key: cord-0871126-cragva7g
authors: Lagoja, Irene M.; De Clercq, Erik
title: Anti‐influenza virus agents: Synthesis and mode of action
date: 2006-12-07
journal: Med Res Rev
DOI: 10.1002/med.20096
sha: bdd32f74cc1be5920e8a91cdcf5c1328404b971b
doc_id: 871126
cord_uid: cragva7g

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 References.1, 2, 3, 4, 5, 6, 7, 8, 9 © 2006 Wiley Periodicals, Inc. Med Res Rev, 28, No. 1, 1–38, 2008

The replicative cycle of influenza virus offers several virus-specific events which could be considered as targets for chemotherapeutic intervention (Fig. 1 ). 10 From Figure 1 it is apparent that the replicative cycle of influenza virus could be interrupted at several stages, that is (i) virus attachment to the cells mediated by the interaction of hemagglutinin (HA) with its receptor at the cell surface, (ii) endocytosis and fusion of the viral envelope with the cell membrane, (iii) uncoating of the viral particles within the endosomes following penetration of H þ ions, through the M2 matrix ion channel, into the interior of the virions, (iv) transcription of the viral (À)RNA genome to messenger (þ)RNA, through the polymerase complex (PA, PB1, and PB2), (v) translation of mRNA to viral proteins, (vi) packaging and budding of progeny virus particles from the cell surface resulting in (vii) the release of these progeny virions, and allowing further spread of the virus infection. In Figure 1 , the sites for chemotherapeutic intervention are highlighted for amantadine, siRNAs (short interfering RNAs) and neuraminidase inhibitors. Here we will review the different anti-influenza virus agents in function of their interaction with the different targets within the viral replication cycle.

Inhibition of binding HA to the epithelial cells could be an efficient means of blocking infection. The crystal structure of HA complexes with various derivatives of sialic acid has been determined. 11 Such knowledge has led to a rational design of carbohydrate-based inhibitors of HA. 12 Collectins also bind to the viral HA and probably prevent infection by interfering with the cellular binding activity of HA. 13 The most effective strategy has been to take advantage of the nature of the interaction of the virus with its receptor, which depends on the thermodynamic advantage offered by engaging in multiple simultaneous binding interactions. Whilst bivalent sialic acid ligands provide some advantage, the most potent and effective sialic acid receptor antagonists that have shown activity in vitro incorporate sialic acid moieties onto polymeric templates, [14] [15] [16] a strategy used advantageously by nature. 17 The structure and physical properties of the template employed to project the sialic acid residues are of importance, and hydrophobic components appear to be necessary for high affinity binding. For example, the heptasaccharide derivative 5, a rather complex bivalent ligand, inhibits influenza virus adsorption to erythrocytes (hemagglutination) with an IC 50 of 0.18 mM, 18 whereas the structurally simpler dimeric ligand 2 inhibits hemagglutination with an IC 50 of 3 mM. 12 Branched, dendrite like amino acid backbones capped with sialic acid moieties afforded molecules that cluster 4, 8, or 16 residues and are effective inhibitors of hemagglutination of erythrocytes. 19 An alternative approach has focused on the incorporation of differing concentrations of the sialoside lipid 4 into liposomes, followed by irradiation-induced polymerization. 20 Following synthetically convergent methodology, three different families of compounds of varying linker span length were generated. Peracetylation of methyl-N-acetyl-b-D-neuraminate 21 afforded 8, which in turn was converted into Sialoside 7 by treatment with 5-hexen-1-ol and Hg(CN) 2 followed by oxidation with KMnO 4 (Scheme 1).

Molecules were made, for example, from ethylene glycol (Scheme 2). The synthesis of the sidechain of the 1 series is exemplified for m ¼ 2.

Synthesis of the side-chain of the 2 series, bearing peptidic linkers-derived from glycine, is exemplified for n ¼ 4 (Scheme 3).

Finally, also urea-based linkers containing piperazine units were investigated, the synthesis of the side-chain of the 3 series is exemplified for P ¼ 3, q ¼ 1 (Scheme 4). 

The influenza virus HA is synthesized as a single polypeptide precursor (HA () ) and is cleaved into HA 1 and HA 2 subunits by host proteases. Proteolytic cleavage of HA at the virion surface is essential for the infectivity of all three influenza types (A, B, C) 22 and, therefore, probably vulnerable to antiviral intervention. 23, 24 Proteolytic inhibitors have been shown to possess anti-influenza activity in mice. 25 In addition, pulmonary surfactant may act as an endogenous inhibitor of proteolytic activation of the influenza-A HA. 26 The protease inhibitor E-aminocaproic acid (E-ACA) decreases virus replication in the lungs of influenza-challenged mice. 27 Mechanistic studies with E-ACA on proteases in mice infected with influenza virus suggest that this compound may act at least in part by inhibition of HA cleavage. 28 Influenza virus is believed to enter mammalian cells by endocytosis in clathrin-coated pits. The virus fuses with endosomal membrane through an irreversible conformational change in the HA molecule caused by a lowering of the vesicle pH by action of an ATP-dependent H þ pump.

BMY-27709 23 inhibits fusion of H1 and H2 influenza viruses by specifically docking in a hydrophobic pocket around the fusion peptide. 29 An initial survey of the SAR associated with the salicyclic acid element of BMY-27709 23 indicated an essential role for the 2-hydroxyl (or 2-MeO) and revealed limited tolerance for additional substituents, except the 5-position, where lipophilic substituents such as CH 3 , Cl, F, or CF 3 , afforded potent antiviral agents with EC 50 s correlating with inhibition of hemolysis. However, more polar functional groups at the 3-position, specifically CN, NO 2 , and CO 2 Me afforded analogs considered to be inactive.

The salicylamide derivatives 23-25 can be obtained by heating the cyclic acetonide 32, 30 simultaneously protecting as well the acid as the phenol moiety, with the corresponding amine in toluene. 31 Alternatively, derivatives 23-25 can be prepared by condensation of the corresponding acid chloride 33 with an amine 34 with Et 3 N/DMAP. 32 Further treatment with Lawesson's reagent yields the corresponding thioamides 24c and 25c (Scheme 5).

The mixtures of the amide diastereomers 24a/25a and the analogous chloro derivatives 24b/25b both exhibited EC 50 s of 0.08 mg/mL for the inhibition of influenza infectivity in cell culture. The most potent inhibitor of these series proved to be the axial thioamide 24c, EC 50 0.02 mg/mL, whilst the equatorial isomer 25c was inactive at concentrations below the half maximally cytotoxic concentration (CC 50 of 10 mg/mL). Structurally similar compounds such as CL61917, CL385319 (26) , and CL62554 (27) (Wyeth-Ayerst) 33 have also been found to be fusion inhibitors of the influenza Avirus. These compounds were more active against H1 (IC 50 s 0.1-12 mg/mL) and H2 (IC 50 s 0.4-1 mg/mL) than against H3 virus (IC 50 24 mg/mL). Tert-butylhydroquinone 28 and its congeners were designed to block the conformational change of HA by a molecular docking programme. 34 However, the HA protein was shown to become resistant to the proteolytic actions of trypsin, thermolysin and proteinase-K after treatment with fusion inhibitors 23, 26b, and 28.

Endosomal acidification can be prevented in a relatively unsophisticated fashion by agents that act as general bases to buffer the gradually declining pH. These are typically basic amine derivatives, which are only effective at concentrations too high to be considered of physiological relevance. For example, millimolar concentrations of the anti-parkinson agent norakin 21 35 and chloroquine 22 36 are thought to function in this fashion.

