Evaluation of Natural Dye Extracts from African Plants for the Photooxygenation of α-Terpinene to the Anthelmintic Ascaridole

In this study, the singlet oxygen photosensitization potential of three natural African plant extracts was investigated using the photooxygenation of α-terpinene (1). Utilizing visible light, the Carpolobia lutea extract achieved high conversions towards the anthelmintic ascaridole (2) of >60% after 90 min of irradiation, while the extracts of Hibiscus sabdariffa and Justicia secunda failed to induce significant photoreactivity. Quenching using 1,4-diazabicyclo[2.2.2]octane (DABCO) confirmed a singlet oxygen pathway for irradiation with the C. lutea extract. Further separation of the C. lutea extract and subsequent photooxygenation screening established several active fractions for ascaridole generation. Advanced HPLC–MS analyses of these active fractions revealed several photosensitizing constituents. These findings establish C. lutea extract as a sustainable and effective photosensitiser with comparable performance to commercial dyes.