Patent Publication Number: US-10307438-B2

Title: Methods of treating hepatitis E viral infection

Description:
CROSS REFERENCE 
     This application claims the benefit of U.S. Provisional Application 62/345,188, filed on Jun. 3, 2016, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     This application relates to various methods of treating Hepatitis E viral (HEV) infection. 
     BACKGROUND 
     Hepatitis E virus (HEV) is believed to be the most common cause of acute hepatitis and jaundice in the world. Although HEV genotype 1 and 2 infect only human beings, genotypes 3 and 4 are zoonotic viruses that also infect swine and other animal species. Acute hepatitis E usually is self-limited. However, HEV genotype 3 can persist in immunocompromised patients, especially organ transplant recipients, causing chronic hepatitis, which may progress to cirrhosis and liver graft failure. Reduction of immunosuppressive therapy, ribavirin (RBV), or pegylated interferon-α have been used with varying success, allowing for viral clearance in up to 78% of patients. However, failure of RBV has been described. Hence, safer and more effective treatment options are needed. 
     SUMMARY 
     One aspect provides for a method of treating a Hepatitis E viral infection comprising administering to a human subject in need thereof a therapeutically effective amount of the compound of Formula (IA) 
     
       
         
         
             
             
         
       
     
     Some methods further comprise concomitantly administering ribavirin to the subject. In some methods, the treatment is ribavirin-free. In some methods, the subject is immunocompromised. In some methods, the subject is pregnant. 
     Another aspect provides for a method of reducing the HEV RNA levels to lower than about 25 IU/mL in a human subject, comprising (1) identifying a human subject with HEV RNA levels greater than about 1000 IU/mL, and (2) administering to that subject a therapeutically effective amount of the compound of Formula (IA). 
     Some methods further comprise concomitantly administering ribavirin to the subject. In some methods, the concomitant administration of the compound of Formula (IA) and ribavirin provides an additive or over-additive lowering of HEV RNA levels in the subject. In some methods, the concomitant administration of the compound of Formula (IA) and ribavirin provides an over-additive lowering of HEV RNA levels in the subject. In some methods, the no ribavirin is administered. 
    
