ABSTRACT
Visual pigment analog studies began with the classical study of Wald, Hubbard, and co-workers where six geometric isomers of retinal were employed to react with the apoprotein opsin. The unexpected finding of stable pigment formation of 1-cis isomers of retinal not only revived the interest in reexamining the stereospecificity of the binding site of opsin but also launched an independent program of visual pigment analog studies at Hawaii. It is clear that the perimeter of the binding site as determined by the stereoisomers of retinal is limited by the atoms present in these isomers. The success in the synthesis of vinylic and allylic fluorine-labeled retinals allows the preparation of labeled pigment analogs. Their photochemical behavior has been examined in an attempt to detect possible altered properties in fluorinated rhodopsin. In laboratory, the introduction of C,0-alkyl substituents was readily effected by the Petersen reaction of R-ionone with a series of a-trimethylsilylalkanoates, followed by straightforward elaboration to the requisite retinal analogs.
