Triphenylphosphine (27.0 g, 115 mmol) was added to a solution of 6-[2-(3-pyridin-3-ylpropoxy)ethyl]-6H-imidazo[4,5-c]tetrazolo[1,5-a]quinoline (28.7 g, 76.9 mmol) in 1,2-dichlorobenzene (1 L). The reaction was heated at reflux temperature overnight. The dark red solution was cooled to room temperature and treated with 1N HCl (225 ml). A tan precipitate formed. The resulting mixture was concentrated in vacuo to yield a dark red/brown solid. This material was treated with 500 ml water and vigorously stirred. Excess triphenylphosphine and triphenylphosphine oxide formed as precipitates and were removed by vacuum filtration. The solid was washed with several portions of water followed by a final wash with dilute HCl (1:5, 1N HCl:water). The red/brown filtrate was collected, washed with ether (3×150 ml), and treated with 10% NaOH solution until the pH reached 12. The crude product formed as a tan precipitate and was collected by filtration. Purification of the crude material was accomplished by treatment (2×) with activated charcoal (Darco-G60) in refluxing methanol. The charcoal was removed by filtration. The desired product formed as a precipitate during concentration of the filtrate.
