Aflatoxin B<sub>1</sub> exo-8,9-epoxide is a toxic metabolite of aflatoxin B<sub>1</sub>. It's formed by the action of cytochrome P450 enzymes in the liver.
In the liver, aflatoxin B<sub>1</sub> is metabolized to aflatoxin B<sub>1</sub> exo-8,9-epoxide by the cytochrome P450 enzymes. The resulting epoxide can react with guanine in the DNA to cause DNA damage.