Treatment of Duchenne muscular dystrophy

There are disclosed compound of Formula (1): A 1 , A 2 , A 3 and A 4 which may be the same or different, represent N or CR 1 , X is a divalent group selected from O, S(O) n , C═W, NR 4 , NC(═O)R 5 and CR 6 R 7 , W is O, S, NR 20 , Y is N or CR 8 , one of R 4 , R 5 , R 6 , R 8 , R 9 and NR 20 represents -L-R 3 , in which L is a single bond or a linker group, additionally, R 1 , R 3 -R 9 , which may be the same or different, independently represent hydrogen or a substituent and R 20 represents hydrogen, hydroxyl, alkyl optionally substituted by aryl, alkoxy optionally substituted by aryl, aryl, CN, optionally substituted alkoxy, optionally substituted aryloxy, optionally substitute alkanoyl, optionally substituted aroyl, NO 2 , NR 30 R 31 , in which R 30 and R 31 , which may be the same or different, represent hydrogen, optionally substituted alkyl or optionally substituted aryl; additionally, one of R 30 and R 31 may represent optionally substituted alkanoyl or optionally substituted aroyl, n represents an integer from 0 to 2, in addition, when an adjacent pair of A 1 -A 4 each represent CR 1 , then the adjacent carbon atoms, together with their substituents may form a ring B, when X is CR 6 R 7 , R 6 and R 7 , together with the carbon atom to which they are attached may form a ring C, or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for the therapeutic and/or prophylactic treatment of Duchenne muscular dystrophy, Becker muscular dystrophy or cachexia.