Influenza virus inhibitors and uses thereof

Abstract

The present invention provides oxabicyclic compounds having strong activity as influenza virus inhibitors, as well as pharmaceutical compositions thereof and methods of use in treatment of influenza virus, particularly influenza A virus, infections.

Description

INFLUENZA VIRUS INHIBITORS AND USES THEREOFTECHNICAL FIELD

[0001] The present invention provides oxabicyclic compounds having strong activity as influenza virus inhibitors, as well as pharmaceutical compositions thereof and methods of treatment of influenza virus infections.BACKGROUND ART

[0002] Influenza viruses cause respiratory infections in humans and are responsible for hundreds of thousands of deaths worldwide annually. In the last century, influenza viruses posed severe threats to public health, causing the 1918 and 2009 (H1N1), 1957 (H2N2), and 1968 (H3N2) pandemics. Each of these pandemics was caused by the influenza A virus (IAV), considered the most virulent influenza subtype. This subtype is associated with seasonal epidemics and more persistent transmission than subtypes B, C, and D, and occasional pandemics characterized by high levels of morbidity and mortality.

[0003] While vaccines remain the cornerstone of influenza prevention, their effectiveness is limited by the antigenic variability of circulating strains and reduced immunogenicity in vulnerable populations such as the elderly (Belongia et al., 2016). Current antiviral drugs, including neuraminidase inhibitors (e.g., oseltamivir) and M2 ion channel blockers (e.g., amantadine), are further limited by the rapid emergence of drug -resistant viral variants (Hayden, 2006; Gubareva et al., 2001; Bright et al. , 2005).

[0004] Hemagglutinin (HA), a surface glycoprotein critical for viral entry into host cells, mediates receptor binding and low pH-triggered membrane fusion within endosomes (Skehel and Wiley, 2000). It is a mechanistically validated, yet underutilized target for smallmolecule antiviral development. Arbidol, the only HA-targeting drug in clinical use, is approved in Russia and China but exhibits only moderate clinical efficacy and has not been approved in Western countries (Blaising etal., 2014). Notably, resistance to arbidol has also been reported (Leneva et al., 2009), underscoring the need for more potent and broadly active HA inhibitors.SUMMARY OF INVENTION

[0005] Disclosed herein are small-molecule inhibitors of several subtypes of the H1N1 influenza virus strain, a strain that causes -50% or more of all IAV infections currentlycirculating in humans (Al Khatib et al., 2019) and characterized by known pandemics such as the 2009 swine flu influenza pandemic and the 1918 Spanish flu pandemic. As shown, the inhibitors disclosed are capable of targeting viruses with divergent amino acid sequences used as typical models for drug development studies, with potent cell-based activity, promising in vivo efficacy, and pharmacokinetic and pharmacodynamic parameters.

[0006] The small-molecule inhibitors disclosed have been discovered through a combined structure-guided design and high-throughput screening approach, and are all based on the structure of 4-(5-(hydroxymethyl)-6,8,9-trimethyl-3-oxabicyclo[3.3. l]non-7-en-2-yl) phenol or 4-(4,4,8-trimethyl-3-oxabicyclo[3.3.1]non-7-en-2-yl)phenol, disclosed in WO 2017 / 106820 (in which the present applicant is a co-applicant) and referred to herein as “the parent Compound S(i2 and “the parent Compound 9” (Scheme 1), respectively. The synthesis of the inhibitors disclosed involves minimal steps, and these compounds are thus amenable to further development and optimization to improve upon their in vivo parameters with future derivatives. The size of these inhibitors is small (-300 Da or less), and their potency is high, meaning that their ligand efficiency is exceptional.

[0007] Central to our workflow is a chemiluminescent neuraminidase (CLNA) activity probe (Shelef et al., 2022), which enables ultrasensitive and reproducible quantification of viral replication in cell-based assays. Using this assay, the parent Compounds SG2 and 9 demonstrated nanomolar-range ED50 values against a panel of IAV strains, including mouse- adapted and clinical isolates. Genetic, biophysical and functional assays (e.g., differential scanning fluorimetry and trypsin protection assay) confirmed that an optimized compound based on the parent Compound 9 and referred to herein as compound 14 most likely binds to a conserved stem region in HA and blocks its conformational rearrangement required for membrane fusion.

[0008] The study described herein employed genetic (escape mutant generation), biochemical / functional (differential scanning fluorimetry, trypsin protection assay) and computational (ligand docking) approaches holistically to define the target protein of these inhibitors as viral hemagglutinin (HA), specifically showing that the structural rearrangements necessary for the membrane fusion-prone conformation of the protein, which are important for viral entry into the host cell, were targeted. These methods thus afforded the mechanistic elucidation of the inhibition mode of this inhibitor scaffold. Its mechanism, targeting a conserved HA pocket, also suggests a lower likelihood of development of resistance when combined with currently available generic neuraminidase inhibitors as partof a combination therapy approach, with the aim of suppressing the emergence of escape mutants such as those described herein. Future development of this scaffold will focus on further improvement of pharmacokinetic and potency parameters, determination of the precise three-dimensional structure of HA in complex with these lead compounds using cryo-EM and / or X-ray crystallography, and in vivo efficacy studies in mice using the CLNA probe to monitor disease progression within the mice’s bodies and optimize the dosage and formulation to confer the highest degree of survival and recovery rate for the mice when treated orally with the lead compounds.Scheme 1. The parent Compounds SG2 (including the cis and trans configuration) and 9SG2-c / s (more polar): 4-((2A,6A,95)-5-(hydroxymethyl)-6,8,9-trimethyl-3- oxabicyclo[3.3.1]non-7-en-2-yl)phenolGl-trans (less polar): 4-((2>,6>,9 ’)-5-(hydroxymethyl)-6,8,9-trimethyl-3- oxabicyclo[3.3.1]non-7-en-2-yl)phenol

[0009] The inhibitors disclosed show strong antiviral activity, promising in vivo efficacy, and favorable pharmacokinetics. Mechanistic studies confirmed that they bind to viralhemagglutinin, likely stabilizing it in its prefusion state and blocking viral entry into the host cell. Their small size, high potency, and conserved, functionally relevant binding site suggest a low risk of resistance and suitability for further optimization and combination therapy with other existing antivirals that target different viral proteins in the influenza virus.

[0010] In one aspect, thus disclosed herein is an oxabicyclic compound of formula I:or a stereoisomer or pharmaceutically acceptable salt thereof, whereinR1, R2, R4, R5, and R6each independently is selected from H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;R3is selected from -CH2OH, H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2- C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;Ar is a 5-14-membered- aryl or heteroaryl, excluding phenyl, optionally substituted, preferably at any carbon atom thereof, with at least one group each independently selected from halogen, oxo, -OH, -CN, (Ci-C8)alkyl, (Ci-C8)haloalkyl, and - NR72, said heteroaryl containing at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized); andR7each independently is H or (Ci-C8)alkyl, or the two R7together with the nitrogen atom to which they are attached form a heterocyclic ring.

[0011] In another aspect, disclosed herein is an oxabicyclic compound of formula II:or a stereoisomer or pharmaceutically acceptable salt thereof, whereinR1, R2, R4, R5, and R6each independently is selected from H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Cujaryl, and halogen;R3 is selected from -CH2OH, H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2- C8 alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Cujaryl, and halogen;Ar is a group of formula:wherein:(i) X is selected from -CN, -N3, -NR72, -NH-S(=O)2-(Ci-C8)alkyl, and -S(=O)2- NR72, wherein Ar is optionally further substituted with at least one group each independently selected from halogen, oxo, -OH, -CN, (Ci-C8)alkyl, (Ci- C8 haloalkyl, and -NR72; or(ii) X is -OH, wherein Ar is further substituted with halogen at a carbon atom ortho to X; andR7each independently is H or (Ci-C8)alkyl, or the two R7together with the nitrogen atom to which they are attached form a heterocyclic ring.

[0012] In a further aspect, disclosed herein is a pharmaceutical composition comprising an oxabicyclic compound of the formula I or II, each as defined above, or a stereoisomer or pharmaceutically acceptable salt thereof (herein also referred to as an “active agent”), and a pharmaceutically acceptable carrier and / or excipient.

[0013] In still a further aspect, disclosed herein is a method for treatment of an influenza virus infection, e.g., influenza A or influenza B virus infection, in a subject in need thereof, comprising administering to said subject a therapeutically effective amount of an oxabicyclic compound of the formula I or II, each as defined above, or a stereoisomer or pharmaceutically acceptable salt thereof, or a pharmaceutical composition thereof.

[0014] In yet a further aspect, disclosed herein is an oxabicyclic compound of the formula I or II, each as defined above, or a stereoisomer or pharmaceutically acceptable salt thereof, for use in the treatment of an influenza virus infection, e.g., influenza A or influenza B virus infection.

[0015] In still another aspect, disclosed herein is use of an oxabicyclic compound of the formula I or II, each as defined above, or a stereoisomer or pharmaceutically acceptable saltthereof, in the preparation of a pharmaceutical composition for treatment of an influenza virus infection, e.g., influenza A or influenza B virus infection.BRIEF DESCRIPTION OF DRAWINGS

[0016] Figs. 1A-1C show the dose response curves and IC50 values obtained using the CLNA assay for the parent Compounds SG2 and 9 against the replication of influenza viruses A / Puerto Rico / 8 / 34 (ATCC) - human isolate and Mount Sinai (mouse adapted), California / 07 / 2009, and Fort Monmouth / 01 / 47. (1A) Compound SG2- trans - A / Puerto Rico / 8 / 34 (ATCC) - human isolate (upper left panel) and Mount Sinai (upper right panel), California / 07 / 2009 (lower left panel), and Fort Monmouth / 01 / 47 (lower right panel); (IB) Compound SG2-cv.s - A / Puerto Rico / 8 / 34 (ATCC) - human isolate (upper left panel) and Mount Sinai (upper right panel), California / 07 / 2009 (lower left panel), and Fort Monmouth / 01 / 47 (lower right panel). (1C) Compound 9 - A / Puerto Rico / 8 / 34 (ATCC) - human isolate (upper left panel) and Mount Sinai (upper right panel), California / 07 / 2009 (lower left panel), and Fort Monmouth / 01 / 47 (lower right panel).

[0017] Figs. 2A-2J show the dose response curves and IC50 values obtained using the CLNA assay for various compounds against the replication of influenza viruses A / Puerto Rico / 8 / 34 Mount Sinai (mouse adapted), California / 07 / 2009, and Fort Monmouth / 01 / 47. (2A) Compound 3 -trans - A / Puerto Rico / 8 / 34 Mount Sinai (left panel) and California / 07 / 2009 (right panel). (2B) Compound 5 -trans - A / Puerto Rico / 8 / 34 Mount Sinai (upper left panel) and California / 07 / 2009 (upper right panel). Compound 5 -cis - A / Puerto Rico / 8 / 34 Mount Sinai (lower panel). (2C) Compound I O- - A / Puerto Rico / 8 / 34 MountSinai (upper left panel) and California / 07 / 2009 (upper right panel). Compound 10-A / Puerto Rico / 8 / 34 Mount Sinai (lower panel). (2D) Compound 14 - A / Puerto Rico / 8 / 34 Mount Sinai (upper left panel), California / 07 / 2009 (upper right panel), and Fort Monmouth / 01 / 47 (lower panel). (2E) Compound \6-lrans - A / Puerto Rico / 8 / 34 Mount Sinai (upper left panel), California / 07 / 2009 (upper right panel), and Fort Monmouth / 01 / 47 (lower panel). (2F) Compound - A / Puerto Rico / 8 / 34 Mount Sinai (upper left panel),California / 07 / 2009 (upper right panel), and Fort Monmouth / 01 / 47 (lower left panel). Compound 19- - A / Puerto Rico / 8 / 34 Mount Sinai (lower right panel). (2G) Compound21 - A / Puerto Rico / 8 / 34 Mount Sinai (upper left panel), California / 07 / 2009 (upper right panel), and Fort Monmouth / 01 / 47 (lower panel). (2H) Compound 21 -trans - A / Puerto Rico / 8 / 34 Mount Sinai (upper left panel), California / 07 / 2009 (upper right panel), and FortMonmouth / 01 / 47 (lower panel). (21) Compounds 36-trans (upper left panel), 3 -trans (upper right panel) and 3 - trans (lower panel) - A / Puerto Rico / 8 / 34 Mount Sinai. (2J) Compounds 36-cis (upper left panel), 31 -cis (upper right panel) and 38-cv.s (lower panel) - A / Puerto Rico / 8 / 34 Mount Sinai.

[0018] Figs. 3A-3B show that compound 14 stabilizes hemagglutinin in a dose-dependent manner. (3 A) DSF melting curves for hemagglutinin in the presence of increasing concentrations of Compound 14 (0 to 50 pM). Fluorescence (normalized to maximum signal) increases as SYPRO Orange binds exposed hydrophobic regions during protein unfolding. Each concentration is represented in a different shade of blue, with darker shades indicating higher compound concentrations. Bolzmann fit was used to extract the melting temperatures (Tm). (3B) ATm as a function of Compound 14 concentration. Data were fit to a one-site binding saturation model, indicating dose-dependent stabilization of hemagglutinin upon ligand binding.

