Objective: A series of tetraketones has been synthesized by way of a one pot synthesis and screened for inhibitory activity against the enzyme lipoxygenase.
Method: An efficient and high yielding one pot synthesis to tetraketones [2−22] has been developed by way of tetraethyl ammonium bromide (Et4N+Br¯ ) mediated condensation of cyclohexane-1, 3-dione  with a variety of aldehydes. Lipoxygenase enzyme solution was prepared so that enzyme concentration in reaction mixture was adjusted to give rates of 0.05 absorbance/minute. The test compounds were prepared in methanol of concentrations 50, 25, 12.5, 6.25 and 3.125 μM. The reaction mixture contained 160 μL (100 mM) sodium phosphate buffer (pH 8.0), 10μL of test-compound solution and 20 μL of lipoxygenase solution. The contents were mixed and incubated for 10 minutes at 25°C. The reaction was then initiated by the addition of 10μL substrate solution (linoleic acid, 0.5 mM, 0.12% w/v tween 20 in the ratio of 1:2), with the formation of (9Z,11E)-(13S)-13-hydroperoxyoctadeca-9,11-dienoate, the change of absorbance at 234 nm was followed for 6 minutes. The concentrations of the test compounds that inhibited the lipoxygenase activity by 50% (IC50) were determined by monitoring the effect of increasing concentrations of these compounds in the assays on the degree of inhibition. The IC50 values were calculated by means of the EZ-Fit Enzyme-Kinetics Program (Perrella Scientific Inc., Amherst, USA).
Result: The tetraketones [2−22] were synthesized in high yields (91–98%) using mild reaction conditions. Most of these compounds showed significant inhibitory activity against the enzyme lipoxygenase. It was found that the presence of substituents which increase delocalization of electrons enhances the inhibitory activity.
Conclusion: It is concluded that the study is likely to lead to the discovery of therapeutically efficient agents against important disorders such as inflammation and asthma.