Elucidating the Structural Isomerism of Fluorescent Strigolactone Analogue CISA-1

The synthesis of a new potent strigolactone analogue (CISA-1), resulting in the formation of two interconverting structural isomers, which could not be identified, was recently reported by Rasmussen et al [Molecular Plant, 2013, 6, 100]. In the present study, a combined computational and experimental approach is used to identify the exact nature of these structural isomers. While standard experimental techniques were not able to determine the identity of the isomers, chromatographic methods excluded E/Z isomerisation. Computational 1H NMR chemical shift values and DFT calculations on interconversion barriers strongly suggest that the CISA-1 isomers were interconverting (Z)-configured atropisomers.