    
     DETAILED DESCRIPTION 
     The phrase “a” or “an” entity as used herein refers to one or more of that entity; for example, a compound refers to one or more compounds or at least one compound. As such, the terms “a” (or “an”), “one or more”, and “at least one” can be used interchangeably herein. 
     The terms “optional” or “optionally” as used herein means that a subsequently described event or circumstance may but need not occur, and that the description includes instances where the event or circumstance occurs and instances in which it does not. For example, “optional bond” means that the bond may or may not be present, and that the description includes single, double, or triple bonds. 
     The term “independently” is used herein to indicate that a variable is applied in any one instance without regard to the presence or absence of a variable having that same or a different definition within the same compound. Thus, in a compound in which R appears twice and is defined as “independently carbon or nitrogen”, both R&#39;s can be carbon, both R&#39;s can be nitrogen, or one R′ can be carbon and the other nitrogen. 
     The term “alkenyl” refers to an unsubstituted hydrocarbon chain radical having from 2 to 10 carbon atoms having one or two olefinic double bonds, preferably one olefinic double bond. 
     The term “C 2-N  alkenyl” refers to an alkenyl comprising 2 to N carbon atoms, where N is an integer having the following values: 3, 4, 5, 6, 7, 8, 9, or 10. The term “C 2-10  alkenyl” refers to an alkenyl comprising 2 to 10 carbon atoms. The term “C 2-4  alkenyl” refers to an alkenyl comprising 2 to 4 carbon atoms. Examples include, but are not limited to, vinyl, 1-propenyl, 2-propenyl (allyl) or 2-butenyl (crotyl). 
     The term “halogenated alkenyl” refers to an alkenyl comprising at least one of F, Cl, Br, and I. 
     The term “alkyl” refers to an unbranched or branched chain, saturated, monovalent hydrocarbon residue containing 1 to 30 carbon atoms. The term “C 1-M  alkyl” refers to an alkyl comprising 1 to M carbon atoms, where M is an integer having the following values: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30. The term “C 1-4  alkyl” refers to an alkyl containing 1 to 4 carbon atoms. The term “lower alkyl” denotes a straight or branched chain hydrocarbon residue comprising 1 to 6 carbon atoms. “C 1-20  alkyl” as used herein refers to an alkyl comprising 1 to 20 carbon atoms. “C 1-10  alkyl” as used herein refers to an alkyl comprising 1 to 10 carbons. Examples of alkyl groups include, but are not limited to, lower alkyl groups include methyl, ethyl, propyl, i-propyl, n-butyl, i-butyl, t-butyl or pentyl, isopentyl, neopentyl, hexyl, heptyl, and octyl. The term (ar)alkyl or (heteroaryl)alkyl indicate the alkyl group is optionally substituted by an aryl or a heteroaryl group respectively. 
     The term “cycloalkyl” refers to an unsubstituted or substituted carbocycle, in which the carbocycle contains 3 to 10 carbon atoms; preferably 3 to 8 carbon atoms; more preferably 3 to 6 carbon atoms (i.e., lower cycloalkyls). Examples of cycloalkyl groups include, but are not limited to, cyclopropyl, 2-methyl-cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. 
     The term “cycloalkyl alkyl” refers to an additionally unsubstituted or substituted alkyl substituted by a lower cycloalkyl. Examples of cycloalkyl alkyls include, but are not limited to, any one of methyl, ethyl, propyl, i-propyl, n-butyl, i-butyl, t-butyl or pentyl, isopentyl, neopentyl, hexyl, heptyl, and octyl that is substituted with cyclopropyl, 2-methyl-cyclopropyl, cyclobutyl, cyclopentyl, and cyclohexyl. 
     The term “cycloheteroalkyl” refers to an unsubstituted or substituted heterocycle, in which the heterocycle contains 2 to 9 carbon atoms; preferably 2 to 7 carbon atoms; more preferably 2 to 5 carbon atoms. Examples of cycloheteroalkyls include, but are not limited to, aziridin-2-yl, N—C 1-3 -alkyl-aziridin-2-yl, azetidinyl, N—C 1-3 -alkyl-azetidin-m′-yl, pyrrolidin-m′-yl, N—C 1-3 -alkyl-pyrrolidin-m′-yl, piperidin-m′-yl, and N—C 1-3 -alkyl-piperidin-m′-yl, where m′ is 2, 3, or 4 depending on the cycloheteroalkyl. Specific examples of N—C 1-3 -alkyl-cycloheteroalkyls include, but are not limited to, N-methyl-aziridin-2-yl, N-methyl-azetidin-3-yl, N-methyl-pyrrolidin-3-yl, N-methyl-pyrrolidin-4-yl, N-methyl-piperidin-2-yl, N-methyl-piperidin-3-yl, and N-methyl-piperidin-4-yl. In the instance of R 4 , the point of attachment between the cycloheteroalkyl ring carbon and the oxygen occurs at any one of m′ 
     The term “heterocycle” refers to an unsubstituted or substituted heterocycle containing carbon, hydrogen, and at least one of N, O, and S, where the C and N can be trivalent or tetravalent, i.e., sp 2 - or sp 3 -hybridized. Examples of heterocycles include, but are not limited to, aziridine, azetidine, pyrrolidine, piperidine, imidazole, oxazole, piperazine, etc. In the instance of piperazine, as related to R 10  for NR′ 2 , the corresponding opposite nitrogen atom of the piperazinyl is substituted by a lower alkyl represented by the following structure: 
     
       
         
         
             
             
         
       
     
