Synthesis of Site-Specifically ¹³C Labeled Linoleic Acids

Soybean lipoxygenase-1 (SLO-1) catalyzes the C-H abstraction from the reactive carbon (C-11) in linoleic acid as the first and rate-determining step in the formation of alkylhydroperoxides. While previous labeling strategies have focused on deuterium labeling to ascertain the primary and secondary kinetic isotope effects for this reaction, there is an emerging interest and need for selectively enriched ¹³C isotopologues. In this report, we present synthetic strategies for site-specific ¹³C labeled linoleic acid substrates. We take advantage of a Corey-Fuchs formyl to terminal ¹³C-labeled alkyne conversion, using ¹³CBr₄ as the labeling source, to reduce the number of steps from a previous fatty acid ¹³C synthetic labeling approach. The labeled linoleic acid substrates are useful as nuclear tunneling markers and for extracting active site geometries of the enzyme-substrate complex in lipoxygenase.