Other methods based on the modification of carbohydrates have also been described: 7) Protection of readily available (S)-(+)-gamma-(hydroxymethyl)-gamma-butyrolactone (XIX) with tert-butyldiphenylsilyl chloride gives ether (XX), which is converted to the seleno derivative (XXI) on treatment with lithium hexamethyldisilazide and trimethylchlorosilane in tetrahydrofuran, followed by reaction with phenylselenylbromide. Reduction of (XXI) with diisobutylaluminum hydride in toluene followed by acetylation gives compound (XXII), which is reacted with (XXIII) and trimethylsilyltriflate in dichloroethane to afford stereoselectively compound (XXIV). The latter is finally submitted to elimination and deprotected by successive treatment with hydrogen peroxide in pyridine and tetrabutylammonium fluoride in tetrahydrofuran. 8) A related route involves treatment of (XX) with lithium diisopropylamide in tetrahydrofuran and diphenylsulfide in HMPA to give (XXV), which is reduced and acetylated to yield (XXVI). Compound (XXVI) is treated with (XXIII) in the presence of tin tetrachloride in dichloromethane to afford (XXVII), which is oxidized with sodium periodate and submitted to elimination by treating in toluene-pyridine, to yield compound (XXVIII). Finally, compound (XXVIII) is deprotected with tetrabutylammonium fluoride in tetrahydrofuran. 9) A third procedure begins with the protection of (XIX) as a tert-butoxycarbonyl ester to yield (XXIX), reduction with diisobutylaluminum hydride in tetrahydrofuran to afford (XXX) and elimination after treatment with thionyl chloride in dichloromethane and potassium tert-butoxide in tetrahydrofuran to give (XXXI). Subsequent reaction of compound (XXXI) with thymine (IX) in the presence of hexamethyldisilazane and trimethylsilyl chloride and N-chlorosuccinimide in tetrahydrofuran gives compound (XXXII), which is treated with potassium tert-butoxide in tetrahydrofuran and deprotected with sodium methoxide in methanol.

6) Another route involves acetylation of the anhydro derivative (XVI) to give (XVII), which is converted to (XVIII) by treatment with sodium bromide in sulfuric acid and submitted to elimination with zinc and sodium hydroxide.

4) Reaction of thymine (IX) with 1-O-acetyl-2,3,5-tri-O-benzoylribose (X) and hexamethyldisilazane, trimethylsilyl chloride and trifluoromethanesulfonic acid in acetonitrile, followed by cleavage of the protecting groups with sodium methoxide in methanol gives 5-methyluridine (XI). Compound (XI) is converted to (XII) by means of 2-acetoxyisobutyryl bromide in acetonitrile, subsequent reaction of (XII) with zinc-copper in dimethylformamide yields (XIII), which is finally deprotected with sodium methoxide in methanol. 5) 5-Methyluridine (XI) can also be converted to (XIV) by means of trimethylorthoacetate in acetic acid. Compound (XIV) is then treated with hydrobromic acid to give (XV), which is treated with zinc in acetonitrile and EDTA or is successively treated with acetic anhydride, zirconium oxide and tributylamine.

4) Reaction of thymine (IX) with 1-O-acetyl-2,3,5-tri-O-benzoylribose (X) and hexamethyldisilazane, trimethylsilyl chloride and trifluoromethanesulfonic acid in acetonitrile, followed by cleavage of the protecting groups with sodium methoxide in methanol gives 5-methyluridine (XI). Compound (XI) is converted to (XII) by means of 2-acetoxyisobutyryl bromide in acetonitrile, subsequent reaction of (XII) with zinc-copper in dimethylformamide yields (XIII), which is finally deprotected with sodium methoxide in methanol. 5) 5-Methyluridine (XI) can also be converted to (XIV) by means of trimethylorthoacetate in acetic acid. Compound (XIV) is then treated with hydrobromic acid to give (XV), which is treated with zinc in acetonitrile and EDTA or is successively treated with acetic anhydride, zirconium oxide and tributylamine.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

Finally, the first total synthesis of stavudine has also been described: Starting from epoxide (XXXIII), readily available in four steps from crotonaldehyde, compound (XXXIV) is obtained after reaction with selenophenol and diethylaluminum fluoride in dichloromethane. Reaction of (XXXIV) with hydrochloric acid in methanol-dichloromethane gives (XXXV), which is acetylated to give (XXXVI). Introduction of silylated thymine (XXIII) catalyzed by tert-butyldimethylsilyl triflate in dichloromethane affords compound (XXXVII), which is converted to (XXXVIII) on treatment with m-chloroperbenzoic acid in dichloromethane. Deprotection of (XXXVIII) provides an anomeric mixture of stavudine and its alpha-anomer (XXXIX).

