indican

Indican is the glycoside indoxyl-β-D-glucoside, a natural product found in several plant species and historically important as a precursor to the indigo dye. In plants such as Indigofera tinctoria, Indigofera suffruticosa, and Isatis tinctoria (woad), indican serves as a storage form of indoxyl. The molecule consists of indoxyl bound to a β-D-glucose moiety via a glycosidic bond. When plant tissue is damaged, plant beta-glucosidases hydrolyze indican to indoxyl and glucose. Indoxyl, in the presence of oxygen, dimerizes to form indigo, the blue pigment, while indirubin may form as a minor red-purple byproduct.

In historical dyeing, indican-rich plant material is fermented and exposed to air to promote hydrolysis and oxidation, yielding indigo that can be collected as a pigment or used directly in dye baths. Modern indigo production increasingly relies on synthetic routes, but natural indican from Indigofera and Isatis species remains of interest to natural-dye producers.

In medical contexts, the term indican can refer to a urinary metabolite derived from intestinal bacterial breakdown of tryptophan. Urinary indican was once used in diagnostic tests for gastrointestinal and hepatic disorders, but such tests are largely obsolete or ancillary today.

See also Indigo dye, Indigofera, Isatis, indirubin.