Efficient synthesis of the very-long-chain n-3 fatty acids, tetracosahexaenoic acid (C24:6n-3) and tricosahexaenoic acid (C23:6n-3).

Tetracosahexaenoic acid (C(24):6n-3, THA, 3) is an essential biosynthetic precursor in mammals of docosahexaenoic acid (C(22):6n-3, DHA, 1), the end-product of the metabolism of n-3 fatty acids. THA 3 is present in commercially valuable fishes, such as flathead flounder. Tricosahexaenoic acid (C(23):6n-3, TrHA, 2), an odd-numbered-chain fatty acid, has been identified from marine organisms such as the dinoflagellate, Amphidinium carterae. To date, few studies have examined THA 3 and TrHA 2 due to difficulties in detecting and identifying these compounds, so their chemical and biological properties remain poorly characterized. Only one methodology for the chemical synthesis of THA 3 has been presented, and no method for the synthesis of TrHA 2 has been reported. We report here the efficient synthesis of THA 3 in four steps in 56% overall yield, and the synthesis of TrHA 2 in six steps in 48% overall yield. We also present the synthesis of Δ(2)-THA 4, an intermediate of β-oxidation of THA 3 to DHA 1, in three steps in 73% overall yield.