     The term “halogenated alkyl” (or “haloalkyl”) refers to an unbranched or branched chain alkyl comprising at least one of F, Cl, Br, and I. The term “C 1-M  haloalkyl” refers to an alkyl comprising 1 to M carbon atoms that comprises at least one of F, Cl, Br, and I, where M is an integer having the following values: 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, or 30. “C 1-3  haloalkyl” refers to a haloalkyl comprising 1 to 3 carbons and at least one of F, Cl, Br, and I. The term “halogenated lower alkyl” (or “lower haloalkyl”) refers to a haloalkyl comprising 1 to 6 carbon atoms and at least one of F, Cl, Br, and I. Examples include, but are not limited to, fluoromethyl, chloromethyl, bromomethyl, iodomethyl, difluoromethyl, dichloromethyl, dibromomethyl, diiodomethyl, trifluoromethyl, trichloromethyl, tribromomethyl, triiodomethyl, 1-fluoroethyl, 1-chloroethyl, 1-bromoethyl, 1-iodoethyl, 2-fluoroethyl, 2-chloroethyl, 2-bromoethyl, 2-iodoethyl, 2,2-difluoroethyl, 2,2-dichloroethyl, 2,2-dibromomethyl, 2-2-diiodomethyl, 3-fluoropropyl, 3-chloropropyl, 3-bromopropyl, 2,2,2-trifluoroethyl or 1,1,2,2,2-pentafluoroethyl. 
     The term “alkynyl” refers to an unbranched or branched hydrocarbon chain radical having from 2 to 10 carbon atoms, preferably 2 to 5 carbon atoms, and having one triple bond. The term “C 2-N  alkynyl” refers to an alkynyl comprising 2 to N carbon atoms, where N is an integer having the following values: 3, 4, 5, 6, 7, 8, 9, or 10. The term “C C 2-4  alkynyl” refers to an alkynyl comprising 2 to 4 carbon atoms. The term “C 2-10  alkynyl” refers to an alkynyl comprising 2 to 10 carbons. Examples include, but are limited to, ethynyl, 1-propynyl, 2-propynyl, 1-butynyl, 2-butynyl or 3-butynyl. 
     The term “halogenated alkynyl” refers to an unbranched or branched hydrocarbon chain radical having from 2 to 10 carbon atoms, preferably 2 to 5 carbon atoms, and having one triple bond and at least one of F, Cl, Br, and I. 
     The term “cycloalkyl” refers to a saturated carbocyclic ring comprising 3 to 8 carbon atoms, i.e. cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl, cycloheptyl or cyclooctyl. The term “C 3-7  cycloalkyl” as used herein refers to a cycloalkyl comprising 3 to 7 carbons in the carbocyclic ring. 
     The term “alkoxy” refers to an —O-alkyl group or an —O-cycloalkyl group, wherein alkyl and cycloalkyl are as defined above. Examples of —O-alkyl groups include, but are not limited to, methoxy, ethoxy, n-propyloxy, i-propyloxy, n-butyloxy, i-butyloxy, t-butyloxy. “Lower alkoxy” as used herein denotes an alkoxy group with a “lower alkyl” group as previously defined. “C 1-10  alkoxy” refers to an —O-alkyl wherein alkyl is C 1-10 . Examples of —O-cycloalkyl groups include, but are not limited to, —O-c-propyl, —O-c-butyl, —O-c-pentyl, and —O-c-hexyl. 
     The term “halogenated alkoxy” refers to an —O-alkyl group in which the alkyl group comprises at least one of F, Cl, Br, and I. 
     The term “halogenated lower alkoxy” refers to an —O-(lower alkyl) group in which the lower alkyl group comprises at least one of F, Cl, Br, and I. 
     The term “amino acid” includes naturally occurring and synthetic α, β γ or δ amino acids, and includes but is not limited to, amino acids found in proteins, i.e. glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, proline, serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginine and histidine. In a preferred embodiment, the amino acid is in the L-configuration. Alternatively, the amino acid can be a derivative of alanyl, valinyl, leucinyl, isoleucinyl, prolinyl, phenylalaninyl, tryptophanyl, methioninyl, glycinyl, serinyl, threoninyl, cysteinyl, tyrosinyl, asparaginyl, glutaminyl, aspartoyl, glutaroyl, lysinyl, argininyl, histidinyl, β-alanyl, β-valinyl, β-leucinyl, β-isoleucinyl, β-prolinyl, β-phenylalaninyl, β-tryptophanyl, β-methioninyl, β-glycinyl, β-serinyl, β-threoninyl, β-cysteinyl, β-tyrosinyl, β-asparaginyl, β-glutaminyl, β-aspartoyl, β-glutaroyl, β-lysinyl, β-argininyl or β-histidinyl. When the term amino acid is used, it is considered to be a specific and independent disclosure of each of the esters of α, β γ or δ glycine, alanine, valine, leucine, isoleucine, methionine, phenylalanine, tryptophan, proline, serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartate, glutamate, lysine, arginine and histidine in the D and L-configurations. 
     The term “aminoacyl” includes N,N-unsubstituted, N,N-monosubstituted, and N,N-disubstituted derivatives of naturally occurring and synthetic α, β γ or δ amino acyls, where the amino acyls are derived from amino acids. The amino-nitrogen can be substituted or unsubstituted. When the amino-nitrogen is substituted, the nitrogen is either mono- or di-substituted, where the substituent bound to the amino-nitrogen is a lower alkyl or an alkaryl. In the instance of its use for Y, the expression “O(aminoacyl)” is used. It is understood that the C3′ carbon of the ribose is bound to the oxygen “O”, which is then bound to the carbonyl carbon of the aminoacyl. 
     The terms “alkylamino” or “arylamino” refer to an amino group that has one or two alkyl or aryl substituents, respectively. 
