合成路线1

3) The esterification of L-malic acid (XX) with methanol and acetyl chloride gives the dimethyl ester (XXI), which is reduced with borane-dimethyl sulfide in THF yielding 3(S),4-dihydroxybutyric acid methyl ester (XXII). Partial protection of (XXII) with trityl chloride in pyridine affords 3(S)-hydroxy-4-(trityloxy) butyric acid methyl ester (XXIII), which is hydrolyzed with NaOH to the corresponding free acid (XXIV). The condensation of (XXIV) with succinic acid monoallyl ester, magnesium salt (XXV) by means of the carbonyl diimidazole (DCI) in THF gives 5(S)-hydroxy-3-oxo-6-(trityloxy)hexanoic acid allyl ester (XXVI), which is reduced with triethylborane and NaBH4 in THF and treated with H2O2 at -70 C to afford 3(R),5(S)-6-(trityloxy)hexanoic acid allyl ester (XXVII). The protection of the hydroxyl groups of (XXVII) with tert-butyldiphenylsilyl chloride and imidazole in DMF gives the fully protected ester (XXVIII), which is treated with trifluoroacetic acid in dichloromethane yielding erythro-3(R),5(S)-bis(tert-butyldiphenylsilyloxy)-6-hydroxyhexanoic acid allyl ester (XXIX). The oxidation of (XXIX) with pyridinium chlorochromate in dichloromethane affords the oxo-ester (XXX), which is condensed with phosphonate (X), as in method 2 above, to give ester (XXXI). The hydrolysis of (XXXI) with triphenylphosphine and palladium tetrakis triphenylphosphine as before yields the protected acid (XXXII), which is finally deprotected with tetrabutylammonium fluoride, also as before. [3(R),5(S)-erythro-isomer].