Background Art Hepatitis B virus (HBV) is a lethal virus, which causes acute/chronic Hepatitis in human body, and finally develops the disease into liver cancer. At present, a remedy for treating the viral disease does not exist though vaccines against the virus have been developed. Up to the present, Ara-A, interferon or the like has been used in treatment of Hepatitis B, however, there are many problems in view of effectiveness and safety.

Recently, various nucleoside compounds having anti-HBV

activity have been reported. For example, 2',3'-dideoxy-3'-thiacytidine [Proc. Natl. Acad. Sci. USA, 88, 8495(1991)], 5-fluoro-2',3'-dideoxy- 3'-thiacytidine [Proc. Natl. Acad. Sci. USA, 88, 8495(1991)], 2',3'- dideoxy- -L-5-fluoro-cytidine [Biochem. Pharm., 47, 171(1994)], 2',3'-dideoxy- -L-5-cytidine [Biochem. Pharm., 47, 171(1994)], etc. are reported as showing anti-HBV activity.

However, these compounds reported up to the present have substantial need to be improved in view of effectiveness and safety.

Therefore, it is required to develop novel compounds having excellent effectiveness with low toxicity.

The inventors have already reported that a racemic nucleoside derivatives expressed by the formula 1, has a remarkable anti-HBV effect (Korea Patent Application No. 96-51536). Now that one isomer from a compound consisting of several stereoisomers exhibits in most cases better efficacy with less side effects, the inventors have completed this invention by preparing the optically active compound of the nucleoside derivative and screening the anti-HBV effects and toxicity of such compound.

An object of this invention is to provide a optically active compound of the nucleoside derivative expressed by the formula 1.

Another object of this invention is to provide a process of manufacturing an optically active compound of the nucleoside derivative expressed by the formula 1.

Further object of this invention is to provide an antiviral agent containing an optically active compound of the nucleoside derivative

expressed by the formula 1. More specifically, the object of this invention is to provide an anti-HBV agent containing an optically active compound of the nucleoside derivative expressed by the formula 1.

Disclosure of the Invention This invention relates to a novel optically active compound of the nucleoside derivative expressed by the following formula 1, its manufacturing method and anti-HBV agent containing the derivative: wherein R1 is hydrogen, phosphate, phosphonate, alkyl or acyl group; R2 is substituted or non-substituted pyrimidine or purine base.

Since a compound expressed by the formula 1 has more than two asymmetric carbon atoms, it may be represented by the following compound expressed by formula la, lb, lc and id: wherein R1 and R2 are same as defined as above.

According to this invention, it is preferred that R1 is hydrogen,

phosphonate or phosphate; R2 is selected from the following groups: wherein R3 is hydrogen, methyl, hydroxymethyl, methoxymethyl, methylthiomethyl, trifluoromethyl, ethyl, propyl, cyclopropyl, vinyl, 2-bromovinyl, fluoro, chloro, bromo, or iodo; R4 is hydrogen, methyl, ethyl, hydroxy, methoxy or acyl of C1~C6; R5 is hydrogen, cyano, carboxyl, alkoxycarbonyl, carbamoyl, or thiocarbamoyl; R6 and R7 are independently hydrogen, hydroxy, amino, fluoro, chloro, bromo or iodo.

An optically active compound of the nucleoside derivative expressed by the following formula 1 according to this invention includes 1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)uracil, <BR> <BR> <BR> 1-(2,3-dideoxy-3 -fluoroapio- p-D-furanosyl)uracil, <BR> <BR> <BR> <BR> 1 -(2,3-dideoxy-3-fluoroapio-a-L-furanosyl)uracil, 1 -(2,3-dideoxy-3-fluoroapio-oc-D-furanosyl)uracil, 1-(2, 3-dideoxy-3 -fluoroapio-p-L-furanosyl)thymine, 1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)thymine,

1-(2,3-dideoxy-3-fluoroapio-α-L-furanosyl)thymine, 1 -(2,3 -dideoxy-3 -fluoroapio-a-D-furanosyl)thymine, 1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-5-fluorouracil, 1 -(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-5-fluorouracil, 1-(2,3-dideoxy-3-fluoroapio-α-L-furanosyl)-5-fluorouracil, 1 -(2,3-dideoxy-3-fluoroapio-a-D-furanosyl)-5-fluorouracil, 1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-5-chlorouracil, 1-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-5-chlorouracil, 1 -(2,3 -dideoxy-3 -fluoroapio-a-L-furanosyl)-5 -chiorouracil, 1 -(2,3 -dideoxy-3-fluoroapio-a-D-furanosyl)-5 -chlorouracil, 1 -(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-5 -bromouracil, 1 -(2,3 -dideoxy-3 -fluoroapio- -D-furanosyl)-5 -bromouracil, 1-(2,3-dideoxy-3-fluoroapio-α-L-furanosyl)-5-bromouracil, 1 -(2,3 -dideoxy-3 -fluoroapio-a-D-furanosyl)-5 -bromouracil, 1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-5-iodouracil, 1 -(2,3 -dideoxy-3 -fluoroapio- -D-furanosyl)-5 -iodouracil, 1 -(2,3 -dideoxy-3 -fluoroapio-a-L-furanosyl)-5 -iodouracil, 1-(2,3-dideoxy-3 -fluoroapio-a-D-furanosyl)-5-iodouracil, 1 -(2,3 -dideoxy-3 -fluoroapio- -L-furanosyl)-2-bromovinyluracil, 1 -(2,3 -dideoxy-3 -fluoroapio- -D-furanosyl)-2-bromovinyluracil, 1 -(2,3 -dideoxy-3 -fluoroapio-a-L-furanosyl)-2-bromovinyluracil, 1 -(2,3 -dideoxy-3 -fluoroapio-a-D-furanosyl)-2-bromovinyluracil, 1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)cytosine, 1 -(2,3 -dideoxy-3-fluoroapio- -D-furanosyl)cytosine, 1 -(2,3 -dideoxy-3 -fluoroapio-a-L-furanosyl)cytosine, 1 -(2,3 -dideoxy-3 -fluoroapio-a-D-furanosyl)cytosine,

1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-5-fluorocytosine, 1-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-5-fluorocytosine, 1-(2,3-dideoxy-3-fluoroapio-a-L-furanosyl)-5-fluorocytosine, 1-(2,3-dideoxy-3-fluoroapio-a-D-furanosyl)-5-fluorocytosine, 1-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-5-methylcytosine, 1-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-5-methylcytosine, <BR> <BR> <BR> <BR> <BR> 1-(2,3-dideoxy-3-fluoroapio-α-L-furanosyl)-5-methylcytosine ,<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> 1-(2,3-dideoxy-3 -fluoroapio-a-D-furanosyl)-5 -methylcytosine,<BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)adenine, <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)adenine, <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3 -dideoxy-3 -fluoroapio-a-L-furanosyl)adenine, <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3 -dideoxy-3 -fluoroapio-a-D-furanosyl)adenine, <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)guanine, 9-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)guanine, <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3 -fluoroapio-a-L-furanosyl)guanine, <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio-α-D-furanosyl)guanine,<BR> ; <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)purine, 9-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)purine, <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3 -fluoroapio-a-L-furanosyl)purine, <BR> <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio-a-D-furanosyl)purine, 9-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-6-hydroxypurine, 9-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-6-hydroxypurine, 9-(2,3-dideoxy-3-fluoroapio-a-L-furanosyl)-6-hydroxypurine, 9-(2,3-dideoxy-3-fluoroapio-α-D-furanosyl)-6-hydroxypurine, 9-(2,3 -dideoxy-3 -fluoroapio- -L-1uranosyl)-6-methylaminopurine, <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-6-m ethylaminopurine,

9-(2,3-dideoxy-3-fluoroapio-a-L-furanosyl)-6-methylaminopuri ne, <BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio-a-D-furanosyl)-6-methylaminopuri ne, <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3 -dideoxy-3 -fluoroapio- -L-furanosyl)-6-chloropurine, 9-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-6-chloropurine, <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio-α-L-furanosyl)-6-chloropurine,& lt;BR> <BR> <BR> <BR> <BR> <BR> <BR> 9-(2,3-dideoxy-3-fluoroapio-α-D-furanosyl)-6-chloropurine, 9-(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-2, 6-diaminopurine, 9-(2,3-dideoxy-3-fluoroapio- -D-furanosyl)-2, 6-diaminopurine, 9-(2,3 -dideoxy-3 -fluoroapio-a-L-furanosyl)-2 ,6-diaminopurine, 9-(2 ,3 -dideoxy-3 -fluoroapio-a-D-furanosyl)-2 ,6-diaminopurine, 2-amino-9-(2, 3-dideoxy-3-fluoroapio- -L-furanosyl)-6-chloropurine, 2-amino-9-(2, 3-dideoxy-3-fluoroapio- -D-furanosyl)-6-chloropurine, <BR> <BR> <BR> <BR> 2-amino-9-(2,3-dideoxy-3-fluoroapio-α-L-furanosyl)-6-chloro purine,<BR> <BR> <BR> <BR> <BR> <BR> 2-amino-9-(2,3-dideoxy-3-fluoroapio-α-D-furanosyl)-6-chloro purine,<BR> <BR> <BR> <BR> <BR> <BR> <BR> 1 -(2,3-dideoxy-3-fluoroapio- -L-furanosyl)-3-carbamoyl- 1,2,4- triazole, 1-(2, 3-dideoxy-3-fluoroapio- -D-furanosyl)-3-carbamoyl-1,2,4- triazole, 1 -(2, 3-dideoxy-3-fluoroapio-a-L-furanosyl)-3-carbamoyl- 1,2,4 - triazole, 1 3 -(2, 3-dideoxy-3-fluoroapio-a-D-furanosyl)-3-carbamoyl- 1,2,4- triazole, etc.

