Patent Description:
Hepatitis C virus (HCV) infection is a major health problem that leads to chronic liver disease, such as cirrhosis and hepatocellular carcinoma, in a substantial number of infected individuals, estimated to be <NUM>-<NUM>% of the world's population. There are an estimated <NUM> million infected people in the United States alone, according to the U. Center for Disease Control. According to the World Health Organization, there are more than <NUM> million infected individuals worldwide, with at least <NUM> to <NUM> million people being infected each year. Once infected, about <NUM>% of people clear the virus, but the rest can harbor HCV the rest of their lives. Ten to twenty percent of chronically infected individuals eventually develop liver-destroying cirrhosis or cancer. The viral disease is transmitted parenterally by contaminated blood and blood products, contaminated needles, or sexually and vertically from infected mothers or carrier mothers to their offspring. Current treatments for HCV infection, which are restricted to immunotherapy with recombinant interferon-α alone or in combination with the nucleoside analog ribavirin, are of limited clinical benefit as resistance develops rapidly. Moreover, there is no established vaccine for HCV. Consequently, there is an urgent need for improved therapeutic agents that effectively combat chronic HCV infection.

The HCV virion is an enveloped positive-strand RNA virus with a single oligoribonucleotide genomic sequence of about <NUM> bases which encodes a polyprotein of about <NUM>,<NUM> amino acids. The protein products of the HCV gene consist of the structural proteins C, E1, and E2, and the non-structural proteins NS2, NS3, NS4A and NS4B, and NS5A and NS5B. The nonstructural (NS) proteins are believed to provide the catalytic machinery for viral replication. The NS3 protease releases NS5B, the RNA-dependent RNA polymerase from the polyprotein chain. HCV NS5B polymerase is required for the synthesis of a double-stranded RNA from a single-stranded viral RNA that serves as a template in the replication cycle of HCV. Therefore, NS5B polymerase is considered to be an essential component in the HCV replication complex (<NPL>); <NPL>)). Inhibition of HCV NS5B polymerase prevents formation of the double-stranded HCV RNA and therefore constitutes an attractive approach to the development of HCV-specific antiviral therapies.

HCV belongs to a much larger family of viruses that share many common features.

The Flaviviridae family of viruses comprises at least three distinct genera: pestiviruses, which cause disease in cattle and pigs; flavivruses, which are the primary cause of diseases such as dengue fever and yellow fever; and hepaciviruses, whose sole member is HCV. The flavivirus genus includes more than <NUM> members separated into groups on the basis of serological relatedness (<NPL>). Clinical symptoms vary and include fever, encephalitis and hemorrhagic fever (<NPL>). Flaviviruses of global concern that are associated with human disease include the Dengue Hemorrhagic Fever viruses (DHF), yellow fever virus, shock syndrome and Japanese encephalitis virus (<NPL>; <NPL>; <NPL>).

The pestivirus genus includes bovine viral diarrhea virus (BVDV), classical swine fever virus (CSFV, also called hog cholera virus) and border disease virus (BDV) of sheep (<NPL>). Pestivirus infections of domesticated livestock (cattle, pigs and sheep) cause significant economic losses worldwide. BVDV causes mucosal disease in cattle and is of significant economic importance to the livestock industry (<NPL>; <NPL>). Human pestiviruses have not been as extensively characterized as the animal pestiviruses. However, serological surveys indicate considerable pestivirus exposure in humans.

Pestiviruses and hepaciviruses are closely related virus groups within the Flaviviridae family. Other closely related viruses in this family include the GB virus A, GB virus A-like agents, GB virus-B and GB virus-C (also called hepatitis G virus, HGV). The hepacivirus group (hepatitis C virus; HCV) consists of a number of closely related but genotypically distinguishable viruses that infect humans. There are at least <NUM> HCV genotypes and more than <NUM> subtypes. Due to the similarities between pestiviruses and hepaciviruses, combined with the poor ability of hepaciviruses to grow efficiently in cell culture, bovine viral diarrhea virus (BVDV) is often used as a surrogate to study the HCV virus.

The genetic organization of pestiviruses and hepaciviruses is very similar. These positive stranded RNA viruses possess a single large open reading frame (ORF) encoding all the viral proteins necessary for virus replication. These proteins are expressed as a polyprotein that is co- and post-translationally processed by both cellular and virus-encoded proteinases to yield the mature viral proteins. The viral proteins responsible for the replication of the viral genome RNA are located within approximately the carboxy-terminal. Two-thirds of the ORF are termed nonstructural (NS) proteins. The genetic organization and polyprotein processing of the nonstructural protein portion of the ORF for pestiviruses and hepaciviruses is very similar. For both the pestiviruses and hepaciviruses, the mature nonstructural (NS) proteins, in sequential order from the amino-terminus of the nonstructural protein coding region to the carboxy-terminus of the ORF, consist of p7, NS2, NS3, NS4A, NS4B, NS5A, and NS5B.

The NS proteins of pestiviruses and hepaciviruses share sequence domains that are characteristic of specific protein functions. For example, the NS3 proteins of viruses in both groups possess amino acid sequence motifs characteristic of serine proteinases and of helicases (<NPL>;<NPL>; <NPL>). Similarly, the NS5B proteins of pestiviruses and hepaciviruses have the motifs characteristic of RNA-directed RNA polymerases (<NPL>).

The actual roles and functions of the NS proteins of pestiviruses and hepaciviruses in the lifecycle of the viruses are directly analogous. In both cases, the NS3 serine proteinase is responsible for all proteolytic processing of polyprotein precursors downstream of its position in the ORF (<NPL>;<NPL>; <NPL>; <NPL>; <NPL>; <NPL>; <NPL>). The NS4A protein, in both cases, acts as a cofactor with the NS3 serine protease (<NPL>;<NPL>; <NPL>). The NS3 protein of both viruses also functions as a helicase (<NPL>;<NPL>;<NPL>). Finally, the NS5B proteins of pestiviruses and hepaciviruses have the predicted RNA-directed RNA polymerases activity (<NPL>; <NPL>; <NPL>; <CIT>;<NPL>).

Interferons (IFNs) have been commercially available for the treatment of chronic hepatitis for nearly a decade. IFNs are glycoproteins produced by immune cells in response to viral infection. IFNs inhibit replication of a number of viruses, including HCV, and when used as the sole treatment for hepatitis C infection, IFN can in certain cases suppress serum HCV-RNA to undetectable levels. Additionally, IFN can normalize serum amino transferase levels. Unfortunately, the effect of IFN is temporary and a sustained response occurs in only <NUM>%-<NUM>% of patients chronically infected with HCV (<NPL>). Most patients, however, have difficulty tolerating interferon treatment, which causes severe flu-like symptoms, weight loss, and lack of energy and stamina.

A number of patents disclose Flaviviridae, including HCV, and treatments using interferon-based therapies. For example, <CIT> discloses methods for retreatment of patients afflicted with HCV using consensus interferon. <CIT> discloses an anti-HCV therapy using ovine or bovine interferon-tau. <CIT> discloses the combination therapy of interleukin-<NUM> and interferon alpha for the treatment of infectious diseases including HCV. <CIT> discloses the use of thymosins, alone or in combination with interferon, for treating HCV. <CIT> discloses a combination HCV therapy employing interferon and a free radical scavenger. <CIT>discloses the use of human interferon tau proteins for treating HCV. Other interferon-based treatments for HCV are disclosed in <CIT>, <CIT>, and <CIT>. A number of patents also disclose pegylated forms of interferon, such as <CIT>, <CIT>and<CIT>; <CIT> and <CIT>; <CIT> and <CIT> and <CIT>; and <CIT>.

Interferon alpha-2a and interferon alpha-2b are currently approved as monotherapy for the treatment of HCV. ROFERON®-A (Roche) is the recombinant form of interferon alpha-2a. PEGASYS® (Roche) is the pegylated (i.e. polyethylene glycol modified) form of interferon alpha-2a. INTRON®A (Schering Corporation) is the recombinant form of Interferon alpha-2b, and PEG-INTRON® (Schering Corporation) is the pegylated form of interferon alpha-2b.

Other forms of interferon alpha, as well as interferon beta, gamma, tau and omega are currently in clinical development for the treatment of HCV. For example, INFERGEN (interferon alphacon-<NUM>) by InterMune, OMNIFERON (natural interferon) by Viragen, ALBUFERON by Human Genome Sciences, REBIF (interferon beta-la) by Ares-Serono, Omega Interferon by BioMedicine, Oral Interferon Alpha by Amarillo Biosciences, and interferon gamma, interferon tau, and interferon gamma-lb by InterMune are in development.

Ribavirin (<NUM>-β-D-ribofuranosyl-<NUM>-<NUM>,<NUM>,<NUM>-triazole-<NUM>-carboxamide) is a synthetic, non-interferon-inducing, broad spectrum antiviral nucleoside analog sold under the trade name, Virazole (<NPL>). <CIT> and <CIT> disclose and claim ribavirin. Ribavirin is structurally similar to guanosine, and has in vitro activity against several DNA and RNA viruses including Flaviviridae (<NPL>).

Ribavirin reduces serum amino transferase levels to normal in <NUM>% of patients, but it does not lower serum levels of HCV-RNA (Gary L. Davis, <NUM>). Thus, ribavirin alone is not effective in reducing viral RNA levels. Additionally, ribavirin has significant toxicity and is known to induce anemia. Ribavirin is not approved for monotherapy against HCV. It has been approved in combination with interferon alpha-2a or interferon alpha-2b for the treatment of HCV.

Ribavirin is a known inosine monophosphate dehydrogenease inhibitor that does not have specific anti-HCV activity in the HCV replicon system (<NPL>).

The current standard of care for chronic hepatitis C is combination therapy with an alpha interferon and ribavirin. The combination of interferon and ribavirin for the treatment of HCV infection has been reported to be effective in the treatment of interferon naive patients (<NPL>), as well as for treatment of patients when histological disease is present (<NPL>). Studies have shown that more patients with hepatitis C respond to pegylated interferon-alpha/ribavirin combination therapy than to combination therapy with unpegylated interferon alpha. However, as with monotherapy, significant side effects develop during combination therapy, including hemolysis, flu-like symptoms, anemia, and fatigue. Davis, <NUM>). Combination therapy with PEG-INTRON® (peginterferon alpha-2b) and REBETOL® (Ribavirin, USP) capsules are available from Schering Corporation. REBETOL® (Schering Corporation) has also been approved in combination with INTRON® A (Interferon alpha-2b, recombinant, Schering Corporation). Roche's PEGASYS® (pegylated interferon alpha-2a) and COPEGUS® (ribavirin), as well as Three River Pharmacetical's Ribosphere® are also approved for the treatment of HCV.

<CIT>, <CIT>, <CIT>, <CIT> and <CIT> disclose the use of pegylated interferon alpha and ribavirin combination therapy for the treatment of HCV. <CIT>, <CIT>, and <CIT>. also disclose the use of pegylated interferon alpha and ribavirin combination therapy for the treatment of HCV.

The development of new antiviral agents for Flaviviridae infections, especially hepatitis C, is currently underway. Specific inhibitors of HCV-derived enzymes such as protease, helicase, and polymerase inhibitors are being developed. Drugs that inhibit other steps in HCV replication are also in development, for example, drugs that block production of HCV antigens from the RNA (IRES inhibitors), drugs that prevent the normal processing of HCV proteins (inhibitors of glycosylation), drugs that block entry of HCV into cells (by blocking its receptor) and nonspecific cytoprotective agents that block cell injury caused by the virus infection. Further, molecular approaches are also being developed to treat hepatitis C, for example, ribozymes, which are enzymes that break down specific viral RNA molecules, antisense oligonucleotides, which are small complementary segments of DNA that bind to viral RNA and inhibit viral replication, and RNA interference techniques are under investigation (<NPL>);<NPL>); and <NPL>).

