SYNTHESIS AND INTERCONVERSION OF THE 4 ISOMERIC 6-OXO-2,4-HEPTADIENOIC ACIDS

The synthesis of the structural isomers of 6-oxo-2,4-heptadienoic acid was undertaken as a means of providing analogs to investigate the structural requirements of maleylacetone cis-trans isomerase. 6-Oxo-2(Z),4(E)-heptadienoic acid and the methyl esters of 6-oxo-2(E),4(Z)-, 6-oxo-2(Z),4(Z)- and 6-oxo-2(E),4(E)-heptadienoic acid were synthesized. Base-catalyzed hydrolysis of these esters furnished the corresponding acids except in the case of the 2Z,4Z isomer, which yielded instead the 2Z,4E acid. A mechanism for isomerization is suggested. Photocatalyzed isomerization of the acids and esters as a possible way of generating the ZZ acid was studied. The properties of the acids, their interaction with the enzyme, and what this suggests about the interaction of substrate maleylacetone with the enzyme is discussed.