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1. (WO1992010497) ENANTIOMERICALLY PURE $g(b)-D-(-)-DIOXOLANE-NUCLEOSIDES
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We claim.
1. A process for the preparation of enantiomerically pure β-D- (-) -dioxolane-nucleosides comprising preparing the dioxolane ring from 1,6-anhydromannose.

2. The process of claim 1 further comprising converting 1,6-anhydromannose to its (2, 3) -isopropylidene derivative.

3. The process of claim 2 further comprising benzoylating the 2,3-isopropylidene derivative of 1,6-anhydromannose to (-)-l,6-anhydro-4-0-benzoyl-2,3-isopropylidene-?-D-mannopyranose.

4. The process of claim 3, further comprising oxidizing the (-) -1, 6-anhydro-4-0-benzoyl-2 , 3-isopropylidene-3-D-mannopyranose to (-) -(2R,4R) -4-(2-benzoxy-l-hydroxyethyl) -2- (hydroxymethyl) -dioxolane.

5. The process of claim 4, further comprising protecting the 2-hydroxy position of the dioxolane with an oxygen protecting group.

6. The process of claim 5, wherein the oxygen protecting group is selected from the group consisting of trimethylsilyl, dimethylhexylsilyl , t-butyldimethylsilyl, t-butyldiphenylsilyl, trityl, alkyl groups, acyl groups, benzoyl, p-N02 benzoyl, toluyl, methylsulfonyl, and p-toluylsulfonyl.

7. The process of claim 5, further comprising removing the benzoyl group from the 2-hydroxyethyl-position to produce (-) - (2R, 4R) -2- (protected-O-methyl) -4- (1, 2-dihydroxyethyl) -dioxolane.

8. The process of claim 7, further comprising oxidizing the (+)-(2R,4R)-2- (protected-oxymethyl) -4- carboxyldioxolane to form a compound selected from the group consisting of (2R,4R)- and (2R,4S)-4-acetoxy-2- (protected-oxymethyl) dioxolane.

9. The process of claim 8, further comprising converting (2R,4R)-and (2R,4S)-4-acetoxy-2-(protected- oxymethyl) -dioxolane to a product selected from the group consisting of (2R,4R)- and (2R,4S)-4-acetoxy-2- (protected-oxymethyl) -dioxolane.

10. The process of claim 1, further comprising condensing the dioxolane ring with a heterocyclic base selected from the group consisting of purine and pyrimidine bases.

11. The process of claim 8, further comprising condensing (2R,4R)-or (2R,4S)-4-acetoxy-2-(protected- oxymethyl) -dioxolane with a heterocyclic base selected from the group consisting of purine and pyrimidine bases.

12. The process of claim 10, wherein the heterocyclic base is selected from the group consisting of adenine, hypoxanthine, N6-alkylpurines, N6-benzylpurine, N6-halopurine, guanine, thymine, cytosine, 6-azapyrimidine, 2-mercaptopyrimidine, and uracil.

13. The process of claim 11, wherein the heterocyclic base is selected from the group consisting of adenine, hypoxanthine, N6-alkylpurines, N6-benzylpurine, N6-halopurine, guanine, thymine, cytosine, 6-azapyrimidine, 2-mercaptopyrimidine, and uracil.

14. The process of claim 1, wherein the dioxolane nucleoside is (-)-l-[ (2B,4β) -2- (hydroxymethyl) -4-dioxolanyl]thymine.

15. An enantiomerically pure β-Ω- (-) -dioxolane nucleoside.

16. The nucleoside of claim 15 that is (-)-l-[ (2B,4β)-2- (hydroxymethyl) -4-dioxolanyl]thymine.

17. A pharmaceutical composition comprising an amount of an enantiomerically pure β-D- (-) -dioxolane nucleoside that is effective to inhibit HIV in humans.

18. The pha.rmaceutical composition of claim 17, wherein the nucleoside is (-)-l-[ (2β,4β) -2- (hydroxymethyl) -4-dioxolanyl]thymine.