Bovine viral diarrhea virus (BVDV) is a pestivirus belonging to the family Flaviviridae and has been used as a surrogate for in vitro testing of potential antiviral agents. While activity against BVDV may suggest activity against other flaviviruses, often a compound can be inactive against BVDV and active against another flavivirus. Sommadossi and La Colla have revealed ("Methods and compositions for treating flaviviruses and pestiviruses", <CIT>) that ribonucleosides containing a methyl group at the <NUM>' "up" position have activity against BVDV. However, it is unclear whether these compounds can inhibit other flaviviruses, including HCV in cell culture or at the HCV NS5B level. Interestingly while this publication discloses a large number of compounds that are <NUM>'-methyl-<NUM>'-X-ribonucleosides, where X is a halogen, fluorine is not considered. Furthermore, a synthetic pathway leading to nucleosides halogenated at the <NUM>' "down" position is not shown by these inventors.

Dengue virus (DENV) is the causative agent of Dengue hemorrhagic fever (DHF). According to the world Health Organization (WHO), two fifths of the world population are now at risk for infection with this virus. An estimated <NUM>,<NUM> cases of DHF require hospitalization each year with a mortality rate of <NUM>% in children.

West Nile virus (WNV), a flavivirus previously known to exist only in intertropical regions, has emerged in recent years in temperate areas of Europe and North America, presenting a threat to public health. The most serious manifestation of WNV infection is fatal encephalitis in humans. Outbreaks in New York City and sporadic occurrences in the Southern United States have been reported since <NUM>.

There is currently no preventive treatment of HCV, Dengue virus (DENV) or West Nile virus infection. Currently approved therapies, which exist only against HCV, are limited. Examples of antiviral agents that have been identified as active against the hepatitis C flavivirus include:.

Substrate-based NS3 protease inhibitors (<CIT>; <NPL>; <CIT>; <CIT>), including alphaketoamides and hydrazinoureas, and inhibitors that terminate in an electrophile such as a boronic acid or phosphonate (<CIT>) are being investigated.

Non-substrate-based NS3 protease inhibitors such as <NUM>,<NUM>,<NUM>-trihydroxy-<NUM>-nitrobenzamide derivatives (<NPL>;<NPL>), including RD3-<NUM> and RD3-<NUM>, the former substituted on the amide with a <NUM> carbon chain and the latter processing a para-phenoxyphenyl group are also being investigated.

SCH <NUM>, a phenanthrenequinone, is an HCV protease inhibitor (<NPL>). In another example by the same authors, SCH <NUM>, isolated from the fungus Penicillium griseofulvum, was identified as a protease inhibitor (<NPL>). Nanomolar potency against the HCV NS3 protease enzyme has been achieved by the design of selective inhibitors based on the macromolecule eglin c. Eglin c, isolated from leech, is a potent inhibitor of several serine proteases such as S. griseus proteases A and B, α-chymotrypsin, chymase and subtilisin (<NPL>).

patents disclose protease inhibitors for the treatment of HCV. For example, <CIT> discloses a class of cysteine protease inhibitors for inhibiting HCV endopeptidase <NUM>. <CIT> discloses synthetic inhibitors of hepatitis C virus NS3 protease. The inhibitor is a subsequence of a substrate of the NS3 protease or a substrate of the NS4A cofactor. The use of restriction enzymes to treat HCV is disclosed in <CIT> Peptides as NS3 serine protease inhibitors of HCV are disclosed in <CIT>. and <CIT> and <CIT>. HCV inhibitor tripeptides are disclosed in <CIT>,<CIT>, and <CIT> and <CIT>. Diaryl peptides as NS3 serine protease inhibitors of HCV are disclosed in <CIT>. Imidazoleidinones as NS3 serine protease inhibitors of HCV are disclosed in <CIT> and <CIT>. <CIT> and <CIT> also disclose HCV protease inhibitors.

Idenix Pharmaceuticals discloses the use of certain branched nucleosides in the treatment of flaviviruses (including HCV) and pestiviruses in International Publication Nos. <CIT> and <CIT>. Specifically, a method for the treatment of hepatitis C virus infection (and flaviviruses and pestiviruses) in humans and other host animals is disclosed in the Idenix publications that includes administering an effective amount of a biologically active <NUM>', <NUM>', <NUM>' or <NUM>'-branched β-D or β-L nucleosides or a pharmaceutically acceptable salt or derivative thereof, administered either alone or in combination with another antiviral agent, optionally in a pharmaceutically acceptable carrier.

<CIT> discloses a family of <NUM>'-methyl nucleosides for the treatment of flavivirus infections. <CIT> discloses a series of <NUM>' or <NUM>' prodrugs of <NUM>', <NUM>', <NUM>', or <NUM>' branch nucleosides for the treatement of flavivirus infections including HCV infections.

Other patent applications disclosing the use of certain nucleoside analogs to treat hepatitis C virus infection include: <CIT> (<CIT>) and <CIT>(<CIT>. (now Shire Biochem, Inc. ); <CIT>(<CIT>) and <CIT> (<CIT>) filed by Merck & Co. , <CIT> (<CIT>, and <CIT>), <CIT>) and <CIT>.

discloses a number of nucleoside compounds disclosed as inhibitors of RNA-dependent RNA viral polymerase. The nucleosides disclosed in this publication are primarily <NUM>'-methyl-<NUM>'-hydroxy substituted nucleosides. <CIT>, discloses a large genus of pyrimidine derivative nucleosides of the <NUM>'-methyl-<NUM>'-hydroxy substitutions. <CIT> discloses a series of thionucleoside derivatives as inhibitors of RNA dependent RNA viral prolymerase. <CIT> discloses a series of carbocyclic nucleoside derivatives that are useful for the treatment of HCV infections.

<CIT> to Emory University, entitled "<NUM>'-Fluoronucleosides" discloses the use of certain <NUM>'-fluoronucleosides to treat HCV. <CIT> to Emory University entitled "<NUM>'-fluoronucleosides" discloses a family of <NUM>'-fluoronucleosides useful for the treatment of hepatitis B, HCV, HIV and abnormal cellular proliferation. The <NUM>' substituent is disclosed to be in either the "up" or "down" position.

)) described the structure activity relationship of <NUM>'-modified nucleosides for inhibition of HCV.

<NPL>) describe the synthesis and pharmacokinetic properties of nucleoside analogues as possible inhibitors of HCV RNA replication. The authors report that <NUM>'-modified nucleosides demonstrate potent inhibitory activity in cell-based replicon assays.

<NPL>) also described the effects of the <NUM>'-modified nucleosides on HCV RNA replication.

<NUM>) Other miscellaneous compounds including <NUM>-amino-alkylcyclohexanes (<CIT>), alkyl lipids (<CIT>), vitamin E and other antioxidants (<CIT>), squalene, amantadine, bile acids (<CIT>), N-(phosphonoacetyl)-L-aspartic acid, (<CIT>), benzenedicarboxamides (<CIT>), polyadenylic acid derivatives (<CIT>), <NUM>,<NUM>-dideoxyinosine (<CIT>), benzimidazoles (<CIT>), plant extracts (<CIT>, <CIT>, and <CIT>), and piperidenes (<CIT>). <NUM>) Other compounds currently in preclinical or clinical development for treatment of hepatitis C virus infection include: Interleukin-<NUM> by Schering-Plough, IP-SOl by Intemeuron, Merimebodib (VX-<NUM>) by Vertex, AMANTADINE® (Symmetrel) by Endo Labs Solvay, HEPTAZYME® by RPI, IDN-<NUM> by Idun Pharma. , XTL-<NUM> by XTL. , HCV/MFS9 by Chiron, CTVACIR® (hepatitis C Immune Globulin) by NABI, LEVOVIRIN® by ICN/Ribapharm, VIRAMIDINE® by ICN/Ribapharm, ZADAXIN® (thymosin alpha-<NUM>) by SciClone, thymosin plus pegylated interferon by Sci Clone, CEPLENE® (histamine dihydrochloride) by Maxim, VX <NUM> / LY <NUM> by Vertex/Eli Lilly, ISIS <NUM> by Isis Pharmaceutical/Elan, IDN-<NUM> by Idun Pharmaceuticals, Inc. , JTK <NUM> by AKROS Pharma, BILN-<NUM> by Boehringer Ingelheim, CellCept (mycophenolate mofetil) by Roche, T67, a β-tubulin inhibitor, by Tularik, a therapeutic vaccine directed to E2 by Innogenetics, FK788 by Fujisawa Healthcare, Inc. , 1dB <NUM> (Siliphos, oral silybin-phosphatdylcholine phytosome), RNA replication inhibitors (VP50406) by ViroPharma/Wyeth, therapeutic vaccine by Intercell, therapeutic vaccine by Epimmune/Genencor, IRES inhibitor by Anadys, ANA <NUM> and ANA <NUM> by Anadys, immunotherapy (Therapore) by Avant, protease inhibitor by Corvas/SChering, helicase inhibitor by Vertex, fusion inhibitor by Trimeris, T cell therapy by CellExSys, polymerase inhibitor by Biocryst, targeted RNA chemistry by PTC Therapeutics, Dication by Immtech, Int. , protease inhibitor by Agouron, protease inhibitor by Chiron/Medivir, antisense therapy by AVI BioPharma, antisense therapy by Hybridon, hemopurifier by Aethlon Medical, therapeutic vaccine by Merix, protease inhibitor by Bristol-Myers Squibb/Axys, Chron-VacC, a therapeutic vaccine, by Tripep, UT <NUM> B by United Therapeutics, protease, helicase and polymerase inhibitors by Genelabs Technologies, IRES inhibitors by Immusol, R803 by Rigel Pharmaceuticals, INFERGEN® (interferon alphacon-<NUM>) by InterMune, OMNIFERON® (natural interferon) by Viragen, ALBUFERON® by Human Genome Sciences, REBIF® (interferon beta-la) by Ares-Serono, Omega Interferon by BioMedicine, Oral Interferon Alpha by Amarillo Biosciences, interferon gamma, interferon tau, and Interferon gamma- lb by InterMune. Rigel Pharmaceuticals is developing a non-nucleoside HCV polymerase inhibitor, R803, that shows promise as being synergistic with IFN and ribavirin. <NUM>) A summary of several investigational drugs, including several discussed above, that are currently in various phases of development for the treatment of HCV, are summarized below:.

Nucleoside prodrugs have been previously described for the treatment of other forms of hepatitis. <CIT> and <CIT> to Idenix Pharmaceuticals, discloses <NUM>'-deoxy-β-L-nucleosides and their <NUM>'-prodrugs for the treatment of HBV. <CIT>discloses various therapeutic esters of acyclovir.

In light of the fact that HCV infection has reached epidemic levels worldwide, and has tragic effects on the infected patient, there remains a strong need to provide new effective pharmaceutical agents to treat hepatitis C that have low toxicity to the host.

Further, given the rising threat of other flaviviridae infections, there remains a strong need to provide new effective pharmaceutical agents that have low toxicity to the host.

There is currently no preventive treatment of Hepatitis C virus (HCV), Dengue virus (DENV) or West Nile virus (WNV) infection, and currently approved therapies, which exist only against HCV, are limited. Design and development of pharmaceutical compounds is essential, especially those that are synergistic with other approved and investigational Flaviviridae, and in particular HCV, therapeutics for the evolution of treatment standards, including more effective combination therapies.

The present invention provides a pharmaceutical composition comprising a (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside (β-D or β-L), or a pharmaceutically acceptable salt thereof, and a pharmaceutically acceptable carrierfor use in the treatment of a host infected with a virus belonging to the Flaviviridae family, including hepatitis C, West Nile Virus and yellow fever virus. In addition, the nucleosides in thepharmaceutical compositions of the present invention show activity against rhinovirus. Rhinoviruses (RVs) are small (<NUM>), non-enveloped viruses that contain a single-strand ribonucleic acid (RNA) genome within an icosahedral (<NUM>-sided) capsid. RVs belong to the Picornaviridae family, which includes the genera Enterovirus (polioviruses, coxsackieviruses groups A and B, echoviruses, numbered enteroviruses) and Hepatovirus (hepatitis A virus). Approximately <NUM> serotypes are identified currently. Rhinoviruses are most frequently associated with the common cold, nasopharyngitis, croup, pneumonia, otitis media and asthma exacerbations.

