Porphobilinogen
Porphobilinogen is an organic compound that occurs in living organisms as an intermediate in the biosynthesis of porphyrins, which include critical substances like hemoglobin and chlorophyll.
The structure of the molecule can be described as molecule of pyrrole with sidechains substituted for hydrogen atoms at positions 2, 3 and 4 in the ring ; respectively, an aminomethyl group, an acetic acid group, and a propionic acid group.