Alovudine can be obtained by several related ways: 1) The acylation of thymidine (I) with 4-chlorobenzoylchloride (II) in pyridine gives 5'-O-(4-chlorobenzoyl)thymidine (IX), which is then treated with diethylamino sulfur trifluoride in methylene chloride at -79 C, and finally with NaHCO3 in refluxing methanol. 2) By reaction of 2,3'-anhydro-1-(2'-deoxy-beta-D-xylofuranosyl)thymine (III) with AlF3 and 1% HF in anhydrous dioxan at 150-7 C. 3) By reaction of (III) with KHF2 or NH4F in diethylene glycol at 190C, or in ethanol at 150 C. 4) The reaction of 2,3'-anhydro-5'-O-(methylsufonyl)-1-(2'-deoxy-beta-D-xylofuranosyl) thymine (IV) with AlF3 and HF as before gives 3'-deoxy-3'-fluoro-5'-O-(methylsulfonyl)thymidine (V), which is then treated with NaOH in refluxing ethanol. 5) By reaction of 5'-O-(triphenylmethyl)thymidine (VI) with diethylamino sulfur trifluoride in THF, and then with aqueous, NaHCO3. 6) By reaction of 3'-O-(methylsulfonyl)thymidine (VII) with KHF2 or NH4F in diethylene glycol at 190 C. 7) By reaction of 2,3'-anhydro-5'-O-(triphenylmethyl)-1-(2'-deoxy-beta-D-xylofuranosyl) thymine (VIII) with 4-6% HF in anhydrous dioxan at 90 C.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

Other methods based on the modification of carbohydrates have also been described: 7) Protection of readily available (S)-(+)-gamma-(hydroxymethyl)-gamma-butyrolactone (XIX) with tert-butyldiphenylsilyl chloride gives ether (XX), which is converted to the seleno derivative (XXI) on treatment with lithium hexamethyldisilazide and trimethylchlorosilane in tetrahydrofuran, followed by reaction with phenylselenylbromide. Reduction of (XXI) with diisobutylaluminum hydride in toluene followed by acetylation gives compound (XXII), which is reacted with (XXIII) and trimethylsilyltriflate in dichloroethane to afford stereoselectively compound (XXIV). The latter is finally submitted to elimination and deprotected by successive treatment with hydrogen peroxide in pyridine and tetrabutylammonium fluoride in tetrahydrofuran. 8) A related route involves treatment of (XX) with lithium diisopropylamide in tetrahydrofuran and diphenylsulfide in HMPA to give (XXV), which is reduced and acetylated to yield (XXVI). Compound (XXVI) is treated with (XXIII) in the presence of tin tetrachloride in dichloromethane to afford (XXVII), which is oxidized with sodium periodate and submitted to elimination by treating in toluene-pyridine, to yield compound (XXVIII). Finally, compound (XXVIII) is deprotected with tetrabutylammonium fluoride in tetrahydrofuran. 9) A third procedure begins with the protection of (XIX) as a tert-butoxycarbonyl ester to yield (XXIX), reduction with diisobutylaluminum hydride in tetrahydrofuran to afford (XXX) and elimination after treatment with thionyl chloride in dichloromethane and potassium tert-butoxide in tetrahydrofuran to give (XXXI). Subsequent reaction of compound (XXXI) with thymine (IX) in the presence of hexamethyldisilazane and trimethylsilyl chloride and N-chlorosuccinimide in tetrahydrofuran gives compound (XXXII), which is treated with potassium tert-butoxide in tetrahydrofuran and deprotected with sodium methoxide in methanol.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

