合成路线1

L-Glyceraldehyde acetonide (I) was subjected to Horner-Emmons reaction with triethyl alpha-fluorophosphonoacetate (II) in the presence of sodium bis(trimethylsilyl)amide to yield a mixture of Z (III) and E (IV) unsaturated esters. Acidic treatment of this mixture, followed by silylation with tert-butyldimethylsilyl chloride gave the desired fluorobutyrolactone (V) along with the open-chain silylated dihydroxyester (VI), which were separated by column chromatography. Reduction of lactone (V) with DIBAL provided an anomeric mixture of lactols (VIIa-b), which was further acetylated to afford (VIIIa-b). N-Glycosylation of the silylated N(4)-benzoylcytosine (IX) using trimethylsilyl triflate gave rise to the mixture of furanosylcytosines (Xa-b). After chromatographic isolation of the desired beta-anomer, deprotection of the silyl ether by means of tetrabutylammonium fluoride yielded (XI). Finally, ammonolysis of the N-benzoyl group of (XI) furnished the title compound.