[0019] Fig. 4 shows cartoon and sphere / stick representation showing the proposed binding pocket in PR8 HA based on drug-resistant escape mutants. The escape mutations congregate around a previously described binding pocket known to be targeted by a different family of IAV fusion inhibitors (Cianci and Krystal, 1998).

[0020] Fig. 5 shows trypsin susceptibility assay. SDS-PAGE analysis of 5 pM HA (wildtype and mutant forms) following trypsin treatment in the presence or absence of 50 pM Compound 14. Samples were preincubated at either pH 8.0 or pH 5.0 and assessed for proteolytic degradation. Wild-type HA is protected from trypsin digestion at pH 5 in the presence of Compound 14 (lane 5, left), indicating inhibition of the pH-induced conformational change. In contrast, HA mutants N461D and N461SZE464G show reduced protection by Compound 14 (lane 5, middle and right gels, respectively), suggesting impaired stabilization. The HA-only condition (lane 4 throughout) serves as a negative control.

[0021] Fig. 6 shows in vivo efficacy of compounds 14 and 21 in a lethal influenza A virus (IAV) mouse model. Mice infected with a lethal dose of IAV were treated subcutaneously with either compound (Cpd) 14 or compound 21. Amantadine (Am) was used as a control. Treated groups exhibited significantly prolonged survival compared to both the untreated and amantadine-treated groups. Improved survival correlated with reduced weight loss following infection. Survival was defined as maintaining body weight within 20% of theinitial pre-infection weight (n=5-10, Log-rank (Mantel-Cox) test, ns - non-significant, * / ?<0.05, ** p < 0.01, **** p < 0.0001).

[0022] Figs. 7A-7D show pharmacokinetic profiles of Compounds 14 and 21 in BALB / c mice. Plasma concentrations (ng / mL) of Compounds 14 (7 A) and 21 (7B) over time following oral administration at doses of 50 mg / kg and 10 mg / kg. Comparison of intravenous (IV) bolus vs. oral dosing for Compounds 14 (7C) and 21 (7D), highlighting differences in absorption and clearance kinetics. Data illustrate dose-dependent plasma exposure and route-dependent bioavailability.DETAILED DESCRIPTION

[0023] In one aspect, the present invention provides an oxabicyclic compound of formulaI:or a stereoisomer or pharmaceutically acceptable salt thereof, whereinR1, R2, R4, R5, and R6each independently is selected from H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;R3is selected from -CH2OH, H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2- C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;Ar is a 5-14-membered- aryl or heteroaryl, excluding phenyl, optionally substituted, preferably at any carbon atom thereof, with at least one group each independently selected from halogen, oxo, -OH, -CN, (Ci-C8)alkyl, (Ci-C8)haloalkyl, and - NR72, said heteroaryl containing at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized); andR7each independently is H or (Ci-C8)alkyl, or the two R7together with the nitrogen atom to which they are attached form a heterocyclic ring.

[0024] The term "alkyl" typically means a linear or branched hydrocarbyl, i.e., a univalent group derived from a linear or branched saturated aliphatic chain by removal of hydrogen atom from any of the carbon atoms, having, e.g., 1-18 carbon atoms and includes methyl,ethyl, / / -propyl, isopropyl, / / -butyl, sec-butyl, isobutyl, tert-butyl, / / -pentyl, isoamyl, neopentyl, 2,2-dimethylpropyl, / / -hexyl, / / -heptyl, / / -octyl, / / -nonyl, / / -decyl, / / -undecyl, n- dodecyl, / / -tridecyl, / / -tetradecyl, / / -pentadecyl, / / -hexadecyl, and the like. Preferred are (Ci- C8)alkyls, more preferably (Ci-C4)alkyls, most preferably methyl, ethyl, / / -propyl, and isopropyl. The alkyl may be interrupted by at least one heteroatom each independently selected from oxygen, nitrogen, and sulfur (optionally oxidized or deoxidized), i.e., contains at least one heteroatom within the backbone residue thereof. Such an interrupted alkyl may also be referred to herein as a “heteroalkyl”.

[0025] The terms "alkenyl" and "alkynyl" typically mean linear or branched hydrocarbyls containing at least one double or triple bond, respectively, i.e., univalent groups derived from unsaturated linear or branched aliphatic chains by removal of hydrogen atom from any of the carbon atoms. Particular alkenyls and alkynyls are (C2-C8)alkenyls such as ethenyl, propenyl, 3-buten-l-yl, and 2-ethenylbutyl, and (C2-C8)alkynyls such as propynyl, 2-butyn- 1-yl, 3-pentyn-l-yl, and 3-hexynyl, wherein (C2-C4)alkenyls and (C2-C4)alkynyls are preferred. Each one of the alkenyl and alkynyl may independently be interrupted by at least one heteroatom each independently selected from oxygen, nitrogen, and sulfur (optionally oxidized or deoxidized), i.e., contain at least one heteroatom within the backbone residue thereof. Such interrupted alkenyl and alkynyl may also be referred to herein as “heteroalkenyl” and “heteroalkynyl”, respectively.

[0026] The term “haloalkyl” as used herein refers to an alkyl group as defined above, substituted, at any position of the alkyl, with at least one halogen. In case the alkyl is substituted with more than one halogens, said substituents may be linked to either the same or different carbon atoms.

[0027] The term “aliphatic ring” or “carbocyclic ring” used herein interchangeably refers to a mono-, bi-, or poly-cyclic non-aromatic hydrocarbon having, e.g., 3-12, but preferably 3-8, carbon atoms. The carbocyclic ring may be saturated, such as cyclopropane, cyclobutane, cyclopentane, cyclohexane, cycloheptane, cyclooctane, and the like; or unsaturated, i.e., having at least one double bond, such as cyclopropene, cyclobutene, cyclopentene, cyclohexene, and the like. The term “cycloalkyl” means a univalent mono-, bi-, or poly-cyclic saturated hydrocarbyl derived from a saturated carbocyclic ring by removal of hydrogen atom from any of the carbon atoms. Examples of such groups include, without limiting, (C3-Ci2)cycloalkyls, preferably (C3-C8)cycloalkyls, such as cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl, cyclooctyl, and the like. The cycloalkylmay be substituted with at least one group each independently selected from -OH, -O-(Ci- C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, and halogen, and may also be oxidized at a carbon atom thereof.

[0028] The term "heterocyclic ring" as used herein refers to a mono-, bi-, or poly-cyclic non-aromatic ring having, e.g., 3-12, but preferably 3-8, atoms, and consisting of at least one carbon atom and at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or di oxidized), which may be saturated or unsaturated, i.e., containing at least one unsaturated bond. The heterocyclic ring may be substituted with at least one group each independently selected from -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, and halogen, and may also be oxidized at either a carbon atom or a heteroatom thereof (in cases said heteroatom is sulfur, it may also be di oxidized). Nonlimiting examples of heterocyclic rings include oxetane, azetidine, thietane, 1 -oxi dothi etan, 1,1-dioxidothietan, pyrrolidine, piperidine, morpholine, thiomorpholine, piperazine, oxazolidine, thiazolidine, imidazolidine, oxazoline, thiazoline, imidazoline, dioxole, dioxolane, dihydrooxadiazole, pyran, dihydropyran, tetrahydropyran, thiopyran, dihydrothiopyran, tetrahydrothiopyran, 1-oxidotetrahydrothiopyran, 1,1- dioxidotetrahydrothiopyran, tetrahydrofuran, pyrazolidine, pyrazoline, tetrahydropyrimidine, dihydrotriazole, tetrahydrotriazole, azepane, dihydropyridine, tetrahydropyridine, and the like. The term "heterocyclyl" as used herein refers to a univalent group derived from a heterocyclic ring by removal of hydrogen atom from any of the ring atoms.

[0029] The term “aromatic ring” as used herein refers to an aromatic carbocyclic ring having, e.g., 6-14 carbon atoms, and consisting of a single ring or multiple rings either condensed or linked by a covalent bond. Non-limiting examples of aromatic rings include benzene, naphthalene, anthracene, naphthacene, phenanthrene, pyrene, chrysene, tetracene, and triphenylene. The aromatic ring may optionally be substituted with one or more groups each independently selected from -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2- C8)alkynyl, and halogen. The term "aryl" denotes a univalent aromatic carbocyclic group derived from an aromatic ring by removal of hydrogen atom from any of the ring atoms.

[0030] The term “heteroaromatic ring” as used herein refers to a mono-, bi-, or poly-cyclic aromatic ring having, e.g., 5-14 atoms, and consisting of at least one carbon atom and at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized). Nonlimiting examples of heteroaromatic rings include thiophene, imidazole, pyridine, furan,pymole, oxazole, thiazole, purine, indole, pyrrole, pyrazine, isoquinoline, pyrazole, isoxazole, thiazole, isothiazole, pyrazine, pyrimidine, pyridazine, carbazole. The heteroaromatic ring may optionally be substituted, at any one of the atoms thereof, with one or more groups each independently selected from -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2- C8)alkenyl, (C2-C8)alkynyl, and halogen. The term “heteroaryl” refers to a univalent group derived from a heteroaromatic ring by removal of hydrogen atom from any of the ring atoms.

[0031] The term "halogen" as used herein refers to a halogen and includes fluoro, chloro, bromo, and iodo, but it is preferably fluoro, chloro or iodo.

[0032] In certain embodiments, disclosed herein is a compound of the formula I, wherein R1and R2each independently is H or (Ci-C3)alkyl. In particular such embodiments, R1and R2each independently is H, methyl, or ethyl, i.e., R1and R2each is H; R1and R2each is methyl; R1and R2each is ethyl; R1is H, and R2is methyl or ethyl; or R1is methyl or ethyl, and R2is H.

[0033] In certain embodiments, disclosed herein is a compound of the formula I, wherein R3is H or -CH2OH.

[0034] In certain embodiments, disclosed herein is a compound of the formula I, wherein R4, R5and R6each independently is H or (Ci-C3)alkyl. In particular such embodiments, R4, R5and R6each independently is H, methyl or ethyl, i.e., R4, R5and R6each is H; R4, R5and R6each is methyl; R4, R5and R6each is ethyl; R4is H, and R5and R6each independently is methyl or ethyl; R5is H, and R4and R6each independently is methyl or ethyl; R6is H, and R4and R5each independently is methyl or ethyl; R4and R5each is H, and R6is methyl or ethyl; R4and R6each is H, and R5is methyl or ethyl; or R5and R6each is H, and R4is methyl or ethyl.

[0035] According to the present invention, the group Ar is 5-14-membered- aryl or heteroaryl as defined above, but excluding (Ce)aryl, i.e., phenyl, wherein said aryl or heteroaryl is optionally substituted, preferably at any carbon atom thereof, with at least one group each independently selected from halogen, oxo, -OH, -CN, (Ci-C8)alkyl, (Ci- C8)haloalkyl, and -NR72.

[0036] In certain embodiments, disclosed herein is a compound of the formula I, wherein Ar is a 6-membered heteroaryl containing one or two nitrogen atoms, preferably one nitrogen atom, optionally substituted at a carbon atom thereof with a group selected from halogen, oxo, -OH, -CN, (Ci-C2)alkyl, (Ci-C2)haloalkyl such as -CH2F, -CHF2 and -CF3, and -NR72, wherein R7each independently is H, methyl or ethyl. In particular such embodiments, Ar isselected from pyridin-4-yl, 6-chl oropyri din-3 -yl, 6-oxo-l,6-dihydropyridin-3-yl, 5- hydroxypyridin-2-yl, 6-hy droxypyri din-3 -yl, 6-cyanopyridin-3-yl, 5-(trifluoromethyl)pyri din-2 -yl, 6-aminopyri din-3 -yl, and 6-(dimethylamino)pyri din-3 -yl (Table 1). Preferred embodiments are those wherein Ar is pyridin-4-yl, 6-hydroxypyridin- 3 -yl, 6-cyanopyridin-3-yl, or 6-aminopyridin-3-yl.Table 1. Particular 6-membered heteroaromatic groups referred to herein as group Ar

[0037] In other embodiments, disclosed herein is a compound of the formula I, wherein Ar is a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring containing at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized). In particular such embodiments, Ar is a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring selected from 4,5-dihydro-l / / -imidazole, 4, 5 -dihydro- H- pyrazole, 4,5-dihydro-17 / -l,2,3-triazole, 1,2,5-oxadiazole, imidazolidin-2-one, and 1,2,5- thiadiazolidine- 1,1 -di oxide (Table 2). Specific such embodiments are those wherein Ar is 17 / -benzo[d]imidazol-5-yl, l / f-indazol-5-yl, l / 7-benzo[ ][l,2,3]triazol-5-yl, benzo[c][l,2,5]oxadiazol-5-yl, 2-oxo-2,3-dihydro-17 / -benzo[d]imidazol-5-yl, or 2,2- dioxido-l,3-dihydrobenzo[c][l,2,5]thiadiazol-5-yl, preferably l / 7-benzo[d]imidazol-5-yl or l / f-indazol-5-yl (Table 3).Table 2Table 3. Particular bicyclic heteroaromatic groups referred to herein as group Ar

[0038] In further embodiments, disclosed herein is a compound of the formula I, wherein Ar is a 5-membered heteroaryl containing at least one heteroatom each independently selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized). In particular such embodiments, Ar is a 5-membered heteroaryl containing at least one nitrogen atom and / or at least one sulfur atom, optionally substituted at a carbon atom thereof with a group selected from halogen, -CN and -NR72, wherein R7each independently is H, methyl or ethyl. Specific such embodiments are those wherein Ar is selected from 5-chlorothiophen-2-yl, 5 -fl ourothi ophen-2 -yl, 5-bromothi ophen-2 -yl, 5 -iodothi ophen-2 -yl, 5-cyanothi ophen-2 -yl, I / / -pyrrol -3 -yl, l / / -pyrazol-4-yl, thiazol-5-yl, 2-chlorothiazol-5-yl, 2-bromothiazol-5-yl,and 2-aminothiazol-5-yl, preferably 5-chlorothiophen-2-yl, 5-flourothiophen-2-yl, 5- bromothiophen-2-yl, 5-iodothiophen-2-yl, or 5-cyanothiophen-2-yl (Table 4).Table 4. Particular 5-membered heteroaromatic groups referred to herein as group Ar

[0039] In certain embodiments, disclosed herein is a compound of the formula I, wherein R1, R2, R4, R5, and R6each independently is H or (Ci-Cajalkyl; R3is H or -CH2OH; and Ar is (i) a 6-membered heteroaryl containing one or two nitrogen atoms, preferably one nitrogen atom, optionally substituted at a carbon atom thereof with a group selected from halogen, oxo, -OH, -CN, (Ci-C2)alkyl, (Ci-C2)haloalkyl, and -NR72, wherein R7each independently is H, methyl or ethyl; (ii) a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring containing at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized); or (iii) a 5-membered heteroaryl containing at least one heteroatom each independently selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized).

