Synthesis of octadecynoic acids and [1-14C] labeled isomers of octadecenoic acids

Geometric and positional isomers of [1-14C] octadecenoic acids have been synthesized by modifications of published procedures. Positional isomers of octadecynoic acids also have been synthesized to obtain the geometric and positional isomers of the unlabeled octadecenoic acid analogs. The syntheses were accomplished by coupling a haloalkyl compound with a substituted acetylene using n-butyl lithium in hexamethylphosphoramide. The coupled product, either a 17- or 18-carbon acetylenic alcohol, could be semihydrogenated and chain extended to afford a carboxy labeled derivative, could be partially hydrogenated and chain extended to afford a carboxyl labeled cis- or trans-octadecenoic acid in the former case. In the latter case, octadecynoic, cis-octadecenoic or trans-octadecenoic acids could be obtained by the appropriate reactions. The methods used in this study enabled the synthesis of 14C-labeled fatty acids in generally higher yields and by simpler reactions than were previously possible.