In contrast to stabilizing the HA at low pH, some compounds are able to destabilize it at neutral pH, causing inactivation by a conformational change before endosomal entry. A series of podocarpic acids interact with HA at neutral pH and prevent the low pH-induced change to the fusogenic conformation. These compounds are similarly effective against H1 and H2 influenza viruses but are less active against H3 or influenza B viruses. In mice infected with a lethal challenge of influenza A compounds LY313177 30b and LY311912 30c gave survival rates of 90% and 80%, respectively, with intraperitoneal doses of up to 200 mg/kg bid for 8 days. 37 The novel antiviral protein cyanovirin-N (CV-N) was initially discovered based on its potent activity against the human immunodeficiency virus (HIV). Remarkably, however, CV-N and related homologs showed highly potent antiviral activity against almost all strains of influenza A and B virus, including clinical isolates and a neuraminidase inhibitor-resistant strain (EC 50 ¼ 0.004-0.04 mg/ mL). When influenza virus particles were pretreated with CV-N, viral titers were lowered significantly (>1,000-fold). Further studies identified influenza virus hemagglutinin as a target for CV-N, showed that antiviral activity and hemagglutinin binding were correlated, and indicated that CV-N's interactions with hemagglutinin involved oligosaccharides. 38 However, all of the fusion inhibitors appear to have a narrow spectrum of activity against H1, H2, or H3 influenza A viruses.

Determination of the molecular mechanism of action of the adamantanes has allowed rational development of additional inhibitors of the M2 ion channel. 39 Amantadine 35 (1-adamantanamine) has been established as effective in the prophylaxis and treatment of influenza A virus infections. [40] [41] [42] [43] Although initially licensed in 1966, the clinical use of adamantines as been limited by central nervous system (CNS) side effects. 44 Current interest in M2 inhibitors not only led to the development of new, highly potent compounds, but also prompted the optimization of the synthesis of amantadine 35 and rimantadine 36. Koch-carbonylation 46 is known as the transformation from carbon monoxide with alcohols or olefins and water to carboxylic acids. However, the reaction usually has to be carried out under severe conditions such as high CO pressure, high temperature, and strong acidic conditions; therefore much attention has been focused on a convenient and environmentally benign process for this synthetic route. 47 The preparation of non-symmetrical ketons by the reaction of acyl chlorides and the corresponding Grignard reagents in the presence of catalytic amounts of metal halides has been previously described in the literature. The reaction conditions have been optimized to an efficient, cheap and fast method for the preparation of adamantyl ketons. 48 Novel amantadine and rimantadine derivatives have been synthesized and evaluated by Kolocouris et al. [49] [50] [51] [52] [53] [54] [55] These new adamantane derivatives were found to inhibit the replication of influenza Avirus at an EC 50 (50% antivirally effective concentration) of 1.2 mg/mL (spiro[cyclopropane-1,2 0 -adamantan]-2-amine, 37), 49 0.56 mg/mL (spiro[pyrrolidine-2,2 0 -adamantane, 38), 49 0.24 mg/mL (spiro[piperidin-2,2 0 -adamantane, 43), 52 0.6 mg/mL (2-1-adamantanyl)pyrrolidine, 47), 52 53 In all cases, these EC 50 values compared favorably to that of amantadine 35 when evaluated under the same experimental conditions. Bananins 56 (Chart 4) show a close structure relationship to the previously discussed adamantane derivatives. They represent a class of antiviral compounds with a unique structural signature incorporating a trioxa-adamantane moiety covalently bound to a pyridoxal derivative. The bananins were synthesized by the reaction of phloroglucinol (most likely in its triketo tautomeric form) with aromatic aldehydes, catalyzed by hydrochloric acid or sodium hydroxide in aqueous solution. 57 Generally, acidic catalysis was used due to the degradation of pyridoxal under highly basic conditions. Alkaline catalysis was used for reaction with aromatic aldehydes such as vanillin to obtain Vanillinbananin (VBN) 55. Bananin synthesis is driven by the creation of the highly symmetric trioxa-adamantane-triol (TAT) cage system. The prototypical compound of the TAT series, the vitamin B6-derived bananin (BAN) 53 can be iodinated with subsequent oxidation to iodobananin (IBN) 54. The iodine in IBN can be replaced by various substituents as exemplified by the synthesis of adeninobananin (ADN) 56, using an activated adenine nucleobase derivative. Interestingly, BAN 53 is susceptible to Michael addition with the natural product eugenol. This NaOH-catalyzed addition leads to eubananin (EUB) 57, which can be transformed by cyclic hemiketal condensation into the ansa-compound ansabananin (ABN) 58, inspired by ansamycins such as rifamycin and geldanamycin. 58 Newer agents related to M2 function (Chart 6) include norbornylamine 60 59 , a novel spirocompound-BL-1743 (61) and bafilomycin A1 (62), a macrolide antibiotic. ICI 130685 59 60 , has advanced into clinical trials but was not approved for clinical use Chart 6.

BL-1743 (61) 61 was found to block the M2 channel when expressed in Xenopus oocytes. 62 However, cross-resistance with amantadine occurs with this compound. Bafilomycin A1 (62) is a specific inhibitor of vacuolar-type H þ ATPase which completely abolishes the acidified cell components (endosomes and lysosomes) in influenza A and B virus-infected, and uninfected, Madin-Darby canine kidney (MDCK) cells. 63 The action of both of these compounds, unlike amantadin 35, is reversible. 64 

There are several opportunities for therapeutic intervention to disrupt the carefully orchestrated role of HA in influenza infectivity. One strategy that has been explored is inhibition of the cellular enzymes responsible for the essential proteolytic cleavage of HA, an important determinant of pathogenicity and cell tropism. 65 However, progress in this area has been confounded by the multitude of cellular and extracellular trypsin-like enzymes capable of performing this step, 66 influenza virus infections. Nevertheless, both the trypsin inhibitor futhan 63 and an anticathepsin B IgG antibody have been shown to possess influenza-inhibitory activity in an in vitro setting. 69, 70 The quinone 64 was identified as a specific inhibitor of the fusion-inducing conformational change (IC 50 ¼ 250 mM); the hydroquinone form 65 71 proved to be more potent, with an IC 50 of 25 mM. Although the chemical properties of 64 and 65 make them unlikely drug candidates, these compounds represent the first of a new mechanistic class of influenza virus inhibitors that demonstrate the feasibility of preventing the conformational change of HA with small molecules of limited complexity. More recently, the flavone 66, which contains some structural elements in common with 64 and 65, has also been postulated to interfere with the fusion of influenza viral and endosomal membrane. 72 Furthermore, 66 has been reported to be a non-competitive inhibitor of influenza virus sialidase (IC 50 ¼ 55 mM). 73 

The host cell transcriptional machinery is used by the influenza virus polymerase complex during viral RNA transcription for capping, cap-methylation and splicing of viral mRNAs. The polymerase transcription complex of influenza viruses consists of a trimeric structure. This complex consists of PB1 (transcriptase), PB2 (cap-binding protein and possibly endonuclease) and PA (essential cofactor of unknown function). Association of the polymerase with RNA template, which harbors essential and influenza virus-specific sequence motifs, and with the nucleoprotein (NP, RNA binding protein) is required for full transcriptase activity. 74 The polymerase of influenza viruses contains an endonuclease activity that cuts the host cell mRNA at approximately 10-16 nucleotides from the 5 0 -cap. It then uses the capped oligonucleotides as primers for the generation of capped, viral mRNA. The endonuclease is a unique and highly conserved target present in all influenza viruses.