[0040] In particular such embodiments, R1, R2, R4, R5, and R6each independently is H, methyl or ethyl; and Ar is (i) selected from pyridin-4-yl, 6-chl oropyri din-3 -yl, 6-oxo-l,6- dihy dropyri din-3 -yl, 5-hydroxypyridin-2-yl, 6-hy droxypyri din-3 -yl, 6-cyanopyridin-3-yl, 5- (trifluoromethyl)pyridin-2-yl, 6-aminopyridin-3-yl, and 6-(dimethylamino)pyridin-3-yl; (ii) a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring selected from 4,5-dihydro-l / Z-imidazole, 4,5-dihydro-U / -pyrazole, 1,2,5-oxadiazole, imidazolidin-2-one, and l,2,5-thiadiazolidine-l,l-dioxide; or (iii) a 5-membered heteroaryl containing at leastone nitrogen atom and / or at least one sulfur atom, optionally substituted at a carbon atom thereof with a group selected from halogen, -CN and -NR72, wherein R7each independently is H, methyl or ethyl. Examples of such compounds are those wherein R1and R2each is H; R1and R2each is methyl; R1and R2each is ethyl; R1is H, and R2is methyl or ethyl; or R1is methyl or ethyl, and R2is H; and / or R4, R5and R6each is H; R4, R5and R6each is methyl; R4, R5and R6each is ethyl; R4is H, and R5and R6each independently is methyl or ethyl; R5is H, and R4and R6each independently is methyl or ethyl; R6is H, and R4and R5each independently is methyl or ethyl; R4and R5each is H, and R6is methyl or ethyl; R4and R6each is H, and R5is methyl or ethyl; or R5and R6each is H, and R4is methyl or ethyl, wherein each the combination of R1, R2, R4, R5, and R6referred to hereinabove represents a particular embodiment.

[0041] In more particular such embodiments, Ar is selected from pyridin-4-yl, 6- chl oropyri din-3 -yl, 6-oxo-l,6-dihydropyridin-3-yl, 5-hydroxypyridin-2-yl, 6- hy droxypyri din-3 -yl, 6-cyanopyridin-3-yl, 5-(trifluoromethyl)pyridin-2-yl, 6-aminopyridin- 3-yl, 6-(dimethylamino)pyri din-3 -yl, l / 7-benzo[d]imidazol-5-yl, l / 7-indazol-5-yl, 1H- benzo[ ][l,2,3]triazol-5-yl, benzofc] [1, 2, 5]oxadiazol-5-yl, 2-oxo-2, 3 -dihydro- I / / -benzo [d]imidazol-5-yl, 2,2-dioxido-l,3-dihydrobenzo[c][l,2,5]thiadiazol-5-yl, 5-chlorothiophen- 2-yl, 5-flourothiophen-2-yl, 5-bromothiophen-2-yl, 5-iodothiophen-2-yl, 5-cyanothiophen- 2-yl, I / / -pyrrol -3 -yl, l / / -pyrazol-4-yl, thiazol-5-yl, 2-chlorothiazol-5-yl, 2-bromothiazol-5- yl, and 2-aminothiazol-5-yl.

[0042] In certain embodiments, disclosed herein is a compound of the formula I according to any one of the embodiments above, wherein (i) R1and R2each is H; R3is -CH2OH; and R4, R5and R6each is methyl (referred to herein as a compound of formula la); (ii) R1, R2and R6each is H; R3is -CH2OH; and R4and R5each is methyl (referred to herein as a compound of formula lb); (iii) R1, R2and R5each is methyl; and R3, R4and R6each is H (referred to herein as a compound of formula Ic); or (iv) R1, R2, R4, R5, and R6each is methyl; and R3is -CH2OH (referred to herein as a compound of formula Id) (Table 5).

[0043] In certain specific such embodiments, the present invention provides a compound of the formula la, more specifically a compound of the formula I, wherein R1and R2each is H; R3is -CH2OH; R4, R5and R6each is methyl; and Ar is l / / -benzo[d]imidazol-5-yl, 5- hydroxypyridin-2-yl, 6-aminopyri din-3 -yl, lZ / -indazol-5-yl, 2,2-dioxido-l,3-dihydrobenzo [c][l,2,5]thiadiazol-5-yl, 6-oxo-l,6-dihydropyridin-3-yl, pyridin-4-yl, benzo[c][l,2,5] oxadiazol-5-yl, 6-(dimethylamino)pyri din-3 -yl, 5 -(trifluoromethyl) pyridin-2-yl, 6- cyanopyridin-3-yl, 6-chl oropyri din-3 -yl, 5-chlorothiophen-2-yl, 5-bromo thiophen-2-yl, 5- iodothi ophen-2 -yl, or 5-cyanothi ophen-2 -yl (herein identified compounds 1, 2, 4, 6, 7, 11, 19, 23, 24, 26, 27, 35, 36, 37, 38, and 60, respectively; Table 6).

[0044] In other specific such embodiments, the present invention provides a compound of the formula lb, more specifically a compound of the formula I, wherein R1, R2and R6each is H; R3is -CH2OH; R4and R5each is methyl; and Ar is 5-hydroxypyridin-2-yl, 1 / 7-indazol- 5-yl, 2,2-dioxido-l,3-dihydrobenzo[c][l,2,5] thiadiazol-5-yl, benzo[c][l,2,5]oxadiazol-5- yl, or 5-(trifluoromethyl)pyridin-2-yl (herein identified compounds 29, 30, 31, 32, and 33, respectively; Table 6).

[0045] In further specific such embodiments, the present invention provides a compound of the formula Ic, more specifically a compound of the formula I, wherein R1, R2and R5each is methyl; R3, R4and R6each is H; and Ar is 2,2-dioxido-l,3-dihydrobenzo[c] [l,2,5]thiadiazol-5-yl, l / / -indazol-5-yl, 6-aminopyri din-3 -yl, 5-hydroxypyridin-2-yl, 1H- benzo[d]imidazol-5-yl, benzofc] [1, 2, 5]oxadiazol-5-yl, 6-cy anopyri din-3 -yl, 6-(dimethylamino)pyri din-3 -yl, 6-hy droxypyri din-3 -yl, 2-oxo-2,3-dihydro-177-benzo[d] imidazol-5-yl, lJ7-pyrazol-4-yl, pyridin-4-yl, 6-oxo-l,6-dihydropyridin-3-yl, 2- aminothiazol-5-yl, thiazol-5-yl, 2-chlorothiazol-5-yl, 2-bromothiazol-5-yl, l / / -pyrrol-3-yl, or 5-cyanothiophen-2-yl (herein identified compounds 13, 14, 16, 18, 21, 39, 41, 42, 45, 46, 47, 49, 50, 54, 55, 56, 57, 58, and 59, respectively; Table 6). In preferred such embodiments, said compound is selected from the compounds herein identified compounds 14 and 21.

[0046] In another aspect, the present invention provides an oxabicyclic compound of formula II:or a stereoisomer or pharmaceutically acceptable salt thereof, whereinR1, R2, R4, R5, and R6each independently is selected from H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;R3 is selected from -CH2OH, H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2- C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;Ar is a group of formula:wherein:(iii) X is selected from -CN, -N3, -NR72, -NH-S(=O)2-(Ci-C8)alkyl, and -S(=O)2- NR72, wherein Ar is optionally further substituted with at least one group each independently selected from halogen, oxo, -OH, -CN, (Ci-C8)alkyl, (Ci- C8)haloalkyl, and -NR72; or(iv) X is -OH, wherein Ar is further substituted with halogen at a carbon atom ortho to X; andR7each independently is H or (Ci-C8)alkyl, or the two R7together with the nitrogen atom to which they are attached form a heterocyclic ring.

[0047] In certain embodiments, disclosed herein is a compound of the formula II, wherein R1and R2each independently is H or (Ci-C3)alkyl. In particular such embodiments, R1and R2each independently is H, methyl, or ethyl, i.e., R1and R2each is H; R1and R2each is methyl; R1and R2each is ethyl; R1is H, and R2is methyl or ethyl; or R1is methyl or ethyl, and R2is H.

[0048] In certain embodiments, disclosed herein is a compound of the formula II, wherein R3is H or -CH2OH.

[0049] In certain embodiments, disclosed herein is a compound of the formula II, wherein R4, R5and R6each independently is H or (Ci-C3)alkyl. In particular such embodiments, R4, R5and R6each independently is H, methyl or ethyl, i.e., R4, R5and R6each is H; R4, R5and R6each is methyl; R4, R5and R6each is ethyl; R4is H, and R5and R6each independently is methyl or ethyl; R5is H, and R4and R6each independently is methyl or ethyl; R6is H, and R4and R5each independently is methyl or ethyl; R4and R5each is H, and R6is methyl or ethyl; R4and R6each is H, and R5is methyl or ethyl; or R5and R6each is H, and R4is methyl or ethyl.

[0050] In certain embodiments, disclosed herein is a compound of the formula II, wherein X is selected from -CN, -N3, -N(CH3)2, -NH-S(=O)2-CH3, and -S(=O)2-NH2; or X is -OH, and Ar is further substituted with halogen at one of the carbon atoms ortho to X or with the same or different halogen at each one of the two carbon atoms ortho to X.

[0051] In certain embodiments, disclosed herein is a compound of the formula II, wherein R1, R2, R4, R5, and R6each independently is H or (Ci-C3)alkyl; R3is H or -CH2OH; and X is selected from -CN, -N3, -N(CH3)2, -NH-S(=O)2-CH3, and -S(=O)2-NH2; or X is -OH, and Ar is further substituted with halogen at either one or both of the carbon atoms ortho to X. Such halogen may be F, Cl, Br, or I, and in case the two carbon atoms ortho to X are substituted, the substituents may be either identical or different.

[0052] In certain embodiments, disclosed herein is a compound of the formula II according to any one of the embodiments above, wherein (i) R1and R2each is H; R3is -CH2OH; and R4, R5and R6each is methyl (formula la); (ii) R1, R2and R6each is H; R3is -CH2OH; and R4and R5each is methyl (formula lb); (iii) R1, R2and R5each is methyl; and R3, R4and R6each is H (formula Ic); or R1, R2, R4, R5, and R6each is methyl; and R3is -CH2OH (formula Id) (Table 5).

[0053] In certain specific such embodiments, the present invention provides a compound of the formula la, more specifically a compound of the formula II, wherein R1and R2each is H; R3is -CH2OH; R4, R5and R6each is methyl; and X is selected from -NH-S(=O)2-CH3; -N3; -N(CH3)2, wherein Ar is further substituted with Cl at one of the carbon atoms meta to X; -S(=O)2-NH2; -CN; and -OH, wherein Ar is further substituted with either I at one of the carbon atoms ortho to X or F at each one of the carbon atoms ortho to X (herein identified compounds 10, 22, 25, 34, 52, 5, and 51, respectively; Table 6).

[0054] In other specific such embodiments, the present invention provides a compound of the formula lb, more specifically a compound of the formula II, wherein R1, R2and R6each is H; R3is -CH2OH; R4and R5each is methyl; and X is selected from -N3, -S(=O)2-NH2, and -CN (herein identified compounds 28, 44 and 53, respectively; Table 6).

