Isolation and characterization of (15Z)-lycopene thermally generated from a natural source

• (15Z)-lycopene, isomerized from the all-E form of a natural source, was purified.
• The obtained (15Z)-lycopene was structurally identified by an NMR analysis.
• A modified theoretical study accounted for the generation of the 15Z-isomer.
• This study demonstrated the occurrence of the isomer from a natural origin.

(15Z)-Lycopene was prepared by thermal isomerization of (all-E)-lycopene derived from tomatoes, and isolated by using a series of chromatographies. The fine red crystalline powder of (15Z)-lycopene was obtained from 556 mg of (all-E)-lycopene with a yield of 0.6 mg (purity: reversed-phase HPLC, 97.2%; normal-phase HPLC, ≥99.9%), and 1H and 13C NMR spectra of the isomer were fully assigned. More refined computational analyses that considered differences in the energy levels of the conformers involved in isomerization have also determined the stabilities of (15Z)-lycopene and other geometric isomers, along with the activation energies during isomerization from the all-E form. The fine control of conditions for HPLC separation and an advanced theoretical insight into geometric isomerization have led to the discovery of the 15Z-isomer generated from a natural source.

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