Divalent metal ions are required for enzymatic catalysis of the endonuclease reaction 75 and a number of potential metal ion chelating compounds have been described for this target. Flutimide 67 (isolated from Delitschia confertaspora) selectively inhibits the cap-dependent transcriptase of influenza A and B viruses. In MDCK cells, flutimide 67 inhibited influenza virus replication with an IC 50 of 5.1 mM and exhibited no cytotoxictiy at concentrations up to 100 mM. 76 Flutimide 67 is a fully substituted 1-hydroxy-3H-pyrazin-2,6-dione containing the following crucial groups: an N-hydroxyimide, an imine and an exocyclic enamine with Z-geometry. 77 The endocyclic imine may help in the stabilization of the exocyclic enamine via extended conjugation. The synthetic pathway to obtain this compound with these unusual structural features is outlined in Scheme 6. The N-alkylation of (S)-Leu-OMe.HCl 71 at 60 C with equimolar amounts of a-bromotert-butyl acetate in CH 3 p-methoxybenzyl (PMB) chloride, the tert-butyl protecting group of the corresponding ester 73 was selectively hydrolyzed with TFA. The acid group of 74 was activated with N-hydroxysuccinimide to produce the active ester 75, which was then reacted with neutralized hydroxylamine to give compound 76, which subsequently could be cyclized to 77. The N-hydroxy group of 77 was conveniently protected with MOM chloride to afford MOM ether 78.

Aldol condensation of 68 with isobutyraldehyde and lithium hexamethyldisilazide (LHMDS) at À78 C exclusively produced the 3S,5S,11R-stereo-isomer of flutimide advanced hydroxy intermediate 79. The aldol product 79 was reacted with methanesulfonyl chloride (MsCl), DIPEA, and DMAP at À23 C to give in quantitative yield the corresponding mesylate 80. The b-elimination reactions turned out to be challenging; finally, reaction of mesylate 80 at 0 C with 3 equiv of DBU in toluene gave 74% combined yield of a 3:1 Z/E mixture of olefins 81a and 81b, respectively. The oxidation of 81a with DDQ in a mixture of CH 2 Cl 2 -H 2 O (2:1) gave the expected oxidized product 82 in moderate yield, due to decomposition of the product, presumably caused by hydration and a subsequent cascade of rearrangement reactions. Finally deprotection with TFA/CH 2 Cl 2 gave Flutimide 67.

BMY-26270 (68) selectively inhibits the endonuclease activity of influenza A and B viruses. 78 L735,882 (69) is an example of a series of 4-substituted 2,4-dioxobutanoic acid endonuclease inhibitors. This compound showed antiviral activity in cell culture against influenza A and B viruses with IC 50 s of 6 and 2 mM respectively, and no apparent cytotoxic effects in MDCK cells at concentrations up to 100 mM. 79 Other members of this series showed antiviral activity with IC 50 s of 0.18 mM and higher. 80 The nucleoside analog 2 0 -deoxyfluoroguanosine (2-FDG) 70 appears to be a specific inhibitor of influenza transcriptase activity that targets the active site of the polymerase subunit PB1. The triphosphate of 2-FDG 70 showed competitive inhibition with GTP in vitro, and incorporation of this nucleoside analog in place of GTP by the influenza virus polymerase leads to chain termination during transcription initiation. 81 The series of various substituted 2 0 -deoxy-2 0 -fluororibosides have been synthesized by enzymic pentosyl transfer from 2 0 -deoxy-2 0 -fluorouridine. 81 Different strains of influenza A and B viruses were sensitive to 2-FDG with IC 50 's ranging from 0.2-1 mM in chicken embryo fibroblast cells and from 2 to 22 mM in MDCK cells. 82 The mean pulmonary viral titer of influenza A and B in mice was significantly reduced after intraperitoneal treatment with 2-FDG (120 mg/kg up to 24 hr post-infection) as compared with untreated controls. This compound also appeared to be more effective than amantadine 35 (against influenza A) and ribavirin 36 (against influenza B). 83 However, both 2-FDG 70 and a pro-drug (2,6-diaminopurine-2 0 -fluororibonucleoside) have not progressed beyond preclinical development.

Extracts and products of plant origin provide an alternative source for substances with virusinhibitory activity. 84 Although T705 (84) can hardly be considered a purine nucleoside base, it has been purported that cellular enzymes recognize T705 (84) as nucleoside base and convert it to the phosphorylated metabolites 93 and 94. 94 Structural similarity with known IMPDH inhibitors (discussed in Section 7) suggested the transformation into the monophosphate 93, leading to a reduction of the GTP pool size in infected cells. However, inhibition of IMPDH by T-705RMP (93) was about 150-fold lower than that by ribavirin (100) Another interesting report of transcription inhibitors is of antisense oligonucleotides targeted at the PB2 genome. An antisense nucleotide that was stabilized by chimera formation between DNA and RNA and had a dumbbell structure on both ends of the nucleotide with cytosine and alkyl loops was synthesized.

This antisense oligonucleotide complementary to influenza viral RNA polymerase components were administered intravenously, in liposome-encapsulated form, to mice, and were shown to significantly prolong survival after infection with the influenza A virus. 97, 98 DNA enzymes targeting the PB2 mRNA translation initiation (AUG) region of the influenza A virus (A/PR/8/34) have been designed. The modified DNA enzymes have one or two N3P-P5P phosphoramidate bonds at both the 3 0 -and 5 0 termini of the oligonucleotides, which significantly enhanced their nuclease-resistance. These modified DNA enzymes had the same cleavage activity as the unmodified DNA enzymes, determined by kinetic analyses, and reduced influenza A virus replication by more than 99%, determined by plaque formation. These DNA enzymes are highly specific since their protective effect was not observed in influenza B virus (B/Ibaraki)-infected MDCK cells. 99 

Inhibition of inosine monophosphate dehydrogenase (IMPDH; E.C.1.1.1.250) results in decrease in the intracellular proof of GTP, required for the synthesis of nucleic acids. This mechanism of action accounts for the anti-influenza activity of LY217896 (99) . Compound 99 is active against several influenza A and B viruses in MDCK cells with IC 50 values of 0.37-1.19 and 0.75-1.54 mg/mL. 100 In addition, this compound protected mice against influenza A and B infection when it was administered orally immediately, or several days, after the experimental infection. However, the development of 99 has been discontinued because of a lack of clinical efficacy and increased patient serum uric acid levels. 101 Ribavirin (Virazole) 100, a synthetic guanosine derivative, is a broad spectrum antiviral that is active against several RNA virus families. Several mechanisms of action have been proposed for the anti-influenza virus activity 102-104 of ribavirin 100 among which IMPH inhibition (see above), inhibition of the mRNA 5 0 -cap formation and inhibition of the virus-coded RNA polymerases that are necessary to initiate and elongate viral mRNAs. 105 

Neuraminidase inhibitors interact with a unique (albeit very late) target in the viral replicative cycle, that is the release of the progeny virus particles from the cells (Fig. 2) . 106 Release of the virus particles from the cells requires the action of the virus-associated neuraminidase which cleaves off the terminal N-acetylneuraminic acid (sialic acid) (linked through an a2 > 6 or a2 > 3 bond with galactose in the influenza A H3N2 and H5N1 receptor, respectively). This cleavage is needed for the virus particles to be released from the infected cells and allows the virus to spread to other cells. Neuraminidase inhibitors prevent this release and thus ''trap'' the newly formed virus particles at the cell surface, thereby inhibiting further virus spread.

Oseltamivir 101, the highly water soluble phosphate salt of the trisubstituted cyclohexene ethylcarboxylate, has been claimed as ''molecule of the month'' in December 2005. 107 However, chemistry still remains a challenge. Since the synthesis has been excessively reviewed before, [108] [109] [110] [111] only the latest developments will be documented.

