Isatin

This finding suggests that the gut flora (absent, of course, in germ free animals) are responsible for the generation of most urinary isatin, but that the tissue material derives from a different source.

One problem in large scale denim dyeing processes using biologically produced indigo is the undesirable red cast caused by indirubin, which is a structural isomer of indigo formed from indoxyl and isatin, a byproduct of the spontaneous oxidation reaction that converts indoxyl to indigo.

Isatin reacts with formaldehyde and a variety of amines in the Mannich reaction to give their respective bases (10), in the absence of an amine, isatin and substituted isatin with formaldehyde give hydroxymethyl isatins (11).