According to this invention, an optically active compound of the nucleoside derivative expressed by the formula 1 may be prepared by the following three methods:

1) Asymmetric synthesis 2) Optical resolution method of the racemic compound expressed by the formula 1 using the enzymes 3) Chemical optical resolution method of the racemic compound of the nucleoside derivative expressed by the formula 1 The inventors have prepared an optically active compound of the nucleoside derivative expressed by the formula 1 by the above three methods.

Method 1) Asymmetric synthesis According to the most general method to obtain an optically active compound of the nucleoside derivative expressed by the formula 1, apiose derivatives having an absolute structure of the following formula 2 or 3 are condensed with appropriate bases, and are separated on column: wherein K8 and Rg are hydrogen, hydroxyl protecting group, preferably alkyl group, acyl group or substituted silyl group, more preferably benzyl group, triphenylmethyl group, acetyl group, benzoyl group, trimethylsilyl group, tertiary butyldimethylsilyl group, or tertiary butyldiphenylsilyl group, respectively; L is acyloxy, halide group or alkoxy group and among them, acetoxy group is preferred.

Thus, optically active compound of the nucleoside derivative expressed by formula 1 wherein Rl is alkyl or acyl can be obtained.

The optically active compound wherein Rl is hydrogen is obtained by the deprotecting reaction of the above-obtained optically active compound. The optically active compound wherein R, is phosphate or phosphonate can be obtained by the reaction with phosphate or phosphonate compound of the optically active compound wherein R is hydrogen, obtained above.

More specifically, optically active compound of the nucleoside derivative expressed by formula 1, according to the present invention, can be obtained by the procedure that comprises the condensation of the compound expressed by formula 2 or 3 with silyl-protected base in the presence of Lewis acid catalyst. Preferred solvents of the condensation reaction include dichloromethane, 1,2- dichloroethane and acetonitrile. Preferred Lewis acid is selected from silyl compounds, such as tin chloride, titanium tetrachloride and trimethylsilyl triplate.

According to this invention, an optically active compound expressed by the formula 2 or 3 is also a novel one designed to use as an intermediate in the manufacture of optically active compound of the nucleoside derivative expressed by the formula 1. This compound can be prepared according to the following reaction scheme 1:

Scheme 1

wherein R8, Rg and L are same as defined above, and R8 and R9 is not same with each other.

More specifically, a process for obtaining an optically active compound of the nucleoside derivative expressed by the formula 1 is conducted in such a manner that: primary alcohol of the well known compound 4 is selectively protected to give a compound 5; the compound 5 is fluorinated by fluorination reagents such as DAST (diethylaminosulfurtrifluoride) to give a compound 6; the protecting group of two primary alcohols from the compound 6 is selectively deprotected to give a compound 7a and 7b; the compound 7a and 7b is cleavaged in the presence of ozone to give lactol 8a and 8b; and the lactol 8 is acylated, alkylated or halogenated to give intermediates 2 and 3.

Method 2) Optical resolution method of the racemic compound expressed by the formula 1 using the enzymes This optical resolution method is based on the principle that, from the D or the L form composing racemic compound, only one optical isomer can be esterificated or de-esterificated selectively by specific enzyme.

The racemic compound wherein Rl is hydrogen in the formula 1, is reacted with some enzymes such as lipase or esterase, thereby to esterificate only one optically active compound selectively. After separating esterificated compound and non-esterificated compound,

the esterificated compound is de-esterificated. Thus, two forms of optically active compound, according to the present invention, of the nucleoside derivative wherein Rl is hydrogen in the formula 1, are obtained separately.

On the other hand, the racemic compound wherein R, is acyl in the formula 1, may be reacted also with some enzymes such as lipase or esterase, thereby to de-esterificate only one optically active compound selectively. After separating de-esterificated compound and non-de-esterificated compound, the non-de-esterificated compound is de-esterificated. Thus, two forms of optically active compound, according to the present invention, of the nucleoside derivative wherein Rl is hydrogen in the formula 1, are obtained separately.

The above lipase or esterase may be obtaind in any one selected from the group consisting of Aspergillus, Mucor, Rhizopus, Penicillium, Candida, Pseudomonas, hog's pancreas (PPL), etc., while esterification reagents include vinyl ester of carboxylic acid having Cl~C20. A substrate used for the selective de-esterification includes acyl ester of C,~C20 derived from racemic compound expressed by the formula 1. The solvents used for this enzymatic reaction include water, organic solvent or co-solvent consisting of water and organic solvent.

Method 3) Chemical Qptical resolution method using optically active compound expressed by the formula 1

An optically active compound of the nucleoside derivative expressed by the formula 1 may be prepared in such a manner that a racemic compound of the nucleoside derivative expressed by the formula 1 is reacted with an optical resolution reagent to give a diastereoisomer salt or complex; the compound is separated by fractional crystallization or column chromatography; and the optical resolution reagent is removed using acid or base. The optical resolution reagents include an optically active amino acid or its derivative, optically active tartaric acid, optically active mandelic acid, an optically active malic acid, camphosulfonic acid and an optically active alkaloids (e.g., quinine, cinchonine and strychnine). As a solvent, water or organic solvent may be used. Meantime, some pharmaceutically acceptable salt may be obtained in such a manner that after dissolving the above compound, so obtained, in an appropriate solvent, the mixture is reacted with acid or base and its preferred salt is a hydrochloride salt.

An object of the present invention is to provide an anti-HBV agent containing an optically active compound of the nucleoside derivative expressed by the formula 1.

The optically active compound of the nucleoside derivative expressed by the formula 1 has 10-500 mg of daily adult dose.

The anti-HBV agent of this invention may be administered orally or parenterally to the body by general method.

The following examples illustrate various aspects of this invention. They are not to be construed to limit the claims in any

manner whatsoever.

Example 1: Synthesis of (2R)-2-hydroxy-2-(benzyloxymethyl)-4- pentene-1-yl-benzoate To a solution of (2S)-2-hydroxy-2-(benzyloxymethyl)-4- penten- 1 -ol (290 mg) in dichloromethane (4 ml), dimethylaminopyridine (32 mg), triethylamine (0.3 ml), and benzoic anhydride (443 mg) were added and the mixture was stirred at room temperature for 2 hours. The resultant mixture was diluted with dichloromethane and washed with 1N hydrochloric acid, saturated sodium bicarbonate solution and brine, successively. The organic layer was dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 8 : 1) to give the titled compound (425 mg, 99.8%) as a white solid.

[α]D20 +4.04 (c 1.68, CHCl3) 1H NMR (CDCl3) 8 : 8.01 (d, 2H), 7.57 (m, 1H), 7.44 (m, 2H), 7.32 7.25 (m, 5H), 5.96~5.86 (m, 1H), 5.14 (dd, 2H), 4.59 (d, 1H), 4.55 (d, 1H), 4.35 (s, 2H), 3.53 (d, 1H), 3.48 (d, 1H), 2.44 (d, 2H) Example 2: Synthesis of (2S)-2-fluoro-2-(benzyloxymethyl)-4- pentene-1-yl-benzoate To a solution of (2R)-2-hydroxy-2-(benzyloxymethyl)-4- pentene- 1 -yl-benzoate (703.6 mg) obtained in Example 1 in dichloromethane (5 ml), diethylaminosulfurtrifluoride (0.5 ml) was

added dropwise at -78 C and the mixture was stirred at the same temperature for 30 minutes. After the reaction temperature was raised up to 0 C, saturated sodium bicarbonate solution was added and the mixture was stirred for 30 minutes. The organic layer was separated, washed with brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 20 : 1) to give the titled compound (540 mg, 76.3%) as a colorless liquid.