[0055] In further specific such embodiments, the present invention provides a compound of the formula Ic, more specifically a compound of the formula II, wherein R1, R2and R5each is methyl; R3, R4and R6each is H; and X is selected from -NH-S(=O)2-CH3; -S(=O)2- NH2; -N3; and -OH, wherein Ar is further substituted with either I at one of the carbon atoms ortho to X or F at each one of the carbon atoms ortho to X (herein identified compounds 20, 40 and 43, 17, and 48, respectively; Table 6).Table 6. Specific oxabicyclic compounds of formulas I and II (compounds marked with asterisk are not included in the scope of the present invention)

[0056] The oxabicyclic compounds of the formulas I and II disclosed herein may have one or more asymmetric centers, e.g., at the carbon atom of the oxabicyclic ring to which the Ar group is attached, and may accordingly exist as stereoisomers, e.g., as enantiomers (R, S, or racemate, wherein a certain enantiomer may have an optical purity of 90%, 95%, 99% ormore) or diastereoisomers. The present invention encompasses all such stereoisomers, as well as mixtures thereof and pharmaceutically acceptable salts thereof.

[0057] Optically active forms of the compounds of the formula I or II may be prepared using any method known in the art, e.g., by resolution of the racemic form by recrystallization techniques; by chiral synthesis; by extraction with chiral solvents; or by chromatographic separation using a chiral stationary phase. A non-limiting example of a method for obtaining optically active materials is transport across chiral membranes, i.e., a technique whereby a racemate is placed in contact with a thin membrane barrier, the concentration or pressure differential causes preferential transport across the membrane barrier, and separation occurs as a result of the non-racemic chiral nature of the membrane that allows only one enantiomer of the racemate to pass through. Chiral chromatography, including simulated moving bed chromatography, can also be used. A wide variety of chiral stationary phases are commercially available.

[0058] In a further aspect, the present invention provides a pharmaceutical composition comprising an oxabicyclic compound of the formula I or II, each according to any one of the embodiments above, or a stereoisomer or pharmaceutically acceptable salt thereof (herein also referred to as the “active agent”), and a pharmaceutically acceptable carrier and / or excipient.

[0059] The term "pharmaceutically acceptable carrier" or "pharmaceutically acceptable excipient" as used herein interchangeably refers to any non-active ingredient such as a solvent, dispersion medium, preservative, antioxidant, coating, isotonic and absorption delaying agent, and the like, that is compatible with pharmaceutical administration, and does not produce an adverse, allergic, or other untoward reaction when administered to a mammal or human as appropriate. For human administration, compositions should meet sterility, pyrogenicity, and general safety and purity standards as required by, e.g., the U.S. Food and Drug Administration (FDA), or the European Medicines Agency (EMA).

[0060] The pharmaceutical compositions disclosed herein can be provided in a variety of formulations, e.g., in a pharmaceutically acceptable form and / or in a salt form, as well as in a variety of dosages.

[0061] In certain embodiments, the pharmaceutical composition disclosed comprises a non-toxic pharmaceutically acceptable salt of a compound of the formula I or II. Suitable pharmaceutically acceptable salts include acid addition salts such as, without being limited to, the mesylate salt, the maleate salt, the fumarate salt, the tartrate salt, the hydrochloridesalt, the hydrobromide salt, the esylate salt, the / / -toluenesulfonate salt, the benzenesulfonate salt, the benzoate salt, the acetate salt, the phosphate salt, the sulfate salt, the citrate salt, the carbonate salt, and the succinate salt. Additional pharmaceutically acceptable salts include salts of ammonium (NH4+) or an organic cation derived from an amine of the formula R4N+, wherein each one of the Rs independently is selected from H, C1-C22, preferably Ci-Ce alkyl, such as methyl, ethyl, propyl, isopropyl, / / -butyl, sec-butyl, isobutyl, Zc / 7-butyl, / / -pentyl, 2,2-dimethylpropyl, / / -hexyl, and the like, phenyl, or heteroaryl such as pyridyl, imidazolyl, pyrimidinyl, and the like, or two of the Rs together with the nitrogen atom to which they are attached form a 3-7 membered ring optionally containing a further heteroatom selected from N, S and O, such as pyrrolidine, piperidine and morpholine. Furthermore, where the compounds of the formula I or II carry an acidic moiety, suitable pharmaceutically acceptable salts thereof may include metal salts such as alkali metal salts, e.g., lithium, sodium or potassium salts, and alkaline earth metal salts, e.g., calcium or magnesium salts.

[0062] Further pharmaceutically acceptable salts include salts of a cationic lipid or a mixture of cationic lipids. Cationic lipids are often mixed with neutral lipids prior to use as delivery agents. Neutral lipids include, but are not limited to, lecithins; phosphatidylethanolamine; diacyl phosphatidylethanolamines such as dioleoyl phosphatidylethanolamine, dipalmitoyl phosphatidylethanolamine, palmitoyloleoyl phosphatidylethanolamine and distearoyl phosphatidylethanolamine; phosphatidylcholine; diacyl phosphatidylcholines such as dioleoyl phosphatidylcholine, dipalmitoyl phosphatidylcholine, palmitoyloleoyl phosphatidylcholine and distearoyl phosphatidylcholine; phosphatidylglycerol; diacyl phosphatidylglycerols such as dioleoyl phosphatidylglycerol, dipalmitoyl phosphatidylglycerol and distearoyl phosphatidylglycerol; phosphatidylserine; diacyl phosphatidylserines such as dioleoyl- or dipalmitoyl phosphatidylserine; and diphosphatidylglycerols; fatty acid esters; glycerol esters; sphingolipids; cardiolipin; cerebrosides; ceramides; and mixtures thereof. Neutral lipids also include cholesterol and other 3P hydroxy-sterols.

[0063] Examples of cationic lipid compounds include, without being limited to, Lipofectin® (Life Technologies, Burlington, Ontario) (1 : 1 (w / w) formulation of the cationic lipid N-[l-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride and dioleoylphosphatidyl-ethanolamine); Lipofectamine™ (Life Technologies, Burlington, Ontario) (3: 1 (w / w) formulation of polycationic lipid 2,3 -di oleyloxy -N-[2(spermine- carboxamido)ethyl]-N,N-dimethyl-l-propanamin-iumtrifluoroacetate anddioleoylphosphatidyl-ethanolamine), Lipofectamine Plus (Life Technologies, Burlington,Ontario) (Lipofectamine and Plus reagent), Lipofectamine 2000 (Life Technologies, Burlington, Ontario) (Cationic lipid), Effectene (Qiagen, Mississauga, Ontario) (Non liposomal lipid formulation), Metafectene (Biontex, Munich, Germany) (Polycationic lipid), Eu-fectins (Promega Biosciences, San Luis Obispo, Calif.) (ethanolic cationic lipids numbers 1 through 12: C52HIO6N604-4CF3C02H, C88H178N8O4S24CF3CO2H,C4OH84N03P CF3C02H, C50H103N7O34CF3CO2H, C55H116N8O26CF3CO2H,C49H102N6O3 4CF3CO2H, C44H89N5O3-2CF3CO2H, C 100H206N12O4 S2-8CF 3 CO2H,C162H330N22O9 I3CF3CO2H, C43H88N4O22CF3CO2H, C43H88N4O32CF3CO2H,C41H78NO8P); Cytofectene (Bio-Rad, Hercules, Calif.) (mixture of a cationic lipid and a neutral lipid), GenePORTER® (Gene Therapy Systems, San Diego, Calif.) (formulation of a neutral lipid (Dope) and a cationic lipid) and FuGENE 6 (Roche Molecular Biochemicals, Indianapolis, Ind.) (Multi-component lipid based non-liposomal reagent).

[0064] Pharmaceutically acceptable salts of the oxabicyclic compound disclosed herein may be formed by conventional means, e.g., by reacting a free base form of the active agent with one or more equivalents of the appropriate acid in a solvent or medium in which the salt is insoluble, or in a solvent such as water which is removed in vacuo or by freeze drying, or by exchanging the anion / cation of an existing salt for another anion / cation on a suitable ion exchange resin.

[0065] The pharmaceutical compositions provided by the present invention may be prepared by conventional techniques, e.g., as described in Remington: The Science and Practice of Pharmacy, 19thEd., 1995. The compositions can be prepared, e.g., by uniformly and intimately bringing the active agent into association with a liquid carrier, a finely divided solid carrier, or both, and then, if necessary, shaping the product into the desired formulation. The compositions may be in liquid, solid or semisolid form, and may further include pharmaceutically acceptable fillers, carriers, diluents or adjuvants, and other inert ingredients and excipients. In one embodiment, the pharmaceutical composition of the present invention is formulated as nanoparticles.

[0066] The pharmaceutical compositions disclosed herein can be formulated for any suitable route of administration, either parenterally or enterally / gastrointestinally. Examples of suitable parenteral administration routes include, without being limited to, intravenous, intraarterial, intrathecal, intrapleural, intratracheal, intraperitoneal, intramuscular, intranasal, nasal, transdermal, subcutaneous, vaginal, topical, or ophthalmic (e.g., as eye drops)administration. Non-limiting examples of suitable enteral administration routes include oral, sublingual, sublabial, supra-lingual, buccal, or rectal administration. The compositions disclosed herein may also be formulated for inhalation. The dosage will depend on the state of the patient and will be determined as deemed appropriate by the practitioner.

[0067] Pharmaceutical compositions formulated for oral administration may be in the form of a liquid, e.g., a solution in an edible solvent such as ethanol, tincture, syrup, or elixir; a semi-solid; or a solid such as tablets, caplets, pills, troches, lozenges, dispersible powder or granules, hard or soft capsules, and sachets. In some particular embodiments, the pharmaceutical composition is in the form of a bi- or multilayer tablet, in which each one of the layers comprise the active agent, and the layers are optionally separated by an intermediate, inactive layer, e.g., a layer comprising one or more disintegrants.

[0068] Useful dosage forms of the pharmaceutical compositions include orally disintegrating systems including, but not limited to, solid, semi-solid and liquid systems including disintegrating or dissolving tablets, soft or hard capsules, gels, fast dispersing dosage forms, controlled dispersing dosage forms, caplets, films, wafers, ovules, granules, buccal / mucoadhesive patches, powders, freeze dried (lyophilized) wafers, chewable tablets which disintegrate with saliva in the buccal / mouth cavity and combinations thereof. Useful films include, but are not limited to, single layer stand-alone films and dry multiple layer stand-alone films.

[0069] In certain embodiments, the pharmaceutical compositions are formulated for oral administration, and are in the form of matrix tablets wherein the release of the active agent is controlled by having said active agent diffuse through a gel formed after the swelling of a hydrophilic polymer brought into contact with dissolving liquid (in vitro) or gastro-intestinal fluid (in vivo). Many polymers have been described as capable of forming such gel, e.g., derivatives of cellulose, in particular the cellulose ethers such as hydroxypropyl cellulose, hydroxymethyl cellulose, methylcellulose or methyl hydroxypropyl cellulose, and among the different commercial grades of these ethers are those showing fairly high viscosity. In other embodiments, the tablets are formulated as bi- or multi-layer tablets, made up of two or more distinct layers of granulation compressed together with the individual layers lying one on top of another, with each separate layer containing a different active agent. Bilayer tablets have the appearance of a sandwich since the edge of each layer or zone is exposed.

[0070] Pharmaceutical compositions for oral administration might be formulated so as to inhibit the release of the active agent in the stomach, i.e., delay the release of said activeagent until at least a portion of the dosage form has traversed the stomach, in order to avoid the acidity of the gastric contents from hydrolyzing the active agent. Particular such compositions are those wherein the active agent is coated by a pH-dependent enteric-coating polymer. Examples of pH-dependent enteric-coating polymer include, without being limited to, Eudragit® S (poly(methacrylicacid, methylmethacrylate), 1 :2), Eudragit® L 55 (poly (methacrylicacid, ethyl acrylate), 1 : 1), Kollicoat® (poly(methacrylicacid, ethylacrylate), 1 : 1), hydroxypropyl methylcellulose phthalate (HPMCP), alginates, carboxymethylcellulose, and combinations thereof. The pH-dependent enteric-coating polymer may be present in the composition in an amount from about 10% to about 95% by weight of the entire composition.

[0071] Another contemplated formulation is depot systems, based on biodegradable polymers. As the polymer degrades, the active agent is slowly released. The most common class of biodegradable polymers is the hydrolytically labile polyesters prepared from lactic acid, glycolic acid, or combinations of these two molecules. Polymers prepared from these individual monomers include poly (D,L-lactide) (PLA), poly (glycolide) (PGA), and the copolymer poly (D,L-lactide-co-glycolide) (PLG).

[0072] Pharmaceutical compositions for oral administration may further comprise one or more agents selected from sweetening agents, flavoring agents, coloring agents and preserving agents in order to provide pharmaceutically elegant and palatable preparations. In addition, said compositions may comprise one or more pharmaceutically acceptable excipients. For example, a tablet may comprise at least one filler, e.g., lactose, ethylcellulose, microcrystalline cellulose, silicified microcrystalline cellulose; at least one disintegrant, e.g., cross-linked polyvinylpyrrolidinone; at least one binder, e.g., polyvinylpyridone, hydroxypropylmethyl cellulose; at least one surfactant, e.g., sodium laurylsulfate; at least one glidant, e.g., colloidal silicon dioxide; and at least one lubricant, e.g., magnesium stearate.

