Solid-Phase Synthesis of Water-Soluble Helically Folded Hybrid α-Amino Acid/Quinoline Oligoamides

We report here a solid phase synthesis methodology that allows the incorporation of α-amino acids (X) into quinoline (Q) oligoamide foldamer sequences. Water-soluble hybrid oligoamides based on the XQ2 trimer repeat motif were shown to adopt helical conformations presenting α-amino acid side chains in a predictable linear array on one face of the helix. In contrast, sequences based on the XQ dimer motif expressed less well-defined behavior, most likely due to local conformational variability precluding long-range order. Also presented is a full structural investigation by NMR of a dodecameric XQ2-type foldamer containing four different amino acid residues (Lys, Ala, Asp, and Ser).