Study on the diastereoselective synthesis of dithymidine phosphorothioatesthrough a D-xylose derived chiral auxiliary and development of a novel catalyst

1,2-Di-O-isopropylidene-3-C-cyanoethyl-5-deoxy-5-isopropylamino-D-xylofuran ose 16a was synthesized The use of 16a as a chiral auxiliary led to the dia stereoselective formation of dithymidine phosphorothioate. The chiral auxil iary was easily removed by treatment with concentrated ammonia. 2-Mesityl-4 ,5-dicyanoimidazole displays higher diastereoselectivity than the 2-bromo-4 ,5-dicyanoimidazole in the coupling reaction. (C) 2000 Elsevier Science Ltd . All rights reserved.