An Impressive Conformational Effect in D,L-alternating Oligopeptides: a single Leucine Counteracts the Influence of Several Norleucine

Abstract. Studies in synthetic D,L-alternating stereo-co-oligo- and polypeptides have indicated that the side chains play a role in the preference of D,L-alternating peptides for specific backbone conformations. In particular recent work has shown that the n-butyl groups of oligonorleucine drastically differ from oligovalines oligoisoleucines and oligoleucines. The difference from oligoleucines is striking and has led us to investigate the conformational behavior of Boc- and -Ome terminated D,L-alternating norleucine/leucine cooligopeptide with one or few residues of leucine. Here we report the conformational study of the linear decapeptides [XNle(1Leu)] and [XNle(1,6Leu)] containing respectively one and two leucine residues.