The inventor has made the unexpected discovery that the <NUM>' substitutions on the β-D or β-L nucleosides in the pharmaceutical compositions of the present invention impart greater specificity for hepatitis C virus as well as exhibiting lower toxicity following administration to a host. The invention comprises pharmaceutical compositions comprising such compounds and a pharmaceutically acceptable carrier for use in a method for treating a Flaviviridae infection, including hepatitis C virus, West Nile Virus and yellow fever virus and rhinovirus infection, that includes the administration of an anti-virally effective amount of a β-D or β-L nucleoside disclosed herein, or its pharmaceutically acceptable salt, in a pharmaceutically acceptable carrier or diluent, optionally in combination or alternation with another effective antiviral agent.

The nucleosides in the pharmaceutical compositions of the present invention, possess the unique properties of having greater specificity for the hepatitis C virus and lower toxicity in culture or when administered into an animal. One potential, but non-limiting reason for this is the presence of the <NUM>'-fluoro substitution on the ribose ring. For example, <CIT>, discloses a family of <NUM>'-fluoro nucleoside compounds that are useful in the treatment of hepatitis C virus infection. In contrast, are <NUM>'-methyl subsitututions such as found in <NUM>'-C-methylcytidine as shown in <CIT> to Idenix wherein the <NUM>'-methyl substitution on the nucleoside ring at the <NUM>' position is not specific to hepatitis C.

Thus, in one aspect, the pharmaceutical composition of the present invention comprises a (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside (β-D or β-L) or a pharmaceutically acceptable salt thereof of the general formula:
<CHM>
wherein the Base is a pyrimidine base represented by the following formula
<CHM>.

and a pharmaceutically acceptable carrier; for use in therapy.

The present invention also provides in various aspects, pharmaceutical compositions for use in the treatment or prophylaxis of hepatitis C virus infection, West Nile virus infection, a yellow fever viral infection or a rhinovirus infection comprising administering to a host an antivirally effective amount of a (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside disclosed herein. The invention also includes pharmaceutical compositions for use in treating or preventing Flaviviridae infection, including all members of the Hepacivirus genus (HCV), Pestivirus genus (BVDV, CSFV, BDV), or Flavivirus genus (Dengue virus, Japanese encephalitis virus group (including West Nile Virus), and Yellow Fever virus).

In various aspects, the (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl β-D-nucleoside has an EC<NUM> (effective concentration to achieve <NUM>% inhibition) when tested in an appropriate cell-based assay, of less than <NUM> micromolar, and more particularly, less than <NUM> or <NUM> micromolar. In other aspects, the nucleoside is enantiomerically enriched.

The present invention also provides pharmaceutical compositions for use in the treatment or prophylaxis of a hepatitis C virus infection, West Nile virus infection, a yellow fever viral infection or a rhinovirus infection in a host comprising administering an effective amount of a pharmaceutical composition comprising (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleosides (β-D or β-L) disclosed herein, or a pharmaceutically acceptable salt thereof, in combination or alternation with one or more other effective antiviral agent(s), in a pharmaceutically acceptable carrier or diluent thereof, as described herein. Nonlimiting examples of the types of antiviral agents or their prodrugs that can be used in combination with the compounds disclosed herein include, but are not limited to: interferon, including interferon alpha 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin <NUM> and interleukin <NUM>; ribavirin; interferon in combination with ribavirin; a protease inhibitor including NS3 inhibitor; a helicase inhibitor; a polymerase inhibitor; gliotoxin; an IRES inhibitor; and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a <NUM>-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadneylic acid; a benzimidazoles; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; silybin-phosphatidlycholine phytosome; and mycophenolate.

The following non-limiting aspects illustrate some general methodology to obtain the nucleosides used in the pharmaceutical compositions of the present invention. Specifically, the synthesis of the present nucleosides can be achieved by either of two general means:.

In addition, the L-enantiomers corresponding to the compounds used in the pharmaceutical compositions of the invention can be prepared following the same general methods (Schemes <NUM> or <NUM>), beginning with the corresponding L-carbohydrate building block or nucleoside L-enantiomer as the starting material.

Thus, the present invention includes at least the following general features:.

Various embodiments of the invention are now described in detail. Also, as used in the description herein and throughout the claims that follow, the meaning of "in" includes "in" and "on" unless the context clearly dictates otherwise.

The terms used in this specification generally have their ordinary meanings in the art, within the context of the invention, and in the specific context where each term is used. Certain terms that are used to describe the invention are discussed below, or elsewhere in the specification, to provide additional guidance to the practitioner in describing the compositions and methods of the invention and how to make and use them. For convenience, certain terms may be highlighted, for example using italics and/or quotation marks. The use of highlighting has no influence on the scope and meaning of a term; the scope and meaning of a term is the same, in the same context, whether or not it is highlighted. It will be appreciated that the same thing can be said in more than one way. Consequently, alternative language and synonyms may be used for any one or more of the terms discussed herein, nor is any special significance to be placed upon whether or not a term is elaborated or discussed herein. Synonyms for certain terms are provided. The use of examples anywhere in this specification, including examples of any terms discussed herein, is illustrative only, and in no way limits the scope and meaning of the invention or of any exemplified term. Likewise, the invention is not limited to various embodiments given in this specification.

As used herein, "about" or "approximately" shall generally mean within <NUM> percent, preferably within <NUM> percent, and more preferably within <NUM> percent of a given value or range. Numerical quantities given herein are approximate, meaning that the term "about" or "approximately" can be inferred if not expressly stated.

The present invention provides pharmaceutical compositions comprising (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleosides and their pharmaceutically acceptable salts for use in the treatment of hepatitis C virus infection, West Nile virus infection, a yellow fever viral infection or a rhinovirus infection in a host.

Pharmaceutically acceptable formulations containing the disclosed compounds are useful in the prevention and treatment of HCV infections. In addition, these formulations can be used prophylactically to prevent or retard the progression of clinical illness in individuals who are anti-HCV antigen positive or who have been exposed to HCV.

The compounds disclosed herein can be converted into a pharmaceutically acceptable ester by reaction with an appropriate esterifying agent, for example, an acid halide or anhydride. The compound or its pharmaceutically acceptable derivative can be converted into a pharmaceutically acceptable salt thereof in a conventional manner, for example, by treatment with an appropriate base. The ester or salt of the compound can be converted into the parent compound, for example, by hydrolysis.

The term "independently" is used herein to indicate that the variable, which is independently applied, varies independently from application to application. Thus, in a compound such as RaXYRa, wherein Ra is "independently carbon or nitrogen", both Ra can be carbon, both Ra can be nitrogen, or one Ra can be carbon and the other Ra nitrogen.

As used herein, the terms "enantiomerically pure" or "enantiomerically enriched"refers to a nucleoside composition that comprises at least approximately <NUM>%, and preferably approximately <NUM>%, <NUM>%, <NUM>% or <NUM>% of a single enantiomer of that nucleoside.

As used herein, the term "substantially free of" or "substantially in the absence of" refers to a nucleoside composition that includes at least <NUM> or <NUM>% by weight, preferably <NUM>% to <NUM>% by weight, and even more preferably <NUM>% to <NUM>% by weight, of the designated enantiomer of that nucleoside. In a preferred embodiment, in the methods and compounds of this invention, the compounds are substantially free of enantiomers.

Similarly, the term "isolated" refers to a nucleoside composition that includes at least <NUM> or <NUM>% by weight, preferably <NUM>% to <NUM>% by weight, and even more preferably <NUM>% to <NUM>% by weight, of the nucleoside, the remainder comprising other chemical species or enantiomers.

The term "alkyl," as used herein, unless otherwise specified, refers to a saturated straight, branched, or cyclic, primary, secondary, or tertiary hydrocarbon of typically C<NUM> to C<NUM>, and specifically includes methyl, trifluoromethyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, cyclohexylmethyl, <NUM>-methylpentyl, <NUM>,<NUM>-dimethylbutyl, and <NUM>,<NUM>-dimethylbutyl. The term includes both substituted and unsubstituted alkyl groups. Alkyl groups can be optionally substituted with one or more moieties selected from the group consisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, or phosphonate, or any other viable functional group that does not inhibit the pharmacological activity of this compound, either unprotected, or protected, as necessary, as known to those skilled in the art, for example, as taught in <NPL>, hereby incorporated by reference.

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<NUM>, CH<NUM>-alkyl, CH<NUM>-alkenyl, CH<NUM>Ph, CH<NUM>-aryl, CH<NUM>O-alkyl, CH<NUM>O-aryl, SO<NUM>-alkyl, SO<NUM>-aryl, tert-butyldimethylsilyl, tert-butyldiphenylsilyl, and <NUM>,<NUM>-(<NUM>, <NUM>,<NUM>,<NUM>-tetraisopropyldisiloxanylidene).

The term "aryl," as used herein, and unless otherwise specified, refers to phenyl, biphenyl, or naphthyl, and preferably phenyl. The term includes both substituted and unsubstituted moieties. The aryl group can be substituted with one or more moieties selected from the group consisting of hydroxyl, amino, alkylamino, arylamino, alkoxy, aryloxy, nitro, cyano, sulfonic acid, sulfate, phosphonic acid, phosphate, or phosphonate, either unprotected, or protected as necessary, as known to those skilled in the art, for example, as taught in <NPL>.

The term "halo," as used herein, includes chloro, bromo, iodo and fluoro.

The term "acyl" refers to a carboxylic acid ester in which the non-carbonyl moiety of the ester group is selected from straight, branched, or cyclic alkyl or lower alkyl, alkoxyalkyl including methoxymethyl, aralkyl including benzyl, aryloxyalkyl such as phenoxymethyl, aryl including phenyl optionally substituted with halogen (F, Cl, Br, I), C<NUM> to C<NUM> alkyl or C<NUM> to C<NUM> 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. dimefhyl-t-butylsilyl) or diphenylmethylsilyl. Aryl groups in the esters optimally comprise a phenyl group.

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 "host," as used herein, refers to a unicellular or multicellular organism in which the virus can replicate, including cell lines and animals, and preferably a human. Alternatively, the host can be carrying a part of the viral genome, whose replication or functions can be altered by the compounds disclosed herein. The term host specifically refers to infected cells, cells transfected with all or part of the viral genome, and animals, in particular, primates and humans. In most animal applications of the present invention, the host is a human patient. Veterinary applications, in certain indications, however, are clearly anticipated by the present invention.

The term "pharmaceutically acceptable salt" is used throughout the specification to describe any pharmaceutically acceptable form of a compound which, upon administration to a patient, provides the active compound. Pharmaceutically acceptable salts include those derived from pharmaceutically acceptable inorganic or organic bases and acids. Suitable salts include those derived from alkali metals such as potassium and sodium, alkaline earth metals such as calcium and magnesium, among numerous other acids well known in the pharmaceutical art.

A (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside or a pharmaceutically acceptable salt thereof is provided of the structure:
<CHM>
wherein the Base is a pyrimidine base represented by the following formula
<CHM>.

In a second embodiment, a (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside or its pharmaceutically acceptable salt thereof is provided of the structure:
<CHM>
wherein Base is:
<CHM>
and wherein R<NUM> is H, R<NUM> is OH, R<NUM>' is H, R<NUM> is H, R<NUM> is NH<NUM> or OH, and R<NUM> is H.

In a third embodiment, a (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside or a pharmaceutically acceptable salt thereof is provided of the structure:
<CHM>.

A fourth embodiment provides a (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside or a pharmaceutically acceptable salt thereof of the structure:
<CHM>.

The present invention also contemplates pharmaceutical compositions comprising <NUM>'-triphosphate triphosphoric acid ester derivates of the <NUM>'-hydroxyl group of a nucleoside compound disclosed herein having the following general structural formula:
<CHM>
wherein Base, X, R<NUM>, R<NUM>', and R<NUM> are as defined as above.

The compounds are also intended to include pharmaceutically acceptable salts of the triphosphate ester as well as pharmaceutically acceptable salts of <NUM>'-diphosphate and <NUM>'-monophosphate ester derivatives of the following structural formulas, respectively. <CHM>
<CHM>
wherein Base, X, R<NUM>, R<NUM>' and R<NUM> are as defined above.

Further non-limiting examples of phosphoric acid derivatives are the nucleosides shown below:
<CHM>
<CHM>
<CHM>.