E a ]20D +10.580 (c 0.58, CHCl3) lH NMR (CDCl3) 8 : 8.03~8.01 (m, 2H), 7.57 (m, 1H), 7.44 (m, 2H), 7.327.26 (m, 5H), 5.88 -5.82 (m, 1H), 5.20~5.16 (m, 2H), 4.59 (s, 2H), 4.53 (d, 1H), 4.48 (d, 1H), 3.73~3.61 (m, 2H), 2.66 2.59 (m, 2H) Example 3: Synthesis of (2R)-2-fluoro-2-(benzyloxymethyl)-4- pentene-1-ol To a solution of (2 S)-2-fluoro-2-(benzyloxymethyl)-4-penten- 1-yl-benzoate (240 mg) obtained in Example 2 in methanol (4 ml), sodium methoxide (25 wt% solution in methanol, 0.1 ml) was added and the mixture was stirred at room temperature for 1 hour. The resultant mixture was diluted with ethylacetate (50 ml), washed with saturated ammonium chloride solution and brine, dried over anhydrous magnesium sulfate, filtered and concentrated. The residue was purified by silica gel column chromatography (n-hexane ethylacetate = 5: 1) to give the titled compound (180 mg, 97.6%) as a

colorless liquid.

[ a PO +3.59 (c 0.72, CHCl3) 'H NMR (CDCl3) a : 7.39~7.31 (m, 5H), 5.85~5.79 (m, 1H), 5.18~5.14 (m, 2H), 4.60 (d, 1H), 4.56 (d, 1H), 3.77 (d, 1H), 3.72 (d, 1H), 3.68~3.58 (m, 2H), 2.55~2.47 (m, 2H), 2.17~2.10 (m, 1H) Example 4: Synthesis of (2R)-2-fluoro-2-(hydroxymethyl)-4- pentene-1-yl-benzoate To a solution of (2S)-2-fluoro-2-(benzyloxymethyl)-4- pentene- 1 -yl-benzoate (300 mg) obtained in Example 2 in dichloromethane (5 ml), borontrichloride (1M solution in dichloromethane, 4.5 ml) was added at -78~C and the mixture was stirred at the same temperature for 1 hour. A mixed solution (10 ml) of dichloromethane and methanol (1 : 1) was added to the mixture dropwise with stirring at the same temperature and the mixture was allowed to warm to 0 0C. n-Hexane was added to the mixture, and impurity was removed by short silica gel column chromatography.

After removal of solvent, the residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 5 : 1) to give the titled compound (166.7 mg, 76.5%) as a colorless liquid.

[α]D20 -15.69~ (c 0.66, CHCl3) 'H NMR (CDCl3) # : 8.07~8.05 (m, 2H), 7.617.57 (m, 1H), 7.48~7.44 (m, 2H), 5.90~5.83 (m, 1H), 5.23~5.19 (m, 2H), 4.58 4.44 (m, 2H), 3.78 (d, 1H), 3.74 (d, 1H), 2.64~2.57 (m, 2H), 2.28 2.15 (m, 1H)

Example 5: Synthesis of 2,3-dideoxy-3'-O-benzyl-3-fluoroapio-L- furanosyl acetate To a solution of (2R)-2-fluoro-2-(benzyloxymethyl)-4- pentene-l-ol (180 mg) obtained in Example 3 in ethylacetate (5 ml)., the ethylacetate solution saturated with ozone was slowly added to the mixture dropwise at -78~C and the mixture was stirred at the same temperature for 2 hours. Methylsulfide (1.5ml) was added to the mixture and the resultant mixture was stirred overnight. After concentrating the mixture, the residue was dissolved in dicloromethane (4 ml) and dimethylaminopyridine (17 mg), triethylamine (0.1 ml) and acetic anhydride (0.1 ml) were added, successively. After stirring for 1 hour, the mixture was diluted with dichloromethane, washed with 1N hydrochloric acid, saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 5 1) to give the titled compound (140 mg, 65%) as a mixture (4:1) of two stereoisomers.

'H NMR (CDCl3) 8 : 7.39~7.26 (m, 5H), 6.44 (dd, 1H), 4.66 4.63 (d, 2H), 4.22~4.02 (m, 2H), 3.80 - 3.62 (m, 2H), 2.65~2.21 (m, 2H), 2.09 (s, 3H) Example 6: Synthesis of 2,3-dideoxy-3'-O-benzoyl-3-fluoroapio- D-furanosyl acetate The title compound (146 mg, 74%) as a mixture (5:1) of two

stereoisomers was obtained in the same manner as described in Example 5, using (2R)-2-fluoro-2-(hydroxymethyl)-4-pentene 1 -yl- benzoate obtained in Example 4 instead of (2R)-2-fluoro-2- (benzyloxymethyl)-4-pentene- 1 -ol.

'H NMR (CDCl3) # : 8.07--8.03 (m, 2H), 7.62--7.58 (m, 1H), 7.49--7.45 (m, 2H), 6.51 (dd, 1H), 4.69-4.54 (m, 2H), 4.32-4.09 (m, 2H), 2.74~2.32 (m, 2H), 2.03 (s, 3H) Example 7: Synthesis of (-)-N4-acetyl-1-(3'-O-benzyl-2,3-dideoxy- 3-fluoroapio- -L-furanosyl) cytosine and (+)-N4-acetyl-1-(3'-O- benzyl-2,3-dideoxy-3-fluoroapio- a -L-furanosyl) cytosine A stirred suspension of N4-acetylcytosine (183 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane (10 ml) was heated to reflux under nitrogen until a clear resolution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (10 ml) followed by 2,3-dideoxy-3'-O-benzyl-3-fluoroapio-L-furanosyl acetate (160 mg) in dichloromethane (5 ml). This suspension was cooled in an ice/water bath to 5~C, and treated with trimethylsilyltrifluoromethane sulfonate (0.23 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (5 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The solution was diluted with dichloromethane, and the organic layer was

separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 5 : 1) to give the titled compounds ( -form: 72 mg, 33.5%; and a -form: 70 mg, 32.6%) as a white solid, respectively.

P-form : 'H NMR (CDCl3) # : 9.57 (m, 1H), 7.81 (d, 1H), 7.39 (d, 1H), 7.377.26 (m, 5H), 6.17 (t, 1H), 4.58 (d, 1H), 4.54 (d, 1H), 4.29 ~4.19 (m, 2H), 3.74~3.60 (m, 2H), 3.05~2.94 (m, 1H), 2.31~2.18 (m, 1H), 2.27 (s, 3H) α-form : H NMR (CDCl3) # : 9.79~9.76 (m, 1H), 7.92 (d, 1H), 7.44 (d, 1H), 7.38~7.26 (m, 5H), 6.18 (dd, 1H), 4.60 (d, 1H), 4.55 (d, 1H), 4.51~4.10 (m, 2H), 3.75~3.60 (m, 2H), 2.732.42 (m, 2H), 2.27 (s, 3H) Example 8: Synthesis of (+)-N4-acetyl-1-(3'-O-benzoyl-2,3- dideoxy-3-fluoroapio- -D-furanosyl) cytosine and (-)-N4-acetyl- 1-(3'-O-benzoyl-2,3-dideoxy-3-fluoroapio-α-D-furanosyl) cytosine A stirred suspension of N4-acetylcytosine (178 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane (10 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (10

ml) followed by 2,3-dideoxy-3 '-O-benzoyl-3 -fluoroapio-D-furanosyl acetate (164 mg) in dichloromethane (5 ml). This suspension was cooled in an ice/water bath to 50C, and treated with trimethylsilyltrifluoromethanesulfonate (0.22 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (5 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The solution was diluted with dichloromethane, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 3 : 1) to give the titled compounds ( -form: 60 mg, 27.6%; and a -form: 65 mg, 29.9%) as a white solid, respectively. form : [a]20 +61.100 (c 0.3, CHCl3) ; lH NMR (CDCl3) # : 8.64 (m, 1H), 8.02~8.00 (m, 2H), 7.83 (d, 1H), 7.62~7.58 (m, 1H), 7.48~7.41 (m, 3H), 6.15 (t, 1H), 4.69~4.54 (m, 2H), 4.43 4.29 (m, 2H), 3.22~3.12 (m, 1H), 2.44~2.31 (m, 1H), 2.24 (s, 3H) a -form : [α]D20 -72.97~ (c 0.33, CHCl3) ; 'H NMR (CDCl3) 8 : 9.24 (m, 1H), 8.04~8.02 (m, 2H), 7.94 (d, 1H), 7.62~7.58 (m, 1H), 7.48~7.44 (m, 3H), 6.25 (dd, 1H), 4.67~4.53 (m, 3H), 4.22 (dd, 1H), 2.85~2.62 (m, 2H), 2.26 (s, 3H) Example 9: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- -L- furanosyl) cytosine

To a solution of (-)-N4-acetyl-1-(3'-O-benzyl-2,3-dideoxy-3- fluoroapio- -L-furanosyl) cytosine (72 mg) in dichloromethane (5 ml), borontrichloride (1.OM solution in dichloromethane, 1 ml) was added at -78~C and the mixture was stirred at the same temperature for 1 hour. A mixed solution (5 ml) of dichloromethane and methanol (1 : 1) was added to the mixture dropwise at the same temperature and the reaction mixture was allowed to warm to O oc. Sodium bicarbonate (20 mg) was added and the mixture was stirred for 10 minutes, filtered and concentrated. To the residue was added methanol (4 ml) followed by sodium methoxide (25 wt% solution in methanol, 0.05 ml) at room temperature. This solution was stirred for 1 hour and neutralized with methanol saturated by hydrochloric acid gas, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 8 :1) to give the title compound (40 mg, 87%) as a white solid.

