Stereodefined synthesis of the four possible stereoisomers of 5,18-diHETE

Because of the structural similarity between 5,18-diHETE and anti-inflammatory resolvin E2, synthesis of 5,18-diHETE was studied. Methyl (R)-3-hydroxyvalerate was converted to the (R)-C9–C20 phosphonium salt via alkylation of the derived iodide with propargyl alcohol dianion and subsequent Castro-Stephens coupling. The (S)-enantiomer was prepared via Mitsunobu inversion. The (R)- and (S)-enantiomers of the γ-TMS-propargylic alcohol corresponding to the C1–C7 part were constructed by asymmetric hydrogen transfer reaction and converted to the (R)- and (S)-enals by adding the aldehyde carbon using the reaction of the derived TMS-epoxide with Et₂AlCN followed by hydride reduction. The (R)-enantiomer of the C1–C8 enal was coupled with the (R)-C9–C20 phosphonium salt by Wittig reaction, and the functional group in the product was transformed to afford 5R,18R-diHETE stereoselectively. Other stereoisomers were synthesized as well.