Glyceollin I is a glyceollin, a type of prenylated pterocarpan. It is a phytoalexin found in the soybean.
Glyceollin synthase is an enzyme responsible for the production of glyceollin. The five substrates of this enzyme are 2-dimethylallyl-(6aS,11aS)-3,6a,9-trihydroxypterocarpan, 4-dimethylallyl-(6aS,11aS)-3,6a,9-trihydroxypterocarpan, NADPH, H<sup>+</sup>, and O<sub>2</sub>, whereas its three products are glyceollin, NADP<sup>+</sup>, and H<sub>2</sub>O.
In in vitro studies, this molecule has been shown to exhibit antiestrogenic properties.