As depicted in Figure 3B , in the catalytic site, for the small size and symmetric overall shape of compound 2, one of the hydroxyl group of the tartaric diamide core are involved in hydrogen bonds with the side chain of the catalytic Asp32 and Asp228, respectively, whereas the other hydroxyl group form hydrogen bond with Thr72, and one of the amide group form hydrogen bond with Gly230. Both sides of compound 2 are benzyl groups, one of the benzyl group occupy the S2 pocket shaped by the Asn233, Arg235 and Ser325 residues, the other benzyl group occupy the S29 pocket, establish a cation-p interaction with the guanidine group of Arg128.