[0073] Pharmaceutical compositions formulated for parenteral administration, i.e., for administration elsewhere in the body than the mouth and alimentary canal (also called the digestive tract), may be in the form of a sterile, optionally injectable, aqueous or oleaginous suspension, which may be formulated according to the known art using suitable dispersing, wetting or suspending agents. The sterile injectable preparation may also be an injectable solution or suspension in a non -toxic parenterally acceptable diluent or solvent. Acceptable vehicles and solvents that may be employed include, without limiting, water,Ringer's solution, polyethylene glycol (PEG), 2-hydroxypropyl-P-cyclodextrin (HPCD), a surfactant such as Tween-80, and isotonic sodium chloride solution.

[0074] Pharmaceutical compositions according to the invention, when formulated for inhalation, may be in any suitable form, e.g., liquid or fine powder, and may be administered utilizing any suitable device known in the art, such as pressurized metered dose inhalers, liquid nebulizers, dry powder inhalers, sprayers, thermal vaporizers, electrohydrodynamic aerosolizers, and the like.

[0075] For instance, nebulizers use oxygen, compressed air, or ultrasonic power to break up solutions and suspensions into small aerosol, i.e., a mixture of gas and solid or liquid particles, droplets that are inhaled from the mouthpiece of the device.

[0076] As shown in the experimental section, the oxabicyclic compound disclosed herein is highly useful in the treatment of an influenza virus infection, e.g., influenza A or influenza B virus infection.

[0077] In still a further aspect, thus disclosed herein is a method for treatment of an influenza virus infection, e.g., influenza A or influenza B virus infection, in a subject in need thereof, said method comprising administering to said subject a therapeutically effective amount of an oxabicyclic compound of the formula I or II, according to any one of the embodiments above, or a stereoisomer or pharmaceutically acceptable salt thereof, or a pharmaceutical composition thereof.

[0078] The term "subject" as used herein refers to any mammal, e.g., a human, non-human primate, horse, ferret, dog, cat, cow, and goat. In a preferred embodiment, the term "subject" denotes a human, i.e., an individual.

[0079] The term "effective amount" as used herein means an amount of a compound of the present invention that will elicit the biological or medical response of a tissue, system, animal, or human that is being sought. The amount must be effective to achieve the desired therapeutic effect as described above, depending, inter alia, on the type and severity of the condition to be treated and the treatment regime. The effective amount is typically determined in appropriately designed clinical trials (dose range studies) and the person versed in the art will know how to properly conduct such trials to determine the effective amount. As generally known, an effective amount depends on a variety of factors including a variety of pharmacological parameters such as half-life of said compound in the body (i.e., absorption-distribution-metabolism-excretion parameters), undesired side effects andtoxicity, if any, and factors such as age and gender. Additional factors may be associated with the specific formulation administered, e.g., the vehicle formulation, the solubility of said compound in the vehicle formulation, and the administration mode.

[0080] It should be noted that the compound provided as a medical treatment according to the method of the present invention, i.e., said oxabicyclic compound or said stereoisomer or pharmaceutically acceptable salt thereof, may be administered in combination with an additional antiviral drug. Non-limiting examples of such antiviral drugs include oseltamivir (Tamiflu®; ethyl (3A,4A,5S)-5-amino-4-acetamido-3-(pentan-3-yloxy)-cyclohex-l-ene-l- carboxylate); Zanamivir (Relenza; (2A,3A,45)-4-guanidino-3-(prop-l-en-2-ylamino)-2- ((lA,2A)-l,2,3-trihydroxypropyl)-3,4-dihydro-2H-pyran-6-carboxylic acid); peramivir (Rapivab; (15,2£,3A,4A)-3-[(15)-l-(acetylamino)-2-ethylbutyl]-4-(carbamimidoylamino)- 2 -hydroxy cyclopentanecarboxylic acid); amantadine (adamantan-1 -amine), rimantadine (1- (adamantanyl)ethanamine), umifenovir (arbidol, ethyl 6-bromo-4-[(dimethylamino)methyl] -5-hydroxy- l -methyl-2-[(phenylsulfanyl)methyl]- l / / -indole-3 -carboxylate), and baloxavir marboxil (Xofluza'-'; {(12a / ?)-12-[(l 15)-7,8-difluoro-6,l l-dihydrodibenzo[Z>,e]thiepin-l l- yl]-6,8-dioxo-3,4,6,8, 12, 12a-hexahydro-l / / -[l ,4]oxazino[3,4-c]pyrido[2, l7 / ] [l,2,4]triazin- 7-yl}oxy)methyl methyl carbonate). In cases said compound is administered in combination with an additional antiviral drug, the two active agents may be administered concomitantly or sequentially at any order, by either the same or different administration route.

[0081] In yet a further aspect, the present invention relates to an oxabicyclic compound of the formula I or II, each according to any one of the embodiments above, or a stereoisomer or pharmaceutically acceptable salt thereof, or a pharmaceutical composition thereof, for use in the treatment of an influenza virus infection, e.g., influenza A or influenza B virus infection.

[0082] In still another aspect, the present invention relates to use of an oxabicyclic compound of the formula I or II, each according to any one of the embodiments above, or a stereoisomer or pharmaceutically acceptable salt thereof, in the preparation of a pharmaceutical composition for treatment of an influenza virus infection, e.g., influenza A or influenza B virus infection.

[0083] For purposes of clarity, and in no way limiting the scope of the teachings, unless otherwise indicated, all numbers expressing percentages temperatures, and other numerical values recited herein, should be interpreted as being preceded in all instances by the term "about", regardless of whether “about” is explicitly prepended to the numerical value.Accordingly, unless indicated to the contrary, the numerical parameters set forth in this specification are approximations that may vary by up to plus or minus 10% depending upon the desired properties to be obtained by the present invention.

[0084] The invention will now be illustrated by the following non-limiting Examples.EXAMPLESStudy 1. Oxabicyclic scaffold featuring aromatic group as small-molecule anti-flu drugsMaterials and Methods

[0085] 2-Dimensional SAR investigation. The lead scaffolds, also referred to herein as the parent Compounds SG2 and 9, are disclosed in WO 2017 / 106820. In the present study, a two-dimensional (2D) structure-activity -relationship (SAR) investigation has been carried out so as to improve upon the original compounds and develop the novel compounds described herein. The rationale underlying the present study encompassed bioisosteric replacement of the primary alcohol and / or phenol groups in SG2 and compound 9 with chemical moieties that pose a lower toxicity risk and offer better pharmacokinetic properties for in vivo trials, while maintaining or improving biological activity and breadth of spectrum in cells.

[0086] Medicinal chemistry. The synthetic route used for the preparation of compounds of Scaffold A was previously described (Hamann et al., 2005) and is shown in Scheme 2. Briefly, for the first set of derivatives containing a primary alcohol group, Diels-Alder cycloaddition of l,3-dimethyl-l,3-butadiene (1) and diethyl ethylidenemalonate (2) provided dicarboethoxycyclohexene (3), which underwent reduction to the corresponding diols (4) with lithium aluminum hydride. This process was followed by / ?-toluenesulfonic acid-mediated cationic cyclization with various aldehydes to yield the target oxabicyclic analogues in good to excellent yields as racemic mixtures of two diastereomers, which were separated using thin layer chromatography (TLC). The cis / trans relationship between the aryl group and the methyl group attached to the bicyclic bridgehead was evaluated through ’H NMR to determine the stereochemistry of each diastereomer. Compounds produced via this synthetic route can also be one of two possible diastereomers. The diastereomers differ in the stereochemical configuration of the methyl group on the bicyclic bridgehead relative to the aromatic group, either in cis or trans configuration (Scheme 1).

[0087] Analogues of Scaffold A without methyl group at position 9 of the 3- oxabicyclo[3.3.1]non-6-ene moiety were prepared in a similar manner, starting from Diels- Alder cycloaddition of l,3-dimethyl-l,3-butadiene (1) and diethyl 2-methylenemalonate (2A), to obtain diethyl 2,4-dimethylcyclohex-3-ene-l,l-dicarboxylate (3A), which underwent reduction to the corresponding diols (4A) with lithium aluminum hydride. The process was followed by -toluenesulfonic acid-mediated cationic cyclization with various aldehydes to yield the target oxabicyclic analogues as racemic mixtures of two diastereomers, which were separated using TLC (Scheme 3, Scaffold B).

[0088] Analogues of Scaffold A without a corresponding hydroxymethyl group linked to the bicyclic moiety were prepared starting with A imonene (5) and different aromatic aldehydes in the acidic environment afforded by Montmorillonite K10 clay to produce analogues of Scaffold A (Scheme 4, Scaffold C). Compounds were dissolved in dimethyl sulfoxide (DMSO) to 50-100 mM and stored at -20°C.Scheme 4ArCHO montmorillomite K10 clayDCM (20 V)20°C, 3 hrC Series Targets

[0089] Chemiluminescent neuraminidase (CLNA) assay for cell-based screening. To evaluate the antiviral efficacy of small-molecule inhibitors against lAVs, the high- throughput CLNA-based assay, described in detail in Shelef et al. (2022), was employed. This assay quantitatively measures neuraminidase enzymatic activity in infected mammalian cells as a surrogate marker for viral replication. The method provides sensitive and reproducible quantification of viral inhibition in the presence of test compounds.

[0090] Cell culture and virus infection. Madin-Darby Canine Kidney (MDCK) cells were maintained and propagated in Dulbecco's Modified Eagle Medium (DMEM) supplemented with 10% fetal bovine serum (FBS), penicillin (20 U / mL), streptomycin (20 pg / mL), and nystatin (5 U / mL), at 37°C in 5% CO2. Virus stocks were grown in MDCK cells in media using the same conditions outlined in the preceding sentence but supplemented with 2% FBS instead of 10%, and containing 0.6 pg / mL trypsin from porcine pancreas (T0303; Sigma Aldrich™) for influenza virus activation. After complete cytotoxic effect (typically 3 days), the corresponding cell slurry was aliquoted and stored at -80°C. Virus titers were determined using the plaque assay methodology as previously described (Shelef etal., 2022).

[0091] Compound treatment. For the CLNA assay, cells were seeded in 96-well plates in tetraplicates and allowed to reach 100% confluence. Cells were then infected with IAV strains (e.g., A / Puerto Rico / 8 / 34 (H1N1), A / California / 07 / 2009 (H1N1), A / Fort Monmouth / 47 (H1N1)), in the presence of various compound concentrations at a multiplicity of infection (MOI) of 0.01-0.1, depending on the viral strain and optimization batch. Test compounds, including the parent Compounds SG2 and 9, and their analogues, were dissolved in DMSO to a stock concentration of 100 mM or 50 mM depending on solubility, and were then diluted in infection medium (IM) containing DMEM and antibiotics / antifungal as listed above, 2% FBS, 0.6 pg / ml trypsin from porcine pancreas (T0303; Sigma Aldrich™) (total volume / well of 100 pL), and virus at MOI as listed above.The quantity of virus used for infection was the same in every dose / replicate of compound tested. The serial dilutions were 50 pM, 5 pM, 0.5 pM, 0.05 pM, 0.005 pM, 0.0005 pM, and 0.00005 pM, or the corresponding 10-fold dilutions starting at 100 pM (depending on the respective solubility of the compound tested). The compound-containing IM was added directly onto the MDCK cell monolayer to determine half-maximal effective dose (ED50) values against viral replication after overnight incubation. Final DMSO concentrations were maintained at <0.5% v / v in all wells, including controls. Infected cells treated with vehicle (DMSO) served as negative controls, while wells treated with known antiviral agents such as oseltamivir or arbidol were used as reference comparators.

[0092] CLNA probe preparation and signal detection. The chemiluminescent neuraminidase (CLNA) probe previously disclosed (Shelef etal., 2022) was added (100 pL) at a concentration of 10 pM in phosphate-buffered saline (PBS) after removal of the culture medium at the final assay time point, typically 16-24 hours post-infection. The CLNA probe is cleaved by viral neuraminidase, releasing a chemiluminescent signal of a green photon proportional to the level of virus present, thus reporting on viral replication that had occurred since infection. Following probe addition directly onto the cells, luminescence was measured within a 5-minute incubation period using a microplate luminometer (e.g., Tecan Infinite M200 Pro). Total light emitted (TLE) per well over 10 minutes was recorded as relative light units (RLU), and background luminescence was negligible when using this probe. Doseresponse curves were generated by plotting normalized luminescence versus log inhibitor concentration. ED50 (herein also alternatively referred to as IC50) values were calculated using non-linear regression analysis with a four-parameter logistic model in GraphPad Prism. Each concentration in the serial dilution was calculated as the average of a triplicate, and results were expressed as mean ± SEM. Reproducibility between biological replicates was confirmed prior to compound advancement.

