Aspects of the present disclosure relate to compounds which have enhanced oral bioavailability. A transition metal complex includes a transition metal coordinated by a macrocycle comprising the pentaaza 15-membered macrocyclic ring corresponding to Formula A and two axial ligands having the formula -OC(O)X1. (Formula A) each of the two axial ligands has the formula -OC(=O)X1 wherein each X1 is independently substituted or unsubstituted phenyl or -C(-X2)(-X3)(-X4)； each X2 is independently substituted or unsubstituted phenyl, or substituted or unsubstituted alkyl； each X3 is independently hydrogen, hydroxyl, alkyl, amino, -X5C(=O)R13 where X5 is NH or O, and R13 is C1-C18 alkyl, substituted or unsubstituted aryl or C1-C18 aralkyl, or -OR14, where R14 is C1-C18 alkyl, substituted or unsubstituted aryl or C1-C18 aralkyl, or together with X4 is (=O)； and each X4 is independenly hydrogen or together with X3 is (=O).