     The term “protected,” as used herein and unless otherwise defined, refers to a group that is added to an oxygen, nitrogen, or phosphorus atom to prevent its further reaction or for other purposes. A wide variety of oxygen and nitrogen protecting groups are known to those skilled in the art of organic synthesis. Non-limiting examples include: C(O)-alkyl, C(O)Ph, C(O)aryl, CH 3 , CH 2 -alkyl, CH 2 -alkenyl, CH 2 Ph, CH 2 -aryl, CH 2 O-alkyl, CH 2 O-aryl, SO 2 -alkyl, SO 2 -aryl, tert-butyldimethylsilyl, tert-butyldiphenylsilyl, and 1,3-(1,1,3,3-tetraisopropyldisiloxanylidene). 
     The term “aryl,” as used herein, and unless otherwise specified, refers to substituted or unsubstituted phenyl (Ph), biphenyl, or naphthyl, preferably the term aryl refers to substituted or unsubstituted phenyl. The aryl group can be substituted with one or more moieties selected from among hydroxyl, F, Cl, Br, I, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, and phosphonate, either unprotected, or protected as necessary, as known to those skilled in the art, for example, as taught in T. W. Greene and P. G. M. Wuts, “Protective Groups in Organic Synthesis,” 3rd ed., John Wiley &amp; Sons, 1999. 
     The terms “alkaryl” or “alkylaryl” refer to an alkyl group with an aryl substituent, such as benzyl. The terms “aralkyl” or “arylalkyl” refer to an aryl group with an alkyl substituent. 
     The term “di(lower alkyl)amino-lower alkyl” refers to a lower alkyl substituted by an amino group that is itself substituted by two lower alkyl groups. Examples include, but are not limited to, (CH 3 ) 2 NCH 2 , (CH 3 ) 2 NCH 2 CH 2 , (CH 3 ) 2 NCH 2 CH 2 CH 2 , etc. The examples above show lower alkyls substituted at the terminus carbon atom with an N,N-dimethyl-amino substituent. These are intended as examples only and are not intended to limit the meaning of the term “di(lower alkyl)amino-lower alkyl” so as to require the same. It is contemplated that the lower alkyl chain can be substituted with an N,N-di(lower alkyl)-amino at any point along the chain, e.g., CH 3 CH(N-(lower alkyl) 2 )CH 2 CH 2 . 
     The term “halo,” as used herein, includes chloro, bromo, iodo and fluoro. 
     The term “acyl” refers to a substituent containing a carbonyl moiety and a non-carbonyl moiety. The carbonyl moiety contains a double-bond between the carbonyl carbon and a heteroatom, where the heteroatom is selected from among O, N and S. When the heteroatom is N, the N is substituted by a lower alkyl. The non-carbonyl moiety is selected from straight, branched, and cyclic alkyl, which includes, but is not limited to, a straight, branched, or cyclic C 1-20  alkyl, C 1-10  alkyl, or lower alkyl; alkoxyalkyl, including methoxymethyl; aralkyl, including benzyl; aryloxyalkyl, such as phenoxymethyl; or aryl, including phenyl optionally substituted with halogen (F, Cl, Br, I), hydroxyl, C 1  to C 4  alkyl, or C 1  to C 4  alkoxy, sulfonate esters, such as alkyl or aralkyl sulphonyl, including methanesulfonyl, the mono, di or triphosphate ester, trityl or monomethoxytrityl, substituted benzyl, trialkylsilyl (e.g. dimethyl-t-butylsilyl) or diphenylmethylsilyl. When at least one aryl group is present in the non-carbonyl moiety, it is preferred that the aryl group comprises a phenyl group. 
     The term “lower acyl” refers to an acyl group in which the non-carbonyl moiety is lower alkyl. 
     The term “purine” or “pyrimidine” base includes, but is not limited to, adenine, N 6 -alkylpurines, N 6 -acylpurines (wherein acyl is C(O)(alkyl, aryl, alkylaryl, or arylalkyl), N 6 -benzylpurine, N 6 -halopurine, N 6 -vinylpurine, N 6 -acetylenic purine, N 6 -acyl purine, N 6 -hydroxyalkyl purine, N 6 -allcylaminopurine, N 6 -thioallcyl purine, N 2 -alkylpurines, N 2 -alkyl-6-thiopurines, thymine, cytosine, 5-fluorocytosine, 5-methylcytosine, 6-azapyrimidine, including 6-azacytosine, 2- and/or 4-mercaptopyrmidine, uracil, 5-halouracil, including 5-fluorouracil, C 5 -alkylpyrimidines, C 5 -benzylpyrimidines, C 5 -halopyrimidines, C 5 -vinylpyrimidine, C 5 -acetylenic pyrimidine, C 5 -acyl pyrimidine, C 5 -hydroxyalkyl purine, C 5 -amidopyrimidine, C 5 -cyanopyrimidine, C 5 -iodopyrimidine, C 6 -Iodo-pyrimidine, C 5 —Br-vinyl pyrimidine, C 6 —Br-vinyl pyrimidine, C 5 -nitropyrimidine, C 5 -amino-pyrimidine, N 2 -alkylpurines, N 2 -alkyl-6-thiopurines, 5-azacytidinyl, 5-azauracilyl, triazolopyridinyl, imidazolopyridinyl, pyrrolopyrimidinyl, and pyrazolopyrimidinyl. Purine bases include, but are not limited to, guanine, adenine, hypoxanthine, 2,6-diaminopurine, and 6-chloropurine. Functional oxygen and nitrogen groups on the base can be protected as necessary or desired. Suitable protecting groups are well known to those skilled in the art, and include trimethylsilyl, dimethylhexylsilyl, t-butyldimethylsilyl, and t-butyldiphenylsilyl, trityl, alkyl groups, and acyl groups such as acetyl and propionyl, methanesulfonyl, and p-toluenesulfonyl. 
     The term “tautomerism” and “tautomers” have their accepted plain meanings. 
     One aspect provides for methods for the treatment of a Hepatitis E viral infection comprising administering to a subject in need thereof a therapeutically effective amount of a compound of Formula (I) 
                         
