Ligands. MG-132 was purchased. X77 was synthetized by us as follows. Rac-X77 was prepared in two separate steps (Scheme S1). Although X77 can be formed in only one step by the four-component Ugi reaction (Patent US9975885B2) we observed slightly higher yields when a pre-formed aldimine was utilized. Hence, reaction of 3-pyridine-carbox-aldehyde with 4-(tert-butyl)aniline in methanol at room temperature gave (E)-N-[4-(tertbutyl)-phenyl]-1-(pyridin-3-yl)-methanimine in quantitative yield. In the subsequent step this aldimine was then treated with 4-imidazole carboxylic acid and cyclohexyl iso-cyanide at 40 °C in methanol to furnish rac-X77 in 45% yield after work-up and purification (Fig. to S18). Finally, X77 and S-X77 were successfully separated by preparative HPLC with a chiral stationary phase.