3,4-Dihydroxyphenylglycol, also known as DHPG or DOPEG, belongs to the class of organic compounds known as catechols. Catechols are compounds containing a 1,2-benzenediol moiety. 3,4-Dihydroxyphenylglycol is an extremely weak basic (essentially neutral) compound. 3,4-Dihydroxyphenylglycol exists in all living organisms, ranging from bacteria to plants to humans. It is a potent antioxidant (PMID: 30007612). In mammals, 3,4-Dihydroxyphenylglycol is the primary metabolite of norepinephrine and is generated through the action of the enzyme monoamine oxidase (MAO). DHPG is then further metabolized by the enzyme Catechol-O-methyltransferase (COMT) to 3-methoxy-4-hydroxyphenylglycol (MHPG). Within humans, 3,4-dihydroxyphenylglycol participates in a number of enzymatic reactions. In particular, 3,4-dihydroxyphenylglycol can be biosynthesized from 3,4-dihydroxymandelaldehyde; which is mediated by the enzyme alcohol dehydrogenase 1A. In addition, 3,4-dihydroxyphenylglycol and guaiacol can be converted into vanylglycol and pyrocatechol through its interaction with the enzyme catechol O-methyltransferase. Outside of the human body, 3,4-dihydroxyphenylglycol is found, on average, in the highest concentration in olives. High levels of DHPG (up to 368 mg/kg of dry weight) have been found in the pulp of natural black olives. This could make 3,4-dihydroxyphenylglycol a potential biomarker for the consumption of olives and olive oil. 3,4-Dihydroxyphenylglycol has been linked to Menkes disease (PMID: 19234788). DHPG level are lower in Menkes patients (3.57 ¬± 0.40 nM) than healthy infants 8.91 ¬± 0.77 nM). Menkes disease (also called ‚Äúkinky hair disease‚Äù) is an X-linked recessive neurodevelopmental disorder caused by defects in a gene that encodes a copper-transporting ATPase (ATP7A). Affected infants typically appear healthy at birth and show normal neurodevelopment for 2-3 months. Subsequently there is loss of milestones (e.g., smiling, visual tracking, head control) and death in late infancy or childhood (PMID: 19234788).