comparable to Zanamivir, showing potent inhibition of influenza virus sialidases and good antiviral activity in vitro.

Sialidase inhibitors related to zanamivir: synthesis and biological evaluation of 4H-pyran 6-ether and ketone

Synthesis of 5R-Acetamido-4S-amino-4H-pyran-6R-O-( -ethyl)propyl and 6R-(1-oxo-2-ethyl)butyl 2-carboxylic acids (4 and 5) and their evaluation as inhibitors of influenza virus sialidase is described. Both compounds showed good inhibitory activity with marked selectivity for influenza A sialidase.

Influenza Neuraminidase Inhibitors Possessing a Novel Hydrophobic Interaction in the Enzyme Active Site: Design, Synthesis, and Structural Analysis of Carbocyclic Sialic Acid Analogues with Potent Anti-Influenza Activity

The design, synthesis, and in vitro evaluation of the novel carbocycles as transition-state-based inhibitors of influenza neuraminidase (NA) are described. The double bond position in the carbocyclic analogues plays an important role in NA inhibition as demonstrated by the antiviral activity of 8 (IC50 = 6.3 microM) vs 9 (IC50 > 200 microM). Structure-activity studies of a series of carbocyclic analogues 6a-i identified the 3-pentyloxy moiety as an apparent optimal group at the C3 position with an IC50 value of 1 nM for NA inhibition. The X-ray crystallographic structure of 6h bound to NA revealed the presence of a large hydrophobic pocket in the region corresponding to the glycerol subsite of sialic acid. The high antiviral potency observed for 6h appears to be attributed to a highly favorable hydrophobic interaction in this pocket. The practical synthesis of 6 starting from (-)-quinic acid is also described.

Sialidases: structures, biological significance and therapeutic potential

The structure-based design of a potent inhibitor of the influenza-virus neuraminidase (sialidase) is one of the outstanding successes of rational drug design. Recent clinical trials of the drug have stimulated many companies to seek a share of the potentially huge flu market. Sialidases, however, are involved in the pathogenesis of a whole range of other diseases, so perhaps the knowledge and expertise gained from the influenza story can be used in the design of other drugs, given that they all share certain structural features.