5-hydroxy-1,4-naphthoquinone; a naphthoquinone naturally
occuring in the leaves, bark, and hulls of the black
walnut tree (Juglans nigra). Fresh juice from these hulls
contains the hydroquinone which autooxidizes on exposure
to air producing the naphthoquinone. Juglone subsequently
reacts with proteins or other amino groups turning black.
Walnut extract is well known for its antiparasitic effects.
It may also have antitumor effects.