Synthesis of 9-CD3-9-cis-Retinal Cofactor of Isorhodopsin.

We report the synthesis of 9-CD3-9-cis-retinal via a six-step procedure from ß-ionone. The steps involve an initial deuteration of the methyl ketone of ß-ionone followed by two consecutive Horner-Wadsworth-Emmons (HWE) coupling reactions and their corresponding DIBAL reductions. A final oxidation of the allylic alcohol of the retinol leads to the target compound. This deuterium labeled retinoid is an important cofactor for studying protein-retinoid interactions in isorhodopsin.