Abstract
Stomata—small pores generally found on the leaves of plants—control gas exchange between plant and the atmosphere. Elucidating the mechanism that underlies such control through the regulation of stomatal opening/closing is important to understand how plants regulate photosynthesis and tolerate against drought. However, up-to-date, molecular components and their function involved in stomatal regulation are not fully understood. We challenged such problem through a chemical genetic approach by isolating and characterizing synthetic molecules that influence stomatal movement. Here, we describe that a small chemical collection, prepared during the development of C–H amination reactions, lead to the discovery of a Stomata Influencing Molecule (SIM); namely, a sulfonimidated oxazole that inhibits stomatal opening. The starting molecule SIM1 was initially isolated from screening of compounds that inhibit light induced opening of dayflower stomata. A range of SIM molecules were rapidly accessed using our state-of-the-art C–H amination technologies. This enabled an efficient structure–activity relationship (SAR) study, culminating in the discovery of a sulfonamidated oxazole derivative (SIM*) having higher activity and enhanced specificity against stomatal regulation. Biological assay results have shed some light on the mode of action of SIM molecules within the cell, which may ultimately lead to drought tolerance-conferring agrochemicals through the control of stomatal movement.
Highlights
Our research into C–H amination technologies has allowed us to construct a chemical library, from which we have identified a set of molecules (SIM/SIM*) that inhibit stomatal opening
The results highlight the power of reaction-driven forward chemical genetics and we believe that a host of small molecules with potentially unique bioactivities are possible through reaction development[49,50,51]
The epidermal peels were immersed in the buffer containing chemical compounds and were incubated under fluorescent white light (50 μmol m−2 s−1) or in the dark at 25 °C for 4 h, and samples in which the stomata were uniformly closed were identified using a stereoscopic microscope (Stereo Discovery; Zeiss, Oberkochen, Germany)
Summary
A variety of arylamines were efficiently prepared by a copper-catalyzed coupling of arenes with the aminating agent, N-fluorobenzenesulfonimide (NFSI). This one-step synthesis[35] provided our initial arylamine collection of 22 products (Fig. 2A). The isomer, sulfonimidated 2,5-diphenyloxazole 7, showed no activity towards inhibition, indicating the structural specificity of SIM1 for its bioactivity. We wish to emphasize that preparation of SIM1 is easy: one-step C–H amination from inexpensive and commercially available reagents/catalyst (Fig. 2D). These findings have shown that fundamental chemistry research into reaction methodologies can yield a library of molecules with unique bioactivity. Pre-SIM1 (the non-imidated diphenyloxazole shown in Fig. 2D) had no such effect, indicating that sulfonimidation via C–H functionalization confers novel activity to simple aromatic structures
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