[ a ]20D -44.410 (c 0.18, CH3OH) UV (H20) A max : 270.5, 224.0 (sh) nm (pH 7), 279.1, 212.5 (sh) nm (pH 2)271.1 nm (pH 11) H NMR (DMSO-d6) 8 : 7.61 (d, 1H), 7.16-- 7. 12 (m, 2H), 6.11 (t, 1H), 5.70 (d, 1H), 5.23 (t, 1H), 4.19 (dd, 1H), 3.94 (dd, 1H), 3.71 3.63 (m, 2H), 2.48~2.20 (m, 2H) Example 10: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- a -L- furanosyl) cytosine The title compound (39 mg, 87.6%) as a white solid was

obtained in the same manner as described in Example 9, using (+)-N4- acetyl-1-(3'-O-benzyl-2,3-dideoxy-3-fluoroapio-α-L-furanosy l) cytosine (70 mg) obtained in Example 7 instead of (-)-N4-acetyl- 1 -(3'- O-benzyl-2,3-dideoxy-3-fluoroapio- P -L-furanosyl) cytosine.

[a]20 +110.87 (c 0.18,CH3OH) UV (H2O) A max : 270.8, 225.0 (sh) nm (pH 7), 279.7, 210.7 (sh) nm (pH 2), 270.1 nm (pH 11) H NMR (DMSO-d6) 8 : 7.54 (d, 1H), 7.12~7.03 (m, 2H), 6.03 (dd, 1H), 5.71 (d, 1H), 5.25 (m, 1H), 4.30~4.27 (m, 1H), 3.95 (dd, 1H), 3.65~3.58 (m, 2H), 2.66~2.04 (m, 2H) Example 11: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- -D- furanosyl) cytosine To a solution of (+)-N4-acetyl-1-(3'-O-benzoyl-2,3-dideoxy-3- fluoroapio- -D-furanosyl) cytosine (60 mg) obtained in Example 8 in methanol (4 ml), sodium methoxide (25wt% solution in methanol, 0.1 ml) was added and the mixture was stirred for 2 hours at room temperature. The resulting solution was neutralized with methanol saturated by hydrochloride gas, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane methanol = 8 1) to give the titled compound (34 mg, 92.6%) as a white solid.

[α]D20 +48.67~ (c 0.17, CH3OH) UV (H2O) A max : 271.3, 225.0 (sh) nm (pH 7), 278.6, 211.2 (sh) nm (pH 2), 270.8 nm (pH 11)

'H NMR (DMSO-d6) 8 : 7.60 (d, 1H), 7.16~7.08 (m, 2H), 6.10 (t, 1H), 5.70 (d, 1H), 5.23 (t, 1H), 4.19 (dd, 1H), 3.94 (dd, 1H), 3.71 3.63 (m, 2H), 2.48~2.18 (m, 2H) Example 12: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- a -D- furanosyl) cytosine The titled compound (39 mg, 98%) as a white solid was obtained in the same manner as described in Example 11, using (-)- N4-acetyl-1-(3'-O-benzoyl-2,3-dideoxy-3-fluoroapio- a -D-furanosyl) cytosine (65 mg) obtained in Example 8 instead of (+)-N4-acetyl-1- (3'-O-benzoyl-2,3-dideoxy-3-fluoroapio- P -D-furanosyl) cytosine.

[a ]20D 84.960 (c 0.95, CH30H) UV (H2O) A max : 270.3, 226.0 (sh) nm (pH 7), 279.0, 211.7 (sh) nm (pH 2), 270.6 nm (pH 11) H NMR (DMSO-d6) 8 : 7.54 (d, 1H), 7.11~7.03 (m, 2H), 6.03 (dd, 1H), 5.71 (d, 1H), 5.24 (t, 1H), 4.25 (dd, 1H), 3.94 (dd, 1H), 3.67 3.58 (m, 2H), 2.62~2.07 (m, 2H) Example 13: Synthesis of (-)-N4-benzoyl-1-(3'-O-benzyl-2,3- dideoxy-3-fluoroapio- -L-furanosyl)-5-fluorocytosine and (+)- N4-benzoyl-1-(3'-O-benzyl-2,3-dideoxy-3-fluoroapio-α-L- furanosyl)-5-fluorocytosine A stirred suspension of N4-benzoyl-5-fluorocytosine (350 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane

(10 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (10 ml) followed by 2,3-dideoxy-3'-0-benzyl-3 -fluoroapio-L-furanosyl acetate (120 mg) in dichloromethane (S ml). This suspension was cooled in an ice/water bath to 50C, and treated with trimethylsilyltrifluoromethanesulfonate (0.17 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (5 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The solution was diluted with dichloromethane, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 5 : 1) to give the titled compounds ( -form: 82 mg, 41.5%; and a -form: 76 mg, 38.5%). <BR> <BR> <BR> <BR> <BR> <P> -form : H NMR (CDCl3) # : 12.9 (bs, 1H), 8.29~7.26 (m, 11H), 6.2 (ps t, 1H), 4.59 (d, 2H), 4.31~4.20 (m, 2H), 3.72~3.64 (m, 2H), 3.10~2.8 (m, 1H), 2.36~2.04 (m, 1H) α-form : H NMR (CDCl3) # : 13.1 (bs, 1H), 8.28~7.30 (m, 11H), 6.20 (d, 1H), 4.60 (d, 2H), 4.44 (m, 1H), 4.10 (dd, 1H), 3.77~3.64 (m, 2H), 2.75~2.61 (m, 1H), 2.41 (m, 1H) Example 14: Synthesis of (+)-N4-benzoyl-1-(3'-O-benzoyl-2,3-

dideoxy-3-fluoroapio- -D-furanosyl)-5-fluorocytosine and (-)-N4- benzoyl-1-(3'-O-benzoyl-2,3-dideoxy-3-fluoroapio- a -D- furanosyl)-5-fluorocytosine A stirred suspension of N4-benzoyl-5-fluorocytosine (500 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane (30 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (10 ml) followed by 2,3-dideoxy-3'-0-benzoyl-3-fluoroapio-D-furanosyl acetate (300 mg) in dichloromethane (5 ml). This suspension was cooled in an ice/water bath to 50C, and treated with trimethylsilyltrifluoromethanesulfonate (0.41 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (5 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The solution was diluted with dichloromethane, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 5 : 1) to give the titled compounds ( -form: 175 mg, 36.1%; and a -form: 230 mg, 47.5%). <BR> <BR> <BR> <BR> <BR> <BR> form: 'H NMR (CDCl3) # : 13.1 (bs, 1H), 8.277.44 (m, 1111), 6.14 (t, 1H), 4.72~4.57 (m, 2H), 4.35 (m, 2H), 3.0 (m, 1H), 2.47 2.33 (m, 1H)

α-form : H NMR (CDCl3) # : 13.1 (bs, 1H), 8.29~7.44 (m, 11H), 6.27 (d, 1H), 4.70~4.54 (m, 3H), 4.20~4.09 (dd, 1H), 2.82-2.57 (m, 2H) Example 15: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- P -L- furanosyl)-5-fluorocytosine To a solution of (-)-N4-benzoyl-1-(3'-O-benzyl-2,3-dideoxy-3- fluoroapio- -L-furanosyl)-5-fluorocytosine (75 mg) in dichloromethane (10 ml), borontrichloride (1.OM solution in dichloromethane, 0.85 ml) was added at -78~C and the mixture was stirred at the same temperature for 1 hour. A mixed solution (5 ml) of dichloromethane and methanol (1 : 1) was added to the mixture dropwise at the same temperature and the reaction mixture was allowed to warm to O C. Sodium bicarbonate (20 mg) was added and the mixture was stirred for 10 minutes, filtered and concentrated. To the residue was added methanol (4 ml) followed by sodium methoxide (25 wt% solution in methanol, 0.05 ml) at room temperature. This solution was stirred for 1 hour and neutralized with dry ice, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 10 : 1) to give the title compound (32 mg, 76%) as a white solid.

