A series of 2-amino-4 H-3, 1-benzoxazin-4-ones have been synthesized and evaluated as inhibitors of the complement enzyme C1r. C1r is a serine protease at the beginning of the complement cascade, and complement activation by β-amyloid may represent a major contributing pathway to the neuropathology of Alzheimer's disease. Compounds such as 7- chloro-2-[(2-iodophenyl) amino] benz [d][1, 3] oxazin-4-one (32) and 7-methyl-2-[(2- ...