Solid-phase synthesis of stereoregulated oligodeoxyribonucleoside phosphorothioates.

An efficient stereocontrolled synthesis of oligodeoxyribonucleoside phosphorothioates on a solid-support by an oxazaphospholidine method was achieved. A detailed investigation on the reagents and conditions for the solid-phase synthesis revealed that the use of the capping and sulfurizing reagents which are regularly used for the conventional synthesis of phosphorothioate DNA resulted in a sluggish removal of the chiral auxiliaries on the phosphorothioate internucleotidic linkages. After optimization of the capping and sulfurizing steps, the deprotection of the internucleotidic linkages were successfully conducted under the regular basic conditions, and P-stereoregulated phosphorothioate DNA oligomers were successfully obtained with excellent diastereopurity.