Synthetic pathways to a mononucleotide prodrug of cytarabine (Ara-C) bearing S-pivaloyl-2-thioethyl (tBuSATE) groups, as biolabile phosphate protections, are reported. Using a common phosphoramidite approach, two different kinds of nucleoside protecting groups have been investigated. During this study, we obsd. an intermol. migration of the Boc protecting group in the course of the tert-butyldimethylsilyl ether cleavage using tetra-Bu ammonium fluorid
