The biological activities of five azido N-substituted phthalimides: potential photoaffinity reagents for gibberellin receptors

Abstract

The biological activities of five azido derivatives of the synthetic GA-like bioregulator 94,377 (1-[3-chlorophthalimido]cyclohexanecarboximide) were examined in a range of gibberellin-sensitive assays including: barley half-seed α-amylase secretion, Rumex chlorophyll retention, d5 maize leaf-sheath elongation, lettuce hypocotyl elongation and cucumber hypocotyl elongation. The five azido derivatives tested possessed an N-substituted phthalimide structure but differed in the placement of the azido moiety. An acyl-azido derivative was devoid of biological activity in all assays examined. Of the four remaining aryl-azido derivatives, three exhibited significant biological activity. The biological activity was both compound and species-dependent; a given azido derivative being highly active in one assay (species) but inactive in another. None of the aryl-azides promoted hypocotyl growth in light-grown cucumber seedlings when tested at 100 μM. However, two of the derivatives that were highly active in other assay systems were capable of displacing [3H]GA4 bound to a soluble binding protein prepared from cucumber seedlings when tested at high concentrations. These results indicate that certain aryl-azido derivatives of 94,377 may be useful in purifying GA binding proteins from responsive tissues and should facilitate the molecular modelling of the actual ligand binding pocket of GA receptors or other GA binding proteins.