[α]D20 -96.1~ (c 0.12, CH3OH) UV (H2O) A max: 280, 234.0 (sh) nm (pH 7) 290, 222 (sh) nm (pH 2) 280, 234 (sh) nm (pH 11)

'H NMR (DMSO-d6) 8 : 7.92 (d, 1H), 7.7~7.48 (m, 2H), 6.09 (t, 1H), 5.23 (m, 1H, OH), 4.23 (dd, 1H), 3.93 (dd, 1H), 3.70~3.57 (m, 2H), 2.48~2.29 (m, 1H), 2.20~2.19 (m, 1H) Example 16: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- a -L- furanosyl)-5-fluorocytosine The titled compound (28 mg, 71.6%) as a white solid was obtained in the same manner as described in Example 15, except using (+)-N4-benzoyl- 1 -(3'-O-benzyl-2,3-dideoxy-3-fluoroapio- a -L- furanosyl)-5-fluorocytosine (70 mg) obtained in Example 13 instead of (-)-N4-benzoyl- 1 -(3 '-0-benzyl-2,3 -dideoxy-3 -fluoroapio- -L- furanosyl)-5 -fluorocytosine.

[a]2% +91.30(c 0.10,CH3OH) UV (H2O) A max: 280, 234.0 (sh) nm (pH 7) 290, 222 (sh) nm (pH 2) 280, 234 (sh) nm (pH 11) H NMR (DMSO-d6) 8 : 7.68 (d, 1H), 7.68~7.47 (m, 211), 5.97 (d, 1H), 5.25 (bs, 1H), 4.38~4.30 (m, 1H), 4.0~3.89 (dd, 1H), 3.65 3.58 (m, 2H), 2.63~2.49 (m, 1H), 2.2~2.1 (m, 1H) Example 17: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- -D- furanosyl)-5-fluorocytosine To a solution of (+)-N4-benzoyl-1-(3'-O-benzoyl-2,3-dideoxy- 3-fluoroapio- -D-furanosyl)-5-fluorocytosine (155 mg) obtained in Example 14 in methanol (20 ml), sodium methoxide (25 wt% solution

in methanol, 0.2 ml) was added and the mixture was stirred for 24 hours at room temperature. The resulting solution was neutralized with dry ice, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 10 : 1) to give the titled compound (74 mg, 87.9%) as a white solid.

[α]D20 +95.8~ (c 0.12, CH3OH) Uv(H2O) A max: 280, 238 (sh) nm (pH 7) 286, 218 (sh) nm (pH 2) 280, 236 (sh) nm (pH 11) H NMR (DMSO-d6) # : 7.92 (d, 1H), 7.78 ~ 7.53 (m, 2H), 6.09 (t, 1H), 5.22 (t, 1H), 4.23 (dd, 1H), 3.92 (dd, 1H), 3.71 3.63 (m, 2H), 2.41 (m, 1H), 2.17 (m, 1H) Example 18: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- a -D- furanosyl)-5-fluorocytosine The titled compound (108 mg, 94.7%) as a white solid was obtained in the same manner as described in Example 17, using (-)- N4-benzoyl-1-(3'-O-benzyl-2,3-dideoxy-3-fluoroapio-α-D- furanosyl)-5-fluorocytosine (210 mg) obtained in Example 14 instead of (+)-N4-benzoyl-1-(3'-O-benzoyl-2,3-dideoxy-3-fluoroapio- -D- furanosyl)-5-fluorocytosine.

[α]D20 -9l.40(c 0.10, CH30H) UV (H2O) A max: 280, 234.0 (sh) nm (pH 7) 288,218 (sh) nm (pH 2) 280, 236 (sh) nm (pH 11)

H NMR (DMSO-d6) 8 : 7.92 (d, 1H), 7.9 -- 7.47 (m, 2H), 5.97 (d, 1H), 5.25 (t, 1H), 4.38~4.30 (m, 1H), 3.94 (dd, 1H), 3.66~3.58 (m, 2H), 2.50- 2.47 (m, 1H), 2.15 (m, 1H) Example 19: Synthesis of (+)-1-(3'-0-benzyl-2,3-dideoxy-3- fluoroapio- -L-furanosyl) thymine and (+)-1-(3'-0-benzyl-2,3- dideoxy-3-fluoroapio- a -L-furanosyl) thymine A stirred suspension of thymine (658 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane (25 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (30 ml) followed by 2,3-dideoxy-3'-O-benzyl-3-fluoroapio-L-furanosyl acetate (700 mg) in dichloromethane (10 ml). This suspension was cooled in an ice/water bath to 5~C, and treated with trimethylsilyltrifluoromethane sulfonate (0.76 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (10 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The solution was diluted with dichloromethane, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 2 : 1) to give the titled

compounds ( -form: 345 mg, 40%; and a -form: 355 mg, 40.7%). <BR> <BR> <BR> <BR> <BR> <BR> <P>P-form :111 NMR (CDCl3) 8 : 8.25 (s, 1H), 7.39~7.31 (m, 5H), 7.12 (s, 1H), 6.22 (dd, 1H), 4.61 (dd, 2H), 4.32~4.12 (m, 2H), 3.75 3.68 (m, 2H), 2.73~2.68 (m, 1H), 2.40~2.26 (m, H), 1.86 (s, 3H). <BR> <BR> <BR> <BR> <BR> a-form :111 NMR (CDCl3) 8 : 8.19 (s, 1H), 7.40~7.31 (m, 5H), 7.36 (s, 1H), 6.24 (dd, 1H), 4.60 (dd, 1H), 4.44~4.36 (m, 1H), 3.99 (dd, 1H), 3.76~3.63 (m, 2H), 2.732.58 (m, 1H), 2.36~2.30 (m, 1H), 1.94 (s, 3H).

Example 20: Synthesis of (-)-1-(3'-O-benzoyl-2,3-dideoxy-3- fluoroapio- -D-furanosyl) thymine and (-)-1-(3'-O-benzoyl-2,3- dideoxy-3-fluoroapio- a -D-furanosyl) thymine A stirred suspension of thymine (446 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane (30 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (10 ml) followed by 2,3-dideoxy-3 '-O-benzoyl-3 -fluoroapio-D-furanosyl acetate (400 mg) in dichloromethane (10 ml). This suspension was cooled in an ice/water bath to 50C, and treated with trimethylsilyltrifluoromethane sulfonate (1.42 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (10 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The

solution was diluted with dichloromethane, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 10 : 1) to give the titled compounds ( -form: 221 mg, 44.8%; and a -form: 200 mg, 40.5%). <BR> <BR> <BR> <BR> <BR> <P>P-form :111 NMR (CDCl3) # : 8.27 (bs, 1H), 8.03 (m, 2H), 7.60 (m, 1H), 7.47 (m, 2H), 7.11 (d, 1H), 6.14 (t, 1H), 4.73~4.57 (m, 2H), 4.424.23 (m, 2H), 2.86~2.80 (m, 1H), 2.52~2.38 (m, 1H) a -form :111 NMR (CDCl3) # : 8.22 (m, 1H), 8.04 (m, 2H), 7.62 (m, 1H), 7.48 (m, 2H), 7.35 (d, 1H), 6.32 (dd, 1H), 4.70~4.47 (m, 3H), 4.04 (dd, 1H), 2.80~2.53 (m, 1H), 2.53~2.47 (m, 1H) Example 21: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- -L- furanosyl) thymine To a solution of(+)-l -(3'-0-benzyl-2,3-dideoxy-3-fluoroapio- P -L-furanosyl) thymine (220 mg) obtained in Example 19 in dichloromethane (30 ml), borontrichloride (1.OM solution in dichloromethane, 4 ml) was added at -780C and the mixture was stirred at the same temperature for 1 hour. A mixed solution (20 ml) of dichloromethane and methanol (1 : 1) was added to the mixture dropwise at the same temperature and the reaction mixture was allowed to warm to O 0C. Sodium bicarbonate (100 mg) was added and the mixture was stirred for 30 minutes, filtered and concentrated. The residue was purified by silica gel column chromatography (n-hexane:

ethylacetate = 1 1:10) to give the title compound (95 mg, 59.1%) as a white solid.

