Preparation of tetradeuterated leukotriene A₄ methyl ester: Methyl-[11,12,14,15-²H₄]-(5S, 6S)-Oxido-(7E,9E,11Z,14Z)-eicosatetraenoate

The chapter presents a study on the preparation of tetradeuterated leukotriene A₄ methyl ester, that is, methyl-[11, 12, 14, 15-²H₄]-(5S,6S)-oxido-(7E,9E, 11Z, 14Z)-eicosatetraenoate. The chapter describes the procedure, including the Wittig coupling step and semireduction step. Gas chromatography-mass spectrometry (GC-MS) coupling offers several advantages over other methods. The two-step procedure described in the chapter allows the short and efficient preparation of tetradeuterated chiral LTA₄ methyl ester. The synthesis of the racemic form of this compound was previously described via sulfonium ylid chemistry, but the critical reaction conditions reported suggested that the Wittig reaction presented here would be more suitable. The semihydrogenation or deuteration of the diyne precursor 7E-(2) presented an interesting challenge, because semireduction of acetylenic compounds is a difficult reaction. Yields and reaction conditions can vary greatly according to the stability and chemical structure of the precursors. Pyridine deactivates the catalyst and stabilizes the epoxidic compounds. The yields of labeled or unlabeled LTA₄ methyl ester were reproducible and found to vary only from 32 to 40% provided that the hydrogen or deuterium absorption was carefully controlled.