Preparation of Fully Guanidinylated ε-Polylysine and Its Antibacterial Activity

Abstract

ε-Poly-L-lysine (PL) is a natural polymer bearing a key amino group that provides it with a cationic nature, high reactivity in water, and consequent broad applicability. Here we prepared a guanidinylated PL (GPL) exhibiting an enhanced cationic nature by guanidinylation of the amino group with 1-amidinopyrazole hydrochloride (AP) and trimethylamine (TEA) (AP-TEA system). In the AP-TEA system using 3 eq of AP for 2 days at room temperature, a GPL with the degree of guanidinylation (DG) of 100% was achieved. The DG value could be controlled by the AP amount. The lower acidity of the GPL relative to PL was confirmed by pH titration; the reduced acidity resulted in enhanced antibacterial activity of the GPL under an alkaline condition (pH 8.0 and 9.0).