They kept one phosphonate group to act as the base but swapped out the other for a less - tightly - bound carboxylate. (worldofchemicals.com)
This research demonstrates a new synthetic transformation of dialkylphosphonates to mixed phosphonates under mild reaction conditions. (unlv.edu)
Moreover, the binding with the MMP active site is discussed in the research paper, «Phosphonate Emerging Zinc Binding Group in Matrix Metalloproteinase Inhibitors», published in Current Drug Targets. (sciencedaily.com)