Abscisic Acid Analogues That Act as Universal or Selective Antagonists of Phytohormone Receptors.

The plant hormone abscisic acid (ABA) plays many important roles in controlling plant development and physiology, from flowering to senescence. ABA is now known to exert its effects through a family of soluble ABA receptors, which in Arabidopsis thaliana has 13 members divided into three clades. Homologues of these receptors are present in other plants, also in relatively large numbers. Investigation of the roles of each homologue in mediating the diverse physiological roles of ABA is hampered by this genetic redundancy. We report herein the in vitro screening of a targeted ABA-like analogue library and identification of novel antagonist hits, including the analogue PBI686 that had been developed previously as a probe for identifying ABA-binding proteins. Further in vitro characterization of PBI686 and development of second-generation leads yielded both receptor-selective and universal antagonist hits. In planta assays in different species have demonstrated that these antagonist leads can overcome various ABA-induced physiological changes. While the general antagonists open up a hitherto unexplored avenue for controlling plant growth through inhibition of ABA-regulated physiological processes, the receptor-selective antagonist can be developed into chemical probes to explore the physiological roles of individual receptors.

Synthesis and structural studies of chiral indium(III) complexes supported by tridentate diaminophenol ligands.

Indium(III) dimethyl, dihalide, and alkoxy-bridged complexes bearing a chiral diaminophenoxy tridentate ligand [NN(H)O](-) were synthesized. The dimethyl complex (NN(H)O)InMe(2) (1) was unreactive toward ethanol and 2-propanol and only partially reactive toward the more acidic phenol. The dihalide complexes (NN(H)O)InX(2) (X = Cl (3), Br (4), I (5)) reacted with NaOEt to form robust alkoxy-bridged complexes with the formula {[(NN(H)O)InX](2)(mu-X)(mu-OEt)} (X = Cl (6), Br (7), I (8)). The reaction of the alkoxy-bridged complexes with water produced hydroxy-bridged dinuclear indium compounds. The hydroxy-bridged complex bearing a chloride ligand [(NN(H)O)InCl(mu-OH)](2) (9) was significantly more reactive toward dissociation and formation of a pyridine adduct than the iodo analogue [(NN(H)O)InI(mu-OH)](2) (10). All compounds were fully characterized in solution by NMR spectroscopy and in the solid state by single-crystal X-ray diffraction. In addition, DFT calculations were used to help explain the reactivity trends observed.