RESUMO
The direct esterification of carboxylic acids with perfluorinated alcohols mediated by XtalFluor-E is reported. The corresponding polyfluorinated esters are obtained in moderate to excellent yields with a broad range of carboxylic acids, including aromatic, heteroaromatic, aliphatic, and nonracemic chiral substrates, using only a slight excess (2 equiv) of the perfluorinated alcohol. Control experiments indicate that the reaction does not proceed through the formation of an acyl fluoride but most likely through a (diethylamino)difluoro-λ4-sulfanyl carboxylate intermediate.
RESUMO
We describe the synthesis of a library of new pseudopeptides and their inhibitory activity of the rabbit 20S proteasome chymotrypsin-like (ChT-L) activity. We replaced a natural α-amino acid by an α- or a ß-hydrazino acid and obtained inhibitors of proteasome up to a submicromolar range (0.7 µM for molecule 24b). Structural variations influenced the inhibition of the ChT-L activity. Models of inhibitor/20S proteasome complexes corroborated the inhibition efficacies obtained by kinetic studies.