The investigated compounds share a common guanidine-containing structure; two of them possess a tricyclic, a bicyclic, and an acyclic guanidinium cores, which are coupled via an ester linkage, ( ) and ( ) in Table . There are eight derivatives that possesses two tricyclic guanidinium cores, (6-9), and in Table . In addition, the derivatives and the three derivatives (3-5), in Table , possesses only a tricyclic guanidinecontaining core and a tricyclic guanidine-containing core linked to a terminal guanidine by an ester linkage, respectively. Relating the structures (1-15; Scheme 1-2) to the estimated binding scores (Table ) suggests that the most influential guanidinium core is the two tricyclic guanidine-containing cores coupled via an ester linkage, as can be seen in the predicted binding scores for the eight derivatives (6-9), , and ( ) in (Table ).