Table 1. Summary of Stability Data.

^aAqueous T_1/2 at pH 1.8 determined by ¹H NMR. The solution concentrations studied were not sufficient to break the buffer capacity of the system.

^bAzetidine nitrogen ¹⁵N shift.

^cQM calculated pK_a values were determined with Jaguar, version 7.6, Schrodinger, LLC, New York, NY, 2009.

^dAzetidine nitrogen pK_a.

^e<5% degradation observed at 24 h.

^f∼50% degradation was observed by the first time point (3–5 min).