Synthesis of alpha-anomeric homopyrimidine oligo DNA phosphorothioates and their physicochemical and biochemical properties.

alpha-Anomeric 2'-deoxycytidine and thymidine were synthesized in a stereospecific manner. With these nucleosides, pyrimidine homooligomers having either exclusively phosphodiester or phosphorothioate linkages were prepared using phosphoramidite method. All tested alpha-DNA.RNA complex was found to be inert toward the action of RNase H, even when phosphorothioate analogs were used as the DNA component. Among the alpha-anomeric homooligomers, alpha-oligocytidilate phosphorothioate exhibited potent inhibitory effect towards the action of RNase H on a DNA.RNA complex.