SYNTHESIS AND CHARACTERIZATION OF POLY-L-LYSINE WITH CONTROLLED LOW-MOLECULAR-WEIGHT

N-Carboxy-(N-epsilon-benzyloxycarbonyl)-L-lysine anhydride (Z-L-lysine NCA) was polymerized in dimethylformamide with triethylamine, diethyl amine or hexylamine as initiator, at varying molar ratios of NCA to in itiator (M/I ratio). After removal of the protecting Z-group the resul ting poly-L-lysine was characterized with H-1 NMR and MALDI TOF MS. Bo th diethylamine-and hexylamine-initiated polymerization yielded poly-L -lysine in which the initiators were incorporated at the carboxylic en d of the polymer. This indicates that the NCA polymerization occurred exclusively via nucleophilic attack of the initiator on the monomer. O n the other hand, when triethylamine was used as the initiator, poly-L -lysine was obtained in which no triethylamine-derived end group could be detected by MS. These polymer chains are most likely end-capped wi th an N-acyl-2,5-dioxopiperazine group at the carboxylic end of the po lymer. Incorporation of diethylamine and hexylamine allowed determinat ion of the degree of polymerization (DP) of the obtained polymers by H -1 NMR. The DP depended linearly on the M/I ratio, for both diethylami ne and hexylamine, with higher DPs for the diethylamine-initiated poly -L-lysine at equal M/I ratio.