4) Reaction of thymine (IX) with 1-O-acetyl-2,3,5-tri-O-benzoylribose (X) and hexamethyldisilazane, trimethylsilyl chloride and trifluoromethanesulfonic acid in acetonitrile, followed by cleavage of the protecting groups with sodium methoxide in methanol gives 5-methyluridine (XI). Compound (XI) is converted to (XII) by means of 2-acetoxyisobutyryl bromide in acetonitrile, subsequent reaction of (XII) with zinc-copper in dimethylformamide yields (XIII), which is finally deprotected with sodium methoxide in methanol. 5) 5-Methyluridine (XI) can also be converted to (XIV) by means of trimethylorthoacetate in acetic acid. Compound (XIV) is then treated with hydrobromic acid to give (XV), which is treated with zinc in acetonitrile and EDTA or is successively treated with acetic anhydride, zirconium oxide and tributylamine.

6) Another route involves acetylation of the anhydro derivative (XVI) to give (XVII), which is converted to (XVIII) by treatment with sodium bromide in sulfuric acid and submitted to elimination with zinc and sodium hydroxide.

Other methods based on the modification of carbohydrates have also been described: 7) Protection of readily available (S)-(+)-gamma-(hydroxymethyl)-gamma-butyrolactone (XIX) with tert-butyldiphenylsilyl chloride gives ether (XX), which is converted to the seleno derivative (XXI) on treatment with lithium hexamethyldisilazide and trimethylchlorosilane in tetrahydrofuran, followed by reaction with phenylselenylbromide. Reduction of (XXI) with diisobutylaluminum hydride in toluene followed by acetylation gives compound (XXII), which is reacted with (XXIII) and trimethylsilyltriflate in dichloroethane to afford stereoselectively compound (XXIV). The latter is finally submitted to elimination and deprotected by successive treatment with hydrogen peroxide in pyridine and tetrabutylammonium fluoride in tetrahydrofuran. 8) A related route involves treatment of (XX) with lithium diisopropylamide in tetrahydrofuran and diphenylsulfide in HMPA to give (XXV), which is reduced and acetylated to yield (XXVI). Compound (XXVI) is treated with (XXIII) in the presence of tin tetrachloride in dichloromethane to afford (XXVII), which is oxidized with sodium periodate and submitted to elimination by treating in toluene-pyridine, to yield compound (XXVIII). Finally, compound (XXVIII) is deprotected with tetrabutylammonium fluoride in tetrahydrofuran. 9) A third procedure begins with the protection of (XIX) as a tert-butoxycarbonyl ester to yield (XXIX), reduction with diisobutylaluminum hydride in tetrahydrofuran to afford (XXX) and elimination after treatment with thionyl chloride in dichloromethane and potassium tert-butoxide in tetrahydrofuran to give (XXXI). Subsequent reaction of compound (XXXI) with thymine (IX) in the presence of hexamethyldisilazane and trimethylsilyl chloride and N-chlorosuccinimide in tetrahydrofuran gives compound (XXXII), which is treated with potassium tert-butoxide in tetrahydrofuran and deprotected with sodium methoxide in methanol.

Finally, the first total synthesis of stavudine has also been described: Starting from epoxide (XXXIII), readily available in four steps from crotonaldehyde, compound (XXXIV) is obtained after reaction with selenophenol and diethylaluminum fluoride in dichloromethane. Reaction of (XXXIV) with hydrochloric acid in methanol-dichloromethane gives (XXXV), which is acetylated to give (XXXVI). Introduction of silylated thymine (XXIII) catalyzed by tert-butyldimethylsilyl triflate in dichloromethane affords compound (XXXVII), which is converted to (XXXVIII) on treatment with m-chloroperbenzoic acid in dichloromethane. Deprotection of (XXXVIII) provides an anomeric mixture of stavudine and its alpha-anomer (XXXIX).

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

4) Reaction of thymine (IX) with 1-O-acetyl-2,3,5-tri-O-benzoylribose (X) and hexamethyldisilazane, trimethylsilyl chloride and trifluoromethanesulfonic acid in acetonitrile, followed by cleavage of the protecting groups with sodium methoxide in methanol gives 5-methyluridine (XI). Compound (XI) is converted to (XII) by means of 2-acetoxyisobutyryl bromide in acetonitrile, subsequent reaction of (XII) with zinc-copper in dimethylformamide yields (XIII), which is finally deprotected with sodium methoxide in methanol. 5) 5-Methyluridine (XI) can also be converted to (XIV) by means of trimethylorthoacetate in acetic acid. Compound (XIV) is then treated with hydrobromic acid to give (XV), which is treated with zinc in acetonitrile and EDTA or is successively treated with acetic anhydride, zirconium oxide and tributylamine.

