合成路线1

The reaction of ganciclovir (I) with trimethyl orthoformate and TFA in DMF gives the cyclic orthoester (XI), which is treated with formic acid in DMF/water to yield ganciclovir O-monoformate (XII). The condensation of (XII) with N-benzyloxycarbonyl-L-valine-N-carboxyanhydride (III) by means of triethylamine in DMF affords the expected monovalinate (XIII), which is deformylated with HCl in methanol/dichloromethane to give the previously reported monoprotected valganciclovir derivative (IV). The preceding reaction sequence can also be performed by substituting trimethyl orthoformate with other orthoesters such as benzyl orthoformate, ethyl orthoacetate, methyl orthoacetate or ethyl orthopropionate.