All dry solvents and reagents were purchased from commercial suppliers and were used without further purification. DIEA was distilled over calcium hydride. Thin-layer chromatography (TLC) analyses were carried out on silica plate 60 F254. Purifications by column chromatography were performed using Biotage Isolera 1 system with FlashPure cartridges (Buchi). NMR experiments were recorded on Bruker 400, 500 or 600 MHz spectrometers at 20 °C. HRMS analyses were obtained with electrospray ionization (ESI) in positive mode on a Q-TOF Micromass spectrometer. Analytical HPLC was performed on a UHPLC Thermoscientific Ultimate 3000 system equipped with a LPG-3400RS pump, a DAD 3000 detector and an WPS-3000TBRS Autosampler, Column Oven TCC-3000SD. Dinucleosides 1–16 were analyzed by RP-HPLC on a Column Nucleodur C18 ec 100-3, 4.6 × 75 mm (Macherey Nagel) at 30 °C. The following HPLC solvent systems were used: 1% CH3CN in 12.5 mM TEAAc (buffer A), 80% CH3CN in 12.5 mM TEEAc (buffer B). Flow rate was 1 mL/min. UV detection was performed at 260 nm. Lyophilized compounds 1–16 were stored at −20 °C for several months without any degradation.