wherein
         (a) R 1  is hydrogen, n-alkyl; branched alkyl; cycloalkyl; or aryl, which includes, but is not limited to, phenyl or naphthyl, where phenyl or naphthyl are optionally substituted with at least one of C 1-6  alkyl, C 2-6  alkenyl, C 2-6  alkynyl, C 1-6  alkoxy, F, Cl, Br, I, nitro, cyano, C 1-6  haloalkyl, —N(R 1′ ) 2 , C 1-6  acylamino, —NHSO 2 C 1-6  alkyl, —SO 2 N(R 1′ ) 2 , COR 1″ , and —SO 2 C 1-6  alkyl; (R 1′  is independently hydrogen or alkyl, which includes, but is not limited to, C 1-20  alkyl, C 1-10  alkyl, or C 1-6  alkyl, R 1″  is —OR′ or —N(R 1′ ) 2 );   (b) R 2  is hydrogen, C 1-10  alkyl, R 3a  or R 3b  and R 2  together are (CH 2 ) n  so as to form a cyclic ring that includes the adjoining N and C atoms, C(O)CR 3a R 3b NHR 1 , where n is 2 to 4 and R 1 , R 3a , and R 3b ;   (c) R 3a  and R 3b  are (i) independently selected from hydrogen, C 1-10  alkyl, cycloalkyl, —(CH 2 ) c (NR 3′ ) 2 , C 1-6  hydroxyalkyl, —CH 2 SH, —(CH 2 ) 2 S(O) d Me, —(CH 2 ) 3 NHC(═NH)NH 2 , (1H-indol-3-yl)methyl, (1H-imidazol-4-yl)methyl, —(CH 2 ) e COR 3″ , aryl and aryl C 1-3  alkyl, said aryl groups optionally substituted with a group selected from hydroxyl, C 1-10  alkyl, C 1-6  alkoxy, halogen, nitro and cyano; (ii) R 3a  and R 3b  both are C 1-6  alkyl; (iii) R 3a  and R 3b  together are (CH 2 ) f  so as to form a spiro ring; (iv) R 3a  is hydrogen and R 3b  and R 2  together are (CH 2 ) n  so as to form a cyclic ring that includes the adjoining N and C atoms (v) R 3b  is hydrogen and R 3a  and R 2  together are (CH 2 ) n  so as to form a cyclic ring that includes the adjoining N and C atoms, where c is 1 to 6, d is 0 to 2, e is 0 to 3, f is 2 to 5, n is 2 to 4, and where R 3′  is independently hydrogen or C 1-6  alkyl and R 3″  is —OR′ or —N(R 3′ ) 2 ); (vi) R 3a  is H and R 3b  is H, CH 3 , CH 2 CH 3 , CH(CH 3 ) 2 , CH 2 CH(CH 3 ) 2 , CH(CH 3 )CH 2 CH 3 , CH 2 Ph, CH 2 -indol-3-yl, —CH 2 CH 2 SCH 3 , CH 2 CO 2 H, CH 2 C(O)NH 2 , CH 2 CH 2 COOH, CH 2 CH 2 C(O)NH 2 , CH 2 CH 2 CH 2 CH 2 NH 2 , —CH 2 CH 2 CH 2 NHC(NH)NH 2 , CH 2 -imidazol-4-yl, CH 2 OH, CH(OH)CH 3 , CH 2 ((4′-OH)-Ph), CH 2 SH, or lower cycloalkyl; or (viii) R 3a  is CH 3 , —CH 2 CH 3 , CH(CH 3 ) 2 , CH 2 CH(CH 3 ) 2 , CH(CH 3 )CH 2 CH 3 , CH 2 Ph, CH 2 -indol-3-yl, —CH 2 CH 2 SCH 3 , CH 2 CO 2 H, CH 2 C(O)NH 2 , CH 2 CH 2 COOH, CH 2 CH 2 C(O)NH 2 , CH 2 CH 2 CH 2 CH 2 NH 2 , —CH 2 CH 2 CH 2 NHC(NH)NH 2 , CH 2 -imidazol-4-yl, CH 2 OH, CH(OH)CH 3 , CH 2 ((4′-OH)-Ph), CH 2 SH, or lower cycloalkyl and R 3b  is H, where R 3′  is independently hydrogen