Occurrence of Z -2-oxo-4-methyl-3-pentene-1,5-dioic acid and its regioisomer 4-methylene-2-oxo-glutaric acid in tulip tissues.

Although Z -2-oxo-4-methyl-3-pentene-1,5-dioic acid ( Z -OMPD) has been identified as a major dicarboxylic acid in tulip tissues, its biosynthetic pathway has not been elucidated. Herein, Z -OMPD was isolated from tulip leaves and chemically synthesized. Comparisons of these samples revealed that Z -OMPD exists as a tautomeric mixture at physiological pH. As a regioisomer of Z -OMPD, we enzymatically and chemically prepared 4-methylene-2-oxo-glutaric acid (4-MEOG) for the first time. Using these compounds as standards, the occurrence of Z -OMPD and 4-MEOG in various tissues of the tulip cultivar "Murasakizuisho" was evaluated directly and by 2,4-dinitrophenylhydrazone derivatization. Z -OMPD was found to be abundant in the aerial tissues, whereas 4-MEOG was almost absent from all tissues. Stability analyses of Z -OMPD and 4-MEOG revealed that no double bond isomerization occurred at physiological pH, suggesting that enzyme systems are responsible for Z -OMPD biosynthesis in tulip tissues.