Thus, several diaryl phosphonate compounds of optimized structure have been investigated as drug candidates against proteases involved in the development of human diseases, such as urokinase-type plasminogen activator which facilitates tumor cell invasion and metastasis by the degradation of the basement membrane and the extracellular matrix, or dipeptidyl peptidase IV, of which inhibition stimulates insulin secretion and reduces the blood glucose level in the treatment of type 2 diabetes [3,59,60]. Here, DPP4 is linked to neoplasm.