Trypsin-catalyzed Oligomerization of L-Lysine Esters

The oligomerization of L-lysine esters with a free α-amino group was done using trypsin as a catalyst in aqueous media, and some reaction parameters were examined. The pH-dependence of the reaction suggested that aminolysis by the substrate species having non-protonated α- and ɛ-amino groups was a dominant factor governing the reaction progress. At the beginning of the reaction lysine oligomers containing up to 8 residues were observed, but much of the dimer was accumulated during prolonged incubation due to secondary hydrolysis of highly polymerized products. The reaction yield depended on the ratio of enzyme and substrate; an overall reaction yield higher than 70% was attained after 2 hr of reaction when 1,000 mM of L-lysine ethyl ester was treated with 200 μM of trypsin at pH 10.0. The oligomerization was apparently enhanced by an addition of NaCl and by using the longer alkyl esters.