Originally the synthesis started from (À)-shikimic acid 102, isolated from Illicium verum (chinese star anise) or (À)-quininic acid 103, isolated from the African Cinchona Tree. 112, 113 Epoxide RO0640792 104 can be seen as key intermediate, which can be converted to oseltamivir phosphate using azide-chemistry, 114 an allylamine route 115 or a t-butylamine-diallylamine route. 116 The latter would allow a safe scale-up for industrial purposes. Due to availability problems of the natural sources in case of a pandemic much effort was paid to cheaper, easier available syntheses. 117 The desymmetrization protocol 118 outlined in Scheme 10 is based on an enzymatic monohydrolysis of an all-cis meso diester 109 to the optically active mono-acid 110. Starting from inexpensive 1,6-dimethoxy phenol 105 the 3-pentyl ether is introduced followed by bromination to the dibromide 106. The Pd-catalyzed double ethoxycarbonylation furnished the isophalic diester 107, which was hydrogenated over Ru-Alox to the all-cis meso-diester 108 with high selectivity and yield. Nearly quantitative and highly selective cleavage of the methyl ether groups of 108 using in situ generated TMS-iodide provided the meso-dihydroxy intermediate 109, ready for the enzymatic desymmetrization. Using pig liver esterase (PLE) at slightly elevated temperature (35 C) afforded the desired (S)-(þ)-monoacid 110 in high yield and selectivity. Using Yamada-Curtius degradation 119 of 110, the 5-amino-functionality is introduced, resulting in the formation of the oxazolidinone 111. Following Boc-protection compound 112 is obtained by heating the mixture in toluene with traces of sodium hydride. By this way an effective and selective formation of the 1,2-double bond with simultaneous cleavage of the oxazolidinone system is achieved. TfO is used to introduce a good leaving group. The 4-amino functionality was finally introduced via S N 2-substitution of 113, using sodium azide with concomitant inversion of configuration under mild alkaline conditions. Azide reduction, N-acetylation, Boc-deprotection and the phosphate salt formation gave the final product 101 in 30% overall yield.

Very recently, a new concept to obtain Oseltamivir 101 by way of a Diels-Alder approach has been reported (Scheme 11). 120 Starting from butadiene 114 and trifluoroethyl acrylate 115 in the presence of the S-proline-derived catalyst 116, Diels-Alder reaction was carried out to obtain 117 in excellent yield. 121 Ammonolysis of 117 produced amide 118 quantitatively. Iodolactamization of 118 using the Knapp protocol 122 generated lactam 119 in high yield. Following N-protection with Boc 2 O dehydroiodination occurred cleanly to give 120, which was allylically brominated using N-bromosuccinimide to generate 121. Treatment of 121 with cesium carbonate quantitatively afforded the diene ethyl ester 122. A novel SnBr 4 catalyzed bromoacetimidation reaction, which was completely regioselective and stereoselective, converted the diene 122 into the bromodiamide 123. Treatment with in situ generated tetra-n-butyl-ammonium hexamethyldisilazane furnished the N-acetylaziridine 124, which could be regioselctively converted into the ether 125 by reaction with 3-pentanol and cupric triflate catalysis (not optimized). Finally, removal of the protecting groups afforded oseltamivir 101.

Scheme 11. Synthesis of oseltamivir101 by Diels-Alder reaction.

The synthetic strategy 123 to prepare Zanamivir 126 124,125 originally started from N-acetylneuraminic acid 127 (Scheme 12). 126, 127 Following protection of the acid function peracetylation gave 128 128 . Lewis acid-catalyzed elimination and an intramolecular cyclization reaction yielded the 3a,7adihydro-4H-pyrano [3,4-d] [1, 3] oxazole derivative 129 which, in turn, achieved upon treatment with trimethylsilylazide the azide 130. Deprotection, followed by reduction of the azide function yielded 4-Amino-Neu5Ac2en 131, which could be converted into the desired guanidine derivative 126. 129 A more recent approach to zanamivir 126 is reported starting from D-glucono-d-lactone 132 (Scheme 13). 130 Following reaction of D-glucono-d-lactone 132 with 2,2-diethoxypropane in acetone and methanol with a catalytic amount of p-TsOH the free alcohol function was benzylated to obtain the ester 133. 131 The corresponding alcohol 134 was obtained by reduction of ester 133 with LiAlH 4 . Subsequent treatment with Dess-Martin periodinane gave aldehyde 135 which was further converted into the imine 136. With the help of a highly selective syn addition of allylmagnesium bromide the amine 137 was obtained which further was N-acetylated and simultaneously debenzylated. Finally, a good leaving group at the alcohol function was introduced to obtain 138. 138 could be converted into the aziridine key intermediate 139 by reaction with NaH and THF. Using NaN 3 in EtOH-water in the presence of NH 4 Cl allowed to open the aziridine ring regioselectively at the less hindered position, and the free amino function was acetylated to obtain 140 (structure confirmed by X-ray). The terminal olefin in 140 was efficiently dihydroxylated by catalytic OsO 4 in the presence of NMO in acetone-water to obtain the diol 141. The primary hydroxyl group of diol 141 was selectively oxidized under TEMPO base conditions 132 , the resulting acid was immediately converted into the corresponding ester, whereas the remaining secondary alcohol was oxidized to the a-ketocarboxylic acid methyl ester 142. Treatment with HF in MeCN 133 afforded the sugar derivative 143, which, in turn, was fully acetylated followed by replacement of the a-acetoxyl group with chlorine to obtain 144. 134 DBU-induced elimination reaction afforded 134, the known azide intermediate in the previously described synthesis of zanamivir 126.

The family of ulosonic acids has provided potential therapeutic leads in developing inhibitors of corresponding enzymes. Zanamivir (126) is a transition state analog of 2,3-didehydro-2-deoxy-Nacetylneuraminic acid (Neu5Ac2en), which exhibits high inhibitory activity to influenza neuraminidase (NA) and has been approved for the treatment of influenza. The syntheses of these ulosonic acids themselves and their analogs have attracted considerable interest in recent years, and become a current research topic. The synthesis of these compounds has previously been reviewed. 111, 135, 136 Compound 145 is a kind of hybride compound between oseltamivir 101 and zanamivir 126 with the heterocyclic core of 126 showing the substitution pattern of 101. Also, 145 shows good inhibitory activity with marked selectivity for influenza A sialidase. 137 Compounds 146, 138 Compounds 155 and 156 were synthesized and evaluated for their properties as influenza neuraminidase inhibitors. 148 Benzoic acid derivatives 154 and 157 149 were designed as aromatic sialic acid analogs. 150 The most potent compound out of a large series of tetra substituted benzoic acid derivatives 156 151 tested in vitro were 154a and 154b, showing an IC 50 of 2.5 Â 10 À6 and >10 À4 M, respectively, against N9 neuraminidase.

Compound 156b was highly selective for type A (H2N2) influenza NA (IC 50 : 1 mM) over type B (B/Lee/40) influenza NA (IC 50 500 mM). The X-ray structure of 4-(N-acetylamino)-5-guanidino-3-(3-pentyloxy)benzoic acid 156b in complex with NA revealed that the lipophilic side chain binds to a newly created hydrophobic pocket formed by the movement of Glu 278 to interact with Arg 226, whereas the guanidine of 156b interacts with a negatively charged pocket created by Asp 152, Glu 120 and Glu 229.

Siastatin B 158 is a broad spectrum sialidase inhibitor isolated from a Streptomyces culture and characterized as an unusual 6-acetamido-3-piperidinecarboxylate. The charge distribution in the zwitterion resembles that in the N-acetylneuraminate oxocarbenium ion, the putative intermediate in the enzyme-catalyzed reaction, and this may account for its effectiveness in binding sialidases. 152 Starting from Siastatin B 158 3,4-dehydro-N-(2-ethylbutyryl)-3-piperidinecarboxylic acids 159 153 have been prepared. The compound 159 exhibits strong inhibition particularly against influenza virus A neuraminidase and confers both in vitro and in vivo antiviral efficacy. 154 1,4,5,6-Tetrahydropyridazine derivatives 160 possess side chains similar to that of oseltamivir 101. They show influenza virus neuraminidase-inhibitory activity in a mM range and were synthesized via a hetero Diels-Alder reaction. 155 Compound 161 is the thioisoster of zanamivir 126. It could be shown, that these thioisosters are as bioactive as their oxygen counterparts as inhibitors of influenza virus sialidase. 156 Chart 19. N and S containing sialic acid analogs158^161.

