A compound of Formula: wherein: R 1 is OH, R 2 is H, R 3, R 4, and R 5 are, independently, substituted C 1 -C 22 alkyl carbonyl, with substituents selected from the group consisting of C 1-3 alkyl, OH, NH 2, and halogen, or H, wherein at least one of R 3, R 4, and R 5 is not H, or an L isomer, the keto tautomer, or an L isomer of the keto tautomer thereof, for use in the treatment of a mitochondrial disorder wherein the mitochondrial disorder is selected from the group consisting of Huntington's disease, Amyotrophic lateral sclerosis, MELAS (Mitochondrial encephalomyopathy with lactic acidemia and stroke-like episodes), MERRF (Myoclonus, epilepsy, and myopathy with ragged red fibers), NARP/MILS (Neurogenic muscular weakness, ataxia, retinitis pigmentosa/Maternally inherited Leigh syndrome), LHON (Lebers hereditary optic neuropathy) "Mitochondrial blindness", KSS (Kearns-Sayre Syndrome), PMPS (Pearson Marrow-Pancreas Syndrome), CPEO (Chronic progressive external opthalmoplegia), Leigh syndrome, Alpers syndrome, Multiple mtDNA deletion syndrome, MtDNA depletion syndrome, Complex I deficiency, complex II deficiency, Complex III deficiency, Cytochrome c oxidase (COX, Complex IV) deficiency, Complex V deficiency, Adenine Nucleotide Translocator deficiency, Pyruvate dehydrogenase deficiency, Ethylmalonic aciduria with lactic acidemia, 3-Methyl glutaconic aciduria with lactic acidemia, Refractory epilepsy with declines during infection, Asperger syndrome with declines during infection, Autism with declines during infection, Attention deficit hyperactivity disorder (ADHD), Cerebral palsy with declines during infection, Dyslexia with declines during infection, maternally inherited thrombocytopenia and leukaemia syndrome, MNGIE (Mitochondrial myopathy, peripheral and autonomic neuropathy, gastrointestinal dysfunction, and epilepsy), MARIAHS syndrome (Mitochondrial ataxia, recurrent infections, aphasia, hypouricemialhypomyelination, seizures, and dicarboxylic aciduria), ND6 dystonia, Cyclic vomiting syndrome with declines during infection, 3-Hydroxy isobutyric aciduria with lactic acidemia, Familial Bilateral Striatal Necrosis (FBSN), Aminoglycoside-associated deafness, Dilated cardiomyopathy, Splenic Lymphoma, Wolfram syndrome, Multiple mitochondrial DNA deletion syndromes, Renal Tubular Acidosis/Diabetes/Ataxis syndrome, mitochondrial renal tubular acidosis, lactic acidemia, encephalomyopathy, 1+proteinuria, pyruvate dehydrogenase deficiency, complex IV deficiency, aminoaciduria, hydroxyprolinuria, and a deficiency of cardiolipin. R 1 is OH, R 2 is H, R 3, R 4, and R 5 are, independently, substituted C 1 -C 22 alkyl carbonyl, with substituents selected from the group consisting of C 1-3 alkyl, OH, NH 2, and halogen, or H, wherein at least one of R 3, R 4, and R 5 is not H, or an L isomer, the keto tautomer, or an L isomer of the keto tautomer thereof, for use in the treatment of a mitochondrial disorder wherein the mitochondrial disorder is selected from the group consisting of Huntington's disease, Amyotrophic lateral sclerosis, MELAS (Mitochondrial encephalomyopathy with lactic acidemia and stroke-like episodes), MERRF (Myoclonus, epilepsy, and myopathy with ragged red fibers), NARP/MILS (Neurogenic muscular weakness, ataxia, retinitis pigmentosa/Maternally inherited Leigh syndrome), LHON (Lebers hereditary optic neuropathy) "Mitochondrial blindness", KSS (Kearns-Sayre Syndrome), PMPS (Pearson Marrow-Pancreas Syndrome), CPEO (Chronic progressive external opthalmoplegia), Leigh syndrome, Alpers syndrome, Multiple mtDNA deletion syndrome, MtDNA depletion syndrome, Complex I deficiency, complex II deficiency, Complex III deficiency, Cytochrome c oxidase (COX, Complex IV) deficiency, Complex V deficiency, Adenine Nucleotide Translocator deficiency, Pyruvate dehydrogenase deficiency, Ethylmalonic aciduria with lactic acidemia, 3-Methyl glutaconic aciduria with lactic acidemia, Refractory epilepsy with declines during infection, Asperger syndrome with declines during infection, Autism with declines during infection, Attention deficit hyperactivity disorder (ADHD), Cerebral palsy with declines during infection, Dyslexia with declines during infection, maternally inherited thrombocytopenia and leukaemia syndrome, MNGIE (Mitochondrial myopathy, peripheral and autonomic neuropathy, gastrointestinal dysfunction, and epilepsy), MARIAHS syndrome (Mitochondrial ataxia, recurrent infections, aphasia, hypouricemialhypomyelination, seizures, and dicarboxylic aciduria), ND6 dystonia, Cyclic vomiting syndrome with declines during infection, 3-Hydroxy isobutyric aciduria with lactic acidemia, Familial Bilateral Striatal Necrosis (FBSN), Aminoglycoside-associated deafness, Dilated cardiomyopathy, Splenic Lymphoma, Wolfram syndrome, Multiple mitochondrial DNA deletion syndromes, Renal Tubular Acidosis/Diabetes/Ataxis syndrome, mitochondrial renal tubular acidosis, lactic acidemia, encephalomyopathy, 1+proteinuria, pyruvate dehydrogenase deficiency, complex IV deficiency, aminoaciduria, hydroxyprolinuria, and a deficiency of cardiolipin.