High Quality Content by WIKIPEDIA articles! Pyrrole is a heterocyclic aromatic organic compound, a five-membered ring with the formula C4H4NH. Substituted derivatives are also called pyrroles. For example, C4H4NCH3 is N-methylpyrrole. Porphobilinogen is a trisubstituted pyrrole, which is the biosynthetic precursor to many natural products. Pyrroles are components of more complex macrocycles, including the porphyrins of heme, the chlorins, bacteriochlorins chlorophyll, porphyrinogens. Pyrrole has very low basicity compared to conventional amines and some other aromatic compounds like pyridine. This decreased basicity is attributed to the delocalization of the lone pair of electrons of the nitrogen atom in the aromatic ring. Pyrrole is a very weak base with a pKaH of about 4. Protonation results in loss of aromaticity, and is, therefore, unfavorable.