Synthesis of Expanded Poly(l-amino acid) Containing Phenylethynyl(terpyridine)platinum(II) Moieties

Abstract

Elaborately designed chiral 3D structures, such as proteins, promise outstanding functions. Herein, expanded poly(l-amino acid)s containing phenylethynyl (terpyridine)platinum(II) moieties are presented. Expanded polypeptides were synthesized by stepwise elongation or unsymmetrical metallosupramolecular polycondensation through a copper-catalyzed coupling reaction between the terminal acetylene and platinum–chloride groups. Robust platinum–acetylide bonds were retained in polar solvents, and the molar mass was determined using 1H diffusion-ordered NMR spectroscopy (DOSY). The resulting expanded poly(l-leucine) and poly(l-valine) were 8-mer and 9-mer, respectively, in solution. Despite the slight differences in the side chains, that is, with or without a CH2 group, the dihedral angles (ϕ and ψ) were effectively regulated to determine the local structures. The CD spectra reflected the individual structures of the right-handed 7/2 and 4/1 helices, which were estimated by theoretical calculations. Appropriate selection of amino acid sequences results in a molecular architecture with the desired three-dimensional structure.