The invention provides the use of a compound of formula (I) or a metal chelate or salt thereof in the manufacture of a therapeutic agent for use in the treatment or prophylaxis of conditions resulting from the presence of free radicals in the human or non-human animal body (wherein in formula (I): each R1 independently represents hydrogen or -CH¿2?COR?5; R5¿ represents hydroxy, optionally hydroxylated alkoxy, amino or alkylamido; each R2 independently represents a group XYR6; X represents a bond, or a C¿1-3? alkylene or oxoalkylene group optionally substituted by a group R?7¿; Y represents a bond, an oxygen atom or a group NR6; R6 is a hydrogen atom, a group COOR8, an alkyl, alkenyl, cycloalkyl, aryl or aralkyl group optionally substituted by one or more groups selected from COOR?8, CONR8¿2, NR82, OR8, =NR8, =O, OP(O) (OR8)R7 and OSO¿3M; R?7 is hydroxy, an optionally hydroxylated, optionally alkoxylated alkyl or aminoalkyl group; R8 is a hydrogen atom or an optionally hydroxylated, optionally alkoxylated alkyl group; M is a hydrogen atom or one equivalent of a physiologically tolerable cation; R3 represents a C¿1-8? alkylene group, a 1,2-cycloalkylene group, or a 1,2-arylene group; and each R?4¿ independently represents hydrogen or C¿1-3? alkyl). Such compounds are particularly effective in relieving symptoms associated with reperfusion of ischemic tissue and in treating or preventing radiation-induced injury.