Thin-layer chromatographic assay of photoactive compounds (furocoumarins) using the fungus penicillium expansum as a test organism

Abstract

A simple method using silica gel thin layers for the detection and determination of phototoxic compounds has been developed, using the fungus Penicillium expansum as a test organism. The method is suitable for the determination of phototoxic components in mixtures or in impure compounds, as the chromatographic separation and the growth-inhibition test based on photoactivity are carried out on the same thin-layer plate. The highly photoactive linear furocoumarins psoralen, bergapten, xanthotoxin and trioxalen can be detected even more sensitively on the thin-layer plate by means of this photoactivity bioassay than by examination under UV light at 366 nm. The occurrence of xanthotoxin and bergapten as minor constituents in the extract of Ammi visnaga could be detected using this method. Sphondin was weakly photoactive. We could not find any photoactivity for the linear furocoumarins imperatorin and isopimpinellin, which have been described by other authors to be slightly photoactive. Samples of these compounds, however, were found to be contaminated with minor amounts of the highly photoactive furocoumarins xanthotoxin and bergapten, respectively.