Fluorescent Penta- and Hexaene Fatty Acids by a Wittig–Horner/Elimination Strategy
journal contributionposted on 15.06.2012, 00:00 by Lukas J. Patalag, Daniel B. Werz
Molecular fluorescent probes have revolutionized biochemical and biophysical studies in the last decades, but with regard to lipids there has been a lack of combining the slim shape of saturated acyl chains with fluorescent properties. Our strategy to pentaene and hexaene fatty acids builds upon commercially available 4-(E)-decenal, which is subjected to a Wittig–Horner reaction after chlorination in α-position. DBU-mediated β-elimination of HCl proceeding the olefination establishes a highly conjugated system to which a salt-free Wittig reaction adds a final double bond leading to a good (Z)-selectivity of 83–86%. The double bond geometry can be optionally isomerized with I2 to furnish the all-(E)-species. The five conjugated alkene moieties result in a longest-wavelength absorption maximum of about 350 nm. A red-shift to 380 nm was realized by addition of another double bond employing a common Wittig–Horner prolongation sequence. Stokes shifts of about 7300 and 7800 cm–1, respectively, were observed.