Retinoids and related compounds. Part 20.1 Synthesis of (11Z)-8,18-ethanoretinal and a conformational study of the rhodopsin chromophore

Abstract

In order to investigate the conformation of the chromophore around the trimethylcyclohexene ring in rhodopsin, (11Z)-8,18-ethanoretinal 6 has been synthesized. Its binding experiment with bovine opsin afforded a new rhodopsin analogue, the opsin shift and CD spectrum of which were similar to those of natural rhodopsin. These experimental results strongly suggest that the torsional angle around the 6–7 single bond in rhodopsin corresponds to the torsional angle in (11Z)-8,18-ethanoretinal 6. In addition, MMX calculations for 2 and 6 have been carried out and are reported.