or alkyl, which includes, but is not limited to, C 1-20  alkyl, C 1-10  alkyl, or C 1-6  alkyl, R 3″  is —OR′ or —N(R 3′ ) 2 );   (d) R 4  is hydrogen, C 1-10  alkyl, C 1-10  alkyl optionally substituted with a lower alkyl, alkoxy, di(lower alkyl)-amino, or halogen, C 1-10  haloalkyl, C 3-10  cycloalkyl, cycloalkyl alkyl, cycloheteroalkyl, aminoacyl, aryl, such as phenyl, heteroaryl, such as, pyridinyl, substituted aryl, or substituted heteroaryl;   (e) R 5  is H, a lower alkyl, CN, vinyl, O-(lower alkyl), hydroxyl lower alkyl, i.e., —(CH 2 ) p OH, where p is 1-6, including hydroxyl methyl (CH 2 OH), CH 2 F, N 3 , CH 2 CN, CH 2 NH 2 , CH 2 NHCH 3 , CH 2 N(CH 3 ) 2 , alkyne (optionally substituted), or halogen, including F, Cl, Br, or I, with the provisos that when X is OH, base is cytosine and R 6  is H, R 5  cannot be N 3  and when X is OH, R 6  is CH 3  or CH 2 F and B is a purine base, R 5  cannot be H;   (f) R 6  is H, CH 3 , CH 2 F, CHF 2 , CF 3 , F, Cl, Br, I, or CN;   (g) X is H, OH, F, Cl, Br, I, OMe, NH 2 , CN, or N 3 ;   (h) Y is OH, H, C 1-4  alkyl, C 2-4  alkenyl, C 2-4  alkynyl, vinyl, N 3 , CN, Cl, Br, F, I, NO 2 , OC(O)O(C 1-4  alkyl), OC(O)O(C 1-4  alkyl), OC(O)O(C 2-4  alkynyl), OC(O)O(C 2-4  alkenyl), OC 1-10  haloalkyl, O(aminoacyl), O(C 1-10  acyl), O(C 1-4  alkyl), O(C 2-4  alkenyl), S(C 1-4  acyl), S(C 1-4  alkyl), S(C 2-4  alkynyl), S(C 2-4  alkenyl), SO(C 1-4  acyl), SO(C 1-4  alkyl), SO(C 2-4  alkynyl), SO(C 2-4  alkenyl), SO 2 (C 1-4  acyl), SO 2 (C 1-4  alkyl), SO 2 (C 2-4  alkynyl), SO 2 (C 2-4  alkenyl), OS(O) 2 (C 1-4  acyl), OS(O) 2 (C 1-4  alkyl), OS(O) 2 (C 2-4  alkenyl), NH 2 , NH(C 1-4  alkyl), NH(C 2-4  alkenyl), NH(C 2-4  alkynyl), NH(C 1-4  acyl), N(C 1-4  alkyl) 2 , N(C 1-18  acyl) 2 , wherein alkyl, alkynyl, alkenyl and vinyl are optionally substituted by N 3 , CN, one to three halogen (Cl, Br, F, I), NO 2 , C(O)O(C 1-4  alkyl), C(O)O(C 1-4  alkyl), C(O)O(C 2-4  alkynyl), C(O)O(C 2-4  alkenyl), O(C 1-4  acyl), O(C 1-4  alkyl), O(C 2-4  alkenyl), S(C 1-4  acyl), S(C 1-4  alkyl), S(C 2-4  alkynyl), S(C 2-4  alkenyl), SO(C 1-4  acyl), SO(C 1-4  alkyl), SO(C 2-4  alkynyl), SO(C 2-4  alkenyl), SO 2 (C 1-4  acyl), SO 2 (C 1-4  alkyl), SO 2 (C 2-4  alkynyl), SO 2 (C 2-4  alkenyl), OS(O) 2 (C 1-4  acyl), OS(O) 2 (C 1-4  alkyl), OS(O) 2 (C 2-4  alkenyl), NH 2 , NH(C 1-4  alkyl), NH(C 2-4  alkenyl), NH(C 2-4  alkynyl), NH(C 1-4  acyl), N(C 1-4  alkyl) 2 , N(C 1-4  acyl) 2 ;   the base is a naturally occurring or modified purine or pyrimidine base represented by the following structures:       

