WO2003010179A1

WO2003010179A1 - Process for the preparation of 2'-3'-dideoxy-2',3'-didehydro-nucleosides

Info

Publication number: WO2003010179A1
Application number: PCT/US2001/023267
Authority: WO
Inventors: Dennis C. Liotta; Woo-Baeg Choi
Original assignee: Emory University
Priority date: 2001-07-24
Filing date: 2001-07-24
Publication date: 2003-02-06

Abstract

The present invention is an efficient synthetic route to 2',3'-dideoxy-2'3'-didehydro-nucleosides. This process utilizes metal mediated allyl chemistry to achieve coupling of a heterocyclic base, including a purine, pyrimidine, or other heterocylic or heteroaryl compound to a glycal to produce a nucleoside with high regio- and enantioselectivity.

Description

PROCESS FOR THE PREPARATION OF 2',3'-DIDEOXY-2',3'-DIDEHYDRO-NUCLEOSIDES

The U.S. government has rights in this invention arising out of grant No. Al 28731 from the U.S. National Institutes of Health.

This application claims priority to U.S.S.N. 60/220,373, filed on July 24, 2000.

BACKGROUND OF THE INVENTION

This application is in the field of synthetic organic chemistry and is specifically an improved method of synthesis of 2',3'-dideoxy-2',3'-didehydro-nucleosides (also referred to as "D4" nucleosides).

A "nucleoside," "nucleoside derivative," or "nucleoside analog" is a compound that consists of a 5-carbon sugar or sugar derivative coupled to a purine base, pyrimidine base, heteroaromatic, or heterocycle. The addition of a phosphate group to the 5' position of the nucleoside forms a nucleotide. Nucleotides are the building blocks of the nucleic acids, ribonucleic acid (RNA) and deoxyribonucleic acid (DNA). A number of nucleoside and nucleotide analogs exhibit activity against HIV.

AIDS (Acquired Immune Deficiency Syndrome) is a catastrophic disease that has reached such global proportions that President Clinton and the National Security Council have declared it a threat to U.S. national security. From July 1998 through June 1999 a total of 47,083 AIDS cases were reported in the US alone. With more than 2.2 million deaths in 1998, HIV/ AIDS has now become the fourth leading cause of mortality and its impact is increasing. The death toll due to AIDS reached a record 2.6 million this year, while new HIV infections continued to spread at a growing rate. More than 16 million people have now died of AIDS, since the late 1970's.

AIDS was first brought to the attention of the Center for Disease Control and Prevention (CDC) in 1981 when seemingly healthy homosexual men came down with Karposi's Sarcoma (KS) and Pneumocystis Carinii Pneumonia (PCP), two opportunistic diseases that were known only to inflict immuno-deficient patients. Several years later, the causative agent of AIDS, a lymphoadenopathy associated retrovirus, the human immunodeficiency virus (HIN) was isolated by the Pasteur Institute in Paris, and later confirmed by an independent source in the National Cancer Institute of the United States.

3'-Azido-3'-deoxy-thymidine (AZT, Zidovudine, Retrovir), was approved by the Food And Drug Administration (FDA) in 1986 and became the first drug to be used in the fight against AIDS. Since the first sale of AZT, several nucleoside analogs have been shown to have potent antiviral activity against the human immunodeficiency virus type I (HIV-I). In particular, a number of 2',3'-dideoxy-2',3'-didehydro-nucleosides have been shown to have potent anti-HIV-1 activity. 2',3'-Dideoxy-2',3'-didehydro-thymidine ("D4T"; also referred to as l-(2,3-dideoxy-β-D-glycero-pent-2-eno-furanosyl)thymine)) is currently sold for the treatment of HIV under the name Stavudine by Bristol Myers Squibb. DuPont Pharmaceuticals, Inc. is currently developing 2',3'-dideoxy-2',3'-didehydro-5- fluoro-cytidine ("D4FC" ) for the treatment of HIV. Other D4 nucleosides that have been tested include 2',3'-dideoxy-2',3'-didehydro-cytidine ("D4C"), 2',3'-dideoxy-2',3'- didehydro-uridine ("D4U"), 2',3'-dideoxy-2',3'-didehydro-adenosine ("D4A"), 2',3'- dideoxy-2',3'-didehydro-inosine ("D4I"), and 2',3'-dideoxy-2',3'-didehydro-guanosine (D4G).

Natural and unnatural D4 nucleosides can serve as synthetic intermediates for the preparation of a large variety of other nucleoside analogs, including but not limited to 2 ',3'- dideoxy, and 2' or 3'-deoxyribo-nucleoside analogs as well as additional derivatives obtained by subsequent functional group manipulations. In view of the importance of 2',3'- dideoxy-2',3'-didehydro-nucleosides, it is desirable to have a facile, efficient and general route of synthesis of these compounds. While several methods exist for the synthesis of 2',3'-dideoxy-2',3'-didehydro-nucleosides, none has the ability to produce efficiently both enantiomeric forms of these compounds using purine bases, pyrimidine bases, heteroaromatics or heterocycles.

On of the earliest syntheses of 2',3'-dideoxy-2',3'-didehydro-nucleosides is the published process for the preparation of 2',3'-dideoxy-2',3'-didehydro-thymidine (D4T). The first reported method to produce D4T involved the base promoted elimination of 3'-O- sulfonyl esters of 2'-deoxynucleosides. This synthetic route is limited to pyrimidine nucleosides and cannot be used in the production of purine nucleosides. Horwitz, J. P., et al, J. Org. Chem. 1966, 31, 205; Horwitz, J. P., et al, J. Org. Chem. 1967, 32, 817; and Horwitz, J. P., et al, J. Am. Chem. Soc. 1964, 86, 1896.

Some 2',3'-dideoxy-2',3'-didehydro-nucleosides have been obtained directly from the corresponding ribonucleosides through their reaction with acetoxyisobutyryl halides, followed by the reductive elimination of the 2',3'-acetoxy-2',3'-halogeno derivatives with chromous ion. U.S. Pat. No. 3,817,982 (1974); Chem. Abstr. 1974, 81, 63942; Russell, A. F., et al, J. Am. Chem. Soc. 1973, 95, 4025; Jain, T. C, et al, J. Org. Chem. 1974, 39, 30; Classon, B., et al, Ada Chem. Scand. Sect B 1982, 32, 251; Robins, M. J., et al, Tetrahedron Letters 1984, 25, 367. In a variation of this method, zinc in dimethylformamide can be used instead of chromous acetate. Robins, M. J., et al, Tetrahedron Letters 1984, 25, 367. The reaction is difficult, and results in several products, and is therefore an inefficient route to obtain the 2',3'-unsaturated compounds. Though this method has been used for the preparation of 2',3'-dideoxy-2',3'-didehydro-adenosine and uridine, its applicability for the synthesis of other unsaturated nucleosides such as inosine and guanosine has been very poor. Jain, T. C, et al, J. Org. Chem. 1974, 39, 30.

U.S. Pat. No. 5,455,339 to Chu describes a method for preparing 2',3'-dideoxy- 2',3'-didehydro-nucleosides that includes:

(i) preparing a nucleoside derivative of the general structure:

wherein B is a nitrogen, oxygen, or sulfur heterocycle of from C₁ to C₁₅, Y is a suitable oxygen protecting group, each R is C(S)SR\ where R' is an alkyl or cyanoalkyl group of to s, or both Rs together are >C=S ; and then;

(ii) deoxygenating the nucleoside derivative to the corresponding 2',3'-dieoxy-2',3'- didehydronucleoside.

