Synthesis and Configuration Analysis of Diastereomers of 5'-O-(2'-Deoxycytidyl)-3'-O-Thymidyl Phosphorothioate

Synthesis and Configuration Analysis of Diastereomers of 5'-O-(2'-Deoxycytidyl)-3'-O-Thymidyl Phosphorothioate

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[Cp(S)T] was performed by the condensation of the protected deoxycytidine, the protected thymidine, 2,5-dichlorophenylphosphorodichloridothioate and 1-hydroxybenzotriazole in THF. Their designation of configuration at phosphorus as $R_p$ and $S_p$ follows from anaylsis of ${31}^P$ NMR spectroscopy and reverse-phase HPLC and the stereospecificity in the hydrolysis catalyzed by Nuclease S1 and snake venom phosphodiesterase. Diastereomerically pure $R_p$ and $S_p$ d[Cp(S)T] were utilized to synthesize oligonucleotides containing the XhoI recognition sequence with a phosphorothioate group at the cleavage site.