The racemic isosteric phosphonate of ganciclovir monophosphate (BW2482U89, SR3745, [3-((2-amino-1,6-dihydro-6-oxo-9H-purin-9-yl)methoxy)-4- hydroxybutyl]phosphonic acid, 1) has potent and selective in vitro activity against human cytomegalovirus. An enantiospecific synthesis of the R-enantiomer of compound 1 starting from L-arabinose was developed. The synthesis involved (1) the preparation of a chiral acyclic moiety, (2) the coupling of the chiral acyclic moiety to diacetylguanine, (3) the introduction of phosphorus, and (4) the final deprotection. The R-enantiomer, which has stereochemistry analogous to the natural compound GMP, was tested against human cytomegalovirus and had an IC50 of 1.7 microM, which was approximately 2-fold more active than the racemic material. Both racemic and chiral compounds were less toxic than ganciclovir to bone marrow progenitor cells in an in vitro assay.