To examine the structural requirements of the enzyme, 6-oxo-2, 4-heptadienoic acids (4) and methyl esters 5 were synthesized (Scheme I) to provide the four possible cis-trans isomeric skeletons, only one of which was reported previously. Base-catalyzed hydrolysis of the esters 5-EZ and 5-EE yielded the corresponding acids. Repeated attempts to hydrolyze methyl 6-oxo-2 (2), 4 (Z)-heptadienoate (5-ZZ), however, led only to the
