Provided herein are therapeutic and/or prophylactic compounds for mitochondrial or oxidative stress diseases such as cancer, amyotrophic lateral sclerosis, Creutzfeldt-Jakob disease, Machado-Joseph disease, spinocerebellar ataxia, Huntington disease, Parkinson disease, Alzheimer disease, myocardial infarction, cerebral infarction, diseases related to aging, diabetes, alcoholic liver injury, chronic obstructive pulmonary disease, mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes (MELAS), and the like, wherein the compound is represented by formula (1), or reduced forms thereof, or pharmaceutically acceptable salts thereof.