The pyrrole ring is a heterocyclic moiety that presents the amino acids proline and hydroxyproline in a hydrogenated form and characteristic residue for Histidine, and analog derivatives. These amino acids are found in the alkaloids, a large class of alkaline organic nitrogen compounds produced by plants. The pyrrole ring represents a valuable framework for developing novel therapeutic agents. For example, pyrrole derivatives or molecules including a pyrrole nucleus, show interesting anti-microbial, anti-viral, anti-malarial, antitubercular, anti-inflammatory, enzyme inhibiting and, and anticancer properties. In addition, compounds from the pyrrole ring are also precursors to certain drugs. For instance, pyrrole is a precursor of the drug tolmetin, and N-methylpyrrole is a precursor to N-methylpyrrolecarboxylic acid. Pyrroles are also found in several drugs, including atorvastatin, ketorolac, and sunitinib. Furthermore, hydrogenation of pyrrole and its derivatives is of fundamental importance in chemical and pharmaceutical processes.

Due to its aromatic appeal, pyrrole is difficult to hydrogenate. It does not easily react as a diene in Diels–Alder reactions, and it does not undergo the usual olefin reactions. The reactivity of pyrrole is similar to benzene and aniline, so it is easy to alkylate and acylate. Under acidic conditions, pyrroles polymerise without difficulty, hence why many electrophilic reagents are yet to be applicable to pyrroles. In contrast, substituted pyrroles (including protected pyrroles), hydrogenated analogs, pyrroline, pyrrolidine, and the benzo-fused derivative indole, have been used in a wide range of chemical transformations.

The aim of this Special Issue is to collate original research articles highlighting the importance of the role of the pyrrole nucleus in therapeutic activities. Submissions focussing on the pharmaceutical potentials and properties of pyrrole analogs, structural analogs of pyrrole (e.g. pyrroline, pyrrolidine), and of compounds containing a pyrrole ring (e.g. indole, indoline) are also encouraged. Review articles discussing the state of the art are also welcome.

Potential topics include but are not limited to the following:

• Pyrrole
• Pyrroline
• Pyrrolidine
• Indole
• Indoline
• Anti-cancer agents
• Anti-bacterial agents
• Pyrrole synthesis
• Polypyrroles