[α]D20 +10.02~ (c 0.18, CH3OH) UV (H2O) A max : 266 nm (pH 7), 268 nm (pH 2), 268 nm (pH 11). <BR> <BR> <BR> <BR> <BR> <P> H NMR (DMSO-d6) # : 11.31 (s, 1H), 7.56 (d, 1H), 6.14 (dd, 1H), 5.26 (t, 1H ), 4.21 (dd, 1H), 3.98~3.90 (m, 1H), 3.73~3.66 (m, 2H), 2.50~2.27 (m, 2H), 1.78 (d, 3H).

13C NMK (CD3OD) :11.36, 39.41 (d), 62.87 (d), 75.16 (d), 87.61, 104.51(d), 110.71, 137.30, 151.25, 165.4.

Example 22: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- a -L- furanosyl) thymine The titled compound (120 mg, 71.4%) as a white solid was obtained in the same manner as described in Example 21, using (+)- 1- (3'-O-benzyl-2,3-dideoxy-3-fluoroapio- a -L-furanosyl) thymine (230 mg) obtained in Example 19 instead of (+)-1-(3'-O-benzyl-2,3- dideoxy-3-fluoroapio- -L-furanosyl) thymine.

[α]D20 +15.43~ (c 0.10, CH3OH) UV (H2O) A max : 268 nm (pH 7), 268 nm (pH 2), 268 nm (pH 11).

H NMR (DMSO-d6) 8 :11.30 (s, 1H), 7.39 (s, 1H), 6.08 (dd, 1H), 5.28 (t, 1H), 4.31~4.23 (m, 1H), 3.90 (dd, 1H), 3.68~3.59 (m, 2H), 2.63~2.48 (m, 1H), 2.17~2.14 (m, 1H), 1.77 (s, 3H).

13C NMR (CD3OD) 8 :11.61, 40.15 (d), 62.70 (d), 75.57 (d), 86.39, 103.80(d), 110.21,136.58,151.27, 165.44.

Example 23: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- -D- furanosyl) thymine To a solution of (-)-1 -(3'-0-benzoyl-2,3-dideoxy-3-fluoroapio- p -D-furanosyl) thymine (180 mg) obtained in Example 20 in methanol (20 ml), sodium methoxide (25 wt% solution in methanol, 0.2 ml) was added and the mixture was stirred for 3 hours at room temperature. The resulting solution was neutralized with dry ice, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 10 : 1) to give the titled compound (85mg, 68.2%) as a white solid.

[α]D20 -11.8~ (c 0.11, CH3OH) UV (H20) A max: 266 nm (pH 7), 268 nm (pH 2), 266 nm (pH 11) 'H NMR (DMSO-d6) : 11.3 (bs, 1H), 7.56 (s, 1H), 6.14 (dd, 1H), 5.25 (t, 1H), 4.22 (dd, 1H), 3.93 (dd, 1H), 3.74~3.66 (m, 2H), 2.43 2.26 (m, 211), 1.77 (s, 3H) 13C NMR (CD3OD) 8 :11.33, 39.40 (d), 62.85 (d), 75.15 (d), 87.60, 104.48 (d), 110.70, 137.28, 151.25, 165.4.

Example 24: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- a -D- furanosyl) thymine The titled compound (60 mg, 85.5%) as a white solid was obtained in the same manner as described in Example 23, using (-)- 1 - (3'-0-benzoyl-2,3 -dideoxy-3 -fluoroapio- a -D-furanosyl) thymine (100 mg) obtained in Example 20 instead of (-)-1-(3'-0-benzoyl-2,3-

dideoxy-3-fluoroapio- -D-furanosyl) thymine.

[a]20 -14.780(c 0.11, CH30H) UV (H2O) A max : 268 nm (pH 7), 268 nm (pH 2), 266 nm (pH 11).

'H NMR (DMSO-d6) 8 :11.3 (bs, 1H), 7.39 (s, 1H), 6.08 (dd, 1H), 5.27 (t, 1H), 4.30~4.22 (m, 1H), 3.89 (dd, 1H), 3.68~3.59 (m, 2H), 2.64~2.49 (m, 1H), 2.22 (m, 1H), 1.22 (s, 3H) 13C NMR (CD3OD) 8 : 11.60, 40.13 (d), 62.71(d), 75.58 (d), 86.41, 103.81(d), 110.21, 136.56, 151.30, 165.44.

Example 25: Synthesis of (+)-1-(3'-0-benzyl-2,3-dideoxy-3- fluoroapio- -L-furanosyl)-5-ethyluracil and (+)-i-(3'-O-benzyl- 2,3-dideoxy-3-fluoroapio-α-L-furanosyl)-5-ethyluracil A stirred suspension of 5-ethyluracil (125 mg) and ammonium sulfate (catalytic amount) in a mixed solution of hexamethyldisilazane (5 ml) and acetonitrile (10 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added chloroform (15 ml) followed by 2,3-dideoxy-3'-O-benzyl-3-fluoroapio-L-furanosyl acetate (120 mg) in chloroform (5 ml). This suspension was cooled in an ice/water bath to 5 C, and treated with trimethylsilyltrifluoromethane sulfonate (0.17 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (5 ml) was added to the mixture and the mixture was allowed

to warm to room temperature and stir for 20 minutes. The solution was diluted with chloroform, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane: ethylacetate = 2 1) to give the titled compounds (P-form: 37 mg, 23.9%; and a -form: 90 mg, 58.1%). form : 'H NM1R (CDCl3) S: 9.42 (s, 1H), 7.37~7.26 (m, 5H), 7.06 (s, 1H), 6.20 (t, 1H), 4.60 (s, 2H), 4.33~4.12 (m, 2H), 3.75 3.71 (m, 2H), 2.78-2.67 (m, 1H), 2.44~2.32 (m, 1H), 2.32~2.27 (m, 2H), 1.08 (t, 3H) a-form :111 NMR (CDCl3) d: 9.75 (s, 1H), 7.37~7.31 (m, 6H), 6.28 (dd, 1H), 4.59 (dd, 2H), 4.43 4.34 (m, 1H), 3.97 (dd, 1H), 3.75 3.61 (m, 2H), 2.70~2.57 (m, 1H), 2.38~2.25 (m, 3H), 1.11 (t, 3H) Example 26: Synthesis of (-)-l-(3'-O-benzoyl-2,3-dideoxy-3- fluoroapio-B -D-furanosyl)-5-ethyluracil and (-)-4-(3 '-O-benzoyl- 2,3-dideoxy-3-fluoroapio-α-D-furanosyl)-5-ethyluracil A stirred suspension of 5-ethyluracil (159 mg) and ammonium sulfate (catalytic amount) in a mixed solution of hexamethyldisilazane (5 ml) and acetonitrile (10 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added chloroform (15 ml)

followed by 2,3-dideoxy-3'-O-benzoyl-3-fluoroapio-D-furanosyl acetate (200 mg) in chloroform (5 ml). This suspension was cooled in an ice/water bath to 5 C, and treated with trimethylsilyltrifluoromethane sulfonate (0.25 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (10 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The solution was diluted with chloroform, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 2 : 1) to give the titled compounds form: 100 mg, 41.0%; and α-form: 90 mg, 51.2%). <BR> <BR> <BR> <BR> <BR> <P> P-form : H NMR (CDCl3) d: 8.83 (s, 1H), 8.08~8.05 (m, 2H), 7.65~7.61 (m, 1H), 7.517.47 (m, 2H), 7.08 (s, 1H), 6.15 (t, 1H), 4.76~4.61 (m, 2H), 4.46~4.26 (m, 2H), 2.95~2.82 (m, 1H), 2.61 2.49 (m, 1H), 2.38 (q, 2H), 1.14 (t, 311) <BR> <BR> <BR> <BR> <BR> α-form : H NMR (CDCl3) # : 8.77 (s, 1H), 8.05~8.02 (m, 2H), 7.62~7.58 (m, 1H), 7.49~7.45 (m, 2H), 7.32 (s, 1H), 6.34 (dd, 1H), 4.694.52 (m, 2H), 4.53~4.46 (m, 1H), 4.05 (dd, 1H), 2.81 2.65 (m, 1H), 2.51 2.40 (m, 1H), 2.37 (q, 2H), 1.13 (t, 3H) Example 27: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- -L- furanosyl)-5-ethyluracil To a solution of (+)-1-(3'-O-benzyl-2,3-dideoxy-3-fluoroapio-

p -L-furanosyl)-5-ethyluracil (37 mg) obtained in Example 25 in dichloromethane (5 ml), borontrichloride (1.OM solution in dichloromethane, 0.85 ml) was added at -78 0C and the mixture was stirred at the same temperature for 2 hours. A mixed solution (5 ml) of dichloromethane and methanol (1 : 1) was added to the mixture dropwise at the same temperature and the reaction mixture was allowed to warm to 0 C. Sodium bicarbonate (20 mg) was added and the mixture was stirred for 30 minutes, filtered and concentrated. The residue was purified by silica gel column chromatography (n-hexane ethylacetate = 1 : 20) to give the title compound (17 mg, 62%) as a white solid.

