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TCI Practical Example: Phosphoroamidite Synthesis Using Diisopropylammonium Tetrazolide

We are proud to present the introduction of the phosphoroamidite group to 5'-O-(4,4'-dimethoxytrityl)thymidine using diisopropylammonium tetrazolide and 2-cyanoethyl N,N,N',N'-tetraisopropylphosphordiamidite.

Used Chemicals

• 5'-O-(4,4'-Dimethoxytrityl)thymidine (= DMT-T) [D3566]
• 2-Cyanoethyl N,N,N',N'-Tetraisopropylphosphordiamidite [C2228]
• Diisopropylammonium Tetrazolide [D6204]
• Dichloromethane

Procedure

2-Cyanoethyl N,N,N',N'-tetraisopropylphosphorodiamidite (0.7 mL, 2.2 mmol, 1.2 eq.) was added to a solution of DMT-T (1.0 g, 1.8 mmol) and diisopropylammonium tetrazolide (160 mg, 0.92 mmol, 0.5 eq.) in dichloromethane (9.2 mL) at room temperature. After the completion of the reaction, saturated aq. NaHCO₃ (5 mL) was added to the solution and extracted with dichloromethane (15 mL, twice). The organic layer was dried over anhydrous sodium sulfate and concentrated under reduced pressure. The crude product was purified by silica gel column chromatography (hexane:ethyl acetate = 70:30 - 50:50, 2% of triethylamine was added to the eluents) to give 1 (1.2 g, 88% yield) as a white crystal.

Experimenter’s Comments

The reaction solution was monitored by NMR.

Analytical Data

Compound 1

¹H NMR (400 MHz, CDCl₃); δ 11.36 (s, 1H), 7.50 (d, J = 4.0 Hz, 1H), 7.36-7.20 (m, 9H), 6.87-6.83 (m, 4H), 6.16-6.15 (m, 1H), 4.56-4.49 (m, 1H), 3.99 (d, J = 4.0 Hz, 1H), 3.73-3.72 (m, 1H), 3.22-3.19 (m, 1H), 2.72 (t, J = 8.0 Hz, 1H), 2.62 (t, J = 1.2 Hz, 1H), 2.41-2.31 (m, 1H), 1.44 (d, J = 1.2 Hz, 3H), 1.18-1.06 (m, 12H).

Lead Reference

• Lewis acid deprotection of silyl-protected oligonucleotides and base-sensitive oligonucleotide analogs
  • F. Ferreira, J.-J. Vasseur, F. Morvan, Tetrahedron Lett. 2004, 45, 6287.

Other Reference

• Microwave-assisted preparation of nucleoside-phosphoramidites
  • G. Meher, T. Efthymiou, M. Stoop, R. Krishnamurthy, Chem. Commun. 2014, 50, 7463.