Application of the concept of activated ketones to the design of novel and potent transition-state analog inhibitors of the aspartyl protease renin is described. Three different classes of peptidic activated ketones were synthesized: 1,1,1-trifluoromethyl ketones, alpha-keto esters, and alpha-diketones. The corresponding alcohols were also evaluated as renin inhibitors in each series. While the trifluoromethyl alcohol 12 (I50 = 4000 nM) was equipotent to the simple methyl alcohol 7 (I50 = 3200 nM), the structurally similar alpha-hydroxy esters (32 and 30, I50's = 5.3 and 4.7 nM, respectively) and alpha-hydroxy ketones (41 and 42, I50 = 23 and 15 nM, respectively) were 150-300-fold more active. The hydrating capability of the activated ketone functionality was important for intrinsic potency in the case of trifluoromethyl ketones, as illustrated by the significantly better activity of trifluoromethyl ketone 13 (I50 = 250 nM) compared to its alcohol analog 12 (I50 = 4000 nM). It was however unimportant for the alpha-keto ester (20 and 31, I50 = 15 and 4.1 nM, respectively) and alpha-diketone (43 and 44, I50 = 52 and 28 nM, respectively) based inhibitors, since their activity was essentially similar to that of the corresponding alcohols. These results collectively suggest that, whereas the trifluoromethyl ketones derive their renin inhibitory potency primarily from their ability to become hydrated, this is not a critical feature for the activity of alpha-dicarbonyl-based inhibitors. The alpha-keto ester and alpha-diketone based renin inhibitors benefit predominantly from the hydrophobic and/or H-bonding type binding interactions of the neighboring ester or acyl group itself, rather than the ability of this group to deactivate the adjacent ketone group and thereby make it susceptible to hydration.