Natural brassinosteroids possess a 22R, 23R configuration that appears essential for biological activity. It is, therefore, interesting to elucidate if the activity of brassinosteroids with a short side chain depends on the C22 configuration. Herein, we describe the synthesis of new brassinosteroids analogs with 24-norcholane type of side chain and R configuration at C22. The initial reaction is the dihydroxylation of a terminal olefin that leads to S/R epimers. Three different methods were tested in order to evaluate the obtained S/R ratio and the reaction yields. The results indicate that Upjohn dihydroxylation is the most selective reaction giving a 1.0:0.24 S/R ratio, whereas a Sharpless reaction leads to a mixture of 1.0:0.90 S/R with 95% yield. Using the latter mixture and following a previous reported method, benzoylated derivatives and both S and R brassinosteroids analogs were synthesized. All synthesized compounds were completely characterized by NMR spectroscopy, and HRMS of new compounds are also given. In conclusion, a synthetic route for preparation of new analogs of brassinosteroids of 24-norcholane type and R configuration at C22 were described. It is expected that this will help to elucidate if a configuration at C22 is a structural requirement for hormonal growth activity in plants.
International audienceIn this work, we report the synthesis of the asymmetrical β-diketone 1-(thiophen-2-yl)-3-(thiophen-3-yl)propane-1,3-dione (HL) and its corresponding bis(β-diketonate)copper(II) complex [Cu₁-(thiophen-2-yl)-3-(thiophen-3-yl)-1,3-propanedionate₂] (CuL2), isolated in 60 and 86% yields, respectively. These two new compounds have been characterized by elemental analysis, FT-IR and UV–Vis spectroscopy and, in the case of HL, by 1H and 13C NMR spectroscopy. Additionally, both compounds were authenticated by X-ray diffraction analysis. The β-diketone HL exists as its keto-enol tautomer both in solution and in the solid-state with the [sbnd]OH group adjacent to the 3-thienyl unit. The CuL2 is essentially flat and the Cu(II) center adopts a perfect square planar geometry. The CuL2 modified electrode was fabricated through the electropolymerization of the monomer in a 0.1 M of tetrabutylammonium tetrafluoroborate (TBATFB) in anhydrous acetonitrile solution, in the potential window −1.0 V to 1.6 V. The thin film Pt|(CuL2)n modified electrode response was studied employing a 0.1 M of TBATFB solution in CH3CN. Likewise, the potentiostatic method was also employed to synthesize the films on Fluorine Doped Tin Oxide electrode (FTO). Images from the electrode surface were obtained using Scanning Electron Microscopy (SEM)
Electrochemical oxidation of four-coordinate square planar Schiff-base Ni(ii) and Cu(ii) complexes leads to the formation of oligomers at the electrode.
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