Total synthesis of densipolic acid and trans-densipolic acid enables quantification in vegetable oils

Densipolic acid (DA, 12-OH-9Z,12Z-octadecadienoic acid) has been identified in Paysonia species, and recent analyses have indicated the presence of DA and its trans-isomer (tDA, 12-OH-9E,12Z-octadecadienoic acid) in edible oils. This study describes the first synthetic approach for DA and tDA using a Wittig reaction and a Julia-Kocienski olefination as stereoselective olefination reactions. A library of 22 vegetable oils was analyzed by LC-MS using these two products as standards. The highest concentrations were found in n3-PUFA rich oils, such as flaxseed oils (99-137 mg/100 g of DA and 89-237 mg/100 g of tDA) and shiso oil (93 mg/100 g of DA and 103 mg/100 g of tDA). Lower concentrations of DA acid were detected in rapeseed oils (3.7-1.4 mg/100 g) and soybean oils (2.6-1.4 mg/100 g), which contain less n3-PUFA. Overall, this is the first quantitative analysis of DA and tDA in food.