Chart 20. p-Nitrophenyl (pNP)-N-acetyl-6-sulfo-D-glucosamines162.

6-Sulfo-d-GlcNAc 162a with a molecular geometry close to that of N-acetylneuraminic acid (Neu5Ac) was hypothesized to serve as a simple Neu5Ac mimic possessing high potential in biochemical and medicinal applications. The hypothesis was evidenced with a neuraminidase inhibition assay using p-nitrophenyl (pNP) 3-, 4-, and 6-sulfo-b-d-GlcNAc and 6-sulfo-b-d-Glc 162a, in which only pNP 6-sulfo-b-d-GlcNAc 162b was found to show substantial activity. 157 The multimeric compounds 163 158 and 164 159 have been developed as potential second generation compounds intended for inhalation in both therapy and prophylaxis of influenza virus infections. They are significantly more antivirally active than the monomer zanamivir 126 and also showed long-lasting protective activity when tested in mouse influenza virus infectivity experiments. Furthermore, polyvalent sialidase inhibitors bearing zanamivir 126 on a poly-Lglutamine backbone have been described. 160 

Peramivir BCX-1812 165a potently inhibits the neuraminidase enzyme N9 from H1N9 virus in vitro with a 50% inhibitory concentration (IC 50 ) of 1.3 AE 0.4 nM. On-site dissociation studies indicate that peramivir 165a remains tightly bound to N9 NA (t1/2 >24 hr), whereas, zanamivir 126 and oseltamivir carboxylate 101 dissociated rapidly from the enzyme (t 1/2 ¼ 1.25 hr). Additional efficacy studies indicate that a single injection of peramivir 165a (2-20 mg/kg) 161 was comparable to a q.d. Â 5 day course of orally administered oseltamivir 101 (2-20 mg/kg/day) in preventing lethality in H3N2 and H1N1 influenza models. 162, 163 A single intramuscular injection of peramivir 165a was found effective in the treatment of influenza virus infections, and this may provide an interesting lead to be used in case of an influenza outbreak. 164, 165 Compound 166 was found to have an IC 50 value of 28 mM against neuraminidase N2 and 115 mM against N9, which is superior to the DANA series compound having the same functional groups. 166 This mode of binding for the guanidino group is analogous to that observed in the crystal structure of zanamivir (3) with influenza A neuraminidase. 167 The 1-ethylpropylamide, diethylamide, dipropylamide, and 4-morpholinylamide of the 167a group showed very good inhibitory activity (IC 50 ¼ 0.015-0.080 mM) against the neuraminidase A form, but modest activity (IC 50 ¼ 3.0-9.2 mM) against the neuraminidase B. Of the 1-carboxy-1-hydroxy derivatives 167b, the diethylamide and the dipropylamide, were also investigated; however, they were less active than the compounds without the 1-hydroxy group. 168 Chart 21. Dimeric, trimeric and tetrameric inhibitors163 and164 of influenza neuraminidase. Synthesis 169 of peramivir 165a (Scheme 14) starts from (À)-lactam (2-azabicyclo[2.2.1]hept-5en-3-one 168, which was hydrolyzed with methanolic HCl; the resultant amino ester on reaction with Boc anhydride produced compound 169. Cycloaddition (3þ2) of compound 169 with the nitrile oxide produced from 2-ethyl-1-nitrobutane, phenyl isocyanate, and triethylamine, gave cycloadduct 170 and other isomers (< 10%). Cycloadduct 170 was isolated from the mixture of isomers and was hydrogenated in methanol with an equivalent amount of aqueous HCl in the presence of PtO 2 at 100 psi to give an amine hydrochloride, which was reacted with acetic anhydride to give the corresponding N-acetyl derivative 171. Compound 171 on reaction with ethereal HCl gave deblocked amine 172. Compound 172 on guanylation with pyrazole carboxamidine hydrochloride in DMF in the presence of diisopropylethylamine gave the corresponding guanidino ester, which on hydrolysis with NaOH gave the desired compound 165a.

A-315675 173 is a novel, pyrrolidine-based compound that was evaluated in this study for its ability to inhibit A and B strain influenza virus neuraminidases in enzyme assays and influenza virus replication in cell culture. A-315675 173 effectively inhibited influenza A N1, N2, N9, and B strain neuraminidases with inhibitor constant (K i ) values between 0.024 and 0.31 nM. These values were comparable to or lower than the K i values measured for oseltamivir carboxylate (GS4071) 101, zanamivir 126. 170 Performing the coupling reaction of N-tert-butoxycarbonyl-2-(tert-butyldimethylsiloxy)pyrrole 178 171 and S-trityl sulfenimine 179 172 with triflic acid (0.8 equiv) in THF/heptane at À40 C yielded 95% of desired isomer 180. 173 Introduction of the cis-propenyl group at C-4 to obtain 181 required a stereoselective trans-addition of the in situ generated propenyl cuprate. Partial reduction of 181 to the hemiaminal with DIBALH was followed by conversion to the a-methoxycarbamate through treatment with PPTS in methanol. Reaction of this compound with TMSCN in the presence of 174, 175 Compound A-192558 174i, is the most potent NA inhibitor in this series (IC 50 ¼ 0.2 mM against NA A and 8 mM against NA B). The X-ray crystallographic structure of A-192558 174i bound to NA revealed the predicted interaction of the carboxylic group with the positively charged pocket (Arg118, Arg292, Arg371) and interaction of the trifluoroacetamino residue with the hydrophobic pocket (Ile222, Trp178) of the enzyme active site. Surprisingly, the ethyl and isopropyl groups of the urea functionality-induced a conformational change of Glu276, turning the Glu276/Glu277 hydrophilic pocket, which normally accommodates the triglycerol side chain of substrate sialic acid, into an induced hydrophobic pocket. 176 Of the 175 series, Z-propenyl-analog 175q was found to be the most potent inhibitor of both A and B neuraminidases (IC 50 ¼ 0.020 and 0.030 mM, respectively), whereas the IC 50 s of the other derivatives were found in a range of 0.045-15 mM. 177 Compound 176b was found the most potent of the benzoic acid analog series 176 (IC 50 ¼ 0.52 mM for influenza A and IC 50 26 mM for influenza B neuraminidases). 178 Novel aand b-amino acid inhibitors of influenza neuraminidase bearing a pyrrolidine moiety, exhibited K i values in the 50 mM range against influenza virus A/N2/Tokyo/3/67 neuraminidase but exhibited weaker activity against influenza virus B/ Memphis/3/89 neuraminidase. Limited optimization of the pyrrolidine series 177 resulted in compound 177a, which was about 24-fold more potent than 2-deoxy-2,3-dehydro-N-acetylneuraminic acid in an anti-influenza cell culture assay using A/N2/Victoria/3/75 virus. Pyrrolidine analogs in which the aor b-amino groups were replaced with hydroxyl groups were 365-and 2,600fold weaker inhibitors, respectively. These results underscore the importance of the amino group interactions with the Asp 152 and Tyr 406 side chains and have implications for anti-influenza drug design. 179 Commercially available 5-norbornen-2-ol 185 was converted to the protected dihydroxy ketone 186 via standard procedure Swern-Oxidation, dihydroxylation and protection. 180 A Bayer-Villiger rearrangement was carried out so as to obtain 187. The undesired, methylene lactone decomposed completely by treatment with aluminum oxide. Following the preparation of the iodolactone 188, treatment with K 2 CO 3 afforded the key intermediate 189, which was deprotected to 190 and subjected to oxidative ring-opening. This provided the desired THF derivative 191 which was converted into the oxime 192. Reduction by catalytic hydrogenation in the presence of Boc-anhydride gave a mixture of two separable acetyl-amino derivatives 193. The more base-labile 5-methylester could selectively be hydrolyzed yielding the monoacid 184a. 181 After protection of the 5-carboxylate group, the 3-carbomethoxyl group of the obtained 184a was hydrolyzed to get 194 and converted into the bromomethyl ketone moiety of 195 via diazomethyl ketone. Condensation of 195 with formamidine in liquid ammonia introduced the imidazole moiety, and upon deprotection the desired compound 184b was afforded.