Wliile this synthesis is an improvement in the art, the method is limited to the synthesis of nucleosides in which the stereocenters are already in place. U.S. Patent No. 5,905,070 to Raymond F. Schinazi and Dennis C. Liotta describes [5-carboxamido or 5-fluoro]-2',3'-dideoxy-2',3'-didehydro-pyrimidine nucleosides and [5- carboxamido or 5-fluoro]-3'-modified-pyrimidine nucleosides. Example 3 of the '070 patent provides a process for the preparation of 2',3'-dideoxy-2',3'-didehydro-nucleosides. The patent states that the procedure can be adapted for a wide variety of bases and can be used to provide either the β-D or the β-L isomer as desired. The process is illustrated below:

1. LiTMS₂, THF,

3. TMSOTf (0.25 X) trans : cis = 14 : 1 ClSTIPP (l.l X)

3 D4T wherein MMPP is magnesium monoperoxyphthalate, R is t-butyldiphenylsilyl, and STIPP is 2,4,6-triisopropylphenyl. PCT WO 99/43691 describes 2'-fluoro-2',3'-dideoxy-2',3'-didehydronucleosides that are useful in the treatment of viral infections. Schemes 9, 10, and 11 of the PCT describe methods for the preparation of L-2'-fluoro-2',3'-didehydro-2',3'-dideoxy- nucleosides. The PCT publication states that previously, the synthesis of 2',3'-unsaturated L-nucleosides had been accomplished via an elimination reaction starting from readily available nucleoside analogs, which involved a lengthy modification procedure. There are few examples of the synthesis of 2',3'-unsaturated purine nucleosides by direct condensation due to the lability of the 2',3'-unsaturated sugar moiety under the coupling conditions in the presence of a Lewis acid, except one case of the pyrimidine analog using a thiophenyl intermediate (Abdel-Medied, A. W.-S., et al, Synthesis, 1991, 313; Sujino, K., et al, Tetrahedron Lett., 1996, 37, 6133). In contrast to the 2',3'-unsaturated sugar moiety, the 2'-fluoro-2',3'-unsaturated sugar, which bears enhanced stability of the glycosyl bond during the condensation with a heterocycle, is more suitable for the direct coupling reaction. As illustrated below (wherein B is a purine or pyrimidine base and R is an oxygen protecting group), (R)-2'-fluorbutenolide (prepared from L-glyceraldehyde acetonide) was used as the key precursor in the preparation of 2'-fluoro-2',3'-dideoxy-2',3'-didehydro- nucleosides. From the acetonide, a mixture of E and Z isomers was obtained via the Homer-Emmons reaction in the presence of triethyl α-fluorophosphonoacetate and sodium bis(trimethylsilyl)amide in THF (Thenappan, A., et al, J. Org. Chem., 1990, 55, 4639; Morikawa, T., et al, Chem. Pharm. Bull, 1992, 40, 3189; Patrich, T.B., et al, J. Org. Chem., 1994, 59, 1210). Due to the difficulties in separating the E and Z isomers, the mixture was carried on to the cyclization reaction under acidic conditions to give the desired lactone and uncyclized diol. The resulting mixture was converted to the silyl lactone and was subjected to reduction with DIBA1-H in CH₂C1₂ at 78 °C to give the lactol. The lactol was treated with acetic anhydride to yield a key acetate intermediate, which was condensed with silylated 6-chloropurine under Norbruggen conditions to afford anomeric mixtures of the protected nucleoside. Treatment of the protected nucleoside with TB AF in THF gave a mixture of free nucleosides that could be separated by silica gel column chromatography. The adenine analogs are obtained by the treatment of 6-chloropuridine with mercapto- ethanol and ΝaOMe in a steel bomb at 90 °C. Further treatment of the adenine analogs under the same conditions afforded the inosine analogs.

I. Organometallic Chemistry

March, J., Advanced Organic Chemistry, Wiley-Interscience Publication: New York, Fourth Edition; 1992, p. 80 states that it has been known since the 1970's in organometallic chemistry that many metals form covalent bonds with olefins, such that the bond is not simply from the metal to one atom, but to the whole π center. In a number of cases, olefins that have been too unstable to isolate have been isolated in the form of metal complexes. This is especially useful in the formation and stabilization of allyl cations. This aspect of metal mediated chemistry has been exploited in the formation of carbon-carbon bonds via a nucleophilic attack of an allylic cation. Trost, B. M., et al. Angew. Chem. Int. Ed. Engl. 1989, 28, 1173; Heck, Palladium Reagents in Organic Synthesis; Academic Press: New York, 1985, ρρ.130-166.

In metal mediated π-allyl chemistry, the metal acts as a nucleophile that, in a concerted fashion, attacks an allylic leaving group, as illustrated below.

This results in an inversion of stereochemistry. Then, another nucleophile attacks the π- allyl complex in a concerted fashion, in turn yielding another inversion of configuration. Thus, the overall result of a metal mediated allyl substitution is retention of configuration.

A π-allyl complex is pseudo-equivalent to an allyl cation, which can be used to impart regiocontrol of the addition of groups. In heterocyclic systems, such as a ribose sugar ring, the cation prefers to be adjacent to the heteroatom due to the extra stabilization afforded by the heteroatom' s lone pair of electrons. Therefore, the attack of the π-allyl complex in a nucleoside sugar derivative is favored at the carbon adjacent to a heteroatom.

Crimmons, M. T., et al, Org. Letters, 2000, 2, 3037 utilized this route to synthesize simple carbocyclic nucleosides; however, the methodology could not be generalized to sugar rings or rings containing heteroatoms due to the sensitivity of the reagents to elimination forming furans (aromatization). Trost, B. M., et al, J. Amer. Chem. Soc. 1996, 118, 3037 attempted to circumvent this problem with a fairly limited synthesis of nucleosides from an isomeric dihydrofuran system through a chiral palladium complex.

L₂* is the chiral bidentate phosphorus ligand

Trost, however, reported that "... alkylation of these diacyloxydihydrofurans with 6- chloropurine using achiral 1,2-diphenylphosphinoethane (dppe) as a ligand and (dba)₃Pd₂(CHCl₃) is not productive

In light of the importance of 2',3'-dideoxy-2',3'-didehydro-nucleosides in antiviral therapy, it is an object of the present invention to provide a general synthetic method of 2',3'-dideoxy-2',3'-didehydro-nucleosides from ribonucleosides and from available precursors with the option of introducing functionality as needed.

It is another object of the present invention to provide a process for the production of 2',3'-dideoxy-2',3'-didehydro-nucleosides that is facile and efficient.

It is a further object of the present invention to provide a process for the production of 2',3'-dideoxy-2',3'-didehydro-nucleosides which is applicable to both purine and pyrimidine nucleosides.

It is an additional object of the present invention to provide a process for the production of 2',3'-dideoxy-2',3'-didehydro-nucleosides that can incorporate heterocycles and heteroaryls other than purines and pyrimidines.

It is a further object of the present invention to provide a process for the production of 2',3'-dideoxy-2',3'-didehydro-nucleosides that can be used as synthetic intermediates for the preparation of a large variety of other nucleoside analogs, including but not limited to 2',3'-dideoxy, and 2' and 3'-deoxyribo nucleoside analogs as well as additional derivatives obtained by subsequent functional group manipulations.

SUMMARY OF THE INVENTION

The present invention is an efficient synthetic route to 2',3'-dideoxy-2',3'- didehydro-nucleosides from available precursors with the option of introducing functionality as needed. The process of synthesis is applicable to a wide range of purine and pyrimidine nucleosides, as well as nucleoside derivatives that include other heterocyclic and heteroaryl compounds. The D4 compounds made according to the present invention can also be used as synthetic intermediates in the preparation of a variety of other nucleoside analogs, including but not limited to 2',3'-dideoxy and 2'- or 3'-deoxyribo- nucleoside analogs as well as additional derivatives obtained by subsequent functional group manipulations.

This process utilizes metal mediated π-allyl chemistry to achieve coupling of a heterocyclic base, including a purine, pyrimidine, or other heterocyclic or heteroaryl compound to a glycal to produce a nucleoside with high regio- and enantioselectivity.