[a]20 +11.780 (c 0.10, CH30H) UV (H2O) A max: 268 nm (pH 7), 268 nm (pH 2), 266 nm (pH 11).

'H NMR (DMSO-d6) d : 7.45 (s, 1H), 6.20 (dd, 1H), 4.31 (dd, 1H), 4.12~4.04 (m, 1H), 3.85~3.79 (m, 2H), 2.59~2.32 (m, 2H), 2.32 (q, 2H), 1.12 (t, 3H) Example 28: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- a -L- furanosyl)-5-ethyluracil The titled compound (40 mg, 60%) as a white solid was obtained in the same manner as described in Example 27, using (+)-1- <BR> <BR> <BR> <BR> (3'-O-benzyl-2,3-dideoxy-3-fluoroapio-α-L-furanosyl)-5-ethy luracil (90 mg) obtained in Example 25 instead of (+)-1-(3'-0-benzyl-2,3- dideoxy-3-fluoroapio- -L-furanosyl)-5-ethyluracil.

[α]D20 +12.51~ (c 0.11, CH3OH)

W (H20) A max : 268 nm (pH 7), 268 nm (pH 2), 266 nm (pH 11).

H NMR (CD3OD) 8 : 7.48 (s, 1H), 6.22 (dd, 1H), 4.38~4.33 (m, 1H), 4.03 (dd, 1H), 3.83~3.72 (m, 2H), 2.77~2.61 (m, 1H), 2.36 2.27 (m, 3H), 1.11 (t, 3H) Example 29: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- -D- furanosyl)-5-ethyluracil To a solution of (+)-1-(3'-O-benzoyl-2,3-dideoxy-3-fluoroapio- p -D-furanosyl)-5-ethyluracil (85 mg) obtained in Example 26 in methanol (20 ml), sodium methoxide (25wt% solution in methanol, 0.2 ml) was added and the mixture was stirred for 3 hours at room temperature. The resulting solution was neutralized with dry ice, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 15 : 1) to give the titled compound (34 mg, 63%) as a white solid.

[α ]20D -12.680 (c 0.09, CH30H) uV (H20) A max: 268 nm (pH 7), 268 nm (pH 2), 266 nm (pH 11) 'H NMR (DMSO-d6) 8 : 11.29 (s, 1H), 7.48 (s, 1H), 6.14 (dd, 1H), 5.27 (t, 1H), 4.21 (dd, 1H), 3.99~3.92 (m, 1H), 3.73~3.66 (m, 2H), 2.49~2.20 (m, 2H), 2.21 (q, 2H), 1.02 (t, 3H) Example 30: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio-α-D- furanosyl)-5-ethyluracil The titled compound (65.8 mg, 89%) as a white solid was obtained in the same manner as described in Example 29, using (-)-1-

(3'-O-benzoyl-2,3-dideoxy-3-fluoroapio-α-D-furanosyl)-5- ethyluracil (100 mg) obtained in Example 26 instead of (-)-1-(3'-0- benzoyl-2,3-dideoxy-3-fluoroapio- -D-furanosyl)-5-ethyluracil.

[aY0 -11.94~ (c 0.11, CH30H) uV (H20) A max : 268 nm (pH 7), 268 nm (pH 2), 266 nm (pH 11). lH NMR (DMSO-d6) 8 :11.3 (s, 1H), 7.33 (s, 1H), 6.12 (dd, 1H), 5.28 (t, 1H), 4.304.22 (m, 1H), 3.90 (dd, 1H), 3.68~3.60 (m, 2H), 2.66~2.54 (m, 1H), 2.24~2.14 (m, 3H), 1.00 (t, 3H) Example 31: Synthesis of (+)-1-(3'-O-benzyl-2,3-dideoxy-3- fluoroapio- -L-furanosyl)-5-iodouracil and (-)-1-(3'-0-benzyl- 2,3-dideoxy-3-fluoroapio- a -L-furanosyl)-5-iodouracil A stirred suspension of 5-iodouracil (500 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane (20 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (25 ml) followed by 2,3-dideoxy-3 '-O-benzyl-3 -fluoroapio-L-furanosyl acetate (500 mg) in dichloromethane (5 ml). This suspension was cooled in an ice/water bath to 5~C, and treated with trimethylsilyltrifluoromethane sulfonate (0.54 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (10 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The

solution was diluted with dichloromethane, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 2 : 1) to give the titled compounds ( -form: 385 mg, 46%; and a -form: 387 mg, 46%). form : IH NMR (CDCl3) 8 : 8.87 (s, 1H), 7.81 (s, 1H), 7.38 7.31 (m, 5H), 6.17 (t, 1H), 4.62 (s, 2H), 4.29~4.18 (m, 2H), 3.73 3.68 (m, 2H), 2.87~2.76 (m, 1H), 2.38~2.26 (m, 1H). a-form lH NMR (CDCl3) 8 : 9.28 (s, 1H), 7.91 (s, 1H), 7.40-- 7.30 (m, 5H), 6.17 (dd, 1H), 4.60 (dd, 2H), 4.494.41 (m, 1H), 4.05 (dd, 1H), 3.77-3.63 (m, 2H), 2.69~2.58 (m, 1H), 2.42~2.33 (m, 1H).

Example 32: Synthesis of (-)-1-(3'-O-benzoyl-2,3-dideoxy-3- fluoroapio- -D-furanosyl)-5-iodouracil and (+)-1-(3'-O-benzoyl- 2,3-dideoxy-3-fluoroapio- a -D-furanosyl)-5-iodouracil A stirred suspension of 5-iodouracil (476 mg) and ammonium sulfate (catalytic amount) in hexamethyldisilazane (10 ml) was heated to reflux under nitrogen until a clear solution was obtained (3h). The solution was allowed to cool to room temperature and hexamethyldisilazane removed under reduced pressure using anhydrous conditions. To the residue was added dichloromethane (25 ml) followed by 2,3-dideoxy-3'-O-benzoyl-3-fluoroapio-D-furanosyl acetate (282 mg) in dichloromethane (7 ml). This suspension was

cooled in an ice/water bath to Soc, and treated with trimethylsilyltrifluoromethane sulfonate (0.4 ml). The reaction mixture was stirred for 30 minutes. Saturated sodium bicarbonate solution (10 ml) was added to the mixture and the mixture was allowed to warm to room temperature and stir for 20 minutes. The solution was diluted with dichloromethane, and the organic layer was separated, washed with saturated sodium bicarbonate solution and brine, dried over anhydrous magnesium sulfate, filtered, and concentrated. The residue was purified by silica gel column chromatography (n-hexane : ethylacetate = 2 : 1) to give the titled compounds (P-form: 130 mg, 28.3%; and a -form: 210 mg, 45.7%). form : IH NMR (CDCl3) d: 8.14 (s, 1H), 8.05~8.03 (m, 2H), 7.76 (s, 1H), 7.63~7.60 (m, 1H), 7.50~7.46 (m, 2H), 6.11 (t, 1H), 4.72~4,57 (m, 2H), 4.42~4.31 (m, 2H), 2.95~2.88 (m, 1H), 2.49 2.35 (m, 1H) a-form : 'H NMR (CDCl3) 8 : 8.16 (s, 1H), 8.06~8.04 (m, 2H), 7.93 (s, 1H), 7.64~7.61 (m, 1H), 7.517.47 (m, 2H), 6.24 (dd, 1H), 4.70~4.54 (m, 2H), 4.18~4.07 (m, 2H), 2.79~2.51 (m, 2H) Example 33: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- -L- furanosyl)-5-iodouracil To a solution of (+)-1-(3'-O-benzyl-2,3-dideoxy-3-fluoroapio- P -L-furanosyl)-5-iodouracil (210 mg) obtained in Example 31 in dichloromethane (5 ml), borontrichloride (1.OM solution in dichloromethane, 2.8 ml) was added at -78"C and the mixture was

stirred at the same temperature for 2 hours. A mixed solution (5 ml) of dichloromethane and methanol (1 : 1) was added to the mixture dropwise at the same temperature and the reaction mixture was allowed to warm to 0 0C. Sodium bicarbonate (50 mg) was added and the mixture was stirred for 30 minutes, filtered and concentrated. The residue was purified by silica gel column chromatography (n-hexane: ethylacetate = 1:10) to give the title compound (98.9 mg, 59%) as a white solid.

[α]D20 +32.27~ (c 0.10, CH3OH) W (H20) A max : 288 nm (pH 7), 286 nm (pH 2), 282 nm (pH 11).

