Structure of a modified nucleoside, 3' alpha-diethylphosphono-3' beta-hydroxy-5'-O-tritylthymidine

The modified nucleoside of the title was synthesized by nucleophilic addition of lithium diethyl phosphite to the corresponding 3'-keto nucleoside under basic conditions. C--P bond formation resulted from attack on the alpha face, trans to C(5') and the thymine ring. One molecule of EtOH crystallized with the nucleoside (C33H37N2O8P.-C2H6O). Intermolecular hydrogen bonds were observed between the O atom of the alcohol and the O(3')hydroxyl H atom, and between the phosphoryl O atom, O(5), and the N(3) H atom of the thymine ring.