2-Cyanoethyl tetraisopropylphosphorodiamidite → N-biotinyl-aminopropyl 2-cyanoethyl N,N-diisopropylphosphoramidite

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To a solution of 150 mg of N-biotinylaminopropanol (2b) in 5 ml of dry DMF was added 65 mg of diisopropylammonium tetrazolide and 0.300 ml of 2-cyanoethyl N,N,N',N'-tetraisopropylphosphorodiamidite. The resulting solution was stirred at room temperature for 1.0 hr and then poured onto 50 ml of 5% aqueous sodium bicarbonate. The mixture was extracted with two 50 ml portions of methylene chloride, and the combined extracts were washed with 5% sodium bicarbonate and brine, dried over sodium sulfate, and evaporated to afford the crude product as a thick oil. This was dissolved in 2 ml of dry methylene chloride affording a solution that was added dropwise to 30 ml of rapidly stirring petroleum ether. The colorless precipitate which formed was collected by suction filtration under argon, affording after drying at room temperature under vacuum 151 mg (60%) of a colorless solid.

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