Khakwani, Samia, et al. “Mass Spectrometry of Heterocyclic Compounds: Benzo[b]pyrazolo[3,4-B]-1,6-Naphthyridines”. Asian Journal of Chemistry, vol. 28, no. 11, Aug. 2016, pp. 2385-7, doi:10.14233/ajchem.2016.19946.