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. 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 independently hydrogen or together with X3 is (═O).