Synthesis of dinucleosides 14–16. (a) 4-chlorobenzenesulfonyl chloride, NEt3, CH2Cl2, 0 °C, 3 h, 90%. (b) (i) 4-chloro-3-nitrobenzaldehyde, AcOH, DCE, 40 °C, 20 min; (ii) NaBH(OAc)3, 40 °C, 16 h, 87%. (c) (i) 4-chlorobenzaldehyde, AcOH, DCE, 40 °C, 20 min. (ii) NaBH(OAc)3, 40 °C, 16 h, 72%. (d) TFA/H2O 8/2, 25 °C, 3 h, 48% for 14; 6 h, 25% for 15; 6 h, 37% for 16.