SYNTHESIS OF RETINALS WITH 8-MEMBERED AND 9-MEMBERED RINGS IN THE SIDE-CHAIN - MODELS FOR RHODOPSIN PHOTOBLEACHING INTERMEDIATES

The triggering process of rhodopsin activation leading to visual trans duction has remained a key problem in the chemistry of vision. In orde r to provide probes to explore this process, retinal analogs ret8 3 an d ret9 4, with the 11-ene cis-locked by 8- and 9-membered rings, have been synthesized. These could lead to pigment analogs which might acco modate a transoid chromophore upon irradiation, thus providing unique models for rhodopsin activation studies. Enzyme assays and flash photo lysis of rhodopsin analogs incorporating ret8 and other retinal analog s showed that the triggering process requires complete 11-cis to trans isomerization involving the entire polyene moiety. The syntheses of r et8 3 and ret9 4 double bond isomers are described.