Azadirachtin was irradiated with UV light, in both oxygen and nitrogen atmospheres. The reactions were followed by supercritical fluid chromatography (SFC) and the chromatograms showed that one photo-product was formed in both cases. High performance liquid chromatography coupled to high field proton NMR spectroscopy (HPLC–NMR) was used to identify the photo-product. The HPLC–NMR data indicated that the (E)-2-methylbut-2-enoate ester group had been converted into a (Z)-2-methylbut-2-enoate ester group. Confirmation was obtained by isomerizing methyl (E)-2-methylbut-2-enoate with UV light to form a mixture of geometric isomers and then recording the 1H NMR shift for the alkene proton. Additional structural information was obtained from the isolated product, confirmed to be the (Z)-2-methylbut-2-enoate geometric isomer of azadirachtin.
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Johnson et al. (1994) studied this question.
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