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 8-ionone. The steps involve an initial deuteration of the methyl ketone of 8-ionone followed by two consecutive Homer-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. (C) 2018 Elsevier Ltd. All rights reserved.