A PRACTICAL ONE-POT SYNTHESIS OF WEINREB-LIKE AMIDES OF (S)- AND (R)-N-BOC-PIPECOLIC ACIDS FROM (+)-PIPERIDINE-2-CARBOXYLIC ACID

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.

An Inexpensive and Scalable Synthesis of Shld

A synthesis of the important FKBP ligand Shld is reported. The synthesis avoids stoichiometric use of expensive and chiral reagents, maintains enantioselectivity and provides a high overall yield (39%). The main features in the method are enantioselective alkylation for preparation of the phenyl acetic acid moiety (building block A), catalytic enantioselective reduction for obtaining the chiral diaryl-1-propanol (building block C), and direct acylation of S-pipecolic tartrate rather than use of expensive Fmoc-pipecolic acid. The assembly of the building blocks A-C is reversed in comparison to previous synthesis, which also eliminates the need for protective groups.

Total synthesis of (+)-antofine and (-)-cryptopleurine

The tylophorine alkaloid anticancer compounds antofine and cryptopleurine have been synthesized in optically active form. Both syntheses employ optically pure α-amino acids as the starting materials, require only seven steps from known 2-ethynylpyrrolidine or 2-ethynylpiperidine derivatives, and are free of protecting groups. Key steps include an alkyne hydration and a chromium carbene complex based net [5+5]-cycloaddition step. Alkyne hydration was accompanied by racemization of the resulting β-aminoketone under most of the conditions examined, and successful minimization of this side reaction was achieved through careful pH control and choice of metal additive. Final ring closure involves a Bischler-Napieralski reaction using a carbamate (antofine) or urea (cryptopleurine) precursor.