New thiaoleic acid methyl esters 1 have been prepared as models for studies on Δ12-saturation, Convergent synthetic pathways to those acids from the 10-(tetrahydropyranyloxy)-dec-1-yne 2 are described. After saponification, their inhibitory effect on the in vivo desaturation of [1-14C] oleic acid into [1-14C] linoleic acid has been evaluated using green algae, Chlorella sorokiniana, as a biological