合成路线1

3) The stereocontrolled cyclization of (E)-3-(2-oxooxazolidin-3-ylcarbonyl)-2-propenoic acid methyl ester (XIX) with 1,1-di(methylsulfanyl)ethylene (XX) catalyzed by a chiral reagent prepared in situ with diisopropoxytitanium dichloride and the chiral dioxolane (XXI), gives [1S-(1alpha,2beta)]-3,3-bis(methylsulfanyl)-2-(2-oxooxazolidin-3-ylcarbonyl)cyclobutane-1-carboxylic acid methyl ester (XXII), which is treated with magnesium methoxide in methanol yielding the dicarboxylic ester (XXIII). The reduction of (XXIII) with LiAlH4 in ether affords the corresponding dimethanol compound (XXIV), which is silylated with tert-butyldiphenylsilyl chloride (BPS-Cl), triethylamine and 4-(dimethylamino)pyridine (DMAP) in dichloromethane giving the bis(silyl) ether (XXV). The reaction of (XXV) with N-chlorosuccinimide (NCS) and AgNO3 in acetonitrile/water yields the cyclobutanone (XXVI), which is reduced with diisobutylaluminum hydride (DIBAL) in toluene affording the silylated [1S-(1alpha,2beta,3beta)]-3-hydroxycyclobutyl-1,2-dimethanol (XXVII). The reaction of (XXVII) with methanesulfonyl chloride and triethylamine gives the expected mesylate (XXVIII), which is condensed with 6-O-(2-methoxyethyl)guanine (XXIX) by means of LiH in DMF to afford the corresponding adduct (XXX). Finally, this compound is deprotected by treatment with HCl in methanol.