Since their discovery in 1936 by McEwen, N-substituted porphyrins have primarily been studied for their use as enzyme inhibitors and for biomedical applications. Probably the most prominent example of this class is the N-methyl mesoporphyrin IX (N-MeMP), which inhibits ferrochelatase, the essential enzyme for the insertion of iron into the tetrapyrrole heterocycle, completing the terminal step in the biosynthesis of heme. Substitution of the pyrrole nitrogen atoms in the interior of the porphyrin result in distortion of the macrocycle leading to nonplanar porphyrin systems with significantly altered properties in terms of basicity and their ability to coordinate metal ions. This is exemplified in a series of highly nonplanar porphyrins prepared from 2,3,7,8,12,13,17,18-octaethyl-5,10,15,20-tetraphenylporphyrin via mono-, di-, tri- or tetra-N-substitution. Such systems combine core (N-substitution) and peripheral (peri interactions) steric strain to yield some of the most distorted porphyrins. Even more complex structures arise from bridging the interior gap either via a coordination with an internal metal ion (N-R-M bridged) or via the direct connection of two nitrogen atoms (N-R-N bridged). Currently, our research focuses on the synthesis of various N-substituted porphyrins to access specific conformations and binding motifs, depending on the substitution type, quantity, regiochemistry, and steric bulk of substituents.

Forgotten treasures: Synthesis and properties of N-substituted porphyrins

253rd National Meeting (2017)

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