A procedure is described for the synthesis of the title compound via phosphotriester intermediates. The preparation of $R_p;and;S_p$ diastereomeric dinucleotide of d[Ap(S)A] was performed by the condensation of protected deoxyadenosine, 2,5-dichlorophenylphosphorodichloridothioate and 1-hydroxybenzotriazole in THF. Their designation of configuration at phosphorus as $R_p;and;S_p$ follows from analysis of $^{31}P$-NMR spectroscopy and reversed-phase HPLC and the stereospecificity in the hydrolysis catalyzed by nuclease Pl.