[0093] Generation of A / Puerto Rico 08 / 34 escape mutants for target / binding site validation. Escape mutants were generated by passaging the Puerto Rico / 08 / 34 (H1N1) strain (PR8) virus in MDCK cells in the presence of increasing concentrations of the parent Compound SG2 or an analogue thereof (starting from the concentration corresponding to the IC50 of the molecule, and increasing this concentration 3 -fold every passage until complete 100% cytotoxic effect was observed in the cells; typically, 3-4 days / passage). The passaging conditions were the same as those used in the CLNA assay, prior to removal of the mediaand without the addition of CLNA. The total number of passages was 9. Once the passage with a concentration of 100 pM inhibitor was achieved, the subsequent passage did not increase in drug concentration and remained at 100 pM to prevent cells dying from compound toxicity and thus allowing for viral replication to continue. At the end of the final passage, the resulting virus-containing media was tested for its ability to cause cytotoxic effect without attenuation by the compound used for passaging, furthermore, the drugresistant virus was assayed using the CLNA assay against 100 pM of this compound to verify that no inhibition occurred.

[0094] Expression and purification of hemagglutinin (HA). The construct encoding the soluble ectodomain of hemagglutinin (HA) from A / Puerto Rico / 8 / 34 (H1N1) (wild type or select escape mutants) was cloned into the pVL1393 vector, including a GP67 secretion signal, a thrombin cleavage site, a T4 fibritin (foldon) trimerization domain, and a C-terminal hexahistidine tag for purification. Recombinant baculovirus was generated via cotransfection of Sf9 insect cells with the pVL1393-HA plasmid and ProGreen bacmid genomic DNA (purchased commercially). Following virus amplification, Trichoplusia ni (T z) cells were infected at a density of l >< 106cells / mL. 72 hours post-infection, cells were centrifuged at 2,000*g for 15 minutes. The supernatant was filtered through a 0.22 pm membrane and loaded onto a HisTrap Excel affinity column (Cytiva) equilibrated with buffer A (20 mM Tris-HCl pH 8,0, 150 mM NaCl, 15 mM imidazole). After extensive washing, bound protein was eluted using buffer B (20 mM Tris-HCl, pH 8,0, 150 mMNaCl, 300 mM imidazole). Eluted fractions were loaded onto a desalting column equilibrated with 20 mM Tris-HCl, pH 8,0, and 150 mM NaCl. The protein was then digested with trypsin (1 : 100, enzyme: substrate ratio) at room temperature for 30 minutes. Digested protein was further purified by size-exclusion chromatography (SEC) using a Superdex 200 16 / 60 column (Cytiva) equilibrated in 10 mM Tris-HCl, pH 8.0, 100 mM NaCl. Fractions corresponding to trimeric HA were pooled, concentrated using a 30 kDa MWCO centrifugal filter unit (Millipore), and analyzed by SDS-PAGE to assess purity.

[0095] Differential scanning fluorimetry (DSF). DSF analyses were performed using a real-time PCR system (Thermo Fisher Scientific) with SYPRO Orange dye (Thermo Fisher Scientific) and clear 96-well PCR plates sealed with optical film. Trypsin-digested wild-type hemagglutinin (HA-WT) (HA1 / HA2) was used at a final concentration of 1 pM. Compound 14 was tested in a 6-point dose-response series ranging from 50 pM to 1.56 pM, with <1%final DMSO per well. Final reaction volumes were 20 pL, consisting of 10 pL protein solution, 0.2 pL compound stock (50x), 5 pL 20* SYPRO Orange, and 4.8 pL of HA buffer (150 mM NaCl, 10 mM Tris, pH 8). All reactions were performed in duplicate. Thermal melting curves were obtained by increasing the temperature from 4°C to 95°C at a ramp rate of l°C / min using a QuantStudio 3 Real-Time PCR System (Thermo Fisher Scientific) equipped with a ROX filter set to detect fluorescence changes associated with protein unfolding.

[0096] Trypsin sensitivity assay. The trypsin sensitivity assay was carried out to evaluate the ability of small molecules to stabilize HA against acid-induced conformational changes. ~5 pM of PR8 Hl hemagglutinin was incubated with ~50 pM of the test compound at 37°C for 1 hour. Following this incubation, the reaction mixture was split into two groups. One group was acidified to pH 5 using 200 mM sodium acetate buffer (pH 5.0), while the other was maintained at pH 8. Both groups were then incubated at 37°C for an additional hour. After acid exposure, samples were neutralized to pH 8.0 with 200 mM Tris buffer (pH 8.5). Trypsin-ultra (New England Biolabs) was added to all samples, except the untreated control, at a 1 :50 enzyme-to-substrate mass ratio. Proteolysis was allowed to proceed at 37°C for 1 hour. Reactions were terminated by adding non-reducing SDS sample buffer followed by heating at 100°C for 5 minutes. Protein digestion patterns were analyzed by SDS-PAGE.

[0097] In vivo efficacy evaluation of Compounds 14 and 21. Compounds 14 and 21 were selected for in vivo efficacy trials due to their exceptional antiviral activity across several divergent H1N1 influenza virus sub-strains and the elimination of the phenol and primary alcohol group (which pose toxicity and metabolism challenges) relative to the parent Compounds SG2 and 9.

[0098] Female BALB / c mice are an accurate representation of human disease, especially with regard to IAV infection. Therefore, we utilized these mice to study the effects of subcutaneously administered antiviral compounds synthesized herein towards IAV infection. The protocol performed was largely based on a protocol previously described, using bioluminescence to monitor the spread of IAV in mice in the presence of a drug (Heaton et al., 2013). On days 1-3, mice (sample size of 5 mice / group) were received at the animal house, divided into experimental cages in groups of 5 per cage, and acclimated in a pathogen-suitable chamber, supplemented with sterile water and appropriate dry-food nutrition. On Day 4, 35 mg / kg of the antiviral drug dissolved in 5% DMSO, 3.3% ethanol,30% polyethylene glycol (PEG)-400, and 61.7% sterile PBS was administered subcutaneously (25-gauge needle, 0.25 mL). Control groups of infected drug-untreated (vehicle-treated) and drug-treated only mice were included, as well as a positive control of very-high dose anti-influenza drug amantadine (135 mg / kg) (Sigma Aldrich). On day 5, the mice were treated with 10 mg / ml ketamine and 2 mg / ml xylazine in sterile PBS (25-gauge needle, 0.1 ml) subcutaneously for anesthesia and given a nasal drip of 40 pl of the Influenza A / Puerto Rico 08 / 34 (mouse adapted) virus (2000 plaque-forming units (PFU)) in sterile PBS, and they also received 35 mg / kg of the antiviral drug subcutaneously on this day, in the same vehicle described above. Mice continued to receive daily drug treatment in the same way, and their weights were monitored and recorded on a daily basis. Mice that lost weight equal to or greater than 20% of their starting weight were euthanized in a CO2 chamber and were deemed as mice that did not survive.

[0099] In vivo pharmacokinetic evaluation of compounds 14 and 21. Oral and intravenous (IV) bioavailability was assessed by administering Compounds 14 and 21 diluted in 10% DMSO, 10% solutol and 80% water to uninfected BALB / c mice via either oral gavage at 10 and 50 mg / kg or intravenous bolus at 1 mg / kg. Plasma concentrations were measured over 24 hours using LC-MS / MS.

[0100] For compound 14, general sample processing procedure (plasma) was undertaken by protein precipitation using a 96-well plate. An aliquot of 5 pL calibration standard, quality control and dilution quality control, single blank and double blank samples were added to the 96-well plate; each sample (except for the double blank) was quenched with 200 pL of internal standards 1 (IS 1 ; 6 in 1 internal standard in acetonitrile (ACN) containing labetalol, tolbutamide, verapamil, dexamethasone, glyburide, and celecoxib at 100 ng / mL for each), respectively (double blank sample was quenched with 200 pL of ACN), and the mixture was then vortex-mixed for 10 min at 800 rpm and centrifuged for 15 min at 3220 *g, 4°C. All 5 pL unknown samples were quenched with 200 pL of IS 1, and the mixture was then vortex- mixed for 10 min at 800 rpm and centrifuged for 15 min at 3220 *g, 4°C. An aliquot of 50 pL supernatant was transferred to another clean 96-well plate then the supernatant was directly injected for LC-MS / MS analysis.

[0101] For compound 21, general sample processing procedure (plasma) was undertaken in a similar manner to that described above, with the differences being that the mixture was vortex-mixed for 5 min at 1000 rpm and centrifuged for 10 min at 3220*g, 4°C; All 5 pLunknown samples were quenched with 200 pL of IS1, and the mixture was then vortex- mixed for 5 min at 1000 rpm and centrifuged for 10 min at 3220*g, 4°C. An aliquot of 70 pL supernatant was transferred to another clean 96-well plate then the supernatant was directly injected for LC-MS / MS analysis.In vitro pharmacokinetic evaluation of compounds 14 and 21

[0102] Human and mouse microsomal stability. To understand how the lead compounds are metabolized by liver enzymes, particularly cytochrome P450s present within microsomes, and to provide information on their likely metabolism in humans and mice, the stability of those compounds was assessed when exposed to human and mouse liver microsomes (abbreviated HLM and MLM, respectively). The appropriate concentrations of microsome working solutions were prepared in 100 mM potassium phosphate buffer. Cold (4°C) ACN, containing 250 nM tolbutamide and 250 nM labetalol as internal standards (IS), was used as the stop solution. Using an Apricot automation workstation, 2 pL / well of compound working solution were added to all 96-well reaction plates except the blank. An Apricot automation workstation was used to add 100 pL / well of microsome solution to all reaction plates. All reaction plates containing mixtures of compound and microsomes were pre-incubated at 37°C for 10 minutes. An Apricot automation workstation was used to add 98 pL / well of 100 mM potassium phosphate buffer to reaction plate NCF60. Reaction plate NCF60 was incubated at 37°C, and timer 1 was started. After pre-incubation, an Apricot automation workstation was used to add 98 pL / well of NADPH to every reaction plate except NCF60. The reaction plates were incubated at 37°C, and timer 2 was started. An Apricot automation workstation was used to add 600 pL / well of stop solution to each reaction plate at its appropriate end time point to terminate the reaction. Each plate was sealed and shaken for 10 minutes. After shaking, each plate was centrifuged at 4000 rpm and 4°C for 20 minutes. After centrifugation, an Apricot automation workstation was used to transfer 300 pL of supernatant from each reaction plate to eight new 96-well plates for LC- MS / MS analysis.

[0103] The equation of first order kinetics was used to calculate T1 / 2 and CLint(mic) (pL / min / mg):

[0104] C 'aco-2 cell permeability . An immortalized cell line of human colorectal adenocarcinoma (Caco-2 cells HTB-37) purchased from ATCC were seeded onto 0.4 pm pore polycarbonate membranes (PC) in 96-well corning insert plates at 3.5* 104cells / cm2, and refreshed growth medium every ~4-5 days until the 21stto 28thday of confluent cell monolayer formation. The transport buffer in the study was Hank's Balanced Salt Solution (HBSS) with 10.0 mM N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES) at pH 7.40±0.05. Test compound was tested at 2.00 pM bi-directionally in duplicate. Digoxin was tested at 10.0 pM bi-directionally in duplicate, while nadolol and metoprolol were tested at 2.00 pM in A to B direction in duplicate. Final DMSO concentration was adjusted to less than 1%. The plate was incubated for 2 hours in CO2 incubator at 37.0°C, with 5% CO2 at saturated humidity without shaking. After mixing with ACN-containing internal standard, all samples were centrifuged at 3220 xg for 10 min. Concentrations of test and control compounds in starting solution, donor solution, and receiver solution were quantified by LC- MS / MS methodologies, using peak area ratio of analyte / internal standard. After transport assay, lucifer yellow rejection assay was applied to determine the Caco-2 cell monolayer integrity. The apparent permeability coefficient Papp(cm / s) was calculated using the equation:Papp = (dCr / dt) X Vr / (A x Co) where dCr / dt is the cumulative concentration of compound in the receiver chamber as a function of time; Vris the solution volume in the receiver chamber (0.0750 mL on the apical side, 0.250 mL on the basolateral side); A is the surface area for the transport, i.e. 0.143 cm2for the area of the monolayer; and Co is the initial concentration in the donor chamber.

