AZIDOTETRAFLUOROPHENYL RETINAL ANALOG - SYNTHESIS AND BACTERIORHODOPSIN PIGMENT FORMATION

The retinal derivative, afluorophenyl)-3,7-dimethyl-2,4,6,8-nonatetrae nal, was synthesized by two routes as a potential photoactivatable cro ss-linking agent for studies in bacteriorhodopsin (BR) of the chromoph ore interaction with its apoprotein. The retinal analogue formed a sta ble, moderately functional BR pigment confirming that the ring cavity of the retinal binding site has a significant tolerance for derivatiza tion on that portion of the molecule. Attempts to cross-link the azido chromophore to the protein by photoactivation were unsuccessful. The electron delocalization effect of the conjugated polyene side chain of the retinal appears to interfere with the formation or reactivity of the nitrene intermediate to the extent that photoactivated cross-linki ng is not achieved. These results demonstrate a limitation to the use of fluorinated aryl azides as photoaffinity reagents.