Khakwani, Samia, et al. “Mass Spectrometry of Pyrazolo[3,4-b]pyrido[2’,3’-B]-1,6-Naphthyridines and Dipyrazolo[3,4-b];3’,4’-H]-1,6-Naphthyridines”. Asian Journal of Chemistry, vol. 28, no. 12, Sept. 2016, pp. 2601-4, doi:10.14233/ajchem.2016.19947.