The IC 50 values of compounds 184a and 184b against NA A (A/Tokyo/3/67) were 410 and 580 nM, respectively. They were 10-fold less potent than the pyrrolidine analog 175c. Against NA B (B/Memphis/3/89), compounds 184a and 184b were about 20-fold less potent than 175c (IC 50 ¼ 960 and 1,000 nM, respectively).

Defensins are low molecular weight antimicrobial peptides produced by phagocytes and in various epithelial locations, including lung and trachea, 182 having a broad spectrum activity against a variety of pathogens including bacteria, fungi, and viruses. Defensins have activity against various enveloped viruses, including influenza. 183 These peptides bind to microbial surfaces and induce formation of membrane pores. 184 Defensins could, therefore, inhibit infectivity of influenza through disrupting the envelope of extracellular viral particles. Defensins present in the airway (Human b defensins 1 and 2) are also chemotactic for dendritic cells and memory T cells, and may, therefore, stimulate adaptive immune responses. 185 Recombinant production of defensins and other low molecular weight antimicrobial peptides is an attractive area for antiviral research because of the broad spectrum activity of these agents and their potential to modulate host defense functions.

Short interfering RNAs (siRNAs) specific for conserved regions of influenza virus genes were found to reduce virus production in the lungs of infected mice, when the siRNAs were given intravenously (i.v.) in complexes with a polycation carrier either before or after initiating virus infection. 186 Delivery of siRNAs specific for highly conserved regions of the nucleoprotein or acidic polymerase significantly reduced lung virus titers in influenza A virus-infected mice and protected the animals from lethal challenge. This protection was specific and not mediated by an antiviral interferon response. The influenza-specific siRNA treatment was broadly effective and protected animals against lethal challenge with highly pathogenic avian influenza A viruses of the H5 and H7 subtypes. 187 That specific siRNAwould be effective against influenza could be readily predicted from equally effective results obtained with other specific siRNAs, that is, against the SARS (severe acute respiratory syndrome) coronavirus in comparable situations. 188 Phosphorothioate oligonucleotides (PS-ONs) (i.e., REP, a 40-mer PS-ON) offer potential, when administered as aerosol in the prophylaxis and therapy of influenza infection. 189 Similarly, antisense phosphorodiamidate morpholino oligomers (ARP-PMOs) could be further pursued for their potential in the treatment of H5N1 influenza A virus infections. 190 

Several drugs are available that could be used, either alone or in combination, in the treatment (prophylaxis or therapy) of a pandemic influenza, whether avian or human, virus infection. These include adamantan(amin)e derivatives (i.e., amantadine), neuraminidase inhibitors (i.e., oseltamivir), ribavirin and interferon. Combinations of different antivirals acting against influenza at different stages of viral replication could be an important area of research in the future should such combination strategy prove clinically successful in the treatment of HIV infection.

Anti-influenza drugs and neuraminidase inhibitors

Targets of anti-influenza chemotherapy other than neuraminidase and proton pump

Antiviral therapy for influenza. A clinical and economic comparative review

The role of antivirals in the control of influenza

Highlights in the development of new antiviral agents

Taking aim at a moving target-Inhibitors of influenza virus part 1: Virus adsorption, entry and uncoating

Therapeutic options for the management of influenza

Prophylaxis and treatment of influenza virus infection

Approaches and strategies for the treatment of influenza virus infections

Influenza: Old and new threats

Crystallographic detection of a second ligand binding site in influenza virus hemagglutinin

Ligand recognition by influenza virus. The binding of bivalent sialosides

Mechanism of binding of surfactant protein D to influenza A viruses: Importance of binding to hemagglutinin to antiviral activity

Polyacrylamides bearing pendant asialoside groups strongly inhibit agglutination of erythrocytes by influenza A virus: Multivalency and steric stabilization of particulate biological systems

Effective Inhibitors of hemagglutination by influenza virus synthesized from polymers having active ester groups. Insight into mechanism of inhibition

Monomeric inhibitors of influenza neuraminidase enhance the hemagglutination inhibition activities of polyacrylamides presenting multiple C-sialoside groups

Basis for the potent inhibition of influenza virus infection by equine and guinea pig a 2-macroglobulin

Cluster sialoside inhibitors for influenza virus: Synthesis, NMR, and biological studies

Solid-phase synthesis of dendritic sialoside inhibitors of influenza A virus hemagglutinin

Polymerized liposomes containing C-glycosides of sialic acid: Potent inhibitors of influenza virus in vitro infectivity

Studies on nucleoside analogs. Part XXVII. Studies on sialic acids. III. Synthesis of 2-O-glycosyl derivatives of N-acetyl-D-neuraminic acid

The molecular biology of influenza virus pathogenicity

A novel mechanism for acquisition of virolence by a human influenza A virus

Role of hemagglutinin cleavage for the pathogenicity of influenza virus

Inhibitory effect of a protease inhibitor, leupeptin, on the development of influenza pneunomia, mediaded by concomitant bacteria

The human mucus protease inhibitor and its mutants are novel defensive compounds against infection with influenza A and Sendai viruses

Resistance of mice to reinfection after E-aminocaproic acid treatment of primary influenza virus infection

Action of epsilon-aminocaproic acid on the proteolysis system during experimental influenza in mice

Molecular mechanism underlying the action of a novel fusion inhibitor of influenza A virus

Salicylamide inhibitors of influenza virus fusion

An approach to the identification of potent inhibitors of influenza virus fusion using parallel synthesis methology

Structure-activity relationships for a series of thiobenzamide influenza fusion inhibitors derived from 1,3,3-trimethyl-5-hydroxy-cyclohexylmethylamine

Inhibition of influenza A virus replication by compounds interfering with the fusogenic function of the viral hemagglutinin

Structure based identification of an inducer of the low-pH conformational change in the influenza virus hemagglutinin: Irreversible inhibition of infectivity

Effect of the virostatic norakin (triperiden) on influenza virus activities

Mechanism of uncoating of influenza B virus in MDCK cells: Action of chloroquine

Inhibition of influenza virus hemagglutinin-mediated membrane fusion by a compound related to podocarpic acid

Potent anti-influenza activity of cyanovirin-N and interactions with viral hemagglutinin

Characterization of inhibition of M2 ion channel activity by BL-1743, an inhibitor of influenza A virus

Antiviral activity of 1-adamantanamine (amantadine)

Selective inhibitors of viral functions

The in vivo antiviral activity of 1-adamantanamine (amantadine). 1. Prophylactic and therapeutic activity against influenza viruses

A controlled trial of amantadine and rimandadine in the prophylaxis of influenza A infections

Antiviral agents in influenza-Summary of influenza workshop VIII

A prospective double-blind study of side effects associated with the administration of amantadine for influenza A virus prophylaxis

In: ''New synthesis with carbon monoxide

Koch carbonylation using silver trifluormethanesulfonate

Influence of catalytic system composition on formation of adamantine containing ketones

Synthesis and antiviral activity evaluation of some aminoadamantane derivatives

Heterocyclic rimantadine analogues with antiviral activity

-Adamantyl)pyrrolidines with potent activity against influenza A virus-identification of aminoadamantane derivatives bearing two pharmacophoric amine groups

Synthesis of 2-(2-adamantyl)piperidines and structure antiinfluenzavirus A activity relationship study using a combination of NMR spectroscopy and molecular modeling

Synthesis and antiviral activity evaluation of some new aminoadamantane derivatives 2

