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.