Probing the Mode of Action of eW5 - A Small Molecule Plant Growth Promoter

Abstract

The work described in this thesis cover two distinct areas of chemistry. The primary body of this thesis looks at a small molecule N-(2-aminoethyl)naphthalene-1-sulfonamide (named eW5, 1) which has been shown to promote various aspects of plant growth (Volume I, Chapters 1-4). Plant hormonal pathways control almost every aspect of plant development and growth. Small molecules can selectively perturb these highly complex and interconnected pathways and have thus demonstrated to be effective tools for the study of plant hormonal signalling. In order to determine the mode of action of eW5, two lines of research were undertaken and are described in the thesis. In the first approach, target identification of 1 was initiated by SAR studies that showed that C–4 substituents were viable, indicating viable incorporation of a photoaffinity tag. Three synthetic approaches towards a chemical probe were explained–ultimately affording N--3-tert-butyl-N-(pent-4-yn-1-yl) benzamide hydrochloride (145) which was shown to retain the growth promoting abilities of 1. A complementary approach using a genetic screen of EMS mutants was also employed to identify the causative gene mutation for eW5-resistance.

In the second aspect of the thesis (Volume II), two separate studies on Ir catalysed aromatic C–H activation are described. The development of the transformation of C–H bonds to form organoboron compounds has allowed for the formation of highly functionalised aromatics and late-stage functionalisation of compounds, making it of significance to the fields of natural product synthesis and medicinal chemistry. In the first of these studies, tandem Ir catalysed borylation – Suzuki-Miyaura cross coupling to 2-halo nicotinates was developed to afford trifunctional pyridines. Fluoro-aromatics represent another interesting class of substrates and as such, the second report describes a systematic study on the regioselectivity of Ir catalysed borylation. It was shown that the fluorine substitution pattern and the boron source were able to alter the standard steric controlled regioselectivity subtly yet distinctly in various substrates.