| Abstract
| - We report the preparation of the deuterated tetradecanoic acids [2,2,3,3-2H4]-, [2,2,3,3,10,10-2H6]-,and [2,2,3,3,13,13-2H6]-tetradecanoic acids (1, 2, and 3, respectively) and their use to investigatethe mechanism of the enzymatic transformation of (Z)-11-tetradecenoic acid into (E,E)-10,12-tetradecadienoic acid. Probes 2 and 3 were prepared from intermediate ketones 7 and 10, whichwere transformed into the labeled bromides 17 and 18 by reduction with NaBD4, tosylation of theresulting alcohol, replacement of the tosyloxy group by deuteride with LiAlD4, hydrolysis, andreaction with N-bromosuccinimide. The resulting bromides were converted into the α-acetylenicesters 21 and 22, respectively, and the additional deuterium labels were introduced by reductionof the conjugated triple bond with Mg in deuterated methanol. The same sequence of reactionsstarting with 11-bromoundecane afforded 27. Saponification of the labeled esters 23, 24, and 27gave the deuterated acids 2, 3, and 1, respectively. The results of the biochemical experimentsshowed that C10−H removal, but not elimination of C13−H, was sensitive to deuterium substitutionin the transformation of (Z)-11-tetradecenoic acid into (E,E)-10,12-tetradecadienoic acid, which isconsistent with the hypothesis that this desaturase reaction involves a first slow, C10−H bondcleavage, with probable formation of an unstable allylic intermediate, followed by a second fastC13−H bond removal and concomitant rearrangement.
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