The nucleoside derivatives, containing at 3′-O or 5′-O-position 2-oxo-1, 3, 2- dithiaphospholane function were found to react in the presence of DBU with a hydroxyl group of appropriately protected nucleosides to yield, after deprotection, dinucleoside phosphorothioates in moderate yields. An asymmetric induction connected with the formation of new chiral phosphorothioate center has been examined.