Briefly, the method for preparing D- and L-2',3'-dideoxy-2',3'-didehydro- nucleosides includes:

a) preparing or obtaining a glycal or a glycal derivative of structure 1 (β-D configuration), 2 (β-L configuration), 3 (α-D configuration), or 4 (α-L configuration)

wherein Z is carbon or a heteroatom (and preferably oxygen), P is a suitable oxygen protecting group, and OR is a good leaving group; and then

b) activating the compound of structure 1, 2, 3 or 4 with a metal to form a respective D or L π-allyl complex of structure 5 or 6

wherein M is a metal capable of forming a π-allyl complex, x is the number of ligands complexed to the metal to complete the valence, and each L is independently an activating mono-, bi- or tridentate ligand with at most one being solvent, and wherein the ML_xis on the opposite face of the displaced OR leaving group, and then

c) reacting the complex of structure 5 or 6 with a purine base, a pyrimidine base, a heteroaromatic, or a heterocycle to form a nucleoside, which is optionally deprotected, of structure 7, 8, 9, or 10

7 8 9 10 wherein P' is hydrogen or a suitable oxygen protecting group, and B is a purine base, pyrimidine base or a nitrogen, oxygen or sulfur containing heteroaromatic or heterocycle.

In one illustrative embodiment, Z is oxygen, ML_X is PdL₂(solvent), OR is -OC(O)NH(Phenyl), P is t-butyldiphenylsilyl, and B is a pyrimidine or purine base.

This reaction proceeds with net retention of stereochemistry (syn facial selectivity), i.e., a nucleoside with an α-3'-substituent produces the corresponding α-D4-nucleoside as the major product and a nucleoside with a β-3'-substituent predominantly produces the corresponding β-D4-nucleoside.

The selection of reaction conditions should take into account the ease of elimination of the 4'-hydrogen in the glycal to form an undesired furan. Some combinations of 5'- protecting groups, 3 '-leaving groups, base (heterocycle), palladium catalyst and solvent systems result in the formation of the undesired elimination product, protected furfural alcohol. In one aspect of the invention, it has been discovered that the combination of a 5'- t-butyldiphenylsilyl-3'-phenylurethane-glycal, unprotected purine or pyrimidine base, (dba)₃Pd , bis-diphosphinoethane and dichloromethane or dichloromethane/DMF/THF produces the desired protected D4 nucleoside in moderate to high yields.

If desired, the D4 nucleoside can then be reduced to a D2 nucleoside using known methods. As one nonlimiting example, Chu demonstrated in U.S. Patent 5,455,339 (1995) that "if the 2',3'-dideoxy-nucleoside is desired, the 2',3'-unsaturated nucleoside prepared ... may be reduced. For example, hydrogen reduction may be effected in ethanol with 10% palladium on carbon." Alternatively, the D4 nucleoside can be modified to form a 2', a 3' or a 5'-substituted-nucleoside or a combination thereof, also using known chemistry to those skilled in the art. As a non-limiting illustrative example, Townsend, et al, Chemistry of Nucleosides and Nucleotides, Volume 1, Plenum Press: New York, teaches oxidation of 2'3'-dideoxy-2'3'-didehydro-nucleosides with osmium tetraoxide yields a ribonucleoside. Further functionalities can be introduced via the 2' or 3' hydroxyls using the teachings of Kuzuhara, H., et al., U.S. Patent 5,144,018 (1992) by activating and substituting the relevant hydroxyl.

BRIEF DESCRIPTION OF THE FIGURES

Figure 1 is a nonlimiting illustrative example of Scheme 1 and 2 according to the present invention of the synthesis of 5' -protected- β-(D and L)-2',3'-dideoxy-2',3'- didehydro-thymidine (18a and b) and 5'-protected-β-(D and L)-2',3'-dideoxy-2',3'- didehydro-6-chloropuridine (19a and b).

Figure 2a is an illustration of Scheme 3 according to the present invention of examples of derivatives which can be synthesized from 5'-protected-D-β-2',3'-dideoxy- 2',3'-didehydro-thymidine (18a) and 5'-protected-D-β-2',3'-dideoxy-2',3'-didehydro-6- chloropuridine (19a).

Figure 2b is an illustration of Scheme 4 according to the present invention of examples of selected derivatives which can be synthesized from 5'-protected-L-β-2',3'- dideoxy-2',3'-di-dehydro-thymidine (18b) and 5'-protected-L-β-2',3'-dideoxy-2',3'- didehydro-6-chloropuridine (19b).

DETAILED DESCRIPTION OF THE INVENTION

The present invention is an efficient synthetic route to 2',3'-dideoxy-2',3'- didehydro-nucleosides from inexpensive precursors with the option of introducing functionality as needed. The process of synthesis is applicable to purine and pyrimidine nucleosides, as well as heterocycles and heteroaryls, including such as guanosine, inosine, cytidine, uridine, thymidine, adenosine, 5-fluorocytidine, and 6-chloropurine.

It has now been discovered that a wide variety of 2',3'-dideoxy-2',3'-didehydro- nucleosides can be prepared from abundant natural deoxyribonucleosides through a π-allyl complex intermediate in good yield. The method for preparing D- and L-2',3'-dideoxy-2',3'-didehydro-nucleosides includes:

a) preparing a glycal of structure 1 , 2, 3, or 4

1: D-glycal 2: L-glycal 3: D-glycal 4: L-glycal

wherein a compound of the general formula 1 represent a 3'-β-OR-D-glycal, a compound of the general formula 2 represent a 3'-β-OR-L stereoisomer, a compound of the general formula 3 represent a 3'-α-OR-D-glycal, and a compound of the general formula 4 represent a 3'-α-OR-L stereoisomer, Z is carbon or a heteroatom, P is a suitable oxygen protecting group, and OR is a good leaving group; and then

b) activating the compound of structure 1, 2, 3 or 4 by nucleophilic attack by a metal to form a respective D or L π-allyl complex of structure 5 or 6

5: D-complex 6: L-complex

wherein Z is carbon or a heteroatom, P is a suitable oxygen protecting group, M is a metal capable of forming π-allyl complexes, x is the number of ligands complexed to the metal to complete the valence, and each L is independently an activating mono-, bi- or tridentate ligand with at most one being solvent; and then

c) reacting the complex of structure 5 or 6 with a purine base, a pyrimidine base, a heteroaromatic, or heterocycle to form a nucleoside of structure 7, 8, 9, or 10

7: β-D nucleoside 8: β-L nucleoside 9: α-D nucleoside 10: α-L nucleoside wherein Z is carbon or a heteroatom, P' is H or a suitable oxygen protecting group, and B is a purine base, pyrimidine base or a nitrogen, oxygen or sulfur heteroaromatic or heterocycle.

If desired, the D4 nucleoside can then be reduced to a D2 nucleoside using known methods; as a nonlimiting example, Chu demonstrated in U.S. Patent 5,455,339 (1995) that "if the 2',3'-dideoxy-nucleoside is desired, the 2',3'-unsaturated nucleoside prepared ... may be reduced. For example, hydrogen reduction may be effected in ethanol with 10% palladium on carbon." Alternatively, the D4 nucleoside can be modified to form a 2',3' or 5'-substituted-nucleoside or a combination thereof, also using known chemistry to those skilled in the art. As a non-limiting illustrative example, Townsend, et al, Chemistry of Nucleosides and Nucleotides, Volume 1, Plenum Press: New York, teaches oxidation of 2'3'-dideoxy-2'3'-didehydro-nucleosides with osmium tetraoxide yields a ribonucleoside. Further functionalities can be introduced via the 2' or 3' hydroxyls using the teachings of Kuzuhara, H., et al., U.S. Patent 5,144,018 (1992) by activating and substituting the relevant hydroxyl.

II. Definitions

As used herein, the term "substantially free of," "substantially in the absence of or "isolated" refers to a nucleoside composition that includes at least 95%, and preferably 99% to 100% by weight, of the designated enantiomer of that nucleoside. In a preferred embodiment, the process produces compounds that are substantially free of enantiomers of the opposite configuration.

The term alkyl, as used herein, unless otherwise specified, refers to a saturated straight, branched, or cyclic, primary, secondary, or tertiary hydrocarbon of C_\ to C₁₀, and specifically includes methyl, trifluoromethyl, ethyl, propyl, isopropyl, cyclopropyl, butyl, isobutyl, t-butyl, pentyl, cyclopentyl, isopentyl, neopentyl, hexyl, isohexyl, cyclohexyl, cyclohexylmethyl, 3-methylpentyl, 2,2-dimethylbutyl, and 2,3-dimethylbutyl. The term includes both substituted and unsubstituted alkyl groups. Moieties with which the alkyl group can be substituted are 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 Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991, hereby incorporated by reference.