Other methods based on the modification of carbohydrates have also been described: 7) Protection of readily available (S)-(+)-gamma-(hydroxymethyl)-gamma-butyrolactone (XIX) with tert-butyldiphenylsilyl chloride gives ether (XX), which is converted to the seleno derivative (XXI) on treatment with lithium hexamethyldisilazide and trimethylchlorosilane in tetrahydrofuran, followed by reaction with phenylselenylbromide. Reduction of (XXI) with diisobutylaluminum hydride in toluene followed by acetylation gives compound (XXII), which is reacted with (XXIII) and trimethylsilyltriflate in dichloroethane to afford stereoselectively compound (XXIV). The latter is finally submitted to elimination and deprotected by successive treatment with hydrogen peroxide in pyridine and tetrabutylammonium fluoride in tetrahydrofuran. 8) A related route involves treatment of (XX) with lithium diisopropylamide in tetrahydrofuran and diphenylsulfide in HMPA to give (XXV), which is reduced and acetylated to yield (XXVI). Compound (XXVI) is treated with (XXIII) in the presence of tin tetrachloride in dichloromethane to afford (XXVII), which is oxidized with sodium periodate and submitted to elimination by treating in toluene-pyridine, to yield compound (XXVIII). Finally, compound (XXVIII) is deprotected with tetrabutylammonium fluoride in tetrahydrofuran. 9) A third procedure begins with the protection of (XIX) as a tert-butoxycarbonyl ester to yield (XXIX), reduction with diisobutylaluminum hydride in tetrahydrofuran to afford (XXX) and elimination after treatment with thionyl chloride in dichloromethane and potassium tert-butoxide in tetrahydrofuran to give (XXXI). Subsequent reaction of compound (XXXI) with thymine (IX) in the presence of hexamethyldisilazane and trimethylsilyl chloride and N-chlorosuccinimide in tetrahydrofuran gives compound (XXXII), which is treated with potassium tert-butoxide in tetrahydrofuran and deprotected with sodium methoxide in methanol.

A new asymmetric synthesis of stavudine has been described: The regioselective epoxidation of allyl alcohol (I) by means of titanium tetraisopropoxide and alpha,alpha-dimethylbenzylperoxide, catalyzed by diisopropyl D-tartrate, followed by esterification with pivaloyl chloride yields the epoxide (II), which is then condensed with lithium acetylide catalyzed by boron trifluoride ethearate in THF, yielding the acetylenic alcohol (III). The cyclization of (III) catalyzed by Mo(CO)6 and trimethylamine oxide affords the dihydrofuran (IV), which is condensed with N,N'-bis(trimethylsilyl)thymine (V) and I2 to give the iodonucleoside (VI). Finally, this compound is dehydroiodinated and deprotected with sodium methoxide in methanol.

The enantioselective epoxidation of allyl alcohol (I) with 2-phenylisopropyl hydroperoxide (II) and Ti(iPrO)4 in the presence of D-diisopropyl tartrate gives the chiral epoxide (III), which is esterified with pivaloyl chloride to yield the pivalate (IV). The opening of the epoxide ring of (IV) by means of lithium acetylide (V) and BF3/Et2O affords the alkynyl alcohol (VI), which is cyclized by means of Mo(CO)6 and trimethylamine oxide to provide the chiral dihydrofuran (VII). The oxidation of (VII) with OsO4 and 4-methylmorpholine-N-oxide (NMMO) gives the diol (VIII), which is treated with Ac2O to yield the diacetate (IX). The condensation of (IX) with N6-benzoyl-N6,7-bis(trimethylsilyl)adenine (X) by means of Tms-OTf affords the nucleoside (XI). Finally, this compound is deprotected by means of NaOMe in methanol.

