Preparation of methyl 11,14,17-eicosatrienoate-8,8,9,9-d ₄ and methyl 8,11,14,17-eicosatetraenoate-8,9-d ₂

Abstract

Methyl 11,14,17-eicosatrienoate-8,8,9,9-d ₄ was obtained by Wittig coupling of 3,6-nonadienyltriphenylphosphonium iodide with methyl 11-oxoundecanoate-8,8,9,9-d ₄. For the synthesis of the phosphonium salt, 2-pentynol was converted to 1-bromo-2-pentyne with triphenylphosphine dibromide. Grignard coupling of 1-bromo-2-pentyne with 3-butynol in the presence of cuprous chloride gave 3,6-nonadiynol. The latter was hydrogenated in the presence of P-2 nickel catalyst to yield 3,6-nonadienol. The dienol was convertedvia the bromide and iodide to the phosphonium salt. The aldehyde ester was prepared starting with the coupling of 7-bromoheptanoic acid and 3-butynol with lithium amide in liquid ammonia. The hydroxyalkynoic acid obtained was converted to the methyl ester and the hydroxy group was converted to the tetrahydropyranyloxy group. Subsequent deuteration of the methyl 11-(2-tetrahydropyranyloxy)-8-undecynoate with deuterium gas andtris-(triphenylphosphine)chlorohodium gave the corresponding tetradeuterated product. The tetrahydropyranyl group was removed and the methyl 11-hydroxy-undecanoate-8,8,9,9-d ₄ was oxidized to the aldehyde ester with pyridinium chlorochromate. Methyl 8,11,14,17-eicosatetraenoate-8,9-d ₂ was obtained by a similar sequence of reactions. The methyl 11-oxo-8-undecenoate-8,9-d ₂ required for the Wittig coupling was obtained by Lindlar deuteration of the protected alkynoic ester to methyl 11-(2-tetrahydropyranyloxy)-8-undecenoate-8,9d ₂. The unsaturated hydroxy ester was oxidized to the aldehyde ester by periodinane with negligible isomerization. The allcis isomers were isolated by silver resin chromatography.