The Biomimetic Synthesis of Polyarylated Fluorenes, Relevant to Selaginellaceae Polyphenols, Leading to the Spontaneous Formation of Stable Radicals

• Published in: ChemPlusChem (Weinheim, Germany) Germany), 2024-04, Vol.89 (4), p.e202300410-n/a
• Main Authors: Nallappan, Sundaravelu, Lapinskaite, Ringaile, Hájíček, Josef, Kunák, Dominik, Čambal, Peter, Nečas, David, Císařová, Ivana, Atalay, Hazal Nazlıcan, Tumer, Tugba B., Tarábek, Ján, Schwarzová‐Pecková, Karolina, Rycek, Lukas
• Format: Article
• Language: English
• Subjects: biomimetic synthesis; cytotoxicity; radicals; selaginellacea polyphenols; spin density distribution
• ISSN: 2192-6506; 2192-6506
• DOI: 10.1002/cplu.202300410

This work reports a biomimetic synthesis of polyarylated fluorene derivatives. The molecules are formed via intramolecular electrophilic aromatic substitution, resembling a cyclization leading towards the natural selaginpulvilins from selaginellins. The scope of the reaction was investigated, and the products were obtained in 60–95 % yields. Some of the compounds decompose to a stable radical. We investigated the nature and the origin of the radical using experimental methods, including EPR or electrochemical measurements, as well as theoretical methods, such as DFT calculations. Based on our observations, we hypothesize, that phenoxy radicals are formed in the first instance, which however undergo internal rearrangement to thermodynamically more stable carbon‐centered radicals. The preliminary data also show the cytotoxic properties of some of the molecules. A biomimetic synthesis of polyarylated fluorenes similar to naturally occurring selaginpulvilines is reported in this work. Some of the synthesized fluorens spontaneously decompose to solid‐state stable radical. Various techniques were employed, including cyclic voltammetry, EPR spectroscopy, and DFT calculation to shine a light on the origin and nature of the radical.