The term lower alkyl, as used herein, and unless otherwise specified, refers to a Ci to C saturated straight, branched, or if appropriate, a cyclic (for example, cyclopropyl) alkyl group, including both substituted and unsubstituted forms. Unless otherwise specifically stated in this application, when alkyl is a suitable moiety, lower alkyl is preferred. Similarly, when alkyl or lower alkyl is a suitable moiety, unsubstituted alkyl or lower alkyl is preferred.

The term alkylamino or arylamino refers to an amino group that has one or two alkyl or aryl substituents, respectively.

The term aryl, as used herein, and unless otherwise specified, refers to phenyl, biphenyl, or naphthyl. 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 bromo, chloro, fluoro, iodo, 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 Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991.

The term alkaryl or alkylaryl refers to an alkyl group with an aryl substituent. The term aralkyl or arylalkyl refers to an aryl group with an alkyl substituent.

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

The term heteroatom, as used herein, refers to oxygen, sulfur, nitrogen, and phosphorus.

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, Ci to C alkyl or Ci to C₄ alkoxy, sulfonate esters such as alkyl or aralkyl sulphonyl including methanesulfonyl, the mono, di or triphosphate ester, trityl or monomethoxytrityl, substituted benzyl, trialkylsilyl (e.g. dimethyl-t-butylsilyl) or diphenyhnethylsilyl. Aryl groups in the esters optimally comprise a phenyl group. The term "lower acyl" refers to an acyl group in which the non-carbonyl moiety is lower alkyl.

The term urethane or carbamide refers to -OC(O)NR⁴R⁵ in which R⁴ and R⁵ are independently 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, C_\ to C₄ alkyl or Ci to C₄ alkoxy, sulfonate esters such as alkyl or aralkyl sulphonyl including methanesulfonyl, the mono, di or triphosphate ester, trityl or monomethoxytrityl, substituted benzyl, trialkylsilyl (e.g. dimethyl-t-butylsilyl) or diphenylmethylsilyl. Aryl groups in the carbamide optimally comprise a phenyl group. The term "lower carbamide" refers to a carbamide group in which the non-carbonyl moiety is a lower alkyl.

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.

The term "metal capable of forming π-complexes" refers to any metal capable of coordinating with a pi bond such as, but not limited to palladium, nickel and molybdenum.

The term "complex" refers to any covalent, ionic, electrostatic, dative or hydrogen bonds to a metal.

The term purine or pyrimidine base includes, but is not limited to, adenine, N⁶-alkyl- purines, N⁶-acylpurines (wherein acyl is C(O)(alkyl, aryl, alkylaryl, or arylalkyl), N⁶-benzylpurine, N⁶-halopurine, N⁶-vinylpurine, N⁶-acetylenic purine, N⁶-acyl purine, N⁶-hydroxyalkyl purine, N⁶-thioalkyl purine, N²-alkylpurines, N²-alkyl-6-thiopurines, thymine, cytosine, 5-fluoro-cytosine, 5-methylcytosine, 6-azapyrimidine, including 6-aza- cytosine, 2- and/or 4-mercapto-pyrmidine, uracil, 5-halouracil, including 5-fluorouracil, C⁵- alkylpyrimidines, C⁵-benzyl-pyrimidines, C⁵-halopyrimidines, C⁵-vinylpyrimidine, C⁵-acetylenic pyrimidine, C⁵-acyl pyrimidine, C⁵-hydroxyalkyl purine, C⁵-amido- pyrimidine, C⁵-cyanopyrimidine, C⁵-nitro-pyrimidine, C⁵-aminopyrimidine, N²-alkyl- purines, N²-alkyl-6-thiopurines, 5-azacytidinyl, 5-aza-uracilyl, triazolopyridinyl, imidazolo- pyridinyl, pyrrolopyrimidinyl, and pyrazolopyrimidinyl. Purine bases include, but are not limited to, guanine, adenine, hypoxanthine, 2,6-diaminopurine, 2-(Br, FI, CI or I)-purine optionally with a substituent including an amino or carbonyl group in the 6-position, and 6- (Br, CI, or I)-purine optionally with a substituent including an amino or carbonyl group in the 2-position. Functional oxygen and nitrogen groups on the base can be protected as necessary or desired. Suitable protecting groups are well known to those skilled in the art, and include trimethylsilyl, dimethylhexylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl, trityl, alkyl groups, and acyl groups such as acetyl and propionyl, methanesulfonyl, and p- toluenesulfonyl.

The term heteroaryl or heteroaromatic, as used herein, refers to an aromatic that includes at least one sulfur, oxygen, nitrogen or phosphorus in the aromatic ring. The term heterocyclic refers to a nonaromatic cyclic group wherein there is at least one heteroatom, such as oxygen, sulfur, nitrogen or phosphorus in the ring. Nonlimiting examples of heteroaryl and heterocyclic groups include furyl, furanyl, pyridyl, pyrimidyl, thienyl, isothiazolyl, imidazolyl, tetrazolyl, pyrazinyl, benzofuranyl, benzothiophenyl, quinolyl, isoquinolyl, benzothienyl, isobenzofuryl, pyrazolyl, indolyl, isoindolyl, benzimidazolyl, purinyl, carbazolyl, oxazolyl, thiazolyl, iso-thiazolyl, 1,2,4-thiadiazolyl, isooxazolyl, pyrrolyl, quinazolinyl, cinnolinyl, phthalazinyl, xanthinyl, hypoxanthinyl, thiophene, furan, pyrrole, isopyrrole, pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, oxazole, isoxazole, thiazole, isothiazole, pyrimidine or pyridazine, and pteridinyl, aziridines, thiazole, isothiazole, 1,2,3-oxadiazole, thiazine, pyridine, pyrazine, piperazine, pyrrolidine, oxaziranes, phenazine, phenothiazine, morpholinyl, pyrazolyl, pyridazinyl, pyrazinyl, quinoxalinyl, xanthinyl, hypoxanthinyl, pteridinyl, 5-azacytidinyl, 5-azauracilyl, triazolopyridinyl, imidazolopyridinyl, pyrrolopyrimidinyl, pyrazolopyrimidinyl, adenine, N⁶-alkylpurines, N⁶-benzylpurine, N⁶-halopurine, N⁶-vinypurine, N⁶-acetylenic purine, N⁶- acyl purine,N -hydroxyalkyl purine, N -thioalkyl purine, thymine, cytosine, 6- azapyrimidine, 2-mercaptopyrmidine, uracil, N⁵-alkylpyrimidines, N⁵-benzylpyrimidines, N⁵-halopyrimidines, N⁵-vinylpyrimidine, N⁵-acetylenic pyrimidine, N⁵-acyl pyrimidine, N⁵- hydroxyalkyl purine, and N⁶-thioalkyl purine, and isoxazolyl. The heteroaromatic group can be optionally substituted as described above for aryl. The heterocyclic or heteroaromatic group can be optionally substituted with one or more substituent selected from halogen, haloalkyl, alkyl, alkoxy, hydroxy, carboxyl derivatives, amido, amino, alkylamino, dialkylamino. The heteroaromatic can be partially or totally hydrogenated as desired. As a nonlimiting example, dihydropyridine can be used in place of pyridine. Functional oxygen and nitrogen groups on the heterocyclic or heteroaryl group can be protected as necessary or desired. Suitable protecting groups are well known to those skilled in the art, and include trimethylsilyl, dimethylhexylsilyl, t-butyldimethylsilyl, and t- butyl-diphenylsilyl, trityl or substituted trityl, alkyl groups, acyl groups such as acetyl and propionyl, methanesulfonyl, and p-toluenylsulfonyl.

