Efficient Synthesis and Biological Evaluation of 1,4-Disubstituted 3-Cyanopyridin-2(1H)-ones as Selective Inhibitors of the Post-Acid Activity of Mammalian 20S Proteasomes

A set of new 1,4-disubstituted 3-cyanopyridin-2(1H)-ones were synthesized in good yields by a simple and handy method using various primary amines for the construction of pyridine ring. The synthesized compounds were tested on three types of catalytic sites of mammalian constitutive 20S proteasome (c20S) and 20S immunoproteasome (i20S). Most of the new compounds (7a–7g) specifically inhibited the post-acid (PA) activity in the low micromolar range. Compounds 7h and 7i poorly inhibited the three types of catalytic activities. Challenging proteases calpain I and cathepsin B were not inhibited.