P-Stereodefined morpholino dinucleoside 3',5'-phosphorothioates.

Here, we present for the first time the synthesis of P-stereodefined morpholino phosphorothioate analogs by using a modified 1,3,2-oxathiaphospholane method (OTP method) and provide valuable structural insights into their stereochemistry. -(2-Thio-4,4-pentamethylene-1,3,2-oxathiaphospholane) derivatives of morpholino-type nucleosides (U-OTPs) were synthesized, separated into pure P-diastereomers and used to prepare P-stereodefined morpholino dinucleoside 3',5'-phosphorothioates.