These purine or pyrimidine bases, heteroaromatics and heterocycles can be substituted with alkyl groups or aromatic rings, bonded through single or double bonds or fused to the heterocycle ring system. The purine base, pyrimidine base, heteroaromatic, or heterocycle may be bound to the sugar moiety through any available atom, including the ring nitrogen and ring carbon (producing a C-nucleoside).

The numbering system for nucleosides and glycals used in this specification is set out below. For ease of reference, and to avoid confusion, the same prime numbering scheme is used for the glycal as that used in the sugar ring of the nucleoside.

III. Detailed Description of Process Steps

Process for Manufacturing β-D- or β-L-Nucleoside

Step One - Preparation of Starting Material (β-D- or β-L-Glycal)

The key starting material for this process is an appropriately substituted β-D- or β-L-glycal. The β-D- or β-L-glycal can be purchased or can be prepared by any known means including standard elimination or oxidation and reduction techniques. In one embodiment, the β-D- or β-L-glycal is prepared from a selected β-D- or β-L nucleoside, for example by formation of a 2,3'-anhydronucleoside followed by elimination of the base from the selected nucleoside according to the following protocol.

3'- -OH-D or L 3'-β-OH-D or L

The 3'-α-OH is first converted to a 3'-β-OH by reacting a 3'-α-OH-deoxyriboheterocycle in a compatible solvent at a suitable temperature with the appropriate coupling reagent to yield the corresponding anhydro-deoxyribo-heterocycle. Possible coupling reagents are any reagents that promote coupling, including but are not limiting to, Mitsunobu reagents (e.g. diisopropyl azodicarboxylate and diethyl azodicarboxylate) with triphenylphosphine or various carbodiimides.

2,3'-Anhydro-nucleoside formation can be carried out at any temperature that achieves the desired results, i.e., that is suitable for the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. Preferred temperatures are from -10°C to room temperature.

Any reaction solvent can be selected that can achieve the necessary temperature and that can solubilize the reaction components. Nonlimiting examples are any aprotic solvent including, but not limiting to, alkyl solvents such as hexane and cyclohexane, toluene, acetone, ethyl acetate, dithianes, THF, dioxane, acetonitrile, dichloromethane, dichloroethane, diethyl ether, pyridine, dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide or any combination thereof, preferably anhydrous THF.

β-D or L β-D or L

Then hydrolysis of the anhydro-deoxyribopyrimidine to yield the 3'-β-OH derivative can be achieved using any suitable base followed by an acidic work up. For example, the hydrolysis can be promoted with 2N aqueous sodium hydroxide and quenched with IN hydrochloric acid until a pH of three is achieved. This reaction can be accomplished at any temperature that allows the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. The preferred temperature is again room temperature.

Appropriate solvents include any protic or aprotic solvent including, but not limiting to, alkyl solvents such as hexane and cyclohexane, toluene, acetone, ethyl acetate, dithianes, THF, dioxane, acetonitrile, dichloromethane, dichloroethane, diethyl ether, pyridine, dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide, or any combination thereof, preferably THF.

The 5 '-hydroxyl group is then protected at the 5' position with a suitable protecting group, preferably with an acyl or silyl group, by methods well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, chloro-t-butyl diphenylsilane may be reacted with the nucleoside to form the corresponding 5'-t-butyl diphenyl silyl nucleoside at room temperature in anhydrous pyridine.

β-D or L D or L

One pot elimination of the heterocyclic or heteroaromatic base and protection of the 3' -OH with a silane, such as reacting the nucleoside with hexamethyldisilazane produces the corresponding 3'-β-O-trimethylsilyl-glycal. Alternatively, these reactions can be carried out sequentially.

The glycal can be formed at any temperature that is suitable for the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. Preferred temperatures are from room temperature to refluxing conditions.

The glycal can be prepared in any solvent that is suitable for the temperature and the solubility of the reagents. Solvents can consist of any aprotic solvent including, but not limiting to, alkyl solvents such as hexane and cyclohexane, toluene, acetone, ethyl acetate, dithianes, THF, dioxane, acetonitrile, dichloromethane, dichloroethane, diethyl ether, pyridine, dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide, or any combination thereof, though preferably neat.

D or L D or L

The 3 '-hydroxyl group can then be selectively deprotected by methods well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, a trimethylsilyl group in the 3'-position can be selectively deprotected over the 5'-t-butyl-diphenyl silyl group with potassium carbonate in a mixture of THF and methanol at room temperature.

Step Two - Preparation of an Activated β-D- or L-Glycal

D or L D or L

The glycal is next activated at the 3' -OH to form a good leaving group 3 '-OR. Examples of R include, but are not limited to, alkyls to form ethers, acyls to form esters, or isothianates to fonn urethanes. In one embodiment, a phenyl urethane is formed via phenyl isothianate.

It is necessary to produce a sufficiently active moiety to facilitate the subsequent -OR elimination reaction; however, the reaction conditions and intermediate should be selected carefully because the elimination of the 4 '-hydrogen is facile under even slightly acidic or basic conditions to generate a stable furan. Since acyl moieties in general are more stable in basic than in acidic conditions, it is preferable to use a base, rather than an acid to convert the hydroxyl to a more activated acyl moiety. Furthermore, the base must be sufficiently strong to induce a reaction, yet weak enough not to promote elimination to the furan. Such bases include, but are not limited to l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and l,5-diazabicyclo[4.3.0]non-5-ene (DBN).

As one non-limiting example, it has been discovered that diisopropylethylamine and triethylamine yield little reaction and sodium hydride or lithium diisopropyl amine (LDA) can generate elimination to the furan during the addition of urethane via phenyl isothianate. Moreover, dusopropylethylamme can produce elimination to the furan during the addition of acetate via acetyl chloride.

The activated glycal can be formed at any temperature that allows the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. Preferred temperatures are from 0 °C to room temperature.

Examples of suitable reaction solvents are any solvents that are appropriate for the temperature and the solubility characteristics the reagents. Solvents include, but are not limited to any aprotic solvent including, but not limiting to, alkyl solvents such as hexane and cyclohexane, toluene, acetone, ethyl acetate, dithianes, THF, dioxane, acetonitrile, dichloromethane, dichloroethane, diethyl ether, pyridine, dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide, or any combination thereof, preferably THF.

Step Three - Preparation of a π-Allyl Complex

The second embodiment of the present invention includes the reaction of the activated glycol, preferably in situ, with a metal complex to form the π-allyl complex. The metal must be "hard" enough to displace the activated leaving group and form a π-allyl complex, such as palladium, nickel, or molybdenum, and preferably palladium.

Metal ligands should be selected that donate adequate electron density to activate the metal for the displacement reaction. Nonlimiting examples are any sufficiently donating arsenic ligand, any sufficiently donating phosphorous ligand, any sufficiently donating bidentate arsenic ligand, or any sufficiently donating bidentate phosphorous ligand. In a preferred embodiment, the metal ligand complex is used in a ratio of 0.1 molar percent to twenty molar percent, preferably 5 molar percent This includes, but is not limited to, bis- diphenylphosphinoethane (dppe) and Trost's ligand. For example, the catalytic palladium can be generated in situ by using catalytic amounts of commercially available (dibenzylideneacetone)₃Pd₂(CHCl₃) and two molar equivalents of dppe to form two equivalents of the suitably active Pd(dppe) species. The metal glycal complex is prepared at any reaction temperature that is suitable for the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. The preferred temperature is room temperature.

The metal/glycal complex is prepared in any solvent that is suitable to the temperature and the solubility of the reagents. Examples of solvents are any aprotic solvents including, but not limiting to, alkyl solvents such as hexane and cyclohexane, toluene, acetone, ethyl acetate, dithianes, THF, dioxane, acetonitrile, dichloromethane, dichloroethane, diethyl ether, pyridine, dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide, or any combination thereof, preferably dichloromethane or dichloroethane.

