A series of acyloxyalkyl and amidooxyalkyl ketones appended to a carbobenzyloxy aspartic acid core have been prepared. The most potent of these new inhibitors was 4i with a K(i) of 0.5 mu M. These two series provide an improved understanding of the binding requirements for the hydrophobic prime side of ICE. (C) 2010 Elsevier Ltd. All rights reserved.