Synthesis and conformational study of poly(0,0′-dicarbobenzoxy-L-β-3,4-dihydroxyphenyl-α-alanine)

High-molecular-weight poly(0,0′-dicarbobenzoxy-L -β-3,4-dihydroxyphenyl-α-alanine) was prepared by the N-carboxyanhydride method. From the results obtained by a study of the optical rotation, nuclear magnetic resonance, and solution infrared absorption, the conformation of poly(0,0′-dicarbobenzoxy-L -β-3,4-dihydroxyphenyl-α-alanine) depended greatly on the solvent taking a right-handed helix with [θ]₂₂₅ = ?13,600 ～ ?18,900 in alkyl halides, a left-handed helix with [θ]₂₂₈ = 22,100 ～ 24,800 in cyclic ethers or trimethylphosphate, and a random coil structure in dichloroacetic acid, trifluoroacetic acid, or hexafluoroacetone sesquihydrate. The polypeptide underwent a right-handed helix-coil transition in chloroform/dichloroacetic acid (or trifluoroacetic acid) mixed solvents and a left-handed helix-coil transition in dioxane/dichloroacetic acid (or trifluoroacetic acid) mixed solvents. The results were compared with those of poly(0-carbobenzoxy-L -tyrosine).