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)； andeach X4 is independently hydrogen or together with X3 is (═；O).
