Pyrocatechol its sulfonic acid is often present in the urine of many mammals. Small amounts of catechol occur naturally in fruits and vegetables along with the enzyme polyphenol oxidase. Upon mixing the enzyme with the substrate and exposure to oxygen (as when a potato or apple is cut) the colorless catechol oxidizes to reddish-brown benzoquinone derivatives.

Levomefolate sodium (L-5-MTHF sodium) is a dietary supplement that can be used to study megaloblastic anemia and neurological disorders.

BRD5459 is a small molecule probe that elevates markers of oxidative stress without leading to cell death.