In the various embodiments, the fluorinated derivatives are preferred. Fluorine is viewed as "isosteric" with hydrogen because of its size (Van der Waals radii for H is <NUM>. 20A and for F <NUM>. However, the atomic weight (<NUM>) and electronegativity of fluorine (<NUM> [Pauling's scale], <NUM> [Sanderson's scale]) are more similar to oxygen (<NUM> [Pauling]. <NUM> [Sanderson]) than hydrogen (<NUM> [Pauling], <NUM> [Sanderson]) (<NPL>). Fluorine is known to be capable of forming a hydrogen bond, but unlike a hydroxyl group (which can act both as proton acceptor and proton donor) fluorine acts only as a proton acceptor. On the other hand, <NUM>'-fluoro-ribonucleosides can be viewed as analogues of both ribonucleosides and deoxynucleosides. They may be better recognized by viral RNA polymerase at the triphosphate level than by the host RNA polymerase thus selectively inhibiting the viral enzyme.

In cases where compounds are sufficiently basic or acidic to form stable nontoxic acid or base salts, administration of the compound as a pharmaceutically acceptable salt may be appropriate. Pharmaceutically acceptable salts include those derived from pharmaceutically acceptable inorganic or organic bases and acids. Suitable salts include those derived from alkali metals such as potassium and sodium, alkaline earth metals such as calcium and magnesium, among numerous other acids well known in the pharmaceutical art. In particular, examples of pharmaceutically acceptable salts are organic acid addition salts formed with acids, which form a physiological acceptable anion, for example, tosylate, methanesulfonate, acetate, citrate, malonate, tartarate, succinate, benzoate, ascorbate, α-ketoglutarate, and α-glycerophosphate. Suitable inorganic salts may also be formed, including, sulfate, nitrate, bicarbonate, and carbonate salts.

Pharmaceutically acceptable salts may be obtained using standard procedures well known in the art, for example by reacting a sufficiently basic compound such as an amine with a suitable acid affording a physiologically acceptable anion. Alkali metal (for example, sodium, potassium or lithium) or alkaline earth metal (for example calcium) salts of carboxylic acids can also be made.

Pharmaceutical compositions of the present invention based upon a β-D or β-L compound disclosed herein or its pharmaceutically acceptable salt can be prepared in a therapeutically effective amount for treating a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection, optionally in combination with a pharmaceutically acceptable additive, carrier or excipient. The therapeutically effective amount may vary with the infection or condition to be treated, its severity, the treatment regimen to be employed, the pharmacokinetics of the agent used, as well as the patient treated.

In one aspect according to the present invention, the compound disclosed herein is formulated in a mixture with a pharmaceutically acceptable carrier. In general, it is preferable to administer the pharmaceutical composition in orally administrable form, but formulations may be administered via parenteral, intravenous, intramuscular, transdermal, buccal, subcutaneous, suppository or other route. Intravenous and intramuscular formulations are preferably administered in sterile saline. One of ordinary skill in the art may modify the formulation within the teachings of the specification to provide numerous formulations for a particular route of administration without rendering the compositions of the present invention unstable or compromising its therapeutic activity. In particular, a modification of a desired compound to render it more soluble in water or other vehicle, for example, may be easily accomplished by routine modification (salt formulation, esterification, etc.).

The amount of compound included within therapeutically active formulations, according to the present invention, is an effective amount for treating the infection or condition, in preferred embodiments, a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection. In general, a therapeutically effective amount of the present compound in pharmaceutical dosage form usually ranges from about <NUM> to about <NUM>,<NUM> or more, depending upon the compound used, the condition or infection treated and the route of administration. For purposes of the present invention, a prophylactically or preventively effective amount of the compositions, according to the present invention, falls within the same concentration range as set forth above for therapeutically effective amount and is usually the same as a therapeutically effective amount.

Administration of the active compound may range from continuous (intravenous drip) to several oral administrations per day (for example, Q. , etc.) and may include oral, topical, parenteral, intramuscular, intravenous, subcutaneous, transdermal (which may include a penetration enhancement agent), buccal and suppository administration, among other routes of administration. Enteric-coated oral tablets may also be used to enhance bioavailability and stability of the compounds from an oral route of administration. The most effective dosage form will depend upon the pharmacokinetics of the particular agent chosen, as well as the severity of disease in the patient. Oral dosage forms are particularly preferred, because of ease of administration and prospective favorable patient compliance.

To prepare the pharmaceutical compositions according to the present invention, a therapeutically effective amount of one or more of the compounds disclosed herein is preferably mixed with a pharmaceutically acceptable carrier according to conventional pharmaceutical compounding techniques to produce a dose. A carrier may take a wide variety of forms depending on the form of preparation desired for administration, e.g., oral or parenteral. In preparing pharmaceutical compositions in oral dosage form, any of the usual pharmaceutical media may be used. Thus, for liquid oral preparations such as suspensions, elixirs and solutions, suitable carriers and additives including water, glycols, oils, alcohols, flavoring agents, preservatives, coloring agents and the like may be used. For solid oral preparations such as powders, tablets, capsules, and for solid preparations such as suppositories, suitable carriers and additives including starches, sugar carriers, such as dextrose, mannitol, lactose and related carriers, diluents, granulating agents, lubricants, binders, disintegrating agents and the like may be used. If desired, the tablets or capsules may be enteric-coated for sustained release by standard techniques. The use of these dosage forms may significantly impact the bioavailability of the compounds in the patient.

For parenteral formulations, the carrier will usually comprise sterile water or aqueous sodium chloride solution, though other ingredients, including those that aid dispersion, also may be included. Where sterile water is to be used and maintained as sterile, the compositions and carriers must also be sterilized. Injectable suspensions may also be prepared, in which case appropriate liquid carriers, suspending agents and the like may be employed.

Liposomal suspensions (including liposomes targeted to viral antigens) may also be prepared by conventional methods to produce pharmaceutically acceptable carriers. This may be appropriate for the delivery of free nucleosides of the nucleoside compounds disclosed herein.

In particularly preferred embodiments according to the present invention, the compositions are used to treat, prevent or delay the onset of a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection. The compounds disclosed herein are preferably administered orally, but may be administered parenterally, topically or in suppository form.

The compounds used in the pharmaceutical compositions according to the present invention, because of their low toxicity to host cells in certain instances, may be advantageously employed prophylactically to prevent a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection or to prevent the occurrence of clinical symptoms associated with the viral infection or condition. In this aspect, according to the present invention, the present compositions are used to prevent or delay the onset of a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection. This prophylactic method comprises administration to a patient in need of such treatment, or who is at risk for the development of the virus or condition, an amount of a pharmaceutical composition according to the present invention effective for alleviating, preventing or delaying the onset of the viral infection or condition. In the prophylactic treatment, it is preferred that the antiviral compound utilized should be low in toxicity and preferably non-toxic to the patient. It is particularly preferred in this aspect of the present invention that the compound that is used should be maximally effective against the virus or condition and should exhibit a minimum of toxicity to the patient. In the case of a Flaviviridae infection, including hepatitis C virus, West Nile Virus, yellow fever virus, and a rhinovirus infection, compounds according to the present invention, which may be used to treat these disease states, may be administered within the same dosage range for therapeutic treatment (i.e., about <NUM> micrograms up to <NUM> gram or more from one to four times per day for an oral dosage form) as a prophylactic agent to prevent the proliferation of the viral infection, or alternatively, to prolong the onset of the viral infection, which manifests itself in clinical symptoms.

In addition, pharmaceutical compositions according to the present invention can be administered in combination or alternation with one or more antiviral agents, including other compounds disclosed herein. Certain compounds disclosed herein may be effective for enhancing the biological activity of certain agents according to the present invention by reducing the metabolism, catabolism or inactivation of other compounds and as such, are co-administered for this intended effect.

It is appreciated that nucleosides disclosed herein have several chiral centers and may exist in and be isolated in optically active and racemic forms. Some compounds may exhibit polymorphism. It is to be understood that the present invention encompasses any racemic, optically active, diastereomeric, polymorphic, or stereoisomeric form, or mixtures thereof, of a compound comprised in a pharmaceutical composition of the invention, which possess the useful properties described herein. It being well known in the art how to prepare optically active forms (for example, by resolution of the racemic form by recrystallization techniques, by synthesis from optically-active starting materials, by chiral synthesis, or by chromatographic separation using a chiral stationary phase).

Carbons of the nucleoside are chiral, their nonhydrogen substituents (the base and the CHOR groups, respectively) can be either cis (on the same side) or trans (on opposite sides) with respect to the sugar ring system. The four optical isomers therefore are represented by the following configurations (when orienting the sugar moiety in a horizontal plane such that the oxygen atom is in the back): cis (with both groups "up", which corresponds to the configuration of naturally occurring β-D nucleosides), cis (with both groups "down", which is a nonnaturally occurring β -L configuration), trans (with the C2' substituent "up" and the C4' substituent "down"), and trans (with the C2' substituent "down" and the C4' substituent "up"). The "D-nucleosides" are cis nucleosides in a natural configuration and the "L-nucleosides" are cis nucleosides in the nonnaturally occurring configuration.

Likewise, most amino acids are chiral (designated as L or D, wherein the L enantiomer is the naturally occurring configuration) and can exist as separate enantiomers.

Examples of methods to obtain optically active materials are known in the art, and include at least the following.

Chiral chromatography, including simulated moving bed chromatography, is used in one embodiment. A wide variety of chiral stationary phases are commercially available.

Some of the compounds described herein contain olefinic double bonds and unless otherwise specified, are meant to include both E and Z geometric isomers.

In addition, some of the nucleosides described herein, may exist as tautomers, such as, keto-enol tautomers. The individual tautomers as well as mixtures thereof are intended to be encompassed within the compounds disclosed herein as illustrated below.

A(<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine:
<CHM>.

In each example above, the first drawn structure is the preferred form.

The active compound can be administered as any salt that upon administration to the recipient is capable of providing directly or indirectly the parent compound, or that exhibits activity itself. Nonlimiting examples are the pharmaceutically acceptable salts (alternatively referred to as "physiologically acceptable salts"). Further, the modifications can affect the biological activity of the compound, in some cases increasing the activity over the parent compound. This can easily be assessed by preparing the salt and testing its antiviral activity according to the methods described herein, or other methods known to those skilled in the art.

In cases where compounds are sufficiently basic or acidic to form stable nontoxic acid or base salts, administration of the compound as a pharmaceutically acceptable salt may be appropriate. Examples of pharmaceutically acceptable salts are organic acid addition salts formed by addition of acids, which form a physiological acceptable anion, for example, tosylate, methanesulfonate, acetate, citrate, malonate, tartarate, succinate, benzoate, ascorate, a-ketoglutarate, a-glycerophosphate, formate, fumarate, propionate, glycolate, lactate, pyruvate, oxalate, maleate, and salicylate. Suitable inorganic salts may also be formed, including, sulfate, nitrate, bicarbonate, carbonate salts, hydrobromate and phosphoric acid. In a preferred embodiment, the salt is a mono- or di- hydrochloride salt.

Pharmaceutically acceptable salts may be obtained using standard procedures well known in the art, for example by reacting a sufficiently basic compound such as an amine with a suitable acid affording a physiologically acceptable anion. Alkali metal (for example, sodium, potassium or lithium) or alkaline earth metal (for example calcium) salts of carboxylic acids can also be made. In one embodiment, the salt is a hydrochloride, hydrobromide, or mesylate salt of the compound. In another embodiment, the pharmaceutically acceptable salt is a dihydrochloride, dihydrobromide, or dimesylate salt.

In another embodiment, for the treatment, inhibition, prevention and/or prophylaxis of any viral infection described herein, the active compound or its derivative or salt can be administered in combination or alternation with another antiviral agent. In general, in combination therapy, effective dosages of two or more agents are administered together, whereas during alternation therapy, an effective dosage of each agent is administered serially. The dosage will depend on absorption, inactivation and excretion rates of the drug as well as other factors known to those of skill in the art. It is to be noted that dosage values will also vary with the severity of the condition to be alleviated. It is to be further understood that for any particular subject, specific dosage regimens and schedules should be adjusted over time according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions.

