Processes for high-yield diastereoselective synthesis of dideoxynucleosides
 The present invention relates to methods for substantially enhancing the stereoselective synthesis of .beta.-anomeric nucleoside analogs. In methods according to the present invention, the introduction of a phenylseleno group onto a blocked lactone sugar precursor may be selected so that the desirable phenylseleno substituent is introduced on the side of the blocked lactone away from the blocking group. This stereospecific introduction of the phenylseleno group in sugar precursor allows the synthesis of nucleoside analogs and in particular, 2',3',-dideoxy- and 2',3'-dideoxy-2',3'-didehydronucleoside analogs in very high yield. In certain preferred embodiments, the preferred phenylseleno blocked lactone is obtained in an amount representing approximately 90% or more of the total amount of the stereoisomers obtained. In even more preferred embodiments, the amount of the preferred stereoisomer is at least 95%, even more preferably at least about 97% of the total amount of phenylseleno blocked lactone produced. 
Vion Pharmaceuticals, Inc.
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inventional inventional inventional
Xiuyan Shu-Hui
Li Chen