Synthesis of 10,15-[13C2]-squalene and -DL-squalene oxide

[3-13C]-Ethyl farnesoate was prepared by alkylating 3-13C-ethyl acetoacetate with geranyl bromide, followed by hydrolysis, decarboxylation and treatment with the anion of triethyl phosphonoacetate. The ester was reduced with LAH, brominated with CBr4φ3P, and the farnesyl bromide coupled with CuI/Li-pyrrolidine to produce [10,15-13C2]-squalene. Epoxidation was effected by treatment with NBS in aqueous THF, followed by K2CO3-mediated HBr elimination. The overall yield of DL-10,15-[13C2]-squalene-2,3-oxide was 1.6%. (author)