Prodrugs of Oligonucleotides: The Acyloxyalkyl Esters of Oligodeoxyribonucleoside Phosphorothioates

In model studies toward development of prodrugs of oligonucleoside phosphorothioates, Rp and Sp, S-alkyl phosphorothiolates 3a-d were prepared by chemoselective S-alkylation of Rp acid Sp dinucleoside phosphorothioate 2 with iodoalkyl acylates 9a-d. When incubated with human serum or porcine liver esterase (PLE), stereospecific conversion of 3a-d to Rp and Sp2 was observed. Stereodifferentiation was also noted in the hydrolysis-Sp faster than Rp3a-c, with serum, and Rp faster than Sp 3a-c, with PLE. In the case of hindered analogs 3c, desulfurized product 4 was also formed along with 2. Mechanisms to account for this product profile obtained during the hydrolysis are proposed. Similarly, bioreversion of acyloxyalkyl oligonucleoside phosphorothioates 15, 16, and 17 to 18, 19, and 20, respectively, was demonstrated by 31P NMR and PAGE.