New polymer syntheses. IV. Polypeptides of lysine and ornithine with pending pyrimidine bases

Starting with β-methoxy methacryloylisocyanate, β-methoxy methacrylisothiocyanate, and β-isocyanatopropionyl chloride, on the one hand, and N^α-Z-lysine or N^α-Z-ornithine, on the other hand, N^α-Z-amino acids with pyrimidine bases in the side chain were synthesized. These Z-protected nucleoamino acids were converted to the corresponding N-carboxyanhydrides (NCAs) via the silylester method. In the case of 2-thiothymine derivatives, the reaction intermediate of the NCA synthesis caused benzylation of the thioxo- group, so that a new class of 2-mercaptopyrimidine derivatives was isolated unexpectedly. The poly(nucleoamino acids) obtained by polymerization of the nucleoamino acid NCAs were characterized by elemental analyses, optical rotations ¹H-nmr and ¹³C-nmr spectra. Vapor pressure osmometry revealed that the DP s were in the range of 20–30. Their spectra suggest a helical secondary structure. While all homopolypeptides are insoluble in water, copolypeptides containing L -lysine N^ε-hydrobromide possess good solubility in water.