N-Substituted poly(alpha-amino acids). 1. Synthesis and characterization of poly(N-methyl-γ-methyl L-glutamate) and poly(N-methyl-γ-ethyl L-glutamate)

The synthesis of high molecular weight poly(N-methyl-γ-methyl L-glutamate) and poly(N-methyl-γ-ethyl L-glutamate) has been performed by permethylation of poly(γ-methyl- and γ-ethyl L-glutamate). Among the various techniques known for low molecular weight materials, only the procedure introduced by Lederer's group2a proved workable in the case of high molecular weight substrates. The degree of methylation was always higher than 95% as shown by elemental analysis, amino acid analysis, and IR techniques. Attempts to obtain polymers starting from N-substituted NCAs other than proline NCA, sarcosine NCA, and N-methylalanine NCA failed in all cases. The N-methylated polymers are readily soluble in dimethylformamide, 2, 2, 2-trifluoroethanol, tetrahydrofurane, and methylene chloride, while they sparingly dissolve in water and methanol. Preliminary CD measurements suggest that the above N-methylated polypeptides adopt an all-trans conformation in solvents such as TFE, methanol, and water. © 1978, American Chemical Society. All rights reserved.