It has been recognized that drug-resistant variants of flaviviruses, pestiviruses or HCV can emerge after prolonged treatment with an antiviral agent. Drug resistance most typically occurs by mutation of a gene that encodes for an enzyme used in viral replication. The efficacy of a drug against the viral infection can be prolonged, augmented, or restored by administering the compound in combination or alternation with a second, and perhaps third, antiviral compound that induces a different mutation from that caused by the principle drug. Alternatively, the pharmacokinetics, biodistribution or other parameter of the drug can be altered by such combination or alternation therapy. In general, combination therapy is typically preferred over alternation therapy because it induces multiple simultaneous stresses on the virus.

For example, one skilled in the art will recognize that any antiviral drug or therapy can be used in combination or alternation with any nucleoside disclosed herein. Any of the viral treatments described in the Background of the Invention can be used in combination or alternation with the compounds described in this specification. Nonlimiting examples of the types of antiviral agents or their prodrugs that can be used in combination with the compounds disclosed herein include: interferon, including interferon alpha 2a, interferon alpha 2b, a pegylated interferon, interferon beta, interferon gamma, interferon tau and interferon omega; an interleukin, including interleukin <NUM> and interleukin <NUM>; ribavirin; interferon alpha or pegylated interferon alpha in combination with ribavirin or levovirin; levovirin; a protease inhibitor including an NS3 inhibitor, a NS3-4A inhibitor; a helicase inhibitor; a polymerase inhibitor including HCV RNA polymerase and NS5B polymerase inhibitor; gliotoxin; an IRES inhibitor; and antisense oligonucleotide; a thiazolidine derivative; a benzanilide, a ribozyme; another nucleoside, nucleoside prodrug or nucleoside derivative; a <NUM>-amino-alkylcyclohexane; an antioxidant including vitamin E; squalene; amantadine; a bile acid; N-(phosphonoacetyl)-L-aspartic acid; a benzenedicarboxamide; polyadenylic acid; a benzimidazoles; thymosin; a beta tubulin inhibitor; a prophylactic vaccine; an immune modulator, an IMPDH inhibitor; silybin-phosphatidylcholine phytosome; and mycophenolate.

Further nonlimiting examples of the types of drugs or their prodrugs described above include: acyclovir (ACV), ganciclovir (GCV or DHPG) and its prodrugs (e.g. valyl-ganciclovir), E-<NUM>-(<NUM>-bromovinyl)-<NUM>'-deoxyuridine (BVDU), (E)-<NUM>-vinyl-<NUM>-β-D-arabonosyluracil (VaraU), (E)-<NUM>-(<NUM>-bromovinyl)-<NUM>-β-D-arabinosyluracil (BV-araU), <NUM>-(<NUM>-deoxy-<NUM>-fluoro-β-D-arabinosyl)-<NUM>-iodocytosine (D-FIAC), <NUM>-(<NUM>-deoxy-<NUM>-fluoro-β-L-arabinosyl)-<NUM>-methyluracil (L-FMAU, or clevudine), (S)-<NUM>-(<NUM>-hydroxy-<NUM>-phosphonylmethoxypropyl)adenine [(S)-HPMPA], (S)-<NUM>-(<NUM>-hydroxy-<NUM>-phosphonylmethoxypropyl)-<NUM>,<NUM>-diaminopurine [(S)-HPMPDAP], (S)-<NUM>-(<NUM>-hydroxy-<NUM>-phosphonyl-methoxypropyl)cytosine [(S)-HPMPC, or cidofivir], and (<NUM> S,<NUM>S)-l-[<NUM>-(hydroxymethyl)-<NUM>,<NUM>-dioxolan-<NUM>-yl]-<NUM>-iodouracil (L-<NUM>-IoddU), entecavir, , lamivudine (3TC), LdT, LdC, tenofovir, and adefovir, the (-)-enantiomer of <NUM>-hydroxymethyl-<NUM>-(<NUM>-fluorocytosin-<NUM>-yl)-<NUM>,<NUM>-oxathiolane ((-)-FTC); the (-)-enantiomer of <NUM>-hydroxymethyl-<NUM>-(cytosin-<NUM>-yl)-<NUM>,<NUM>-oxathiolane (3TC); carbovir, acyclovir, famciclovir, penciclovir, AZT, DDI, DDC, L-(-)-FMAU, D4T, amdoxovir, Reverset, Racivir, abacavir, L-DDA phosphate prodrugs, and β-D-dioxolanyl-<NUM>-chloropurine (ACP), non-nucleoside RT inhibitors such as nevirapine, MKC-<NUM>, DMP-<NUM> (sustiva), protease inhibitors such as indinavir, saquinavir, Kaletra, atazanavir; and anti-HIV compounds such as BILN-<NUM>, ISIS <NUM>; viramidine, NM <NUM>, VX-<NUM>, JKT-<NUM>, levovirin, isatoribine, albuferon, Peg-infergen, VX-<NUM>, R803, HCV-<NUM>, R1479 and DMP45.

Hosts, including humans, infected with pestivirus, flavivirus, HCV infection, or any other condition described herein, or another organism replicating through a RNA-dependent RNA viral polymerase, or for treating any other disorder described herein, can be treated by administering to the patient an effective amount of the active compound or a pharmaceutically acceptable salt thereof in the presence of a pharmaceutically acceptable carrier or dilutent. The active materials can be administered by any appropriate route, for example, orally, parenterally, intravenously, intradermally, subcutaneously, or topically, in liquid or solid form.

A preferred dose of the compound for a Flaviviridae infection, including hepatitis C virus, West Nile Virus and yellow fever virus and rhinovirus infection will be in the range from about <NUM> to about <NUM> one to four times per day. Lower doses may be useful, and thus ranges can include from <NUM> - <NUM>,<NUM> one to four times per day. The effective dosage range of the pharmaceutically acceptable salts can be calculated based on the weight of the parent nucleoside to be delivered. If the salt exhibits activity in itself the effective dosage can be estimated as above using the weight of the salt, or by other means known to those skilled in the art.

The compound is conveniently administered in unit any suitable dosage form, including but not limited to one containing <NUM> to <NUM>, preferably <NUM> to <NUM> of active ingredient per unit dosage form. An oral dosage of <NUM>-<NUM> is usually convenient, including in one or multiple dosage forms of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> mgs. Also contemplated are doses of <NUM>-<NUM>, or <NUM>-<NUM> or <NUM>-<NUM>. Furthermore, lower doses may be utilized in the case of administration by a non-oral route, as, for example, by injection or inhalation.

Ideally the active ingredient should be administered to achieve peak plasma concentrations (Cmax) of the active compound of from about <NUM> to <NUM> µM, preferably about <NUM> to <NUM> µM. This may be achieved, for example, by the intravenous injection of a <NUM> to <NUM>% solution of the active ingredient, optionally in saline, or administered as a bolus of the active ingredient.

The concentration of active compound in the drug composition will depend on absorption, inactivation and excretion rates of the drug as well as other factors known to those of skill in the art. It is to be noted that dosage values will also vary with the severity of the condition to be alleviated. It is to be further understood that for any particular subject, specific dosage regimens should be adjusted over time according to the individual need and the professional judgment of the person administering or supervising the administration of the compositions, and that the concentration ranges set forth herein are exemplary only and are not intended to limit the scope or practice of the claimed composition. The active ingredient may be administered at once, or may be divided into a number of smaller doses to be administered at varying intervals of time.

A preferred mode of administration of the active compound is oral. Oral compositions will generally include an inert diluent or an edible carrier. They may be enclosed in gelatin capsules or compressed into tablets. For the purpose of oral therapeutic administration, the active compound can be incorporated with excipients and used in the form of tablets, troches, or capsules. Pharmaceutically compatible binding agents, and/or adjuvant materials can be included as part of the composition.

The tablets, pills, capsules, troches and the like can contain any of the following ingredients, or compounds of a similar nature: a binder such as microcrystalline cellulose, gum tragacanth or gelatin; an excipient such as starch or lactose, a disintegrating agent such as alginic acid, Primogel, or corn starch; a lubricant such as magnesium stearate or Sterotes; a glidant such as colloidal silicon dioxide; a sweetening agent such as sucrose or saccharin; or a flavoring agent such as peppermint, methyl salicylate, or orange flavoring. When the dosage unit form is a capsule, it can contain, in addition to material of the above type, a liquid carrier such as a fatty oil. In addition, dosage unit forms can contain various other materials which modify the physical form of the dosage unit, for example, coatings of sugar, shellac, or other enteric agents.

The compound can be administered as a component of an elixir, suspension, syrup, wafer, chewing gum or the like. A syrup may contain, in addition to the active compounds, sucrose as a sweetening agent and certain preservatives, dyes and colorings and flavors.

The compound or a pharmaceutically acceptable salt thereof can also be mixed with other active materials that do not impair the desired action, or with materials that supplement the desired action, such as antibiotics, antifungals, anti-inflammatories, or other antivirals, including other nucleoside compounds. Solutions or suspensions used for parenteral, intradermal, subutaneous, or topical application can include the following components: a sterile diluent such as water for injection, saline solution, fixed oils, polyethylene glycols, glycerine, propylene glycol or other synthetic solvents; antibacterial agents such as benzyl alcohol or methyl parabens; antioxidants such as ascorbic acid or sodium bisulfite; chelating agents such as ethylenediaminetetraacetic acid; buffers such as acetates, citrates or phosphates and agents for the adjustment of tonicity such as sodium chloride or dextrose. The parental preparation can be enclosed in ampoules, disposable syringes or multiple dose vials made of glass or plastic.

If administered intravenously, preferred carriers are physiological saline or phosphate buffered saline (PBS).

In a preferred embodiment, the active compounds are prepared with carriers that will protect the compound against rapid elimination from the body, such as a controlled release formulation, including implants and microencapsulated delivery systems. Biodegradable, biocompatible polymers can be used, such as ethylene vinyl acetate, polyanhydrides, polyglycolic acid, collagen, polyorthoesters and polylactic acid. Methods for preparation of such formulations will be apparent to those skilled in the art. The materials can also be obtained commercially from Alza Corporation.

Liposomal suspensions (including liposomes targeted to infected cells with monoclonal antibodies to viral antigens) are also preferred as pharmaceutically acceptable carriers. These may be prepared according to methods known to those skilled in the art. For example, liposome formulations may be prepared by dissolving appropriate lipid(s) (such as stearoyl phosphatidyl ethanolamine, stearoyl phosphatidyl choline, arachadoyl phosphatidyl choline, and cholesterol) in an inorganic solvent that is then evaporated, leaving behind a thin film of dried lipid on the surface of the container. An aqueous solution of the active compound or its monophosphate, diphosphate, and/or triphosphate derivatives is then introduced into the container. The container is then swirled by hand to free lipid material from the sides of the container and to disperse lipid aggregates, thereby forming the liposomal suspension.

Antiviral Testing Of Candidate Compounds With HCV Replicon System In Huh7 Cells.

Huh7 cells harboring the HCV replicon can be cultivated in DMEM media (high glucose, no pyruvate) containing <NUM>% fetal bovine serum, 1X non-essential Amino Acids, Pen-Strep-Glu (<NUM> units/liter, <NUM> microgram/liter, and <NUM>/liter, respectively) and <NUM> to <NUM> microgram/milliliter G418. Antiviral screening assays can be done in the same media without G418 as follows: in order to keep cells in logarithmic growth phase, cells are seeded in a <NUM>-well plate at low density, for example <NUM> cells per well. The test compound is added immediately after seeding the cells and incubated for a period of <NUM> to <NUM> days at <NUM> in an incubator. Media is then removed, and the cells are prepared for total nucleic acid extraction (including replicon RNA and host RNA). Replicon RNA can then be amplified in a Q-RT-PCR protocol, and quantified accordingly. The observed differences in replicon HCV RNA levels compared to the untreated control is one way to express the antiviral potency of the test compound.

In another typical setting, a compound might reduce the viral RNA polymerase activity, but not the host RNA polymerase activity. Therefore, quantification of rRNA or beta-actin mRNA (or any other host RNA fragment) and comparison with RNA levels of the no-drug control is a relative measurement of the inhibitory effect of the test compound on cellular RNA polymerases.