[0105] The efflux ratio was calculated using the equation:Efflux Ratio = Papp(BA) / Papp(AB)

[0106] Percent recovery was calculated using the equation:%Solution Recovery = 100 * [(VrxCr) + (VaxCa)] / (VaxCo) where Va is the volume in the donor chambers (0.0750 mL on the apical side, 0.250 mL on the basolateral side); and Ca and Crare the final concentrations of transport compound in donor and receiver chambers, respectively.ResultsStructure-guided discovery of HA-targeting inhibitors

[0107] To identify small-molecule inhibitors of IAV hemagglutinin (HA), a structurebased drug design strategy was employed, targeting a conserved internal pocket in the stem region of HA near the fusion peptide. This pocket is critical for the pH-induced conformational change that enables viral and endosomal membrane fusion. We were inspired by the mechanism of the antiviral arbidol (targeting a different site). Arbidol acts as a molecular glue that binds between the three HA subunits, stabilizes the pre-fusion conformation of HA, and prevents this transition. With that in mind, we performed a 2D structure optimization of the parent Compounds SG2 and 9, based on concepts of bioisosteric replacement and with the aim of yielding compounds more suitable for in vivo efficacy and pharmacokinetic studies. Some of the designed compounds indeed had improved in vitro pharmacokinetics relative to the parent Compounds, likely as a result of the structural markers introduced. 57 compounds were synthesized, of which about 40 compounds advanced to phenotypic screening, and 17 compounds performed well in cell-based assays against the replication of various influenza viruses. The structures of the specific compounds synthesized are shown in Table 6 above, and further information regarding each one of them is presented in Table 7.CLNA-based high-throughput cellular antiviral screening

[0108] Antiviral efficacy was assessed using the chemiluminescent neuraminidase (CLNA) assay previously developed (Shelef etal., 2022). This assay quantitatively measures neuraminidase activity in infected cells as a surrogate for viral replication, and offers ultrahigh sensitivity, rapid processing, no required incubation time with the probe, direct correlation with plaque-reduction assay (Shelef et cd.. 2022), and improved signal -to-noise ratios compared to traditional bioluminescence assays such as 4-MUNANA.

[0109] Screening was conducted in MDCK cells infected with different IAV strains, including A / Puerto Rico / 8 / 34 (ATCC and Mount Sinai), California / 07 / 2009, and Fort Monmouth / 01 / 47. Luminescence was measured 16-24 hours post-infection. The 17 bestcompounds (Fig. 2) demonstrated dose-dependent inhibition of viral replication, with half- maximal effective dose (ED50) values in the low micromolar to nanomolar range and a good spectrum of activity towards divergent IAV H1N1 viruses.Table 7. Data regarding the compounds synthesized in this study

[0110] Two lead compounds, Compound 14 and Compound 21, were selected based on potency and modifications relative to the parent Compound SG2 that are predicted to perform well pharmacokinetically and have no toxicity markers. Compounds 14 and 21 exhibited exceptional ED50 against three different influenza virus sub-strains (Fig. 2) and were thus chosen for subsequent in vivo studies and pharmacokinetic profiling.Mechanistic characterization of HA inhibition

[0111] To confirm the mechanism of action, a differential scanning fluorimetry (DSF) assay confirmed direct interaction with HA. Incubation of purified recombinant HA from the A / Puerto Rico / 8 / 1934 strain with Compound 14 (Fig. 3) resulted in a dose-dependent shift in the melting temperature (Tm), consistent with structural stabilization and binding to a cryptic hydrophobic region in the stem of HA (Kadam and Wilson, 2017).Generation of compound-resistant escape mutants

[0112] H1N1 viruses were serially passaged 9 times with the parent Compound SG2 and analogues in MDCK cells in sub-optimal inhibitory concentrations, increasing the drug concentration on each passage. Thus, drug -resistant mutants were generated. The HA gene of these mutants was amplified using RT-PCR and sequenced, showing that the mutations surround a known drug-binding pocket near the HA fusion peptide, thus, a binding hypothesis was generated using molecular docking with Schrodinger’s Glide SP for the parent Compound SG2 (Fig. 4). Mutations in the HA gene of PR8 obtained include: A1410G (N461D), G1404U (V459L), and A1411G / A1420G double mutant (N461S / E464G), and T102C / G1201T double mutant (G391V / Y17H).Mechanistic validation of escape mutant phenotype using trypsin-protection assays

[0113] To further probe the mechanism of action of Compound 14, we employed a trypsin susceptibility assay to evaluate whether the compound can stabilize HA against low pH- triggered conformational changes associated with membrane fusion. Purified HA-WT, as well as two of the HA escape mutants identified above (N461D and N461SZE464G), were incubated with or without Compound 14, followed by exposure to pH 4.8 or pH 8, and subsequent treatment with trypsin (Fig. 5). Proteolytic sensitivity was assessed by SDS- PAGE analysis. As expected, acidification increased HA susceptibility to trypsin digestion, consistent with a structural transition to the post-fusion state. However, the presence of Compound 14 markedly protected wild-type HA from trypsin cleavage at low pH, indicating that the compound inhibits the acid-induced conformational change. In contrast, this protective effect was diminished in the N461D and N461S / E464G mutants, suggesting that these substitutions compromise the ability of Compound 14 to bind or stabilize HA. These findings confirm that Compound 14 acts as a fusion inhibitor by locking HA in its pre-fusion conformation, and that residues near positions 461-464 may play a critical role in compound interaction or HA stabilization (Fig. 5).In vivo protection from lethal influenza infection

[0114] To evaluate in vivo efficacy, female BALB / c mice were infected intranasally with a 5O*LD5O dose (2,000 plaque-forming units) of PR8 (mouse-adapted) and treated daily with 35 mg / kg of Compound 14 or 21 by subcutaneous injection as described in the methods section. Vehicle-treated mice experienced complete mortality by day 4. Treatment with Compound 14 led to 60% survival on day 4, while Compound 21 conferred full protection (100% survival on day 4). Treated mice exhibited significantly attenuated weight loss, consistent with reduced viral burden (Steuerman et al. , 2018; Frishberg et al. , 2019). Due to the extremely high dose of virus and compliance with animal ethics guidelines, all mice had lost >20% of their body weight by day 5 despite showing lower disease burden, and thus had to be euthanized. Therefore, their recovery from the disease could not be evaluated. Mice treated with Compounds 14 or 21 only, without undergoing infection, exhibited no disease or toxicity phenotype, while infected mice treated with a high dose of amantadine (positive control; IC50 in the mid-micromolar range in cells) showed an effect less significant than compounds 14 and 21 (Fig. 6).In vitro pharmacokinetics of lead compounds

[0115] The results of the in vitro pharmacokinetics studies, summarized in Tables 8-9, provide support for the in vivo pharmacokinetics data detailed in the following section. Of note is the fact that compounds 14 and 21 had a high permeability coefficient Pappin human intestinal cells (Caco-2), were not substrates for cellular efflux transporters in these cells, and their half-lives when exposed to human liver microsomes were similar to those of the clinically available drugs propafenone and diclofenac.Oral and intravenous pharmacokinetics of lead compounds

[0116] Oral bioavailability was assessed by administering Compounds 14 and 21 to uninfected BALB / c mice via oral gavage at 10 and 50 mg / kg. Intravenous bioavailability was assessed by administering the compounds via IV bolus at 1 mg / kg. Plasma concentrations were measured over 24 hours using LC-MS / MS. Compound 21 reached peak concentrations of -2200 ng / mL within 2-4 hours and maintained plasma levels above its in vitro ED50 for over 8 hours. Compound 14 exhibited a similar pharmacokinetic profile with slightly more rapid clearance at the lower dose. The weights of the mice did not significantly change during this time, and they did not exhibit signs of toxicity. In contrast, IV bolus 1 mg / kg showed that the compounds are cleared more rapidly (Fig. 7).Table 8. The results of the in vitro permeability assay, showing the capacity of Compounds 14 and 21 vs. that of nadolol, metoprolol and dogoxin as positive controls, to permeate across intestinal membranes and involvement of efflux transportersND - not determinedBinning criteria of permeability*:Low permeability: Papp< 0.600 (x IO’6cm / s)Moderate permeability: 0.600 < Papp< 6.00 (x 10’6cm / s)High permeability: Papp> 6.00 (x IO’6cm / s)Proposed based on WuXi routine Caco-2 permeability assay conditions (2.00 pM dosing concentration and 120 minutes incubation). The boundaries for low and high permeability binning are equivalent to 50.0% and 85.0% of the “calculated fraction absorbed (Fa) in human.Table 9. The metabolic stability of Compounds 9, 14 and 21 when exposed to human and mouse liver microsomes based on their intrinsic clearanceNCF - no co-factor. No NADPH was added to NCF samples (replaced by buffer) during the 60-minute incubationR2- correlation coefficient of the linear regression for the determination of kinetic constant.CLint(mic) - intrinsic clearanceCLint(mic) = 0.693 / Ti / 2 / mg microsome protein per mbCLint(iiver) - CLint(mic)xmg microsomal protein / g liver weight x g liver weight / kg body weightREFERENCESAl Khatib, H.A.; Al Thani, A.A.; Gallouzi, I.; Yassine, H.M., Epidemiological and genetic characterization of pHINl and H3N2 influenza viruses circulated in MENA region during 2009-2017. BMC Infect Dis, 2019, 19, 314Belongia, E.A. et al. Variable influenza vaccine effectiveness by subtype: a systematic review and meta-analysis of test-negative design studies. Lancet Infect Dis., 2016, 16(8), 942-951Blaising, J.; Polyak, S.J.; Pecheur, E.-L, Arbidol as a broad-spectrum antiviral: an update. Antiviral Res. , 2014, 107, 84-94Bright, R.A.; Medina, M-j.; Xu, X.; Perez-Oronoz, G.; Wallis, T.R.; Davis, X.M., Povinelli, L.; Cox, N.J.; Klimov, A.I., Incidence of adamantane resistance among influenza A (H3N2) viruses isolated worldwide from 1994 to 2005: a cause for concern. Lancet, 2005, 366(9492), 1175-1181Cianci, C.; Krystal, M., Development of antivirals against influenza. Expert Opinion on Investigational Drugs, 1998, 7(2), 149-165Frishberg, A.; Peshes-Yaloz, N.; Cohn, O.; Rosentul, D.; Steuerman, Y.; Valadarsky, L.; YTankovitz, G.; Mandelboim, M.; Iraqi, F.A.; Amit, I.; Mayo, L.; Bacharach, E.; Gat- Viks, I., Cell composition analysis of bulk genomics using single-cell data. Nat Methods, 2019, 16(4), 327-332Gubareva, L.V.; Kaiser, L.; Matrosovich, M.N.; Soo-Hoo, Y.; Hayden, F.G., Selection of influenza virus mutants in experimentally infected volunteers treated with oseltamivir. J Infect Dis., 2001, 183(4), 523-531Hamann, L.G.; Meyer, J.H.; Ruppar, D.A.; Marschke, K.B.; Lopez, F.J.; Allegretto, E.A.; Karanewsky, D.S., Structure-activity relationships and sub-type selectivity in an oxabicyclic estrogen receptor alpha / beta agonist scaffold. Bioorg Med Chem Lett., 2005, 15(5), 1463-1466Hayden, F.G., Antiviral resistance in influenza viruses - implications for management and pandemic response. N Engl J Med., 2006, 354(8), 785-788Heaton, N.S.; Leyva-Grade, V.H.; Tan, G.S.; Eggink, D.; Hai, R.; Palese, P., In vivo bioluminescent imaging of influenza a virus infection and characterization of novel cross- protective monoclonal antibodies. J Virol., 2013, 87(15), 8272-8281Kadam, R.U.; Wilson, I. A., Structural basis of influenza virus fusion inhibition by the antiviral drug Arbidol. Proc Natl Acad Sci USA, 2017, 114(2), 206-214Leneva, I. A.; Russell, R.J.; Boriskin, Y.S.; Hay, A. J., Characteristics of arbidolresistant mutants of influenza virus: implications for the mechanism of anti -influenza action of arbidol. Antiviral Res., 2009, 812), 132-140Pan, W Dong, Z.; Li, F.; Meng, W Feng, L.; Niu, X.; Li, C.; Luo, Q.; Li, Z.; Sun, C.; Chen, L., Visualizing influenza virus infection in living mice. Nat Commun, 2013, 4, 2369Shelef, O.; Gutkin, S.; Feder, D.; Ben-Bassat, A.; Mandelboim, M.; Haitin, Y.; Ben- Tai, N.; Bacharach, E.; Shabat, D., Ultrasensitive chemiluminescent neuraminidase probe for rapid screening and identification of small-molecules with antiviral activity against influenza A virus in mammalian cells. Chem. Sci., 2022, 13, 12348-12357Skehel, J. J.; Wiley, D.C., Receptor binding and membrane fusion in virus entry: the influenza hemagglutinin. Annu Rev Biochem., 2000, 69, 531-569Steuerman, Y.; Cohen, M.; Peshes-Yaloz, N.; Valadarsky, L.; Cohn, O.; David, E.; Frishberg, A.; Mayo, L.; Bacharach, E.; Amit, I.; Gat-Viks, I., Dissection of influenza infection in vivo by single-cell RNA sequencing. Cell Syst., 2018, 6(6), 679-691. e4

Claims

CLAIMS1. A compound of formula I:or a stereoisomer or pharmaceutically acceptable salt thereof, whereinR1, R2, R4, R5, and R6each independently is selected from H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;R3is selected from -CH2OH, H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;Ar is a 5-14-membered- aryl or heteroaryl, excluding phenyl, optionally substituted with at least one group each independently selected from halogen, oxo, -OH, -CN, (Ci- C8)alkyl, (Ci-C8)haloalkyl, and -NR72, said heteroaryl containing at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized); andR7each independently is H or (Ci-C8)alkyl, or the two R7together with the nitrogen atom to which they are attached form a heterocyclic ring.

