Compounds of formula (I):

##STR00001##

wherein R.sup.1, R.sup.2 and R.sup.3 are as defined herein are able to rescue dysfunctional mitochondria and are therefore of use in the treatment and prevention of neurodegenerative disorders as well as acute radiation syndrome and myalgic encephalomyelitis (ME, chronic fatigue syndrome) or post viral syndrome, including chronic symptoms arising from infection with SARS-CoV2 (long COVID).