RESUMO
C-linked carbo-ß(2)-amino acids (ß(2)-Caa), a new class of ß-amino acid with a carbohydrate side chain having d-xylo configuration, were prepared from d-glucose. The main idea behind the design of the new ß-amino acids was to move the steric strain of the bulky carbohydrate side chain from the Cß- to the Cα-carbon atom and to explore its influence on the folding propensities in peptides with alternating (R)- and (S)-ß(2)-Caas. The tetra- and hexapeptides derived were studied employing NMR (in CDCl(3)), CD, and molecular dynamics simulations. The ß(2)-peptides of the present study form left-handed 12/10- and 10/12-mixed helices independent of the order of the alternating chiral amino acids in the sequence and result in a new motif. These results differ from earlier findings on ß(3)-peptides of the same design, containing a carbohydrate side chain with d-xylo configuration, which form exclusively right-handed 12/10-mixed helices. Quantum chemical calculations employing ab initio MO theory suggest the side chain chirality as an important factor for the observed definite left- or right-handedness of the helices in the ß(2)- and ß(3)-peptides.