To determine the cellular metabolism of the compounds, Huh-<NUM> cells are obtained from the American Type Culture Collection (Rockville, MD), and are grown in <NUM><NUM> tissue culture flasks in minimal essential medium supplemented with non-essential amino acids, <NUM>% penicillin-streptomycin. The medium is renewed every three days, and the cells are sub cultured once a week. After detachment of the adherent monolayer with a <NUM> minute exposure to <NUM> of trypsin-EDTA and three consecutive washes with medium, confluent Huh-<NUM> cells are seeded at a density of <NUM> × <NUM><NUM> cells per well in a <NUM>-well plate and exposed to <NUM> µM of [<NUM>H] labeled active compound (<NUM> dpm/pmol) for the specified time periods. The cells are maintained at <NUM> under a <NUM>% CO<NUM> atmosphere. At the selected time points, the cells are washed three times with ice-cold phosphate-buffered saline (PBS). Intracellular active compound and its respective metabolites are extracted by incubating the cell pellet overnight at -<NUM> with <NUM>% methanol followed by extraction with an additional <NUM> µL of cold methanol for one hour in an ice bath. The extracts are then combined, dried under gentle filtered air flow and stored at -<NUM> until HPLC analysis.

Within <NUM> week prior to the study initiation, the cynomolgus monkey is surgically implanted with a chronic venous catheter and subcutaneous venous access port (VAP) to facilitate blood collection and underwent a physical examination including hematology and serum chemistry evaluations and the body weight was recorded. Each monkey (six total) receives approximately <NUM> µCi of <NUM>H-labled compound combined with each dose of active compound at a dose level of <NUM>/kg at a dose concentration of <NUM>/mL, either via an intravenous bolus (<NUM> monkeys, IV), or via oral gavage (<NUM> monkeys, PO). Each dosing syringe is weighed before dosing to gravimetrically determine the quantity of formulation administered. Urine samples are collected via pan catch at the designated intervals (approximately <NUM>-<NUM> hours pre-dose, <NUM>-<NUM>, <NUM>-<NUM> and <NUM>-<NUM> hours post-dosage) and processed. Blood samples are collected as well (pre-dose, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> and <NUM> hours post-dosage) via the chronic venous catheter and VAP or from a peripheral vessel if the chronic venous catheter procedure should not be possible. The blood and urine samples are analyzed for the maximum concentration (Cmax), time when the maximum concentration is achieved (Tmax), area under the curve (AUC), half life of the dosage concentration (T<NUM>/<NUM>), clearance (CL), steady state volume and distribution (Vss) and bioavailability (F).

Human bone marrow cells are collected from normal healthy volunteers and the mononuclear population are separated by Ficoll-Hypaque gradient centrifugation as described previously by <NPL>; and <NPL>. The culture assays for CFU-GM and BFU-E are performed using a bilayer soft agar or methylcellulose method. Drugs are diluted in tissue culture medium and filtered. After <NUM> to <NUM> days at <NUM> in a humidified atmosphere of <NUM>% CO<NUM> in air, colonies of greater than <NUM> cells are counted using an inverted microscope. The results are presented as the percent inhibition of colony formation in the presence of drug compared to solvent control cultures.

Fifty microliters of 2X drug dilutions were added per well in a <NUM> well plate. A "no drug" (media only) control was used to determine maximum amount of mitochondrial DNA produced and ribosomal DNA 3TC @ <NUM> was used as a negative control, and ddC @ <NUM> was used as a toxic control. Ribosomal DNA levels were used to determine specific toxicicity to mitochondria or generally cytotoxicity. HepG2 cells (<NUM>,<NUM> cells/well at <NUM>µl) were added to the plate. The plate was incubated at <NUM> in a humidified <NUM>% CO<NUM> atmosphere for <NUM> days. After incubation, the supernatant was removed and stored for lactic acid quantification, and total DNA was extracted from cells as described in the RNeasy <NUM> handbook (February <NUM>), pages <NUM>-<NUM>. No DNA digestions were performed, therefore total RNA and DNA were extracted.

The extracted DNA was amplified and the change in mitochondrial DNA and ribosomal DNA for each sample was determined. The fold difference in mitochondrial DNA normalized for ribosomal DNA relative to control was calculated.

Lactic acid quantification was performed by the D-Lactic Acid/ L-Lactic acid test kit (Boehringer Mannheim/ R-Biopharm/ Roche). The total amount of lactic acid produced for each sample was found as well as the fold change in lactic acid production (% of lactic acid / % of rDNA) as described in the manufacturers instructions.

<NUM>µl of 2X drug dilutions were added per well in a <NUM> well plate. Final concentrations of drug ranged from <NUM> to <NUM>. A "no drug" (media only) control was used to determine the minimum absorbance values and a "cells + media only" control was used for maximum absorbance value. A solvent control was also used. Cells were then added (PBM: <NUM> × <NUM><NUM> cells/well; CEM : <NUM> × <NUM><NUM> cells/well; Vero, HepG2, Huh-<NUM>, and Clone A: <NUM> × <NUM><NUM> cells/well) and incubated at <NUM> in a humidified <NUM>% CO<NUM> atmosphere for <NUM>-<NUM> days (PBM :<NUM> days; CEM : <NUM> days, all others :<NUM> days). After incubation, <NUM>µl of MTS dye was added from Cell Titer Aqueous One Solution Cell Proliferation Assay to each well and the plate was re-incubated for <NUM>-<NUM> hours. The absorbance (<NUM>) was then read on an ELISA plate reader using the media only/ no cell wells as blanks. Percent inhibition was found and used to calculate the CC<NUM>.

In vivo toxicity was also determined following injections into female Swiss mice of the various nucleosides disclosed herein. Intraperitoneal injections were given on days <NUM>, day <NUM>, day <NUM>, day <NUM>, and day <NUM> of varying doses of the particular nucleoside. Separate animals were injected with vehicle as control groups. In these studies, each dosing group contained <NUM>-<NUM> mice. The average weight change in each of the mice was measured as a sign of toxicity of the compound.

Madin-Darby Bovine Kidney (MDBK) cells were grown in Dulbecco's modified eagle medium supplemented with <NUM>% horse serum and <NUM>µg/ml penicillin-streptomycin. Cells were seeded in a <NUM>-well plate at <NUM> ×<NUM><NUM> cells /well and incubated for <NUM> at <NUM> in a humidified <NUM>% CO<NUM> atmosphere. Cells were infected with either cytopathic (NADL strain) or noncytopathic (SD-<NUM> strain) BVDV at a virus dilution of <NUM>-<NUM> and incubated for <NUM>. Cell monolayers were washed three times with medium. Fresh medium-containing test compounds in dose response concentrations or ribavirin, as a positive control, were added to cultures and medium containing no drug was added to the no-drug controls. After <NUM> incubation, supernatant was collected and viral RNA was extracted using the QIAmp Viral RNA Mini Kit (Qiagen, CA). Viral load was determined by Q-RT-PCR using primers specific for either NADL or SD-<NUM> (<NUM>).

The following non-limiting embodiments illustrate some general methodologies to obtain the nucleosides disclosed herein. Two representative general methods for the preparation of compounds disclosed herein are outlined in Schemes <NUM> and <NUM> while more specific examples of these general methods are provided in Scheme <NUM> (Example <NUM>), and Scheme <NUM> (Example <NUM>). Scheme <NUM> represents a generalized process starting from a (<NUM>R) <NUM>-deoxy-<NUM>-methyl-<NUM>-fluoro-carbohydrate and forms the nucleosides disclosed herein by condensing with a nucleobase. Scheme <NUM> starts from a pre-formed, pyrimidine nucleoside, optionally substituted at C-<NUM>' and constructs the C-<NUM>' (R) methyl, fluoro nucleosides disclosed herein. These schemes illustrate the syntheses of compounds disclosed herein wherein there is a furanose ring in the (β-D-ribo configuration. Those skilled in the art of nucleoside and nucleotide synthesis will readily appreciate that known variations of the conditions and processes of the following preparative procedures and known manipulations of the nucleobase can be used to prepare these and other compounds of the present invention. Additionally, the L-enantiomers corresponding to the compounds of the invention can be prepared following the same methods, beginning with the corresponding L-carbohydrate building block or nucleoside L-enantiomer as the starting material.

Step <NUM> in Scheme <NUM> introduces the <NUM>-methyl group by using an appropriate alkylating agent such as methyllithium, trimethylaluminum, or methylmagnesium bromide in an anhydrous solvent such as tetrahydrofuran (THF), chloroform, or diethyl ether. Compounds <NUM>-<NUM> through <NUM>-<NUM> can be purely α or β or they may exist as an anomeric mixture containing both α and β anomers in any ratio. However, the preferred anomeric configuration of structure <NUM>-<NUM> is β.

Step <NUM> introduces the fluorine atom at the <NUM>- position of the alkyl furanoside. This can be achieved by treatment of the tertiary alcohol, <NUM>-<NUM>, with a commercially available fluorinating reagent such as (diethylamino)sulfur trifluoride (DAST) or Deoxofluor in an anhydrous, aprotic solvent such as tetrahydrofuran, chloroform, dichloromethane, or toluene. Preferably the stereochemistry proceeds with inversion of configuration at C-<NUM>. That is, starting from a C-<NUM> hydroxyl "up" (or arabinofuranoside) in structure <NUM>-<NUM>, the C-<NUM> fluorine is "down" in the intermediate ribofuranoside <NUM>-<NUM>.

In step <NUM>, the optional protecting groups (Pg) can be deprotected and reprotected to groups more suitable for the remaining manipulations (<NPL>). For example, benzyl ethers (Bn) may be difficult to remove in the protected nucleoside, <NUM>-<NUM> and may be deprotected and replaced with a group more facile to remove from the nucleoside of structural type <NUM>-<NUM>. Furthermore, the anomeric position (C-<NUM>) can also be optionally manipulated to a suitable group for the coupling reaction with the nucleobase (step <NUM>). Several methods for anomeric manipulations are established to those skilled in the art of nucleoside synthesis. Some non-limiting examples by treatment of the alkyl furanoside (<NUM>-<NUM>, R = alkyl) with a mixture of acetic anhydride, acetic acid, and a catalytic amount of sulfuric acid (acetolysis) to provide structure <NUM>-<NUM> where R = Ac, with optional protecting groups. Also, the alkyl group in <NUM>-<NUM> may be converted to an acetate, benzoate, mesylate, tosylate, triflate, or tosylate, for example, by first hydrolyzing the <NUM>-Oalkyl group to a <NUM>-hydroxyl group by using a mineral acid consisting of but not limited to sulfuric acid, hydrochloric acid, and hydrobromic acid or an organic acid consisting of but not limited to trifluoroacetic acid, acetic acid, and formic acid (at ambient temperature or elavated temperature). The reducing sugar could then be converted to the desired carbohydrate by treatment with acetyl chloride, acetic anhydride, benzoyl chloride, benzoic anhydride, methanesulfonyl chloride, triflic anhydride, trifyl chloride, or tosyl chloride in the presence of a suitable base such as triethylamine, pyridine, or dimethylaminopyridine.

The nucleosidic linkage is constructed by treatment of intermediate <NUM>-<NUM> or <NUM>-<NUM> with the appropriate persilylated nucleobase in the presence of a lewis acid such as tin tetrachloride, titanium tetrachloride, trimethylsilyltriflate, or a mercury (II) reagent (HgO/HgBr<NUM>) usually at an elavated temperature in an aprotic solvent such as toluene, acetonitrile, benzene, or a mixture of any or all of these solvents.

The optional protecting groups in the protected nucleosides or structural formula <NUM>-<NUM> can be cleaved following established deprotection methodologies (<NPL>).

The starting material for this process is an appropriately substituted purine or pyrimidine nucleoside with a <NUM>'-OH and <NUM>'-H. The nucleoside can be purchased or can be prepared by any known means including standard coupling techniques. The nucleoside can be optionally protected with suitable protecting groups, preferably with acyl or silyl groups, by methods well known to those skilled in the art, as taught by <NPL>.

The pyrimidine nucleoside can then be oxidized at the <NUM>'-position with the appropriate oxidizing agent in a compatible solvent at a suitable temperature to yield the <NUM>'-modified nucleoside. Possible oxidizing agents are a mixture of dimethylsulfoxide, trifluoroacetic anhydride or acetic anhydride (a Swern/Moffat oxidiation), chromium trioxide or other chromate reagent, Dess-Martin periodinane, or by ruthenium tetroxide/sodium periodate.

