To enhance the inhibitory activity, SAR study efforts around P1' of 123 provided compounds containing imidazole (125) and 5‐chlorofuran (126) with equipotent activity to lead 123 (Figure 30). Next, the exploration of P1 3‐pyridyl unit of 123 revealed pyridazine (127) and pyrazine (128) which were only tolerated, albeit without any improvement.