Homogentisic acid

Homogentisic acid is the common name for 2,5-dihydroxyphenylacetic acid.

It is less commonly known as "Melanic acid", the name chosen by William Prout.

Pathology
Accumulation of excess homogentisic acid is a result of the failure of the enzyme homogentisic acid 1,2-dioxygenase (typically due to a mutation) and is associated with alkaptonuria.