2. The compound of claim 1, wherein R1and R2each independently is H or (Ci- C3)alkyl.

3. The compound of claim 2, wherein R1and R2each independently is H or methyl.

4. The compound of claim 1, wherein R3is H or -CH2OH.

5. The compound of claim 1, wherein R4, R5and R6each independently is H or (Ci-C3)alkyl.

6. The compound of claim 5, wherein R4, R5and R6each independently is H or methyl.

7. The compound of claim 1, wherein Ar is a 6-membered heteroaryl containing one or two nitrogen atoms, optionally substituted at a carbon atom thereof with a group selectedfrom halogen, oxo, -OH, -CN, (Ci-C2)alkyl, (Ci-C2)haloalkyl, and -NR72, wherein R7each independently is H or (Ci-C2)alkyl.

8. The compound of claim 7, wherein Ar is selected from pyridin-4-yl, 6-chloropyridin- 3-yl, 6-oxo-l,6-dihydropyridin-3-yl, 5-hydroxypyridin-2-yl, 6-hy droxypyri din-3 -yl, 6- cyanopyridin-3-yl, 5-(trifluoromethyl)pyridin-2-yl, 6-aminopyri din-3 -yl, and 6- (dimethylamino)pyridin-3-yl.

9. The compound of claim 1, wherein Ar is a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring containing at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized).

10. The compound of claim 9, wherein Ar is a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring selected from 4,5-dihydro-UT-imidazole, 4, 5 -dihydro- H- pyrazole, 4,5-dihydro-l / 7-l,2,3-triazole, 1,2,5-oxadiazole, imidazolidin-2-one, and 1,2,5- thiadiazolidine- 1 , 1 -dioxide.

11. The compound of claim 10, wherein said Ar is selected from lH-benzo[d]imidazol-5-yl, l / T-indazol-5-yl, l / / -benzo[t / ][l,2,3]triazol-5-yl, benzo[c][l,2,5]oxadiazol-5-yl, 2-oxo-2,3-dihydro-l / 7-benzo[d]imidazol-5-yl, and 2,2-dioxido-l,3- dihydrobenzo[c][l,2,5]thiadiazol-5-yl.

12. The compound of claim 1, wherein Ar is a 5-membered heteroaryl containing at least one heteroatom each independently selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized).

13. The compound of claim 12, wherein Ar is a 5-membered heteroaryl containing at least one nitrogen atom and / or at least one sulfur atom, optionally substituted at a carbon atom thereof with a group selected from halogen, -CN and -NR72, wherein R7each independently is H or (Ci-C2)alkyl.

14. The compound of claim 13, wherein Ar is selected from 5 -chi orothi ophen-2 -yl, 5- flourothiophen-2-yl 5-bromothiophen-2-yl, 5 -iodothi ophen-2 -yl, 5-cyanothiophen-2-yl,I / / -pyrrol -3 -yl, l / / -pyrazol-4-yl, thiazol-5-yl, 2-chlorothiazol-5-yl, 2-bromothiazol-5-yl, and 2-aminothiazol-5-yl.

15. The compound of claim 1, wherein:R1, R2, R4, R5, and R6each independently is H or (Ci-Cajalkyl;R3is H or -CH2OH; andAr is (i) a 6-membered heteroaryl containing one or two nitrogen atoms, optionally substituted at a carbon atom thereof with a group selected from halogen, oxo, -OH, -CN, (Ci-C2)alkyl, (Ci-C2)haloalkyl, and -NR72, wherein R7each independently is H or (Ci- C2)alkyl; (ii) a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring containing at least one heteroatom selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized); or (iii) a 5-membered heteroaryl containing at least one heteroatom each independently selected from oxygen, nitrogen, and sulfur (optionally oxidized or dioxidized).

16. The compound of claim 15, wherein:R1, R2, R4, R5, and R6each independently is H or methyl; andAr is (i) selected from pyridin-4-yl, 6-chl oropyri din-3 -yl, 6-oxo-l,6-dihydropyridin- 3-yl, 5-hydroxypyridin-2-yl, 6-hy droxypyri din-3 -yl, 6-cy anopyri din-3 -yl, 5-(trifluoromethyl)pyridin-2-yl, 6-aminopyridin-3-yl, and 6-(dimethylamino)pyridin-3-yl; (ii) a bicyclic heteroaryl consisting of phenyl conjugated to a heterocyclic ring selected from 4,5-dihydro-lJT-imidazole, 4,5-dihydro-lJT-pyrazole, 1,2,5-oxadiazole, imidazolidin-2-one, and ,2,5-thiadiazolidine-l, 1-dioxide; or (iii) a 5-membered heteroaryl containing at least one nitrogen atom and / or at least one sulfur atom, optionally substituted at a carbon atom thereof with a group selected from halogen, -CN and -NR72, wherein R7each independently is H or (Ci-C2)alkyl.

17. The compound of claim 16, wherein Ar is selected from U / -benzo[d]imidazol-5-yl, UT-indazol-5-yl, 17 / -benzo[ ][l,2,3]triazol-5-yl, benzo[c][l,2,5]oxadiazol-5-yl, 2-oxo- 2,3-dihydro-U / -benzo[d]imidazol-5-yl, 2,2-dioxido-l,3-dihydrobenzo[c][l,2,5]thiadiazol- 5-yl, 5 -chi or othi ophen-2 -yl, 5-flourothiophen-2-yl, 5-bromothiophen-2-yl, 5-iodothiophen- 2-yl, 5-cyanothiophen-2-yl, UT-pyrrol-3-yl, UT-pyrazol-4-yl, thiazol-5-yl, 2- chlorothiazol-5-yl, 2-bromothiazol-5-yl, and 2-aminothiazol-5-yl.

18. The compound of any one of claims 1-17, wherein:(i) R1and R2each is H; R3is -CH2OH; and R4, R5and R6each is methyl (formula la);(ii) R1, R2and R6each is H; R3is -CH2OH; and R4and R5each is methyl (formula lb);(iii) R1, R2and R5each is methyl; and R3, R4and R6each is H (formula Ic); or(iv) R1, R2, R4, R5, and R6each is methyl; and R3is -CH2OH (formula Id).Id19. The compound of claim 18, wherein:(i) R1and R2each is H; R3is -CH2OH; R4, R5and R6each is methyl (formula la); and Ar is selected from lJ / -benzo[d]imidazol-5-yl, 5-hydroxypyridin-2-yl, 6- aminopyri din-3 -yl, lJT-indazol-5-yl, 2,2-dioxido-l,3- dihydrobenzo[c][l,2,5]thiadiazol-5-yl, 6-oxo-l,6-dihydropyridin-3-yl, pyridin-4-yl, benzo[c][l,2,5]oxadiazol-5-yl, 6-(dimethylamino)pyri din-3 -yl, 5- (trifluoromethyl)pyridin-2-yl, 6-cyanopyridin-3-yl, 6-chl oropyri din-3 -yl, 5- chlorothiophen-2-yl, 5-bromothiophen-2-yl, 5-iodothiophen-2-yl, and 5- cy anothi ophen-2 -y 1 ;(ii) R1, R2and R6each is H; R3is -CH2OH; R4and R5each is methyl (formula lb); and Ar is selected from 5-hydroxypyridin-2-yl, lJT-indazol-5-yl, 2,2-dioxido- l,3-dihydrobenzo[c][l,2,5]thiadiazol-5-yl, benzo[c][l,2,5]oxadiazol-5-yl, and 5-(trifluoromethyl)pyridin-2-yl; or(iii) R1, R2and R5each is methyl; R3, R4and R6each is H (formula Ic); and Ar is selected from 2,2-dioxido-l,3-dihydrobenzo[c][l,2,5]thiadiazol-5-yl, 1H- indazol-5-yl, 6-aminopyri din-3 -yl, 5-hydroxypyridin-2-yl, 1H- benzo[d]imidazol-5-yl, benzo[c][l,2,5]oxadiazol-5-yl, 6-cyanopyridin-3-yl, 6- (dimethylamino)pyri din-3 -yl, 6-hy droxypyri din-3 -yl, 2-oxo-2,3-dihydro-lJT-benzo[d]imidazol-5-yl, U / -pyrazol-4-yl, pyridin-4-yl, 6-oxo-l,6- dihy dropyri din-3 -yl, 2-aminothiazol-5-yl, thiazol-5-yl, 2-chlorothiazol-5-yl, 2- bromothiazol-5-yl, U / -pyrrol-3-yl, and 5-cyanothiophen-2-yl.

20. The compound of claim 19, wherein R1, R2and R5each is methyl; R3, R4and R6each is H (formula Ic); and Ar is lJT-indazol-5-yl or U / -benzo[d]imidazol-5-yl.

21. A compound of formula II:or a stereoisomer or pharmaceutically acceptable salt thereof, whereinR1, R2, R4, R5, and R6each independently is selected from H, -OH, -O-(C1-C8)alkyl, (C1-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (C6-C14)aryl, and halogen;R3 is selected from -CH2OH, H, -OH, -O-(Ci-C8)alkyl, (Ci-C8)alkyl, (C2-C8)alkenyl, (C2-C8)alkynyl, (C3-C8)cycloalkyl, (Ce-Ci4)aryl, and halogen;Ar is a group of formula:wherein:(i) X is selected from -CN, -N3, -NR72, -NH-S(=O)2-(C1-C8)alkyl, and -S(=O)2- NR72, wherein Ar is optionally further substituted with at least one group each independently selected from halogen, oxo, -OH, -CN, (Ci-C8)alkyl, (Ci- C8)haloalkyl, and -NR72; or(ii) X is -OH, wherein Ar is further substituted with halogen at a carbon atom ortho to X; andR7each independently is H or (Ci-C8)alkyl, or the two R7together with the nitrogen atom to which they are attached form a heterocyclic ring.

22. The compound of claim 21, wherein R1and R2each independently is H or (Ci- C3)alkyl.

23. The compound of claim 22, wherein R1and R2each independently is H or methyl.

24. The compound of claim 21, wherein R3is H or -CH2OH.

25. The compound of claim 21, wherein R4, R5and R6each independently is H or (Ci-C3)alkyl.

26. The compound of claim 25, wherein R4, R5and R6each independently is H or methyl.

27. The compound of claim 21, wherein X is selected from -CN, -N3, -N(CH3)2, -NH- S(=O)2-CH3, and -S(=O)2-NH2; or X is -OH, and Ar is further substituted with halogen at one of or both the carbon atoms ortho to X.

28. The compound of claim 21, wherein:R1, R2, R4, R5, and R6each independently is H or (C1-C3)alkyl;R3is H or -CH2OH; andX is selected from -CN, -N3, -N(CH3)2, -NH-S(=O)2-CH3, and -S(=O)2-NH2; or X is -OH, and Ar is further substituted with I at one of the carbon atoms ortho to X, or with F at each one of the carbon atoms ortho to X.

29. The compound of any one of claims 21-28, wherein:(i) R1and R2each is H; R3is -CH2OH; and R4, R5and R6each is methyl (formula la);(ii) R1, R2and R6each is H; R3is -CH2OH; and R4and R5each is methyl (formula lb);(iii) R1, R2and R5each is methyl; and R3, R4and R6each is H (formula Ic); or(iv) R1, R2, R4, R5, and R6each is methyl; and R3is -CH2OH (formula Id).

30. The compound of claim 29, wherein:(i) R1and R2each is H; R3is -CH2OH; R4, R5and R6each is methyl; and X is selected from -NH-S(=O)2-CH3, -N3, -N(CH3)2 wherein Ar is further substituted with Cl at one of the carbon atoms meta to X, -S(=O)2-NH2, -CN,and -OH wherein Ar is further substituted either with I at one of the carbon atoms ortho to X or with F at each one of the carbon atoms ortho to X;(ii) R1, R2and R6each is H; R3is -CH2OH; R4and R5each is methyl; and X is selected from -N3, -S(=O)2-NH2, and -CN; or(iii) R1, R2and R5each is methyl; R3, R4and R6each is H; and X is selected from - NH-S(=O)2-CH3, -S(=O)2-NH2, -N3; and -OH wherein Ar is further substituted either with I at one of the carbon atoms ortho to X or with F at each one of the carbon atoms ortho to X.

31. A pharmaceutical composition comprising a compound according to any one of claims 1-30, or a stereoisomer or pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrier.

32. The pharmaceutical composition of claim 31, formulated for oral, rectal, sublingual, sublabial, buccal, intravenous, intraarterial, intramuscular, intraperitoneal, intrathecal, intrapleural, intratracheal, subcutaneous, vaginal, topical, nasal, or ophthalmic, or for inhalation.

33. A composition according to claim 31 or 32, for use in the treatment of an influenza virus infection.

34. The composition for use of claim 33, wherein said influenza virus infection is influenza A virus infection.

35. A method for treatment of an influenza virus infection in a subject in need thereof, comprising administering to said subject a therapeutically effective amount of a compound according to any one of claims 1-30, or a stereoisomer or pharmaceutically acceptable salt thereof.

36. The method of claim 35, wherein said influenza virus infection is influenza A virus infection.

37. The method of claim 35 or 36, wherein said compound is administered in combination with an additional antiviral drug such as oseltamivir, zanamivir, peramivir, amantadine, rimantadine, arbidol, and baloxavir marboxil.

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