Synthesis and bioactivity of labelled germination stimulants for the isolation and identification of the strigolactone receptor

Strigolactones are highly potent germination stimulants for seeds of the parasitic weeds Striga and Orobanche spp. The induction of seed germination is thought to proceed via a receptor-mediated mechanism. Isolation and purification of the strigolactone receptor by affinity chromatography using immobilized avidin or streptavidin requires a biotin labelled strigolactone analogue. For this purpose biotin has been attached, directly as well as indirectly, via a hydrophilic linker to the amino function of optically active amino-GR24. Using the same amino substituted synthetic stimulant GR24, labelled stimulants have been prepared which may be suitable for the identification of the receptor by means of fluorescence correlation spectroscopy, scanning force microscopy or photoaffinity techniques. Bioassays of the labelled stimulants reveal that the germination activity on seeds of Striga hermonthica is retained. Crystal data for the diastereoisomer (+)-8 are reported.