TMR-sieber linker free acid (4.34 mg, 5 μmol) was stirred with disuccinimidyl carbonate (1.74 mg, 7.5 μmol) and N,N-dimethyl aminopyridine (0.92 mg, 7.5 μmol) in DMF (1 mL) at room temperature. After 10 minutes, all the reaction mixture was added to tetra-(tri-butylammonium) salt of 5-(3-aminopropynyl)-2′-deoxyuridine-5′-triphosphate (10 μmol). The reaction was stirred at room temperature for 4 hrs and stored in the fridge overnight. The reaction mixture was then diluted with chilled water (10 mL) and all the resulting solution was applied onto a short column of DEAE A-25. The column was initially eluted with 0.1 M TEAB buffer and then 0.7 M TEAB buffer. The 0.7 M TEAB eluents were collected and evaporated under reduced pressure. The residue was co-evaporated with MeOH (2×10 mL) and then purified by preparative HPLC. The title compound was obtained as triethylammonium salt in 31% yield (based on the quantification of TMR at 555 nm in water (pH 7)). 1HNMR in D2O indicated two diastereoisomers, due to the sieber linker moiety and there were approximately three triethylammonium count ions. 1HNMR [D2O]: 8.18 (1H, m), 8.06 (1H, m), 7.76 (0.55H, s), 7.74 (0.45H, s), 7.36-7.09 (5H, m), 6.89-6.72 (3H, m), 6.59-6.37 (5H, m), 6.12 (0.55H, t, J 6.6), 6.05 (0.45H, t, J 6.6), 5.99 (0.45H, d, J 2.5), 5.91 (1.1H, m), 5.88 (0.45H, s), 4.49 (0.55H, m), 4.43 (0.45H, m), 4.00-3.35 (9H, m), 3.30-2.95 (32H, m), 2.65-2.52 (4H, m), 2.25-2.05 (4H, m), 1.62-1.42 (4H, m) and 1.23 (27H, t, J 7.3). 31P [D2O]: −9.91 (γP, d, J 19.2), [−11.08 (αP, d, J 20.1) and −11.30 (αP, d, J 20.1), due to two diastereoisomers] and −22.57 (βP, m). MS[(ES(−)], m/z 1369.1 (M−).
