A solution of 20.8 g (60 mmole) of 4-[6-(acetylcyclopropylamino)-3-amino-2-pyridinyl]-1-piperazinecarboxylic acid, ethyl ester, 44 ml of ethanol and 27 ml of 48% tetrafluoroboric acid was cooled to 0° C. and treated dropwise with a solution of 4.56 g (66 mmol) of sodium nitrite in 8 ml of water under a nitrogen atmosphere keeping the temperature 0°-5° C. After the addition was complete, the reaction was stirred at 0°-5° C. for one hour and treated with 150 ml of anhydrous ether keeping the temperature below 10° C. The solid was removed by filtration, the precipitate was washed with ethanol/ether (1:1), ether and dried in vacuo to give 24.5 g of the title compound, mp 100°-105° C. (dec.).
