Porphobilinogen (PBG) 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.[1]
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 (1 being the nitrogen atom); respectively, an aminomethyl group −CH2−NH2, an acetic acid (carboxymethyl) group −CH2−COOH, and a propionic acid (carboxyethyl) group −CH2−CH2−COOH.