RADIOIODINATED GIBBERELLIN PHOTOAFFINITY PROBES

Oxidation gf the gibberellin photoaffinity reagent GA(4)-17-ylsulfanyl ethyl 4-azidosalicylate 2 yields separable isomeric sulfoxides. Oxidat ion at the sulfur atom occurs during the radio-iodination of 2, leadin g to low radiochemical yield. The sulfoxides themselves can be efficie ntly radio-iodinated to specific activities approaching 1000 Ci mmol(- 1) and recovered in high yield after ion-exchange purification. They a re biologically active in the induction of alpha-amylase in aleurone c ells of wild oat, Avena fatua and, thus, are useful probes for the stu dy of gibberellin perception in this system. The synthesis of 6-[2-(5- iodosalicyloyloxy)ethyl]sulfinylhexanoic acid is also described. This molecule has been designed to act as a mimic of the hydrophobic side-c hain of the radioiodinated photoaffinity probe and, thus, may be a use ful additive for the reduction of non-specific labelling in photoaffin ity experiments.