Synthesis of Shld Derivatives, Their Binding to the Destabilizing Domain, and Influence on Protein Accumulation in Transgenic Plants.

A series of 35 analogues of Shld with modifications in the A-residue and the C-residues were prepared and investigated for binding to FKBP and GFP accumulation in transgenic plants. The modifications investigated explored variations that were supposedly inside or outside the receptor binding site with the latter being important by influencing the overall polarity of the compounds in order to improve the absorption in plants. The binding of the new compounds to the destabilizing domain was determined using a fluorescence polarization competition assay, and the GFP expression in engineered Arabidopsis thaliana was studied. The results showed that modifications of the C-building block phenol with acidic, basic, and neutral groups led to better ligands with some being better than Shld in the plant. Generally small, polar substituents showed the best GFP accumulation.