On the same basis, labeling of 3 and 4 with 5‐aminofluorescein (14) was achieved to give the conjugates 15 and 17, respectively (Scheme 1). Treatment of 17 with 2‐(4‐nitrophenyl)ethanol in a Mitsunobureaction led to double protection of the fluorescein moiety (→18) and desilylation yielded 19. Dimethoxytritylation (→20) and subsequent phosphitylations afforded the new building blocks 21 and 22. Synthesis