This invention discloses novel gamma secretase inhibitors of the formula: wherein: L is —O—, —N(R6)—, —S—, —S(O)—, or —S(O2)—; R1 is selected from the group consisting of aryl and heteroaryl; R2 is selected from the group consisting of alkyl, —C(O)—Y, —X—C(O)—Y, -alkylene-X—C(O)—Y, -alkylene-C(O)—Y, -alkylene-cycloalkylene-X—C(O)—Y, -alkylene-cycloalkylene-C(O)—Y, -cycloalkylene-alkylene-X—C(O)—Y, -cycloalkylene-alkylene-C(O)—Y, -cycloalkylene-X—C(O)—Y, -cycloalkylene-C(O)—Y, -alkylene-cycloalkylene-alkylene-X—C(O)—Y, -alkylene-cycloalkylene-alkylene-C(O)—Y, aryl, and heteroaryl; R3 is selected from the group consisting of aryl, heteroaryl, alkyl, cycloalkyl, arylalkyl, arylcycloalkyl, heteroarylalkyl, heteroarylcycloalkyl, arylheterocycloalkyl, and alkoxyalkyl; each R4 and R5 is independently selected from the group consisting of H and alkyl; and Y is selected from the group consisting of —NR8R9, —N(R6)—(CH2)b—NR8R9, aryl, heteroaryl, alkyl, cycloalkyl, arylalkyl, arylcycloalkyl, heteroarylalkyl, heteroarylcycloalkyl, and aryl heterocycloalkyl; or Y is selected from the group consisting of: One or more compounds of formula I, or formulations comprising such compounds, may be useful, e.g. in treating Alzheimer's Disease.