合成路线1

Synthesis of the intermediate chiral tetrahydropyran-carboxylic acid methyl ester (VII): The selective reduction of the exocyclic double bond of the glycoside (I) with H2 over Pd/C in ethanol gives a mixture of the equatorial epimer (II) along with some axial compound that is eliminated by crystallization. The cleavage of the benzylidene protecting group of (II) with H2, over Pd/C in EtOH, followed by selective monoesterification of the primary OH group with PPh3, DIAD and benzoic acid yields the benzoate ester (III). The protection of (III) with Tbdms-Cl and imidazole affords the silyl ether (IV), which is debenzoylated by means of DIBAL in dichloromethane to afford the hydroxymethyl compound (V). The oxidation of (V) by means of RuCl3 and NaIO4 pin acetonitrile/CCl4 provides the chiral carboxylic acid (VI), which is finally esterified with CH3-I and K2CO3 in DMF to furnish the desired tetrahydropyran-carboxylic acid methyl ester (VII).