'H NMR (DMSO-d6) 8 : 11.70 (s, 1H), 8.15 (s, 1H), 6.09 (t, 1H), 5.24 (t, 1H), 4.23 (dd, 1H), 4.02~3.90 (m, 1H), 3.72~3.63 (m, 2H), 2.44~2.30 (m, 2H).

Example 34: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- a -L- fu ranosyl)-5-iodou racil The titled compound (111 mg, 69%) as a white solid was obtained in the same manner as described in Example 33, using (-)-1-(3 '-0-benzyl-2,3 -dideoxy-3 -fluoroapio- a -L-furanosyl)-5- iodouracil (201 mg) obtained in Example 31 instead of (+)-1-(3'-0- benzyl-2,3-dideoxy-3-fluoroapio- -L-furanosyl)-5-iodouracil.

[ a ]20D -34.48~ (c 0.10, CH30H) W (H20) A max : 288 nm (pH 7), 288 nm (pH 2), 278 nm (pH 11).

H NMR (DMSO-d6) 8 :11.70 (s, 1H), 8.12 (s, 1H), 6.06 (dd, 1H), 5.29 (t, 1H), 4.36~4.29 (m, 1H), 3.91 (dd, 1H), 3.70~3.60 (m, 2H),

2.682.59 (m, 1H), 2.30~2.21 (m, 1H).

Example 35: Synthesis of (-)-1-(2,3-dideoxy-3-fluoroapio- -D- furanosyl)-5-iodouracil To a solution of (-)-1-(3'-O-benzoyl-2,3-dideoxy-3- fluoroapio- P -D-furanosyl)-5-iodouracil (58 mg) obtained in Example 32 in methanol (4 ml), sodium methoxide (25wt% solution in methanol, 0.1 ml) was added and the mixture was stirred for 3 hours at room temperature. The resulting solution was neutralized with dry ice, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 15 : 1) to give the titled compound (35.5 mg, 80%) as a white solid.

[a ]20D -43.79~ (c 0.08, CH30H) UV (H20) A max: 286 nm (pH 7), 288 nm (pH 2), 280 nm (pH 11).

'H NMR (DMSO-d6) 8 :11.70 (s, 1H), 8.15 (s, 1H), 6.08 (t, 1H), 5.25 (t, 1H), 4.23 (dd, 1H), 3.98~3.90 (m, 1H), 3.73~3.66 (m, 2H), 2.49~2.30 (m, 2H).

Example 36: Synthesis of (+)-1-(2,3-dideoxy-3-fluoroapio- a -D- furanosyl)-5-iodouracil The titled compound (76 mg, 77%) as a white solid was obtained in the same manner as described in Example 35, using (+)-1-(3'-O-benzoyl-2,3-dideoxy-3-fluoroapio-α-D-furanosyl) -5- iodouracil (120 mg) obtained in Example 32 instead of (-)-1-(3'-0- benzoyl-2,3 -dideoxy-3 -fluoroapio- t3-D-furanosyl)-5-iodouracil.

[a]20 +28.74~ (c 0.07, CH30H) W (H20) A max : 288 nm (pH 7), 290 nm (pH 2), 280 nm (pH 11). lH NMR (DMSO-d6) 8 :11.70 (s, 1H), 7.86 (s, 1H), 6.06 (dd, 1H), 5.29 (t, 1H), 4.36~4.29 (m, 1H), 3.91 (dd, 1H), 3.69~3.60 (m, 2H), 2.66~2.49 (m, 1H), 2.30~2.20 (m, 1H) Example 37: Preparation of (-)-1-(2,3-dideoxy-3-fluoroapio- P -L- furanosyl) cytosine by enzymatic optical resolution 1st method ( # )- 1 -(2,3-dideoxy-3-fluoroapio- P -furanosyl) cytosine (104.3 mg) was dissolved in t-butyl alcohol by heating, and cooled to room temperature. Vinylacetate (5 ml) and Amano-AK (151.7 mg) were added to the mixture and the mixture was stirred at room temperature for 5 hours. The resulting mixture was filtered, and concentrated under reduced pressure. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 10 1) to give two compounds having Rf = 0.65 and Rf = 0.08, respectively. One compound (48 mg) having higher polarity (Rf = 0.08) was the titled compound, when compared with a standard material.

2nd method The titled compound (30 mg) was obtained in the same manner as described in the 1st method, using Amano-PS (20 mg) instead of Amano-AK.

3rd method The titled compound (32 mg) was obtained in the same manner as described in the 1 st method, using pseudomonas fluorescence lipase (26.5 mg) instead of Amano-AK.

4th method The titled compound (42 mg) was obtained in the same manner as described in the 1st method, using acetonitrile (6 ml) instead of t-butylalcohol.

Example 38: Preparation of (+)-1-(2,3-dideoxy-3-fluoroapio- P -D- furanosyl) cytosine by enzymatic optical resolution The compound (80 mg) of Rf = 0.65 obtained in Example 37 was dissolved in methanol solution (10 ml) saturated with ammonia.

The mixture was stirred at room temperature for 1 hour, and concentrated. The residue was purified by silica gel column chromatography (dichloromethane : methanol = 10 : 1) to give the titled compound (45 mg) as a white solid. It was confirmed that this compound was the titled compound, when compared with a standard material.

Example 39: Preparation of (-)-1-(2,3-dideoxy-3-fluoroapio- -L- furanosyl) cytosine by an optical resolution reagent 1 st method (#)-1-(2,3-dideoxy-3-fluoroapio- -furanosyl) cytosine (500

mg) and (-)-N-acetyl-phenylglycine (420 mg) were dissolved in methanol (1 ml). Acetone (5 ml) was added to the mixture and the mixture stood at room temperature for 30 minutes. The precipitate was filtered and dried. This solid was dissolved in methanol (15 ml), and an anion-exchange resin (10 g) was added to the solution. The solution was stood at room temperature for 1 hour, and filtered. The filtrate was evaporated to give the titled compound (140 mg) as a white solid. It was confirmed that this compound was the titled compound, when compared with a standard material.

2nd method The titled compound (102 mg) was obtained in the same manner as described in the 1st method, using L-mandelic acid (390 mg) as an optical resolution reagent instead of (-)-N-acetyl- phenylglycine.

Example 40: Preparation of (+)-1-(2,3-dideoxy-3-fluoroapio- -D- furanosyl) cytosine by an optical resolution reagent The mother liquor of the example 39 was evaporated under reduced pressure. The residue was recrystallized several times using methanol to give the titled compound (121 mg) as a white solid. It was confirmed that this compound was the titled compound, when compared with a standard material.

Experimental example 1: Antiviral assay Antiviral assay was performed by the following method. D

form compound obtained in Example 24, L form compound obtained in Example 22 and racemic compound thereof were used respectively as a test compound, and lamivudine was used as a reference compound.

Chronically HBV-producing human liver cells HepG2 2.2.15 were seeded into 24 well tissue culture plates and grown to confluence. Test compounds were then added daily for a continuous 9 day period. Culture medium (changed daily during the treatment period) were collected and stored for analysis of extracellular (virion) HBV after 0, 3, 6 and 9 days of treatment. HBV DNA was then analyzed in a quantitative and qualitative manner for overall levels of HBV DNA.

The experimental result is shown in Table 1.

Table 1 The result of antiviral assay. Test compounds EC50( A M) CC50( tj M) SI(CC5EC50) Racemic compounda 0.2 2,321 11,605 D form of Example 24 5.6 >1,000 >179 L form of Example 22 0.01 2,232 223,200 Reference compound 0.06 2,000 33,333 a composed with D form of Example 24 and L form of Example 22. blamivudine.

Experimental example 2: Acute oral toxicity test Acute oral toxicity test was performed by the following method.

Five male ICR mice aged with 4 weeks and weighing between 20 and 25 g were used as a group. 250 mg/kg, 500 mg/kg, 1,000 mg/kg and 2,000 mg/kg, as single dose, of L form compound obtained in Example 22 were administered to four test groups, respectively. All mice were fasted during 16 h prior to compound administration. The test compound was suspended in corn oil to make 20 ml/kg of administration volume regardless dose, and the suspension was administered orally to the test groups separately. The observations of clinical symptoms were performed during 2 weeks from drug administration. The results were recorded daily, and body weights were determined at least three times. After 2 weeks, that is, observation period, autopsy was performed. The organs and the tissues of mice were observed with naked eyes, and the results were recorded.

As a result, it was observed that LD50 of the test compound, calculated from the result, was at least 2,000 mg/kg. And abnormal phenomena were not observed in the clinical symptoms and in the result of autopsy. At the test doses, the mortality rates were 0%.