A new synthesis of stavudine has been reported: The condensation of thymine (I) with methyl 2-deoxyribofuranoside (II) by means of N-bromosuccinimide (NBS) followed by protection with TBDPS-Cl gives the intermediate (III), which is cyclized by means of trimethylsilyl triflate (TMS-OTf), yielding the cyclothymidine derivative (IV). The deprotection of (IV) with tetrabutylammonium fluoride affords the unprotected compound (V), which is finally treated successively with triflate anhydride, 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and Zn/acetic acid. The unprotected intermediate compound (V) can also be obtained by cyclization of thymidine (VI) by means of NBS in DMF, catalyzed by trifluoroacetic acid.

The synthesis of [1'-14C]-labeled stavudine has been published: The reaction of labeled D-ribofuranose (I) first with methanol and acetyl chloride and then with benzoyl chloride gives 2,3,5-tri-O-benzoyl-1-O-methyl-D-ribofuranoside (II), which is acetylated with acetic anhydride and acetic acid to 1-O-acetyl-2,3,5-tri-O-benzoyl-beta-D-ribofuranoside (III). The condensation of (III) with thymine (IV) by means of hexamethyldisylazane (HMDS), trimethylsilyl chloride (TMS-Cl) and trifluoromethanesulfonic acid, followed by a basic hydrolysis with NaOMe affords 1-(beta-D-ribofuranosyl)thymine (V), which is treated with methanesulfonyl chloride in pyridine giving the trimesylate (VI). The reaction of (VI) with sodium benzoate in hot DMF yields the benzoylated internal ether (VII), which is treated with acetyl bromide in acetic acid/HBr affording 1-[2-bromo-2-deoxy-5-O-benzoyl-3-O-(methanesulfonyl)-beta-D-ribofuranos yl]thymine (VIII). The reaction of (VIII) with Zn in the same solvent as before gives 5'-O-benzoylstavudine (IX), which is finally debenzoylated with NaOCH3 in methanol.

An improved process for the preparation of high purity stavudine in a good yield was reported: The reaction of 5-methyluridine (I) with mesyl chloride and NMM in acetone, followed by a treatment with 6N NaOH gives the 2,2?anhydro-5-methyluridine derivative (II), which is treated successively with potassium benzoate in DMF, HBr in acetic acid, and finally with Zn in DMF to yield 2?3?anhydro-5?O-benzoylthymidine (III). Finally, this compound is debenzoylated with hot butylamine.

4) Reaction of thymine (IX) with 1-O-acetyl-2,3,5-tri-O-benzoylribose (X) and hexamethyldisilazane, trimethylsilyl chloride and trifluoromethanesulfonic acid in acetonitrile, followed by cleavage of the protecting groups with sodium methoxide in methanol gives 5-methyluridine (XI). Compound (XI) is converted to (XII) by means of 2-acetoxyisobutyryl bromide in acetonitrile, subsequent reaction of (XII) with zinc-copper in dimethylformamide yields (XIII), which is finally deprotected with sodium methoxide in methanol. 5) 5-Methyluridine (XI) can also be converted to (XIV) by means of trimethylorthoacetate in acetic acid. Compound (XIV) is then treated with hydrobromic acid to give (XV), which is treated with zinc in acetonitrile and EDTA or is successively treated with acetic anhydride, zirconium oxide and tributylamine.

The benzoylation of thymidine (I) with benzoyl chloride, PPh3 and DIAD in THF gives the 5'-O-benzoylthymidine (II), which is converted into the anhydro compound (III) by reaction with PPh3 and DIAD in DMF. The reaction of (III) with PhSeH in refluxing DMF affords the phenylselenium derivative (IV), which is treated with H2O2 and HOAc in THF to provide the benzoylated anhydrothymidine (V). Finally this compound is debenzoylated by means of NaOMe in methanol.

The reaction of 2-deoxy-D-ribose (I) with MeOH and HCl gives the methylglycoside (II), which is selectively silylated with TBDPSCl and DMAP in pyridine to yield the monosilylated glycoside (III). The reaction of (III) with TsCl in pyridine affords the 3'-tosylate (IV), which is condensed with the bis(trimethylsilyl)thymine (VI) by means of TMS-OTf in MeCN to provide 5'-O-(tert-butydiphenylsilyl)-3'-O-tosylthymidine (VII). Finally this compound is treated with TBAF in refluxing THF.

