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

Abstract 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).