Heterocyclic rimantadine analogues with antiviral activity

Synthesis, anti-influenza virus activity and conformational properties

The adamantane-derived bananins are potent inhibitors of the helicase activities and replication of SARS coronavirus

A system of protein target sequences foranti-RNA-viral chemotherapy by a vitamin B6-derived zinc chelating trioxa-adamantane-triol

Natural product origins of Hsp90 inhibitors

Synthesis of substituted 1-norbornylamines with antiviral activity

Prevention and treatment of experimental influenza A virus infection in volunteers with a new antiviral ICI 130685

Growth impairment resulting from expression of influenza virus M2 protein in Saccharomyces cerevisiae: Identification of a novel inhibitor of influenza virus

Novel assay for the influenza virus M2 channel activity

Inhibitory effect of bafilomycin A1, a specific inhibitor of vacuolar-type proton pump, on the growth of influenza A and B viruses in MDCK cells

Characterization of inhibition of M2 ion channel activity by BL-1743, an inhibitor of influenza A virus

Influenza viruses, cell enzymes, and pathogenicity

Enhancement of the infectivity of influenza A and B viruses by proteolytic cleavage of the hemagglutinin polypeptide

Sequence requirements for cleavage activation of influenza virus hemagglutinin expressed in mammalian cells

Cell tropism of influenza virus mediated by hemagglutinin activation at the stage of virus entry

Inhibition of influenza virus A/WSN replication by a trypsin inhibitor, 6-amidino-2-naphthyl p-guanidinobenzoate

Inhibition of influenza virus A/WSN replication by serine protease inhibitors and anti-protease antibodies

Inhibition of the fusion-inducing conformational change of influenza hemagglutinin by benzoquinones and hydroquinones

Mode of action of the anti-influenza virus activity of plant flavonoid, 5,7,4 0 -trihydroxy-8-methoxyflavone, from the roots of Scutellaria baicalensis

Inhibition of influenza virus sialidase and antiinfluenza virus activity by plant flavonoids

Fields virology

Metal Ion Catalysis of RNA cleavage by the influenza virus endonuclease

A novel antiviral agent which inhibits the endonuclease of influenza viruses

Synthesis of natural flutimide and analogous fully substituted pyrazine-2,6-diones, endonuclease inhibitors of influenza virus

Identification of Nhydroxamic acid and N-hydroxyimide compounds that inhibit the influenza virus polymerase

A novel antiviral agent which inhibits the endonuclease of influenza viruses

Anti-influenza virus activities of 4-substituted 2,4-dioxobutanoic acid inhibitors

Inhibition of influenza virus transcription by 2 0 -deoxy-2 0 -fluoroguanosine

Purine 2 0 -deoxy-2 0 -fluororibosides as antiinfluenza virus agents

Inhibition of influenza A and B viruses by 2 0 -deoxy-2 0 -fluororibosides

Plants as a source of potential antiviral agents

Van Hoof L. Plant products as potential antiviral agents

In vitro anti-influenza virus activity of the pavine alkaloid (À)-thalimonine isolated from Thalictrum simplex

Novel virus proliferation inhibition/ virucidal method and novel pyradine nucleotide/pyradine nucleoside analogue. Patent Application. International application number: PCT/JP2002/008250

vitro and in vivo activities of anti-influenza virus compound T-705

Nitrogenous heterocyclic carboxamide derivatives or salts thereof and antiviral agents containing both. Patent Application. International application number: PCT/JP99/04429

Novel pyrazine derivatives or salts thereof, pharmaceutical compositions containing the derivatives or the salts and intermediates for the preparation of both. Patent Application

Novel pyrazine derivatives or salts thereof, pharmaceutical composition containing the same, and production intermediates thereof

Rational development of practical catalysts for aromatic carbon-nitrogen bond formation

Transition metal catalyzed synthesis of arylamines and aryl ethers from aryl halides and triflates: Scope and mechanism

Mechanism of action of T-705 against influenza virus

Synthesis and biological evaluation of novel bisheterocycle-containing compounds as potential anti-influenza virus agents

A novel class of potent influenza virus inhibitors: Polysubstituted acylthiourea and its fused heterocycle derivatives

In vitro and in vivo anti-influenza A virus activity of antisense oligonucleotides

Antisense oligonucleotides directed against the viral RNA polymerase gene enhance survival of mice infected with influenza A

A new modified DNA enzyme that targets influenza virus A mRNA inhibits viral infection in cultured cells

Evaluation of the antiinfluenza virus activities of 1,3,4-thiadiazol-2-ylcyanamide (LY217896) and its sodium salt

Oral LY217896 for prevention of experimental influenza A virus infection and illness in humans

Oral ribavirin treatment of influenza A and B

Antiviral therapy with small particle aerosols

Intravenous ribavirin by constant infusion for serious influenza and parainfluenzavirus infection

Biochemistry and clinical applications of ribavirin

Neuraminidase inhibitors for influenza

Molecule of the month: Oseltamivir phosphate (Tamiflu)

Design of neuraminidase inhibitors as anti-influenza virus agents

Neuraminidase inhibitors as anti-influenza virus agents

The synthetic development of the anti-influenza neuraminidase inhibitor oseltamivir phosphate (Tamiflu 1 ): A challenge for synthesis & process research

Recent advances in the discovery and synthesis of neuraminidase inhibitors

Influenza neuraminidase inhibitors possessing a novel hydrophobic interaction in the enzyme active site: Design, synthesis, and structural analysis of carbocyclic sialic acid analogs with potent anti-influenza activity

Structure-activity relationship studies of novel carbocyclic influenza neuraminidase inhibitors

Industrial synthesis of the key precursor in the synthesis of the anti-influenza drug oseltamivir phosphate

Azide-free transformation of epoxides into 1,2-diamino compounds: Synthesis of the anti-influenza neuraminidase inhibitor oseltamivir phosphate (Tamiflu)

Research and development of a second-generation process for Oseltamivir phosphate, prodrug for a neuraminidase inhibitor

Oseltamivir becomes plentiful-but still not cheap

Stereo-specific synthesis of shimikic acid derivatives with improved efficiency Patent Application: Appl. No: 09/811

Phosphorus in organic synthesis. VII. Diphenyl phosphorazidate (DPPA). A new convenient reagent for a modified Curtius reaction

A Short Enantioselctive pathway for the synthesis of the anti-influenza neuramidase inhibitor Oseltamivir from 1,3-butadiene and acrylic acid

Triflimide activation of a chiral oxazaborolidine leads to a more general catalytic system for enantioselective diels-alder addition

Synthesis and reactions of iodo lactams

Synthesis of some 2,3-didehydro-2-deoxysialic acids structurally varied at C-4 and their behavior towards sialidase from Vibrio cholerae

Rational design of potent sialidase-based inhibitors of influenza virus replication

Synthesis of the potent influenza neuraminidase inhibitor 4-guanidino Neu5Ac2en. X-ray molecular structure of 5-acetamido-4-amino-2,6-anhydro-3,4,5-trideoxy-D-erythro-Lgluco-nonionic acid

Boy B, A synthesis of 4-guanidino-2-deoxy-2,3-didehydro-Nacetylneuraminic acid

A convenient method for the introduction of nitrogen and sulfur at C-4 on a sialic acid analog

Synthesis of 2 0 -(4-methylumbelliferyl)-?(-D-N-acetylneuraminic acid and detection of skin fibroblast neuraminidase in normal humans and in sialidosis

The synthesis of 2,3-didehydro-2,4-dideoxy-4-guanidinyl-Nacetylneuraminic acid: A potent influenza virus sialidase inhibitor

Synthesis of 4-Azido-4-deoxy-5-Neu-5,7,8,9Ac 4 2en1Me. A key intermediate for the synthesis of GG167 from D-glucono-d-lactone

Synthesis of a stable conformationally constrained 2,7-anhydrosialic acid derivative