Step Four - Preparation of a β-D- or L-Nucleoside

D or L β^{"D or L}

In step four, the 2',3'-dideoxy-2',3'-didehydro-nucleoside is prepared by reaction of the π- allyl complex with a deprotonated (anionic) purine base, pyrimidine base, heteroaromatic, or heterocycle. Solubilizing substituents can be added to the purine base, pyrimidine base, heteroaromatic or heterocycle to promote solubility in the desired solvent system. It should also be understood that certain functional groups of the purine base, pyrimidine base, heteroaromatic or heterocycle might need to be protected to prevent unnecessary side reactions. The reactive moieties can be protected using conventional means and appropriate protecting groups well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, the free amine on cytosine may be protected by reaction with benzoyl chloride or any other suitable acyl compound to prevent unnecessary coupling at the N⁴ position, or to assist in solubilizing the compound in the organic solvent. The protected or unprotected purine base, pyrimidine base, heteroaromatic, or heterocycle is then reacted with another base, preferably DBU or DBN, to form the suitable nucleophile which then attacks the π- allyl complex to produce the β-2',3'-dideoxy-2',3'-didehydro-nucleoside. The base addition can take place at any reaction temperature that is suitable for the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. Preferred temperatures are from room temperature to refluxing conditions.

The reaction can take place in any solvent that provides the appropriate temperature and the solubility of the reagents. Examples of solvents include any aprotic solvent such as an alkyl solvent such as hexane and cyclohexane, toluene, acetone, ethyl acetate, dithianes, THF, dioxane, acetonitrile, dichloromethane, dichloroethane, diethyl ether, pyridine, dimethylformamide (DMF), dimethylsulfoxide (DMSO), dimethylacetamide or any combination thereof, preferably a combination of THF and sufficient DMF to enhance the solubility of the reagents, though excessive DMF slows the reaction rate.

Subsequently the nucleoside is deprotected at the 5' position by methods well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, a t-butyldiphenylsilyl protected 5'-OH can be deprotected with a IN TBAF solution of THF at room temperature.

Process for Manufacturing an -D- or L-Nucleoside

Step One - Preparation of a Suitable Starting Material, a-D- or L-Glycal

An α-D- or L-glycal can be prepared by any published or unpublished means including standard elimination or oxidation and reduction techniques. One embodiment of the process for the synthesis of a α-D- or L-glycal is provided by the following protocol.

The method of synthesis includes, first protecting a 3'-α-OH-deoxyriboheterocycle at the 5' position with a suitable protecting group, preferably with an acyl or silyl group, by methods well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, chloro-t- buxyl diphenylsilane may be reacted with the nucleoside to form the corresponding 5'-t- buxyl diphenylsilyl nucleoside at room temperature in anhydrous pyridine.

D or L D or L

The 3 '-hydroxyl group can then be selectively deprotected by methods well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, a trimethylsilyl group in the 3 '-position can be selectively deprotected over the 5'-t-butyl-diphenyl silyl group with potassium carbonate in a mixture of THF and methanol at room temperature. Step Two - Preparation of an Activated a-D- or L-Glycal

D or L D or L

The glycal is next activated at the 3' -OH to form a good leaving group 3 '-OR. Examples of R include, but are not limited to, alkyls to form ethers, acyls to form esters, or isothianates to form urethanes. In one embodiment, a phenyl urethane is formed via phenyl isothianate.

It is necessary to produce a sufficiently active moiety to facilitate the subsequent - OR elimination reaction; however, the reaction conditions and intermediate should be selected carefully because the elimination of the 4 '-hydrogen is facile under even slightly acidic or basic conditions to generate a stable furan. Since acyl moieties in general are more stable in basic than in acidic conditions, it is preferable to use a base, rather than an acid to convert the hydroxyl to a more activated acyl moiety. Furthennore, the base must be sufficiently strong to induce a reaction, yet weak enough not to promote elimination to the furan. Such bases include, but are not limited to l,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and l,5-diazabicyclo[4.3.0]non-5-ene (DBN).

As one non-limiting example, it has been discovered that diisopropylethylamine and triethylamine yield little reaction and sodium hydride or lithium diisopropyl amine (LDA) can generate elimination to the furan during the addition of urethane via phenyl isothianate. Moreover, diisopropylethylamine can produce elimination to the furan during the addition of acetate via acetyl chloride.

The activated glycal can be formed at any temperature that allows the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. Preferred temperatures are from 0°C to room temperature.

Step Three - Preparation of a π-Allyl Complex

D or L D or L

The second embodiment of the present invention includes the reaction of the activated gfycol, preferably in situ, with a metal complex to form the π-allyl complex. The metal must be "hard" enough to displace the activated leaving group and form a π-allyl complex, such as palladium, nickel, or molybdenum, and preferably palladium.

Metal ligands should be selected that donate adequate electron density to activate the metal for the displacement reaction. Nonlimiting examples are any sufficiently donating arsenic ligand, any sufficiently donating phosphorous ligand, any sufficiently donating bidentate arsenic ligand, or any sufficiently donating bidentate phosphorous ligand. hi a preferred embodiment, the metal ligand complex is used in a ratio of 0.1 molar percent to twenty molar percent, preferably 5 molar percent This includes, but is not limited to, bis- diphenylphosphinoethane (dppe) and Trost's ligand. For example, the catalytic palladium can be generated in situ by using catalytic amounts of commercially available (dibenzylideneacetone)₃Pd₂(CHCl₃) and two molar equivalents of dppe to form two equivalents of the suitably active Pd(dppe) species.

The metal/glycal complex is prepared at any reaction temperature that is suitable for the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. The preferred temperature is room temperature.

Step Four - Preparation of a a-D- or L-Nucleoside

In step four, the 2',3'-dideoxy-2',3'-didehydro-nucleoside is prepared by reaction of the π-allyl complex with a deprotonated (anionic) purine base, pyrimidine base, heteroaromatic, or heterocycle. Solubilizing substituents can be added to the purine base, pyrimidine base, heteroaromatic or heterocycle to promote solubility in the desired solvent system. It should also be understood that certain functional groups of the purine base, pyrimidine base, heteroaromatic or heterocycle might need to be protected to prevent unnecessary side reactions. The reactive moieties can be protected using conventional means and appropriate protecting groups well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, the free amine on cytosine may be protected by reaction with benzoyl chloride or any other suitable acyl compound to prevent unnecessary coupling at the N⁴ position, or to assist in solubilizing the compound in the organic solvent. The protected or unprotected purine base, pyrimidine base, heteroaromatic, or heterocycle is then reacted with another base, preferably DBU or DBN, to form the suitable nucleophile which then attacks the π-allyl complex to produce the β-2',3'-dideoxy-2',3'-didehydro- nucleoside.

The base addition can take place at any reaction temperature that is suitable for the reaction to proceed at an acceptable rate without promoting decomposition or excessive side products. Preferred temperatures are from room temperature to refluxing conditions.

Subsequently the nucleoside is deprotected at the 5' position by methods well known to those skilled in the art, as taught in Greene, et al, Protective Groups in Organic Synthesis, John Wiley and Sons, Second Edition, 1991. For example, a t-butyldiphenylsilyl protected 5' -OH can be deprotected with a IN TBAF solution of THF at room temperature.

Examples of the compounds, illustrated in Figures 2a and 2b, which may be prepared according to the present invention include 3'-α-OH-thymidine (11), anl ydrothymidine (12), 3'-β-OH-thymidine (13), 5'-protected 3'-β-OH-thymidine (14), 5'- protected 3 '-β-O-trimethylsily l-glycal (15), 5'-protected-3'-β-OH-glycal (16), activated 5'- protected-3'-β-glycal (17), 5'-protected β-2',3'-dideoxydidehydrothymidine (18), 5'- protected β-2',3'-dideoxydidehydro-6-chloropuridine (19), 5 '-protected α-2',3'-dideoxy- didehydro-6-chloropuridine, and β-2',3'-dideoxydidehydrothymidine (20).

The following working examples provide a further understanding of the method of the present invention. These examples are of illustrative purpose, 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 herein without departing from the general scope of the method of synthesis.

