Central-to-Helical-to-Axial Chirality Transfer in Chiroptical Sensing with Ferrocene Chromophore

The effect of attaching the achiral, cyclic 1-aminocyclohexanecarboxylic acid (Ac6c) directly to aminoferrocene unit (Ac6c−NH−Fc) appears be a promising route for development new chiroptical sensor based on ferrocene chromophore. Three compounds (Boc−AA−Ac6c−NH−Fc; AA = L-Ala, L-Val, L-Phe) were synthesized, spectroscopically characterized (IR, NMR, CD), and conformationally analyzed (DFT). chiral information was transferred from L-amino chromophore by predominant formation P-helical structures with ten-membered hydrogen-bonded rings (β-turns). perturbation appearance negative CD signal near 470 nm originates relative orientation linked amide cyclopentadienyl planes, described dihedral angle χ. sterically demanding Ac6c amino makes trans-like configurations more favorable thus restricts χ, which then leads peak in curve.