The invention relates to compounds of the following formula:and their pharmaceutically acceptable salts, pharmaceutical compositions containing this compounds, and methods of using this compound for the treatment of various diseases or conditions, including but not limited to diseases and / or conditions of, or involving, the Central Nervous System (CNS), including schizophrenia adrenoleukodystrophy, mitochondrial diseases (e.g. Leigh syndrome, Alpers' disease, and MELAS), Huntington's disease, trichotillomania, HIV-associated neurocognitive disorder, hypoxic-ischemic encephalopathy, drug craving, and drug addiction.