The reaction between a free thiol and a maleimide produces a thiosuccinimide product. The process is a type of “click chemistry” reaction. On the left-hand side of the image, a free thiol (SH) group is shown with a maleimide group. In the center of the image, an arrow pointing from left to right has the word “click” in it to symbolize a click chemistry reaction. The final product on the right-hand side of the image shows that the maleimide group and the free thiol have reacted to form a thiosuccinimide product.