(3S)-3-甲基-6-亚甲基-2,5-哌嗪二酮

(5-benzyl-3,6-dioxo-piperazin-2-yliden)-acetic acid methyl ester

(1-phenyl-ethylidene-(seqtrans))-succinic acid

4-hydroxy-2-keto-4-methylglutaric lactone

3-hydroxyhexane-2,5-dione