2-(2,6-Dioxo-3-piperidyl)-5-[3-(ethylamino)propylamino]isoindoline-1,3-dione

4-({[(9H-fluoren-9-yl)methoxy]carbonyl}amino)-4-[(3-methoxy-3-oxopropyl)(methyl)carbamoyl]butanoic acid

4-({8-[(tert-butoxy)carbonyl]-8-azaspiro[4.5]decan-1-yl}({[(9H-fluoren-9-yl)methoxy]carbonyl})amino)butanoic acid

4-({2-[(tert-butoxy)carbonyl]-2-azabicyclo[3.3.1]nonan-8-yl}({[(9H-fluoren-9-yl)methoxy]carbonyl})amino)butanoic acid

4-[(2-{1-[(tert-butoxy)carbonyl]pyrrolidin-2-yl}cyclohexyl)({[(9H-fluoren-9-yl)methoxy]carbonyl})amino]butanoic acid

4-({1-[(tert-butoxy)carbonyl]-4-methylpyrrolidin-3-yl}({[(9H-fluoren-9-yl)methoxy]carbonyl})amino)butanoic acid

(2R)-2-[4-({[(9H-fluoren-9-yl)methoxy]carbonyl}amino)-3-hydroxybutanamido]-4-methoxy-4-oxobutanoic acid

4-[(2-{[(tert-butoxy)carbonyl]amino}cycloheptyl)({[(9H-fluoren-9-yl)methoxy]carbonyl})amino]butanoic acid

4-({1-[(tert-butoxy)carbonyl]-4-methylpiperidin-3-yl}({[(9H-fluoren-9-yl)methoxy]carbonyl})amino)butanoic acid

4-{[2-({[(tert-butoxy)carbonyl]amino}methyl)cyclopentyl]({[(9H-fluoren-9-yl)methoxy]carbonyl})amino}butanoic acid

4-({1-[(tert-butoxy)carbonyl]-6',7'-dihydrospiro[azetidine-3,5'-pyrrolo[1,2-b][1,2,4]triazole]-7'-yl}({[(9H-fluoren-9-yl)methoxy]carbonyl})amino)butanoic acid