Substituted porphyrins

1. A method of protecting cells from oxidant-induced toxicity comprising contacting said cells with an effective amount of a compound of formula

or pharmaceutically acceptable salt thereof,

wherein

R 1 and R 3 are the same and are:

R 2 and R 4 are the same and are:

Y is halogen or —CO 2 X, and

X is the same or different and is an alkyl and each R 5 is the same or different and is H or alkyl,

so that said protection is effected.

2. The method according to claim 1 wherein said compound is complexed with a metal selected from the group consisting of manganese, iron, copper, cobalt, nickel or zinc.

3. The method according to claim 2 wherein said metal is manganese.

4. The method according to claim 1 wherein said cells are mammalian cells.

5. The method according to claim 4 wherein said cells are cells of an isolated organ.

6. The method according to claim 4 wherein said cells are cells of an organ transplant.

7. A method of treating a patient suffering from a condition that results from or that is exacerbated by oxidant-induced toxicity comprising administering to said patient an effective amount of a compound of formula

or pharmaceutically acceptable salt thereof,

wherein

R 1 and R 3 are the same and are:

R 2 and R 4 are the same and are:

Y is halogen or —CO 2 X, and

X is the same or different and is an alkyl and each R 5 is the same or different and is H or alkyl,

so that said treatment is effected.

8. The method according to claim 7 wherein said compound is complexed with a metal selected from the group consisting of manganese, iron, copper, cobalt, nickel or zinc.

9. The method according to claim 8 wherein said compound is complexed with manganese.