The reaction of gamma-lactone (I) with N-(phenylsulfanyl)phthalimide (II) by means of LiHMDS in THF gives the 2,2-bis(phenylsulfanyl)lactone (III), which is reduced with DIBAL in THF to yield 5-O-(tert-butyldiphenylsilyl)-2,3-dideoxy-2,2-bis(phenylsulfanyl)-D-ribose (IV). The reaction of (IV) with acetic anhydride affords the acetylated ribose (V), which is condensed with bis(trimethylsilyl)thymine (VI) by means of TMS-OTf in acetonitrile to provide the glycosylated thymine (VII). The oxidation of (VII) with 1 mol of MCPBA in dichloromethane gives the sulfinyl compound (VIII), which is treated with tributylamine in refluxing xylene to yield the 2',3'-didehydro compound (IX). The oxidation of (IX) with MCPBA in dichloromethane gives the phenylsulfonyl derivative (X), which is desulfurized with sodium amalgam in methanol, yielding the silylated intermediate (XI). Finally, this compound is desilylated with TBAF in THF.

The reaction of 5-methyluridine (I) with 1,1-dimethoxycyclopentane (II) by means of TsOH in hot dichloroethane gives the corresponding cyclic ketal (III), which is protected with 4-methoxybenzyl bromide and NaH in DME yielding the N,O-diprotected compound (IV). Elimination of the ketal protecting group of (IV) with dichloroacetic acid in water affords N3,O5?bis(4-methoxybenzyl)-5-methyluridine (V), which is treated with PPh3, I2 and imidazole in hot toluene/acetonitrile to provide 2',3'-didehydro-2',3'-dideoxy-N3,O5?bis(4-methoxybenzyl)-5-methyluridine (VI). Finally this compound is deprotected with ammonium cerium (IV) nitrate in acetonitrile/water.

The sulfonation of 5-methyluridine (I) with MsCl and NMM in acetone gives the trimesylate (II) which is treated with sodium benzoate in hot acetamide to yield the cyclic benzoylated anhydro compound (III). The reaction of (III) with acetyl bromide in methanol/ethyl acetate affords the bromo derivative (IV), which is debrominated with Zn in the same solvent with a catalytic amount of HOAc to furnish the unsaturated sugar derivative (V). Finally this compound is debenzoylated with hot butylamine.

The reaction of 5-methyl-5'-O-(triphenylmethyl)uridine (I) with MsCl and pyridine gives the dimesylate (II), which is treated with Li2Te in THF to yield the tritylated derivative (III) of the target compound.

The reaction of gamma-lactone (I) with N-(phenylsulfanyl)phthalimide (II) by means of LiHMDS in THF gives the 2,2-bis(phenylsulfanyl)lactone (III), which is reduced with DIBAL in THF to yield 5-O-(tert-butyldiphenylsilyl)-2,3-dideoxy-2,2-bis(phenylsulfanyl)-D-ribose (IV). The reaction of (IV) with acetic anhydride affords the acetylated ribose (V), which is condensed with bis(trimethylsilyl)thymine (VI) by means of TMS-OTf in acetonitrile to provide the glycosylated thymine (VII). The oxidation of (VII) with 1 mol of MCPBA in dichloromethane gives the sulfinyl compound (VIII), which is treated with tributylamine in refluxing xylene to yield the 2',3'-didehydro compound (IX). The oxidation of (IX) with MCPBA in dichloromethane gives the phenylsulfonyl derivative (X), which is desulfurized with sodium amalgam in methanol, yielding the silylated intermediate (XI). Finally, this compound is desilylated with TBAF in THF.

The reaction of 5-methyluridine (I) with trityl chloride (II) and pyridine gives the 5'-O-trityl analogue (III), which is submitted to an oxidative cleavage of the vicinal dihydroxy group by means of NaIO4 in EtOH/water to yield the dialdehyde (IV). The double Wittig olefination of (IV) by means of methyltriphenylphosphonium bromide (V) and t-BuOK in toluene affords the bis alkene (VI), which is submitted to a ring closing metathesis by means of the Grubb's catalyst in dichloromethane to provide the unsaturated nucleoside (VII). Finally, this compound was deprotected by means of 80% AcOH to furnish the target Stavudine.

