Thermal decomposition of matrix metalloproteinase inhibitors: Evidence of solid state dimerization

The thermal properties of three matrix metalloproteinase (MMP) inhibitors were investigated using a variety of instrumental methods. Differential scanning calorimetry revealed highly exothermic processes for all compounds above 200 °C, and thermogravimetric analysis resulted in significant step-wise weight losses at the temperatures corresponding to the exothermic transitions. Hot stage microscopy observations for several compounds showed evolution of gas bubbles from crystals at temperatures that correlated with the exotherms. Thermal decomposition involving the hydroxamic acid functional group was suspected and further evaluated using various analytical techniques including reversed-phase HPLC, LC-MS-MS, TGA-FTIR and NMR. The mechanism proposed in the thermal decomposition involves a Lossen Rearrangement to form a dimeric species containing a urea linkage.