Synthesis and conformation of poly(L-2-anthraquinonylalanine)

A novel nonnatural amino acid that carries a 2-anthraquinonyl group, L-2-anthraquinonylalanine, was first synthesized and converted to the corresponding N-carboxyanhydride (NCA). The NCA was polymerized to give poly(L-2-anthraquinonylalanine) in the form of a diblock copolymer with poly(ethylene glycol) that is linked to the C-terminal. A triblock copolymer was also prepared with poly(γ-benzyl L-glutamate)s that are attached to both N- and C-terminals. CD spectra of the diblock copolymer showed a helical conformation that is different from a right-handed α-helix. Conformational analysis and theoretical CD calculation suggested that the poly(anthraquinonylalanine) unit prefers a left-handed α-helix with the lowest energy side-chain orientation.