Gyun Lee, Y. et al. 2015. Synthesis and Acid Catalytic Activity of 1,5,3,7-Diazadiphosphocine-1,5-dicarboxylic Acids. Asian Journal of Chemistry. 27, 4 (Feb. 2015), 1481–1483. DOI:https://doi.org/10.14233/ajchem.2015.18518.