New method for the preparation of 3′- and 2′-O-phosphoramidites of 2′- and 3′-difluoromethyluridine derivatives

Hydrogenation of 2-deoxy-2'-difluoromethylene-5'-O-dimethoxytrityluridine (1) and 3'-deoxy-3'-difluoromethylene-5'-O-dimethoxytrityluridine (7), gave the corresponding 2- and 3'-difluoromethyluridine derivatives 2a and 8a. Detritylation of compounds 2a, 2b and 8a, 8b resulted in the formation of 1-(2-deoxy-2-C-difluoromethyl-beta-D-arabino-pentofuranosyl)uracil (3a) and 1-(3-deoxy-3-C-difluoromethyl-beta-D-xylo-pento furanosyl)- uracil (9a) as well as corresponding minor isomers 3b and 9b. Compounds 3a and 3b were also obtained from 2-deoxy-2'-difluoromethylene-3,5'-O-(tetra-isopropyldisiloxane-1,3-diyl)uridine (4). Finally, phosphitylation of 2a and 8a provided the title 2- and 3'-0-phosphorarnidites 6 and 10.