Synthesis of 13C single and double labelled retinals, precursors for NMR studies of visual pigments and related systems

The synthesis of retinals enriched with 13C at positions 11, 13, 14, 15, 12&20, 13&14, and 14&15 in high isomeric purity is reported. The importance of these retinals in studying the structure and properties of rhodopsin and bacteriorhodopsin by 13C NMR spectroscopy is briefly described.