3.3. Solid-Phase 2′ Modification by Modifying Phosphoramidite

2′ modification of support-bound 2′-OH/2′-O-TC oligonucleotide (III) was carried out as a standard cycle of automatic phosphoramidite synthesis with the use of 0.1 M modifying (5′-amino-modifier C6 or 5′-alkyne-modifier) phosphoramidite in anhydrous acetonitrile and 0.25 M 5-ethylthio-1H-tetrazole in anhydrous acetonitrile as an activator (coupling time was 10 min) (see Scheme S2, steps a–c).