New Families of Inherently Chiral Monomers with Different Atropisomeric Cores for Applications as Oligomeric Films in Chiral Electrochemistry

Enantioselective electroanalysis is a very attractive target, potentially enabling to discriminate between the enantiomers of electroactive chiral probes without preliminary separation steps. Inherently chiral electroactive monomers based on atropisomeric biheteroaromatic cores and oligothiophene wings have recently proved excellent starting materials for the electrodeposition of electrode surfaces consisting of inherently chiral oligomers, of outstanding enantiodiscrimination ability for chiral electroactive probes, in terms of large potential differences in voltammetry experiments [1-2]. In this context, we would like to present new inherently chiral monomers that have different atropisomeric properties and cores: i) the new inherently chiral monomer Naph2T4, based on a biaromatic atropisomeric core, and advantageously obtainable in enantiopure form without HPLC separation steps, by a synthetic route hinging on enantiopure 2,2’-dibromo-1,1’-binaphthalenes; ii) an inherently chiral monomer based on a 2,2′-biindole core (N-R)-Ind2Ph2T4, as the prototype of a new inherently chiral monomer family, whose properties could be modulable through functionalization of the pyrrolic N atoms (with alkyl chains of different lengths); iii) an inherently chiral monomer based on a 2,2′-biindole core with the N atom functionalized with an alcoholic residue (N-OH)-Ind2Ph2T4 The monomers were electrochemically characterized by cyclic voltammety experiments, the electrooligomerization conditions were then optimized to convert the monomers into oligomeric films. The films show good stability upon subsequent potential cycling in monomer-free solution, as required for use as an enantioselective electrode surface and subsequently their enantioselection capabilities were tested using the model chiral probe N,N-dimethyl-1-ferrocenylethylamine, which can be regarded as a benchmark given that it displays an electrochemically and chemically reversible oxidation, but also probes of pharmaceutical interest (such as L- and D- DOPA and L- and D-Tryptophan). We have verified the general validity of the inherently chiral concept, which does not depend on the chemical nature of the atropisomeric scaffold, by testing the electro-oligomerized chiral surfaces starting from monomers with different molecular design. In order to fully clarify the enantioselection capacity of all these heteroaromatic systems, we also propose a comparison of these new inherently chiral surfaces with the benchmark monomer BT2T4. References: [1] S. Arnaboldi, M. Magni, P. R. Mussini, Curr. Op. in Electrochemistry 8 (2018) 60-72. [2] S. Arnaboldi, S. Grecchi, M. Magni, P.R. Mussini, Curr. Op. in Electrochemistry 7 (2018) 188-199.