Melting points were determined on a Mel-temp II laboratory device and are uncorrected. Nuclear magnetic resonance spectra were recorded on a Bruker 250 and AMX400 400 MHz spectrometers with tetramethylsilane as the internal reference; chemical shifts (δ) are reported in parts per million (ppm), and the signals are described as s (singlet), d (doublet), t (triplet), q (quartet), bs (broad singlet), dd (doublet of doublet), and m (multiplet). UV spectra were obtained on a Beckman DU 650 spectrophotometer. Optical rotations were measured on a Jasco DIP-370 Digital Polarimeter. Mass spectra were measured on a Micromass Inc. Autospec High Resolution double focussing sector (EBE) MS spectrometers. Infrared spectra were recorded on a Nicolet 510 FT-LR spectrometer. Elemental analyses were performed by Atlantic Microlab, Inc., Norcross, GA. All reactions were monitored using thin layer chromatography on Analtech, 200 mm silica gel GF plates. Dry 1,2-dichloroethane, dichloromethane, acetonitrile and THF were obtained by drying over 4A molecular sieves.

EXAMPLES

I. Preparation of Anhydrothymidine (12)

Thymidine (11, 24.2g, 100 mmol) and triphenylphosphine (52.6g, 200 mmol, 2 eq.) were suspended in THF (400 mL), and the suspension was concentrated under vacuum to dryness. Acetonitrile (800 mL) was added, and the resulting solids were broken and suspended. With a vigorous stirring, the suspension was cooled to -10°C in an ice- methanol bath. Diisopropyl azodicarboxylate (21 mL, 100 mmol, 1 eq.) was added dropwise at less than -10 °C. Upon completion of the addition, the mixture was allowed to warm up to room temperature over 1 hour, then aged at room temperature for 14 hours. The resulting slurry was poured into ethyl acetate (1000 mL) at room temperature and the mixture was stirred for 1 hour. Solids were collected by filtration, washed with ethyl acetate (100 mL), and dried under vacuum to give an off-white solid (21.4g, 94 mmol, 94% yield) 12. 1H NMR of 12 (in DMSO-D6) 7.54 (s, 1H); 5.79 (d, 1H, J=3.6Hz); 5.23 (s, 1H); 5.05 (t, 1H, J=5.4Hz); 4.17 (dt, 1H, J=2.4, 12.0Hz); 3.46 (m, 2H); 2.48 (m, 2H); 1.73 (s, 3H).

II. Preparation of 3'-β-OH-Thymidine (13) and 5'-Protected-3'-β-OH-Thymidine (14)

The anhydrothymidine 12 (11.4g, 50 mmol) was suspended in THF (250 mL). With a vigorous stirring, 2N aqueous NaOH solution (35 mL, 70 mmol, 1.4 eq.) was added at room temperature and the mixture was aged at room temperature for 5 hours. The solution was acidified with IN aqueous HC1 solution (75 mL, 75 mmol). (The pH of the resulting solution was ca. 3.) The mixture was then concentrated to dryness under vacuum. Additional THF (300 mL) was added and concentrated to dryness. With additional THF (300 mL), concentration was repeated. 1H NMR of 13 (in DMSO-d6) 7.79 (d, 1H, J=1.2Hz); 6.04 (dd, 1H, J=2.4, 8.3Hz); 5.33 (bs, 1H); 4.75 (t, 1H, J=5.4Hz); 4.21 (m, 1H); 3.78-3.55 (m, 3H); 2.51 (m, 1H); 1.82 (dd, 1H, J=2.2, 14.7Hz); 1.74 (d, 3H, J=1.0Hz).

The resulting solids were suspended in dry pyridine (100 mL). TBDPSC1 (17.5 mL, 67 mmol, 1.3 eq.) was added to it at room temperature and the mixture was aged at room temperature for 14 hours. The mixture then concentrated under vacuum to remove most of the pyridine and the resulting oil was partitioned between ethyl acetate (300 mL) and water (200 mL). The organic layer was separated, washed with 0.5 N HC1 (aq. 200 mL) and water (200 mL), respectively. The organic layer was concentrated to an oil, which was further purified by crystallization using 5:1 hexanes : ethyl acetate mixture (800 mL) to provide a white solid 14 (20.2g, 42 mmol, 84% yield). Second crop (1.2g, 2.5 mmol, 5% yield) was obtained from the filtrate by crystallization using 10:1 hexanes : ethyl acetate (500 mL). Total yield was 89 %. 1H NMR of 14 (in CDC1₃) 8.00 (bs, 1H); 7.77 (s, 1H); 7.70-7.37 (m, 10H); 6.24 (dd, 1H, J=2.9, 8.5Hz); 4.56 (m, 1H); 4.11 (m, 2H); 3.83 (m, 1H); 3.67 (d, 1H, J=2.9Hz); 2.64 (m, 1H); 2.09 (dd, 1H, J=2.2, 15.4Hz); 1.82 (d, 3H, J=1.0Hz).

III. Preparation of 5'-Protected-3'-β-0-TrimethylsiIyIglycal (15) and 5'-Protected-3'- β-OH-Glycal (16)

The 3'-β-OH thymidine derivative 14 (9.6g, 20 mmol) was suspended in hexamethyl disilazane (100 mL). Ammonium sulfate (2.7g, 20 mmol, 1 eq.) was added and the mixture was heated to reflux for 4 hours. The mixture was cooled to room temperature and concentrated to dryness. The resulting mixture was taken up with a 4:1 mixture of hexanes : ethyl acetate (100 mL), and the solution was passed through a pad of silica gel (70 mL in volume). The pad was washed with the same solvent mixture (300 mL). The combined filtrate was concentrated to dryness to give an oil 15 (8.2g, 19.2 mmol, 96% yield). 1H NMR of 15 (in CDC1₃) 7.72-7.35 (m, 10H); 6.60 (d, 1H, J=2.4Hz); 5.07 (t, 1H, J=2.7Hz); 4.82 (dd, 1H, J=2.4Hz); 4.27 (m, 1H); 3.94 (dd, 1H, J=4.6, 11.2Hz); 3.91 (dd, 1H, J=6.3, 11.5Hz); 1.08 (s, 9H); 0.01 (s, 9H).

The oily 15 was dissolved in a mixture of THF/methanol (70 nιL/70 mL). A milled potassium carbonate (2.8g, 20 mmol) was added portion-wise at RT and the mixture was aged for 2 hours at room temperature. The mixture was concentrated to dryness and further purified by column chromatography using a 8:1 mixture of hexanes : ethyl acetate to give a pale-yellow oil 16 (3.5g, 10 mmol, 50% yield for two steps). 1H NMR of 16 (in CDC1₃) 7.74-7.37 (m, 10H); 6.61 (d, 1H, J=3.2Hz); 5.23 (t, 1H, J=3.0Hz); 5.01 (m, 1H); 4.34 (m, 1H); 4.13 (m, 2H); 2.72 (d, 1H, J=9.5Hz); 1.06 (s, 9H).

IV. Preparation of Activated 5'-Protected-3'-β-Glycal (17) and 5'-Protected β-2',3'- Dideoxydidehydrothymidine (18)

The β-OH-glycal 16 (223 mg, 0.63 mmol) was dissolved in dichloromethane (15 mL). The solution was cooled to 0 °C and to it were added phenyl isothianate (0.075 mL, 0.69 mmol) and DBU (0.102 mL, 0.69 mmol). The mixture was allowed to warm up to room temperature and aged for 1 hour. 1H NMR of 17 (in CDC1₃) 7.70-7.27 (m, 15H); 6.70 (d, 1H, J=3.0Hz); 5.87 (dd, 1H, J=2.7, 7.1Hz); 5.28 (t, 1H, J=2.7Hz); 4.53 (dd, 1H, J=2.6, 12.7Hz); 4.02 (m, 2H); 1.07 (s, 9H).

