Radio-iodinated gibberellin photoaffinity probes

Abstract

Oxidation of the gibberellin photoaffinity reagent GA₄-17-ylsulfanylethyl 4-azidosalicylate 2 yields separable isomeric sulfoxides. Oxidation at the sulfur atom occurs during the radio-iodination of 2, leading to low radiochemical yield. The sulfoxides themselves can be efficiently radio-iodinated to specific activities approaching 1000 Ci mmol^–1 and recovered in high yield after ion-exchange purification. They are biologically active in the induction of α-amylase in aleurone cells of wild oat, Avena fatua and, thus, are useful probes for the study 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-chain of the radioiodinated photoaffinity probe and, thus, may be a useful additive for the reduction of non-specific labelling in photoaffinity experiments.