The optionally protected nucleoside <NUM>'-ketone is then alkylated using such alkylating agents as methyllithium, trimethylaluminum, methylmagnesium bromide, or similar reagents in an anhydrous solvent such as tetrahydrofuran (THF), chloroform, or diethyl ether usually at temperatures below <NUM>. Compounds of the structural formula <NUM>-<NUM> are preferred to have the <NUM>'(S) or <NUM>'-methyl "down", <NUM>'-OH "up" configuration.

The nucleoside of structure <NUM>-<NUM> can be deprotected and reprotected with a number of protecting groups such as an O-acyl (alkyl or aryl), O-sulfonyl, or an N-acyl (alkyl or aryl) for the base. This optional reprotection step need not be limited to protecting groups that function as chemical protecting groups. Other protecting groups such as long chain acyl groups of between <NUM> and <NUM> carbon units or amino acids can be introduced independently on the nucleobase or the sugar. The protecting groups can serve as prodrugs of the active substance.

Step <NUM> introduces the fluorine atom at the <NUM>' position of the pre-formed nucleoside. This can be achieved by treatement of the tertiary alcohol, <NUM>-<NUM>, with a commercially available fluorinating reagent such as (diethylamino)sulfur trifluoride (DAST) or Deoxofluor in an anhydrous, aprotic solvent such as tetrahydrofuran, chloroform, dichloromethane, or toluene. Preferably the stereochemistry proceeds with inversion of configuration at the <NUM>' position. That is, starting from a C-<NUM>' hydroxyl "up" (or arabinonucleoside) in structure <NUM>-<NUM>, the C-<NUM>' fluorine is "down" in the intermediate nucleoside <NUM>-<NUM>. The absolute configuration of a nucleoside of structure <NUM>-<NUM> is (<NUM>'S) while the absolute configuration of a nucleoside of structure <NUM>-<NUM> is (<NUM>'R).

Subsequently, the nucleosides of structural type <NUM>-<NUM> can be deprotected by methods well known to those skilled in the art, as taught by <NPL>.

The following working examples provide a further understanding of the method of the present invention and further exemplify the general examples in Schemes <NUM> and <NUM> above. These examples are of illustrative purposes, and are not meant to limit the scope of the invention. Equivalent, similar or suitable solvents, reagents or reaction conditions may be substituted for those particular solvents, reagents or reaction conditions described without departing from the general scope of the method.

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mmol) was dissolved in anhydrous diethyl ether and cooled to -<NUM>. To this solution was added MeLi (<NUM>, <NUM> in diethyl ether). After the reaction was complete, the mixture was treated with ammonium chloride (<NUM>, <NUM>) and the organic phase was separated, dried (Na<NUM>SO<NUM>), filtered, and concentrated to dryness. Silica gel chromatography followed by crystallization from diethyl ether-hexanes afforded pure compound <NUM>-<NUM> (<NUM>). <NUM>H NMR (<NUM>, CDCl<NUM>): δ <NUM> (s, <NUM>), <NUM> (s, <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (m, <NUM>), <NUM> (s,<NUM>), <NUM> (m, <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM>-<NUM> (m, <NUM>); <NUM>C NMR (<NUM>, CDCl<NUM>): δ <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>.

Step <NUM>: Compound <NUM>-<NUM> was dissolved in CH<NUM>Cl<NUM> and was treated with DAST (<NUM>, <NUM> mmol) at room temperature. The solution was stirred at room temp overnight. The so-obtained mixture was poured into sat NaHCO<NUM> (<NUM>) and washed with sat NaHCO<NUM> (<NUM> × <NUM>). The organic layer was further worked up in the usual manner. Silica gel chromatography (<NUM>:<NUM> EtOAc-hexanes) gave crude compound <NUM>-<NUM> (<NUM>) that was sufficiently pure for the next step. <NUM>H NMR (<NUM>, CDCl<NUM>): δ <NUM> (d, <NUM>, J = <NUM>), <NUM> (s, <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (m, <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM>-<NUM> (m, <NUM>); <NUM>C NMR (<NUM>, CDCl<NUM>): δ <NUM> (d, J = <NUM>), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> (d, J = <NUM>), <NUM> (d, J = <NUM>), <NUM> (d, J = <NUM>), <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>; <NUM>F NMR (<NUM>, CDCl<NUM>): δ -<NUM> (m, 1F).

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mmol) was dissolved in <NUM>:<NUM> EtOH-EtOAc and treated with Pd/C (~<NUM>) and cyclohexene (~<NUM>). The mixture was heated to reflux overnight and then filtered through celite. The solvent was removed in vacuo and the residue was dissolved in pyridine (~<NUM>). To this solution was added benzoyl chloride (<NUM>, <NUM> mmol) and the mixture was stirred at room temp overnight. The pyridine was removed in vacuo and the residue was partitioned between CH<NUM>Cl<NUM> and sat NaHCO<NUM> (<NUM>). The organic phase was dried (Na<NUM>SO<NUM>), filtered, and the solution was concentrated to dryness. Column chromatography provided <NUM> of pure compound <NUM>-<NUM>. <NUM>H NMR (<NUM>, CDCl<NUM>): δ <NUM> (d, <NUM>, J = <NUM>), <NUM> (s, <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (m, <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM>-<NUM> (m, <NUM>); <NUM>F NMR (<NUM>, CDCl<NUM>): δ -<NUM> (m, 1F).

Step <NUM>: A solution of bis(trimethylsilyl)-N-benzoylcytosine (<NUM>, <NUM> mmol) and compound <NUM>-<NUM> (<NUM>, <NUM> mmol) in <NUM>,<NUM> dichloroethane (<NUM>) and toluene (<NUM>) was treated with TMSOTf (<NUM>, <NUM> mmol). After most of the starting material disappeared as judged by TLC, the solution was cooled to room temp, washed with water (<NUM> × <NUM>), brine (<NUM> × <NUM>), dried (Na<NUM>SO<NUM>), filtered, and concentrated to dryness. Flash chromatography followed by crystallization from CH<NUM>Cl<NUM>-hexanes afforded compound <NUM>-<NUM> (<NUM>). mp <NUM>; <NUM>H NMR (<NUM>, CDCl<NUM>): δ <NUM> (d, <NUM>, J = <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (app d, <NUM>, J = <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM> (dd, <NUM>, J =<NUM>, <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM>-<NUM> (m, <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM>-<NUM> (m, <NUM>), <NUM> (s, <NUM>); <NUM>F NMR (<NUM>, CDCl<NUM>): δ <NUM> (m, 1F).

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mmol) was dissolved in methanolic ammonia and stirred at room temp for <NUM>. The solution was concentrated to dryness and chromatographed (SiO<NUM>) eluting with <NUM>:<NUM> EtOH-CH<NUM>Cl<NUM>. The yield was about <NUM> of pure (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine, <NUM>-<NUM>. <NUM>H NMR (<NUM>, DMSO-d<NUM>): δ <NUM> (d, <NUM>, J = <NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>), <NUM>-<NUM> (m, <NUM>, J= <NUM>, <NUM>), <NUM> (s, <NUM>, exchangeable with D<NUM>O), <NUM> (s, <NUM>, exchangeable with D<NUM>O), <NUM> (d, <NUM>, J = <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (d, <NUM>, J = <NUM>, exchangeable with D<NUM>O), <NUM> (d, <NUM>); <NUM>F NMR (<NUM>, DMSO-d<NUM>): δ <NUM> (m, 1F).

<CHM>
TIDPS = <NUM>,<NUM>-(<NUM>,<NUM>,<NUM>,<NUM>-Tetraisopropyldisiloxanylidene).

Step <NUM>: To a suspension of cytidine (<NUM>, <NUM> mol) in DMF (<NUM>) is added benzoic anhydride (<NUM>, <NUM> mol). The mixture was stirred at room temperature for <NUM>. The DMF was removed in vacuo and the residue was triturated with diethyl ether. The resulting solid was collected by suction filtration and washed with diethyl ether (<NUM> x <NUM>). Further drying in vacuo at room temperature gave the N<NUM> benzamide (<NUM>, <NUM>%). A portion of this material (<NUM>, <NUM> mol) was dissolved in anhydrous pyridine (<NUM>) and was treated with <NUM>,<NUM>-dichloro-<NUM>,<NUM>,<NUM>,<NUM>-tetraisopropyl-disiloxane (<NUM>, <NUM> mol) at room temp. The solution was stirred at room temperature overnight. The mixture was concentrated to near dryness in vacuo and coevaporated with toluene (<NUM> x <NUM>). The residue was treated with EtOAc (<NUM>) and washed with HCl (<NUM> x <NUM>, <NUM> N), NaHCO<NUM> (<NUM> %, <NUM> x <NUM>). The organic layer was washed dried (Na<NUM>SO<NUM>), filtered, and evaporated to dryness. Compound <NUM>-<NUM> (<NUM>, ><NUM>%) was isolated as a white foam and used without further purification.

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mol) was dissolved in dry THF (<NUM>). Anhydrous dmso (<NUM>, <NUM> mol) was added and the resulting solution was cooled to between -<NUM> and -<NUM>. Trifluoroacetic anhydride (<NUM>, <NUM> mol) was added dropwise over <NUM> minutes and the solution was stirred between -<NUM> and -<NUM> for <NUM> hrs after which anhydrous triethylamine (<NUM>, <NUM> mol) was added over <NUM>. The crude reaction containing ketone <NUM>-<NUM> was dissolved in EtOAc (<NUM>), and the resulting solution was washed with H<NUM>O (<NUM> x <NUM>), dried (Na<NUM>SO<NUM>) and the solvents were removed in vacuo to give a yellow solid that was purified on a silica gel column eluting with a stepwise gradient of Et<NUM>O (<NUM>-<NUM>%) in hexanes followed by a stepwise gradient of EtOAc (<NUM>-<NUM>%) in hexanes. The crude ketone so-obtained (~<NUM>) was crystallized from petroleum ether to give ketone <NUM>-<NUM> (<NUM>, <NUM>% from cytidine) as a white solid and <NUM> of unreacted starting material, <NUM>-<NUM>, as a yellow solid.

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mmol) was dissolved in anhydrous toluene (~<NUM>) and the solvent was removed in vacuo with exclusion of moisture. The residue was then further dried in vacuo (oil pump) for another <NUM>. With strict exclusion of moisture, the residual foam was dissolved in anhydrous diethyl ether (<NUM>) under argon. The resulting solution was cooled to -<NUM> under argon and MeLi (<NUM>, <NUM>, <NUM> mol) was added dropwise via additional funnel. After the addition was complete, the mixture was stirred for <NUM> at -<NUM>. Aqueous <NUM> NH<NUM>Cl (<NUM>) was added slowly. After warming to room temperature, the mixture was washed with H<NUM>O (<NUM> x <NUM>), dried (Na<NUM>SO<NUM>), and then concentrated to dryness to give a brown foam (~<NUM>, ><NUM>%).

The reaction was performed two more times using <NUM> and <NUM> of compound <NUM>-<NUM>. The combined crude products (<NUM>, <NUM> mol) were dissolved in THF (<NUM>) and treated with concd HOAc (<NUM>, <NUM> mol). To the solution was added TBAF (<NUM>, <NUM> in THF). The solution was stirred at room temp for <NUM> and the mixture was treated with silica gel (<NUM>) and concentrated to dryness. The powder was placed on a silica gel column packed in CH<NUM>Cl<NUM>. Elution with <NUM>:<NUM> EtOH-CH<NUM>Cl<NUM> afforded a dark waxy solid that was pre-adsorbed on silica gel (<NUM>) and chromatographed as before. Compound <NUM>-<NUM> (<NUM>, <NUM> % from <NUM>-<NUM>) was isolated as an off-white solid. <NUM>H NMR (DMSO-d<NUM>): δ <NUM> (s, <NUM>, CH<NUM>), <NUM>-<NUM> (m, <NUM>,), <NUM>-<NUM> (m, <NUM>,), <NUM> (t, <NUM>, J = <NUM>, OH-<NUM>'), <NUM> (s, <NUM>, OH-<NUM>'), <NUM> (d, <NUM>, J = <NUM>, OH-<NUM>'), <NUM> (s, <NUM>, H-l'), <NUM> (d, <NUM>, J = <NUM>), <NUM> (Ψt, <NUM>, J = <NUM>), <NUM> (Ψt, <NUM>, J = <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (s, <NUM>, NH). Calcd for C<NUM>H<NUM>N<NUM>O<NUM> • <NUM><NUM>O: C, <NUM>; H, <NUM>; N, <NUM>. Found: C, <NUM>; H, <NUM>; N, <NUM>.

