4-(carbomethoxymethyl)-5-carbomethoxy-1,6-cyclopentano-2-pyridone

4-(1-carbomethoxypropyl)-5-carbomethoxy-1,6-cyclopentano-2-pyridone

methyl 4-ethyl-3,10-dioxo-3,4,6,7,8,10-hexahydro-1H-pyrano[3,4-f]indolizine-5-carboxylate

ethyl 2-acetoxy-2-(6-(acetylaminomethyl)-1,1-(ethylenedioxy)-5-oxo-1,2,3,5-tetrahydroindolizin-7-yl)butanoate