As depicted in Figure 3A , after compound 1 docking into 1W51 structure, the protonated 2-NH 3 group of the lysine moiety form hydrogen bond with Asp228, Gly230 and Thr231, respectively, the 6-NH group form hydrogen bond with Tyr198. The benzyl ring (P1) fills the S1 pocket shaped by the Tyr71, Phe108, and Trp115 residues, while carbobenzyloxy moiety (P29) fills the S29 pocket shaped by the Tyr71, R128, and Y198 residues, so as to allow the carbonyl group to form hydrogen bond with the Thr72 residue, the benzyl group to establish a cation-p interaction with the guanidine group of Arg128.