Identification of an Impurity in The Synthesis of Pharmacologically Active Pyrazolotriazolopyrimidines by a Combined Spectrometric Approach

Pyrazolotriazolopyrimidines are synthetic organic compounds showing interesting pharmacological activity. Good structural characterization and reliable evaluation of possible impurities is very important. We report here a detailed mass spectrometric investigation using different ionization techniques such as electron ionization, fast atom bombardment and Ionspray (IS). The approach allowed a reliable identification of an impurity, present in some of the derivatives examined, having a molecular weight 28 Da higher than the expected compound. It was identified as an ethyl derivative due to an unusual alkylating activity of ethyl orthoformate. The position of the ethyl group on the pyrazolotriazolopyrimidine ring was determined by 1H NMR. Finally, the use of IS combined with tandem mass spectrometry allowed a complete structural characterization of the target compounds as well as of the impurity.