A concise synthesis of (2S, 3S)-BocAHPBA and (R)-BocDMTA, chiral building blocks for peptide-mimetic HIV protease inhibitors

A New synthetic approach of Neu5Ac from D-glucono-?d-lactone

Synthesis of oligomers derived from amide-linked neuraminic acid analogues

Recent Progress in syntheses of higher 3-deoxy-2-ulosonic acids and their derivatives

Recent advances in anti-influenza agents with neuraminidase as target

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

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

Structure-activity relationship studies of novel carbocyclic influenza neuraminidase inhibitors

Stereospecific Synthesis of a GS4104 metabolite: Determination of absolute stereochemistry and influenza neuraminidase inhibitory activity

Synthesis of a Carbocyclic sialic acid analogue for the inhibition of influenza virus neuraminidase

Dihydropyrancarboxamides related to zanamivir: A new series of inhibitors of influenza virus sialidases. 1. Discovery, synthesis, biological activity, and structure-activity relationships of 4-guanidinoand 4-amino-4H-pyran-6-carboxamides

Synthesis and antiinfluenza evaluation of orally active bicyclic ether derivatives related to zanamivir

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

Novel inhibitors of influenza sialidases related to zanamivir. Heterocyclic replacements of the glycerol side chain

Synthesis of 6-, 7-and 8-carbon sugar analogues of potent anti-influenza 2,3-didehydro-2,3-dideoxy-N-acetylneuraminic acid derivatives

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

Hydrophobic benzoic acids as inhibitors of influenza neuraminidase

Aromatic sialic acid analogues as potential inhibitors of influenza virus neuraminidase

Structures of aromatic inhibitors of influenza virus neuraminidase

Design and synthesis of benzoic acid derivatives as influenza neuraminidase inhibitors using structure-based drug design

Synthesis of the sialidase inhibitor siastatin B

Synthesis of 6-acetamido-5-amino-and 5-guanidino-3,4-dehydro-N-(2-ethylbutyryl)-3-piperidinecarboxylic acids related to zanamivir and oseltamivir, inhibitors of influenza virus neuraminidases

Dihydropyrancarboxamides related to zanamivir: A new series of inhibitors of influenza virus sialidases. 1. Discovery, synthesis, biological activity, and structure-activity relationships of 4-guanidinoand 4-amino-4H-pyran-6-carboxamides

Synthesis and evaluation of 1,4,5,6-tetrahydropyridazine derivatives as influenza neuraminidase inhibitors

Synthesis and biological evaluation of sulfur isosters of the potent influenza virus sialidase inhibitors 4-amino-4-deoxy-and 4-deoxy-4-guanidino-Neu5Ac2en

N-Acetyl-6-sulfo-D-glucosamine as a promising mimic of Nacetyl neuraminic acid

Dimeric zanamivir conjugates with various linking groups are potent, long-lasting inhibitors of influenza neuraminidase including H5N1 avian influenza

Highly potent and long-acting trimeric and tetrameric inhibitors of influenza virus neuraminidase

Synthesis and anti-influenza evaluation of polyvalent sialidase inhibitors bearing 4-guanidino-Neu5Ac2en derivatives

Oral administration of cyclopentane neuraminidase inhibitors protects ferrets against influenza virus infection

Cyclopentane neuraminidase inhibitors with potent in vitro anti-influenza virus activities

Comparison of the anti-influenza virus activity of RWJ-270201 with those of oseltamivir and zanamivir

Anti-influenza virus activity of peramivir in mice with single intramuscular injection

Comparison of the anti-influenza virus activity of cyclopentane derivatives with oseltamivir and zanamivir in vivo

Synthesis of 6-, 7-and 8-carbon sugar analogues of potent anti-influenza 2,3-didehydro-2,3-dideoxy-N-acetylneuraminic acid derivatives

Systematic structure-based design and stereoselective synthesis of novel multisubstituted cyclopentane derivatives with potent antiinfluenza activity

Syntheses and neuraminidase inhibitory activity of multisubstituted cyclopentane amide derivatives

BCX-1812 (RWJ-270201): Discovery of a novel, highly potent, orally active, and selective influenza neuraminidase inhibitor through structure-based drug design

In vitro characterization of A-315675, a highly potent inhibitor of A and B strain influenza virus neuraminidases and influenza virus replication

N-(tert-Butoxycarbonyl)-2-(tert-butyldimethylsiloxy)pyrrole: A promising compound for synthesis of chiral nonracemic hydroxylated pyrrolidine derivatives

Asymmetric synthesis of amino acids using sulfinimines (thiooxime S-oxides)

Synthesis of an influenza neuraminidase inhibitor intermediate via a highly diastereoselective coupling reaction

Total Synthesis of A-315675: A potent inhibitor of influenza neuraminidase

Enantioselective synthesis of antiinfluenza compound A-315675

Design, Synthesis, and structural analysis of influenza neuraminidase inhibitors containing pyrrolidine cores

Structure-based characterization and optimization of novel hydrophobic binding interactions in a series of pyrrolidine influenza neuraminidase inhibitors

Pyrrolidinobenzoic acid inhibitors of influenza virus neuraminidase: Modifications of essential pyrrolidinone ring substituents

Novel a-and b-amino acid inhibitors of influenza virus neuraminidase

Synthesis of 2-substituted (AE)(2R, 3R, 5R)-tetrahydrofuran-3,5-dicarboxylic acid derivatives

Design, synthesis, and structural analysis of inhibitors of influenza neuraminidase containing a 2,3-disubstituted tetrahydrofuran-5-carboxylic acid core

Antimicrobial peptides and proteins in the innate defense of the airway surface

Direct inactivation of viruses by human granulocyte defensins

Crystal structure of defensin HNP-3, an amphiphilic dimer: Mechanisms of membrane permeabilization

b-Defensins: Linking innate and adaptive immunity through dendritic and T cell CCR6

Inhibition of influenza virus production in virusinfected mice by RNA interference

Protection against lethal influenza virus challenge by RNA interference in vivo

Using siRNA in prophylactic and therapeutic regimens against SARS coronavirus in Rhesus macaque

Rep 9: A potent broad spectrum aerosol prophylaxis and therapy against influenza infection in vivo

Inhibition of multiple influenza A subtypes in cell culture with antisense phosphorodiamidate morpholino oligomers

She received her M.S. degree in 1994 and her Ph.D. in 1998 in the fields of organic synthesis, both at the Leopold Franzens Universität Innsbruck (Austria)

At present Irene M. Lagoja is a research fellow of the FWO (Fonds Wetenschappelijk Onderzoek) Vlaanderen. Her main research interests are heterocyclic chemistry (synthesis of new potential antiviral drugs) and nucleoside chemistry

He received his M.D. degree in 1966 and his Ph.D. in 1972 both at the Katholieke Universiteit Leuven (K.U.Leuven) in Belgium. After having spent 2 years at Stanford University Medical School as a postdoctoral fellow, he returned to the K.U. Leuven Medical School, where he became docent (assistant professor) in 1973, professor in 1975, and full professor in 1977. He has been teaching the courses of Cell Biology, Biochemistry, Microbiology and Virology in the first, second and third undergraduate years of the Medical School at the

He is a titular member of the Belgian Royal Academy of Medicine and the Academia Europaea, and has also held the Prof. P. De Somer Chair of Microbiology at the K.U. Leuven. Prof. De Clercq's scientific achievements are in the antiviral chemotherapy field, and, in particular, the development of new antiviral agents for the treatment of various viral infections, including AIDS. He has (co)-discovered a number of antiviral drugs, currently used in the treatment of various virus infections, such as herpes simplex (valaciclovir), herpes zoster (brivudin), AIDS (stavudine), CMV (cytomegalovirus) infections (cidofovir), HBV (hepatitis B virus) infections (adefovir), and HIV infections (AIDS) (tenofovir disoproxil fumarate, marketed as Viread TM , and