Diisopropylammonium Tetrazol-1-ide

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

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 tetrazole (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.

The reaction solution was monitored by NMR.

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).

• Lewis acid deprotection of silyl-protected oligonucleotides and base-sensitive oligonucleotide analogs
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