     
       
         
         
             
             
         
       
         
         
           
             wherein
           Z is N or CR 12 ;   R 7 , R 8 , R 9 , R 10 , and R 11  are independently H, F, Cl, Br, I, OH, OR′, SH, SR′, NH 2 , NHR′, NR′ 2 , lower alkyl of C 1 -C 6 , halogenated (F, Cl, Br, I) lower alkyl of C 1 -C 6 , lower alkenyl of C 2 -C 6 , halogenated (F, Cl, Br, I) lower alkenyl of C 2 -C 6 , lower alkynyl of C 2 -C 6  such as C≡CH, halogenated (F, Cl, Br, I) lower alkynyl of C 2 -C 6 , lower alkoxy of C 1 -C 6 , halogenated (F, Cl, Br, I) lower alkoxy of C 1 -C 6 , CO 2 H, CO 2 R′, CONH 2 , CONHR′, CONR′ 2 , CH═CHCO 2 H, or CH═CHCO 2 R′,   wherein R′ is an optionally substituted alkyl, which includes, but is not limited to, an optionally substituted C 1-20  alkyl, an optionally substituted C 1-10  alkyl, an optionally substituted lower alkyl; an optionally substituted cycloalkyl; an optionally substituted alkynyl of C 2 -C 6 , an optionally substituted lower alkenyl of C 2 -C 6 , or optionally substituted acyl, which includes but is not limited to C(O) alkyl, C(O)(C 1-20  alkyl), C(O)(C 1-10  alkyl), or C(O)(lower alkyl) or alternatively, in the instance of NR′ 2 , each R′ comprise at least one C atom that are joined to form a heterocycle comprising at least two carbon atoms; and   R 12  is H, halogen (including F, Cl, Br, I), OH, OR′, SH, SR′, NH 2 , NHR′, NR′ 2 , NO 2  lower alkyl of C 1 -C 6 , halogenated (F, Cl, Br, I) lower alkyl of C 1 -C 6 , lower alkenyl of C 2 -C 6 , halogenated (F, Cl, Br, I) lower alkenyl of C 2 -C 6 , lower alkynyl of C 2 -C 6 , halogenated (F, Cl, Br, I) lower alkynyl of C 2 -C 6 , lower alkoxy of C 1 -C 6 , halogenated (F, Cl, Br, I) lower alkoxy of C 1 -C 6 , CO 2 H, CO 2 R′, CONH 2 , CONHR′, CONR′ 2 , CH═CHCO 2 H, or CH═CHCO 2 R′; with the proviso that when base is represented by the structure c with R 11  being hydrogen, R 12  is not a: (i) —C≡C—H, (ii) —C═CH 2 , or (iii) —NO 2 .   
         
           
         
       
    
     It is understood that the phosphorous atom is chiral and that it has a corresponding Cahn-Ingold-Prelog designation of “R” or “S” which have their accepted plain meanings. It is contemplated that compounds of Formula I include compounds with both R and S stereochemistry at the phosphorous (“Rp” or “Sp”), including resolved Rp and Sp diastereomers as well as equal (racemic) and unequal (scalemic) mixtures thereof. 
     Another aspect provides for methods for the treatment of a Hepatitis E viral infection comprising administering to a subject in need thereof a therapeutically effective amount of the compound of Formula (IA) 
     
       
         
         
             
             
         
       
     