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mol) was dissolved in anhydrous pyridine and concentrated to dryness in vacuo. The resulting syrup was dissolved in anhydrous pyridine under argon and cooled to <NUM> with stirring. The brown solution was treated with benzoyl chloride (<NUM>, <NUM> mol) dropwise over <NUM>. The ice bath was removed and stirring continued for <NUM> whereby TLC showed no remaining starting material. The mixture was quenched by the addition of water (<NUM>) and concentrated to dryness. The residue was dissolved in a minimal amount of CH<NUM>Cl<NUM> and washed with satd NaHCO<NUM> (<NUM> x <NUM>) and H<NUM>O (<NUM> x <NUM>). The organic phase was dried (Na<NUM>SO<NUM>) and filtered, concentrated to dryness and chromatographed on silica gel eluting with a stepwise gradient of EtOAc-hexanes (<NUM>-<NUM>%) to provide compound <NUM>-<NUM> as yellow foam (<NUM>, <NUM>%). <NUM>H NMR (CDCl<NUM>): δ <NUM> (s, <NUM>, CH<NUM>), <NUM> (m, <NUM>, H-<NUM>), <NUM>-<NUM> (m, <NUM>, H-<NUM>',5a'), <NUM> (d, <NUM>, J= <NUM>, H-<NUM>'), <NUM> (s, <NUM>, H-<NUM>'), <NUM>-<NUM> (m, <NUM>, Ar), <NUM>-<NUM> (m, <NUM>, Ar), <NUM> (d, <NUM>, J = <NUM>), <NUM>-<NUM> (m, <NUM>, Ar), <NUM> (d, <NUM>, J = <NUM>). Calcd for C<NUM>H<NUM>N<NUM>O<NUM>: C, <NUM>; H, <NUM>; N, <NUM>. Found: C, <NUM>; H, <NUM>; N, <NUM>.

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mol) was dissolved in anhydrous toluene (<NUM>) under argon and cooled to -<NUM>. DAST (<NUM>, <NUM> mmol) was added slowly and the cooling bath was removed after the addition was complete. Stirring was continued for <NUM> and the mixture was poured into satd NaHCO<NUM> (<NUM>) and washed until gas evolution ceased. The organic phase was dried (Na<NUM>SO<NUM>), concentrated, and purified by silica gel chromatography eluting with <NUM>:<NUM> EtOAc-hexanes. Yield was <NUM> (<NUM>%) of pure <NUM>-<NUM> as a white solid. mp <NUM> (CH<NUM>Cl<NUM>-hexanes); <NUM>H NMR (CDCl<NUM>): δ <NUM> (d, <NUM>, J = <NUM>, CH<NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>, H-<NUM>'), <NUM> (d, <NUM>, J = <NUM>, H-<NUM>'), <NUM> (dd, <NUM>, J = <NUM>, <NUM>, H-5a'), <NUM> (dd, <NUM>, J = <NUM>, <NUM>, H-<NUM>'), <NUM> (d, <NUM>, J = <NUM>, H-<NUM>'), <NUM>-<NUM> (m, <NUM>, Ar), <NUM>-<NUM> (m, <NUM>, Ar), <NUM> (d, <NUM>, J = <NUM>), <NUM>-<NUM> (m, <NUM>, Ar), <NUM> (bs, <NUM>, NH). <NUM>F NMR (CDCl<NUM>): δ <NUM> (m). Calcd for C<NUM>H<NUM>FN<NUM>O<NUM> • <NUM><NUM>O: C, <NUM>; H, <NUM>; N, <NUM>. Found: C, <NUM>; H, <NUM>; N, <NUM>.

Step <NUM>: Compound <NUM>-<NUM> (<NUM>, <NUM> mol) was suspended in methanolic ammonia (ca <NUM> N, <NUM>) and stirred at room temperature overnight. The solvent was removed in vacuo, co-evaporated with methanol (<NUM> x <NUM>), and pre-adsorbed onto silica gel. The white powder was placed onto a silica gel column (packed in CHCl<NUM>) and the column was eluted with <NUM>% EtOH in CHCl<NUM>, then <NUM>% EtOH and finally <NUM>% EtOH in CHCl<NUM>. Concentration of the fractions containing the product, filtration through a <NUM> disk, and lyophillization from water afforded compound <NUM>-<NUM>, <NUM> (<NUM>%). <NUM>H NMR (DMSO-d<NUM>): δ <NUM> (d, <NUM>, J= <NUM>, CH<NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>, H-<NUM>'), <NUM>-<NUM> (m, <NUM>, H-<NUM>', H-<NUM>', H-5a'), <NUM> (app s, <NUM>, OH-<NUM>'), <NUM> (d, <NUM>, J= <NUM>, H-<NUM>'), <NUM> (d, <NUM>, J= <NUM>, H-<NUM>), <NUM> (d, <NUM>, J = <NUM>, H-<NUM>'), <NUM> (s, <NUM>, NH<NUM>), <NUM> (s, <NUM>, NH<NUM>), <NUM> (d, <NUM>, J = <NUM>z, H-<NUM>). <NUM>F NMR (DMSO-d<NUM>): δ <NUM> (m). Calcd for C<NUM>H<NUM>FN<NUM>O<NUM> • <NUM><NUM>O: C, <NUM>; H, <NUM>; N, <NUM>. Found: C, <NUM>; H, <NUM>; N, <NUM>. Compound <NUM>-<NUM> (<NUM>, <NUM> mmol) was converted to the hydrochloride salt by dissolving in water (<NUM>) and adjusting the pH to approximately <NUM> with <NUM> HCl. The water was removed in vacuo and the residue was crystallized from aqueous EtOH to give <NUM>-<NUM> as the hydrochloride salt (<NUM>). mp <NUM> (dec); <NUM>H NMR (DMSO-d<NUM>): δ <NUM> (d, <NUM>, J = <NUM>, CH<NUM>), <NUM> (dd, <NUM>, J = <NUM>, <NUM>, H-<NUM>'), <NUM>-<NUM> (m, <NUM>, H-<NUM>', H-<NUM>', H-5a'), <NUM> (d, <NUM>, J = <NUM>, H-<NUM>'), <NUM> (d, <NUM>, J= <NUM>, H-<NUM>), <NUM> (d, <NUM>, J= <NUM>, H-<NUM>), <NUM> (s, <NUM>, NH), <NUM> (s, <NUM>, NH). <NUM>F NMR (DMSO-d<NUM>): δ <NUM> (m). Calcd for C<NUM>H<NUM>FN<NUM>O<NUM> • HCl: C, <NUM>; H, <NUM>; N, <NUM>. Found: C, <NUM>; H, <NUM>; N, <NUM>.

The anti-flavivirus activity of the compounds was determined as described by <NPL>)). The compound was dissolved in DMSO and added to the culture media at final concentrations ranging from <NUM> to <NUM>. A <NUM>-days incubation resulted in dose-dependant reduction of the replicon HCV RNA (<FIG>). A <NUM>-log reduction of replicon RNA (or EC<NUM> value) was reached at approximately <NUM>. Measurement of the reduction of rRNA gave an indication of the inhibitory effect on cellular polymerases. Subtraction of this cellular toxicity value from the antiviral values resulted in the therapeutic index line and EC<NUM> value. Based on these calculations, an average EC<NUM> value, corrected for cellular toxicity, of approximately <NUM> was obtained. <FIG> shows the dose-dependant reduction of the replicon HCV RNA based on the treatment with (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine. The viral reduction was compared to the reduction of cellular RNA levels (ribosomal RNA) to obtain therapeutic index values. EC<NUM> represents the effective concentration <NUM>% at <NUM> hours following the dose dependant administration of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine. <FIG> shows the prolonged reduction in replicon HCV RNA up to <NUM> days following treatment with <NUM> and <NUM> µM.

The activity of (<NUM>R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine in the replicon system is summarized in Table <NUM>. The EC<NUM> values for (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine as well as <NUM>'-C-methylcytidine and <NUM>'-C-methyladenosine are shown for three separate replicon clones (HCV-WT (Wild Type), <NUM>-<NUM> and <NUM>-<NUM>) as well as two other clones (S282T and rRNA). The EC<NUM> values for (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine were in the range of <NUM> to <NUM>µM for the replicon clones. In contrast the EC<NUM> values for <NUM>'-C-methylcytidine were in the range of <NUM>-<NUM>µM. Interestingly, the EC<NUM> values for <NUM>'-C-methyladenosine were comparable to those of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine. The activity of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine and <NUM>'-C-methylcytidine in other replicons tested is shown in Table <NUM>.

Table <NUM> shows the potency of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine-<NUM>'-triphosphate (TP) in the NS5B polymerase assay. The inhibitory concentration <NUM>% was determined to be in the range of <NUM> to <NUM>µM.

A summary of the toxicity data for (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine using the mitochondrial toxicity assay is shown in Tables <NUM> and <NUM>. Table <NUM> shows the lack of effects of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine and <NUM>'-C-methylcytidine on mitochondrial DNA synthesis and lack of effects on lactic acid increase in this assay. Results shows the relative lack of toxicity of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine. Table <NUM> shows a cytotoxicity analysis in various cell lines (Clone A, Huh7, HepG2, MDBK, PBM, CEM, Vero, MRC-<NUM>). Cytotoxic concentration <NUM>% (CC<NUM>) was greater than <NUM>-<NUM>µM in all clones tested for (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine as well as <NUM>'-C-methylcytidine. In contrast is the relative toxicity of <NUM>'-C-methyladenosine.

The effects the nucleoside analogs tested on human bone marrow cells is depicted in Table <NUM>. As shown, the IC<NUM> values for <NUM>'-methyl-<NUM>'-fluorocytidine were significantly higher (<NUM>, BFU-E) and <NUM> (CFU-GM) as compared to <NUM>'-methylcytidine or AZT. Results show that <NUM>'-methyl-<NUM>'-fluorocytidine was significantly less toxic than compared to the other nucleoside compounds.

<FIG> depicts the average weight change (%) of female Swiss mice in vivo the toxicity analysis of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine at various doses. Intraperitoneal injections were given on days <NUM> to day <NUM> of the <NUM>, <NUM>, <NUM>, <NUM>, <NUM>/kg. Each dosing group contained <NUM> mice and no mice died during the <NUM>-day study. No significant toxicity was observed in the mice.

<FIG> and Table <NUM> summarize the pharmacokinetic parameters of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine in Rhesus monkeys given a single dose (<NUM>/kg) oral (Table <NUM>, <FIG>) or intravenous dose (<FIG>) of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine.

Summary of the range of antiviral activity of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine is shown in Table <NUM>. Table <NUM> shows that in addition to HCV virus (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine shows activity against Rhinovirus, West Nile virus, Yellow Fever virus, and Dengue virus.

Table <NUM> shows the lack of activity of (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methylcytidine on HCV surrogate models BVDV as well as other viruses including HIV, HBV and Corona virus. In contrast, <NUM>'-C-methylcytidine and <NUM>'-C-methyladenosine show greater activity in the HCV surrogate model, BVDV. These results show the necessity for screening this series of compounds against the HCV replicon system versus surrogate HCV systems.

Claim 1:
A pharmaceutical composition comprising a (<NUM>'R)-<NUM>'-deoxy-<NUM>'-fluoro-<NUM>'-C-methyl nucleoside (β-D or β-L) or a pharmaceutically acceptable salt thereof of the structure:
<CHM>
wherein the Base is a pyrimidine base represented by the following formula
<CHM>
X is O;
R<NUM> is H and R<NUM> is a monophosphate, a diphosphate, or a triphosphate; or
R<NUM> and R<NUM> are H;
R<NUM> is H; and
R<NUM> is NH<NUM> or OH;
and a pharmaceutically acceptable carrier; for use in therapy.