New C4- and C1-derivatives of furo[3,4-c]pyridine-3-ones and related compounds: Evidence for site-specific inhibition of the constitutive proteasome and its immunoisoform

A C4 derivative of 1,1-dimethyl-furo[3,4-c]pyridine-3-one (compound 10) and a thieno[2,3-d]pyrimidine-4-one (compound 40) have been identified as β1c (10) and β2c or β2i (40) site-specific inhibitors of 20S proteasomes.