     The compound of Formula (IA) is also known as sofosbuvir or by the IUPAC name (S)-isopropyl 2-(((S)-(((2R,3R,4R,5R)-5-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)-4-fluoro-3-hydroxy-4-methyltetrahydrofuran-2-yl)methoxy)(phenoxy)phosphoryl)amino)propanoate, and is described in, for example, U.S. Pat. No. 7,964,580. The compound of Formula (IA) is a compound of Formula (I). 
     Concomitant administration refers to the administration of two or more agents in any manner in which the pharmacological effects of both agents are manifested in the subject at the same time. Although concomitant administration includes simultaneous administration (e.g. via fixed-dose combinations of two or more agents), it does not require that a single pharmaceutical composition, the same type of formulation, the same dosage form, or even the same route of administration be used for administration of the agents, or that the agents be administered at the same time. For example, administration of a compound of Formula (I) and an additional antiviral agent may be concurrent, alternate, or any variation thereof, meaning that when the effective amounts of the compound of Formula (I) and the additional antiviral agent are administered during the same duration, the specific order of administration on a daily basis can be: the compound of Formula (I) followed by the additional antiviral agent, the compound of Formula (I) and the additional antiviral agent together, the additional antiviral agent followed by the compound of Formula (I), or any variation thereof. Additionally, it is contemplated that dosage frequencies of the compound of Formula (I) and the additional antiviral agent may differ. As one non-limiting example, the compound of Formula (I) may be administered QD while the additional antiviral agent is administered BID. 
     In certain embodiments, a compound of the present disclosure (e.g., a compound of Formula (I)), is formulated as a tablet, which may contain one or more other compounds useful for treating HCV. 
     In certain embodiments, such tablets are suitable for once daily dosing. 
     In certain methods, the subject is a human. 
     In some methods, the subject is immunocompromised. In other methods, the subject is not immunocompromised. In some methods, the subject is pregnant. In some methods, the subject is not pregnant. 
     Some methods further comprise concomitantly administering a first antiviral agent and a second antiviral agent to the subject, wherein the first antiviral agent is a compound of Formula (I) and the second antiviral agent is another therapeutic agent which may inhibit HEV viral replication. Some methods further comprise concomitantly administering ribavirin to the subject (i.e. a method described above wherein the second antiviral agent is ribavirin). Some methods further comprise concomitantly administering an interferon to the subject. 
     In some aspects, the concomitant administration of a first antiviral agent and a second antiviral agent provides an additive effect or an over-additive effect in lowering HEV RNA levels in a subject. As used herein, the term “additive effect” refers to the combined effect of two or more pharmaceutically active agents that is approximately equal to the sum of the effect of each agent given alone, and the term “over-additive effect” refers to the combined effect of two or more pharmaceutically active agents that is greater than the sum of the effect of each agent given alone. For example, in some methods, the concomitant administration of a compound of Formula (I) and ribavirin provides an over-additive lowering of HEV RNA levels in a subject. For example, in some methods, the concomitant administration of a compound of Formula (IA) and ribavirin provides an over-additive lowering of HEV RNA levels in a subject. 
     Certain methods provide for prophylaxis of HEV infection. For example, certain methods disclosed herein involve administration prior an event that would expose the subject to HEV or that would otherwise increase the subject&#39;s risk of acquiring HEV. Other methods involve administration after such events. Other methods involve administration both prior to and after such events. Examples of events that could increase an individual&#39;s risk of acquiring HEV include, without limitation, exposure to areas with poor sanitation; exposure to areas with limited access to safe drinking water; exposure to animal feces; eating or exposure to meat and offal (including liver) of deer, boars, and pigs; eating or exposure to figatellu (a sausage prepared from raw pig liver); eating or exposure to shellfish; receiving a blood transfusion; exposure to blood. 
     Certain methods provide for reducing the HEV RNA levels in a subject to lower than about 25 IU/mL. For example, certain methods comprise (1) identifying a human subject with HEV RNA levels greater than about 1000 IU/mL, and (2) administering to that subject a therapeutically effective amount of the compound of Formula (IA). Other methods provide for maintaining the HEV RNA levels in a subject to lower than about 25 IU/mL. In certain of these methods, no ribavirin is administered. In certain of these methods, no interferon is administered. 
     In certain methods, the effective amount of a compound of Formula (I) can be from about 100 mg to about 800 mg per day. For example, the effective amount of a compound of Formula (I) can about 200 mg, about 300 mg, about 400 mg, about 500 mg, about 600 mg, about 700 mg, or about 800 mg per day. In some aspects, the effective amount of a compound of Formula (I) is 400 mg per day. In some aspects, the effective amount of the compound of Formula (IA) is 400 mg per day. 
     In certain methods wherein ribavirin is administered, the amount of ribavirin is from about 100 mg to about 1400 mg per day. In certain aspects, the amount of ribavirin is from about 800 mg to about 1200 mg per day. 
     In certain methods, the duration of treatment is from about one week to about 48 weeks. In certain methods, the duration of treatment is about 24 weeks. In certain methods, the duration of treatment is about 12 weeks. In certain methods, the duration of treatment is about 8 weeks. In certain methods, the duration of treatment is about 4 weeks. 
     EXAMPLES 
     Example 1 
     A 55 year-old male human subject was identified as having AIDS, Kaposi&#39;s sarcoma, non-Hodgkin&#39;s lymphoma, compensated cirrhosis, and a history of alcoholism. An HEV RNA test of the subject was conducted, and the result was positive, at approximately 20,000 IU/mL. The subject was started on ribavirin monotherapy, wherein ribavirin was administered to the subject at 800 mg once per day. Despite ribavirin monotherapy treatment for over one year, the subject remained HEV-positive. The subject was then started on a treatment wherein ribavirin administration was continued at 800 mg per day and sofosbuvir was also administered at 400 mg per day. After four weeks of such treatment, the subject&#39;s HEV RNA levels were below the lower limit of detection of about 25 IU/mL.