合成路线1

The glycosyl intermediates (VIIIb) and (VIIIc) can be prepared by several related methods. Wittig condensation of 2,3-O-isopropylidene-D-glyceraldehyde (XVI) with (1-carbethoxyethylidene)triphenylphosphorane (XVII) in dry CH2Cl2 provides the unsaturated ester (XVIII) (7). Diastereoselective dihydroxylation of (XVIII) to give diol (XIX) is accomplished using a variety of reagents, including Sharpless oxidation with AD-mix-beta/methanesulfonamide (7), NMMO or t-BuOOH and catalytic OsO4, K3Fe(CN)6 and catalytic K2OsO2(OH)4, tetradecyltrimethylammonium permanganate (TDTAP) and KMnO4, optionally in the presence of crown ether or RuCl3/CeCl3/NaIO4 (4) and NaMnO4/NaHCO3 (5). After conversion of dihydroxy ester (XIX) to the cyclic sulfite (XX) by means of SOCl2 and Et3N, oxidation employing TEMPO/NaOCl or RuCl3/NaIO4 provides the correspondng sulfate ester (XXI). Ring opening of the cyclic sulfate (XXI) with HF-triethylamine complex or with tetrabutyl- or tetraethylammonium fluoride produces the respective ammonium fluorosulfates (XXIIa-c), which undergo cyclization to fluorolactone (XXXIII) under acidic conditions. Subsequent acylation of the dihydroxy ribonolactone (XXIII) with benzoyl chloride and DMAP followed by reduction of the resulting dibenzoyloxy lactone (XXIV) with either Red-Al or LiAlH(O-t-Bu)3 yields lactol (XXV) (4, 5), which is either acetylated to (VIIIb) using Ac2O and DMAP in THF (4) or chlorinated to (VIIIc) with sulfuryl chloride and TBAB (5). Alternatively, cyclization and deprotection of dihydroxy ester (XIX) with ethanolic HCl leads to 2-methyl-D-arabino-γ-lactone (XXVI), which, after protection as the dibenzoate ester (XXVII) with benzoyl chloride in dry pyridine, is fluorinated to (XXIV) using either diethylaminosulfur trifluoride (DAST) or bis(2-methoxyethyl)aminosulfur trifluoride (Deoxofluor) in THF (7). In a further method, dihydroxy ester (XIX) is selectively acylated at the secondary hydroxyl group with benzoyl chloride in pyridine to produce compound (XXVIII), which is fluorinated to (XXIX) by treatment with DAST or Deoxofluor in THF. Deprotection and cyclization of compound (XXIX) with TFA in hot CH3CN/H2O gives 3-O-benzoyl-2-methyl-2-deoxy-2-fluoro-D-ribono-γ-lactone (XXX), which is further benzoylated to (XXIV) by means of benzoyl chloride n the presence of DMAP and pyridine in AcOEt (7). Scheme 3.