The reaction of 3'-deoxythymidine (I) with MsCl and TEA in acetone gives the mesylate (II), which is treated with aq. NaOH at 45-50 C to yield the anhydro compound (III). Finally, this compound is treated with KOH in refluxing tert-butanol to afford the target Stavudine.

The reaction of 5-methyluridine (I) with TrCl and pyridine gives the 5'-O-trityl derivative (II), which is oxidized with NaIO4 in ethanol/water to yield the dialdehyde (III). The Wittig reaction of (III) with methyltriphenylphosphonium bromide (IV) and t-BuOK in toluene to afford the bis vinyl compound (V), which is submitted to a ring closing metathesis reaction catalyzed by a Ru catalyst in dichloromethane to provide the unsaturated nucleoside (VI). Finally, this compound is deprotected by means of AcOH in water to furnish the target Stavudine.

1) The first method ever reported involves the mesylation of thymidine (I) to give dimesylate (II), which is treated with sodium hydroxide in ethanol to yield oxetane (III). Finally, (III) is converted to stavudine by means of potassium tert-butoxide in DMSO. This process has been modified in order to obtain large quantities or to obtain [2-14C]-stavudine starting from [2-14C]-thymidine. 2) A second closely related method, but using a different protecting group strategy, involves tritylation of the primary hydroxyl group of thymidine to give (IVa), which is then mesylated to give (Va). Elimination with TBAF/THF or t-BuOK/DMSO yields compound (VI), which is finally deprotected with acetic acid. 3) A third synthesis starting from thymidine involves its protection with monomethoxytrityl chloride or picolyl chloride to give (IVb) or (IVc), respectively, which are mesylated to give (Vb) or (Vc). These are treated with phenyl diselenide and lithium aluminum hydride in tetrahydrofuran to yield compounds (VIIb) or (VIIc), which are treated with m-chloroperbenzoic acid in dichloromethane to afford (VIIIb) or (VIIIc). Finally, (VIIIb) is deprotected with methylamine in water and (VIIIc) is deprotected with acetic acid.

Finally this compound can be deprotected by conventional methods: (a) The acylation of 1,2-O-isopropylidene-alpha-D-xylofuranose (I) with benzoyl chloride and pyridine gives the 5-O-benzoyl derivative (II), which is acylated again with Ac2O in pyridine to yield the 3-O-acetyl-5-O-benzoyl derivative (III). The reaction of (III) with Ac2O in acetic acid affords the triacetyl derivative (IV) which is condensed with fully silylated thymine (V) by means of SnCl4 in acetone to provide the corresponding adduct (VI). The selective hydrolysis of the acetate groups of (VI) with sulfuric acid in hot acetonitrile gives 1-(5-O-benzoyl-beta-D-xylofuranosyl)thymine (VII), which is treated with MsCl and pyridine to yield the dimesylate (VIII). The reaction of (VIII) with NaI in refluxing dimethoxyethane affords, after column chromatography, 5'-O-benzoyl-3'-deoxy-2',3'-dideoxythymidine (IX), which is finally deprotected with NaOMe in methanol. (b) The reaction of the 5-O-benzoyl derivative (II) with MsCl and pyridine gives the mesylate (X), which is acylated with Ac2O in HOAc to yield 1,2-di-O-acetyl-5-O-benzoyl-3-O-(methylsulfonyl)-alpha-D-xylofuranose (XI). The condensation of (XI) with the fully silylated thymine (V) by means of SnCl4 in acetone affords the expected adduct (XII), which is treated with H2SO4 in hot MeCN to provide 1-(5'-O-benzoyl-3'-O-(methylsulfonyl)-beta-D-xylofuranosyl)thymine (XIII). Finally this compound is treated with MsCl and pyridine to yield the dimesylate (VIII), already reported. (c) The 1-(5-O-benzoyl-beta-D-xylofuranosyl)thymine (VII) can also be treated with TsCl and pyridine to give the ditosylate (XIV), which is then treated with NaI in refluxing dimethoxyethane to yield 5'-O-benzoyl-3'-deoxy-2',3'-dideoxythymidine (IX), already reported.