Preparation of magnetic resonance contrast agents activated by β-galactosidase

The preparation of β-EgadMe and α-EgadMe, magnetic resonance (MR) contrast agents that can be used for in vivo detection of β-galactosidase, is described. Diastereomerically pure β-EgadMe can be synthesized by kinetically resolving the starting material as described in Step 1. The total time for the preparation of the racemic mixture of β-EgadMe is about 8 d, and the total time for an diastereomerically resolved agent is about 9 d. The final metallated agent is stable at room temperature as a solid or in aqueous buffer (pH 5.5–10) indefinitely. Diastereomerically pure α-EgadMe can be prepared by beginning the synthesis with enantiomerically pure bromopropionic acid. The total time for the preparation of racemic α-EgadMe or diastereomerically pure α-EgadMe is about 8 d. The final metallated agent is stable at room temperature as a solid or in aqueous buffer (pH 5.5–10) indefinitely.