Catalyst solution was separately prepared using bis(diphenylphosphino)ethylene (40 mg, 0.1 mmol) and (dba)₃Pd₂ (0) (46 mg, 0.1 mmol of Pd) in dichloromethane (5 mL), and added to the reaction mixture at RT. Base solution was prepared separately with thymine (80 mg, 0.63 mmol) and DBU (0.102 mL, 0.69 mmol) in THF/DMF mixture (5 nιL/5 mL), and added to the reaction mixture at RT. The mixture was then heated to reflux for 4 h. The reaction mixture was concentrated to dryness and the resulting mixture was purified using column chromatography using 1:1 hexanes : ethyl acetate to give the d4 nucleoside 18 (180 mg, 0.39 mmol, 62% yield) as a mixture of 95:5 of β:α isomers. 1H NMR of β-isomer of 18 (in CDC1₃) 8.07 (bs, 1H); 7.66-7.34 (m, 10H); 7.15 (d, 1H, J=1.2Hz); 6.99 (dd, 1H, J=1.7, 3.2Hz); 6.37 (m, 1H); 5.86 (m, 1H); 4.93 (m, 1H); 3.90 (m, 2H); 1.59 (s, 3H); 1.07 (s, 9H).

V. Preparation of 5'-Protected-3'-β-GIycal (17) and 5'-Protected β-2',3'-Dideoxy- Didehydro-6-Chloropuridine (19)

The β-OH-glycal 16 (208 mg, 0.59 mmol) was dissolved in dichloromethane (20 mL). The solution was cooled to 0 °C and to it were added phenyl isothianate (0.070 mL, 0.65 mmol) and DBU (0.096 mL, 0.65 mmol). The mixture was allowed to warm up to room temperature and aged for 1 hour. 1H NMR of 17 (in CDC1₃) 7.70-7.27 (m, 15H); 6.70 (d, 1H, J=3.0Hz); 5.87 (dd, 1H, J=2.7, 7.1Hz); 5.28 (t, 1H, J=2.7Hz); 4.53 (dd, 1H, J=2.6, 12.7Hz); 4.02 (m, 2H); 1.07 (s, 9H).

Catalyst solution was separately prepared using bis(diphenylphosphino)ethane (40 mg, 0.1 mmol) and (dba)₃Pd₂ (0) (46 mg, 0.1 mmol of Pd) in dichloromethane (5 mL), and added to the reaction mixture at room temperature. Base solution was prepared separately with 6-Chloropurine (93 mg, 0.65 mmol) and DBU (0.096 mL, 0.65 mmol) in dichloromethane (5 mL), and added to the reaction mixture at room temperature. The mixture was then heated to reflux for 24 hours. The reaction mixture was concentrated to dryness and the resulting mixture was purified using column chromatography using 5:1 hexanes : ethyl acetate then 3:2 mixture to give the d4 nucleoside (107 mg, 0.22 mmol, 37% yield) as a mixture of 95:5 of β:α isomers. ^!H NMR of β-isomer of 19 (in CDC1 ) 8.73 (s, 1H); 8.21 (s, 1H); 7.60-7.28 (m, 10H); 7.14 (m, 1H); 6.47 (dt, 1H, J=1.7, 6.0Hz); 6.09 (ddd, 1H, J=1.3, 2.0, 5.9Hz); 5.06 (m, 1H); 3.82 (m, 2H); 1.04 (s, 9H).

VI. Preparation of 5'-Protected α-2',3'-Dideoxydidehydro-6-Chloropuridine (19)

The α-OH-glycal (200 mg, 0.58 mmol) was dissolved in dichloromethane (20 mL). The solution was cooled to 0 °C and to it were added phenyl isothianate (0.070 mL, 0.65 mmol) and DBU (0.096 mL, 0.65 mmol). The mixture was allowed to warm up to room temperature and aged for 1 hour. Catalyst solution was separately prepared using bis(diphenylphosphino)ethane (40 mg, 0.1 mmol) and (dba)₃Pd₂ (0) (46 mg, 0.1 mmol of Pd) in dichloromethane (5 mL), and added to the reaction mixture at room temperature. Base solution was prepared separately with 6-chloropurine (93 mg, 0.65 mmol) and DBU (0.096 mL, 0.65 mmol) in dichloromethane (5 mL), and added to the reaction mixture at room temperature. The mixture was then heated to reflux for 16 hours. The reaction mixture was concentrated to dryness and the resulting mixture was purified using column chromatography using 5:1 hexanes : ethyl acetate then 3:2 mixture to give the D4 nucleoside 19 (67 mg, 0.14 mmol, 24% yield) as a mixture of 3:7 of β:α isomers. 1H NMR of α-isomer of 19 (in CDC1₃) 8.78 (s, 1H); 8.13 (s, 1H); 7.70-7.28 (m, 10H); 7.17 (d, 1H, J=1.4Hz); 6.50 (d, 1H, J=5.8Hz); 6.14 (d, 1H, J=5.8Hz); 5.23 (m, 1H); 3.85 (m, 2H); 1.07 (s, 9H). VII. Preparation of β-2',3'-dideoxydidehydrothymidine, D4T (20)

The silyl D4-nucleoside 18 (430 mg, 0.9 mmol) was dissolved in THF (10 mL), and to it was added IN TBAF solution in THF at room temperature. The mixture was stirred for 30 minutes at room temperature. The mixture was concentrated, chromatographed with ethyl acetate to give the known D4T, 20 (160 mg, 0.71 mmol, 80% yield). NMR was identical to that of D4T.

This invention has been described with reference to its preferred embodiments. Variations and modifications of the invention, will be obvious to those skilled in the art from the foregoing detailed description of the invention.

Claims

We claim:

1. A process for converting a 3'-β-glycal to a β-D- or β-L-2',3'-dideoxy-2',3'- didehydronucleoside or a 3'-α-glycal to a α-D- or α-L-2',3'-dideoxy-2',3'- didehydronucleoside comprising the steps of:

a) activating of a glycal of structure 1, 2, 3, or 4

wherein Z is carbon or a heteroatom, P is a suitable oxygen protecting group, and R is a H, a silyl, or an activating group

with a metal to form a D or L π-allyl complex of structure 5 or 6

wherein M is a metal capable of forming a π-allyl complex, and each L is independently an activating ligand; and then

b) reacting the complex of structure 5 or 6 with a heterocyclic or heteroaryl base to form a nucleoside of structure 7, 8, 9 or 10

10 wherein P' is H or a suitable oxygen protecting group, and B is a purine base, pyrimidine base, nitrogen, oxygen, or sulfur heterocycle or heteroaromatic of Ci

2. The process of claim 1 wherein ML₃ is PdL₂(solvent).

3. The process of claim 1, wherein Z is oxygen, ML_X is PdL₂(solvent), OR is -OC(O)NH(Phenyl), P is t-butyldiphenylsilyl, and B is a pyrimidine or purine base.

4. The process of claim 1, wherein the starting material is 5'-t-butyldiphenylsilyl-3' phenylurethane-glycal.

5. The process of claim 1 , wherein the base is an unprotected purine or pyrimidine base.

6. The process of claim 1, wherein the metal used to form the π-allyl complex is (dba)₃Pd₂ with bis-diphosphinoethane.

7. The process of claim 1, wherein the solvent is dichloromethane or dichloromethane/DMF/THF.

8. The process of claim 1, wherein at least one L is 1,2-diphenylphosphinoethane (dppe).

9. The process of claim 1, further comprising reducing the 2',3'-dideoxy-2',3'- didehydronucleoside (D4) to a 2',3'-dideoxy-nucleoside (D2).

10. The process of claim 1, wherein the base is selected from the group consisting of guanosine, inosine, cytidine, uridine, thymidine, adenosine, 5-fluorocytidine, and 6- chloropurine.

11. The process of claim 1, wherein the metal capable of forming π-complex is selected from the group consisting of palladium, nickel and molybdenum.

12. The process of claim 1 wherein L is a bidentate ligand.

13. The process of claim 1 wherein at most one L is independently solvent and the remaining are a bidentate ligand.

14. The process of claim 1, wherein the β-D-2',3'-dideoxy-2',3'-didehydronucleoside is β- D-2',3 '-dideoxy-2',3 '-didehydro-5-fluorocytidine.

15. The process of claim 1, wherein the β-D-2',3'-dideoxy-2',3'-didehydronucleoside is β- D-2 ' ,3 ' -dideoxy-2 ' ,3 ' -didehydro-thymidine.